To see the other types of publications on this topic, follow the link: Heat Convection.
Journal articles on the topic 'Heat Convection'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Heat Convection.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Wang, Yin, Pik-Yin Lai, Hao Song, and Penger Tong. "Mechanism of large-scale flow reversals in turbulent thermal convection." Science Advances 4, no. 11 (November 2018): eaat7480. http://dx.doi.org/10.1126/sciadv.aat7480.
Full textAbstract:
It is commonly believed that heat flux passing through a closed thermal convection system is balanced so that the convection system can remain at a steady state. Here, we report a new kind of convective instability for turbulent thermal convection, in which the convective flow stays over a long steady “quiet period” having a minute amount of heat accumulation in the convection cell, followed by a short and intermittent “active period” with a massive eruption of thermal plumes to release the accumulated heat. The rare massive eruption of thermal plumes disrupts the existing large-scale circulation across the cell and resets its rotational direction. A careful analysis reveals that the distribution of the plume eruption amplitude follows the generalized extreme value statistics with an upper bound, which changes with the fluid properties of the convecting medium. The experimental findings have important implications to many closed convection systems of geophysical scale, in which massive eruptions and sudden changes in large-scale flow pattern are often observed.
2
Fuentes, J. R., Andrew Cumming, Matias Castro-Tapia, and Evan H. Anders. "Heat Transport and Convective Velocities in Compositionally Driven Convection in Neutron Star and White Dwarf Interiors." Astrophysical Journal 950, no. 1 (June 1, 2023): 73. http://dx.doi.org/10.3847/1538-4357/accb56.
Full textAbstract:
Abstract We investigate heat transport associated with compositionally driven convection driven by crystallization at the ocean–crust interface in accreting neutron stars, or growth of the solid core in cooling white dwarfs. We study the effect of thermal diffusion and rapid rotation on the convective heat transport, using both mixing length theory and numerical simulations of Boussinesq convection. We determine the heat flux, composition gradient, and Péclet number, Pe (the ratio of thermal diffusion time to convective turnover time) as a function of the composition flux. We find two regimes of convection with a rapid transition between them as the composition flux increases. At small Pe, the ratio between the heat flux and composition flux is independent of Pe, because the loss of heat from convecting fluid elements due to thermal diffusion is offset by the smaller composition gradient needed to overcome the reduced thermal buoyancy. At large Pe, the temperature gradient approaches the adiabatic gradient, saturating the heat flux. We discuss the implications for cooling of neutron stars and white dwarfs. Convection in neutron stars spans both regimes. We find rapid mixing of neutron star oceans, with a convective turnover time of the order of weeks to minutes depending on rotation. Except during the early stages of core crystallization, white dwarf convection is in the thermal-diffusion-dominated fingering regime. We find convective velocities much smaller than recent estimates for crystallization-driven dynamos. The small fraction of energy carried as kinetic energy calls into question the effectiveness of crystallization-driven dynamos as an explanation for observed magnetic fields in white dwarfs.
3
Xiao, Hui, Zhimin Dong, Rui Long, Kun Yang, and Fang Yuan. "A Study on the Mechanism of Convective Heat Transfer Enhancement Based on Heat Convection Velocity Analysis." Energies 12, no. 21 (November 1, 2019): 4175. http://dx.doi.org/10.3390/en12214175.
Full textAbstract:
This paper explores the mechanism of convective heat transfer enhancement in a new perspective. In this paper, a new parameter called heat convection velocity is proposed based on the field synergy principle. It is defined as the velocity projection on the temperature gradient vector and reflects the magnitude of the velocity component that contributes to heat convection. Three typical cases are taken into consideration to investigate the influence factors of Nusselt number theoretically. The results indicate that the Nusselt number can be enhanced by increasing the mean heat convection velocity and the dimensionless mean temperature difference. Through theoretical analysis, three suggestions are found for designing heat transfer enhancement components: (a) the overall synergetic effect should be improved; (b) the fluid with lower temperature gradient should be guided to the region where the temperature gradient is higher; (c) temperature distribution should be an interphase distribution of hot and cold fluid. Besides, the heat convection velocity is used to investigate the mechanism of convective heat transfer in the smooth tube. It is found that the increase of Nusselt number is due to the increase of heat convection velocity. In addition, according to design suggestions, a new insert is invented and inserted in the circular tube. With heat convection velocity analysis, it is found that there is much potential of increasing heat convection velocity for enhancing the convective heat transfer in the circular tube.
4
Ward, S., J. M. V. Rayner, U. Möller, D. M. Jackson, W. Nachtigall, and J. R. Speakman. "Heat transfer from starlings sturnus vulgaris during flight." Journal of Experimental Biology 202, no. 12 (June 15, 1999): 1589–602. http://dx.doi.org/10.1242/jeb.202.12.1589.
Full textAbstract:
Infrared thermography was used to measure heat transfer by radiation and the surface temperature of starlings (Sturnus vulgaris) (N=4) flying in a wind tunnel at 6–14 m s-1 and at 15–25 degrees C. Heat transfer by forced convection was calculated from bird surface temperature and biophysical modelling of convective heat transfer coefficients. The legs, head and ventral brachial areas (under the wings) were the hottest parts of the bird (mean values 6.8, 6.0 and 5.3 degrees C, respectively, above air temperature). Thermal gradients between the bird surface and the air decreased at higher air temperatures or during slow flight. The legs were trailed in the air stream during slow flight and when air temperature was high; this could increase heat transfer from the legs from 1 to 12 % of heat transfer by convection, radiation and evaporation (overall heat loss). Overall heat loss at a flight speed of 10.2 m s-1 averaged 11. 3 W, of which radiation accounted for 8 % and convection for 81 %. Convection from the ventral brachial areas was the most important route of heat transfer (19 % of overall heat loss). Of the overall heat loss, 55 % occurred by convection and radiation from the wings, although the primaries and secondaries were the coolest parts of the bird (2.2-2.5 degrees C above air temperature). Calculated heat transfer from flying starlings was most sensitive to accurate measurement of air temperature and convective heat transfer coefficients.
5
Zhang, Tong, Shanshan Geng, Xin Mu, Jiamin Chen, Junyi Wang, and Zan Wu. "Thermal Characteristics of a Stratospheric Airship with Natural Convection and External Forced Convection." International Journal of Aerospace Engineering 2019 (September 8, 2019): 1–11. http://dx.doi.org/10.1155/2019/4368046.
Full textAbstract:
Though convective heat transfer is one of the main factors that dominate the thermal characteristics of stratospheric airships, there is no specific correlation equations for the calculation of convective heat transfer of airships. The equations based on flat plate and sphere models are all in use. To ameliorate the confusing situation of diverse convective heat transfer equations and to end the misuse of them in the thermal characteristic analysis of stratospheric airships, a multinode steady-state model for ellipsoid airships is built. The accuracy of the five widely accepted equations for natural convective heat transfer is compared and analysed on the proposed large-scale airship model by numerical simulation, so does that of the five equations for external forced convective heat transfer. The simulation method is verified by the available experimental data. Simulation results show that the difference of the five natural convection equations is negligible, while that of the five external forced convection equations must be considered in engineering. Forced convection equations with high precision and wide application should be further investigated.
6
Zhang, Nan, Yan Wang, and Xiaomeng Lin. "Mesoscale Observational Analysis of Isolated Convection Associated with the Interaction of the Sea Breeze Front and the Gust Front in the Context of the Urban Heat Humid Island Effect." Atmosphere 13, no. 4 (April 9, 2022): 603. http://dx.doi.org/10.3390/atmos13040603.
Full textAbstract:
An isolated convection was unexpectedly initiated in the evening of 1 August 2019 around the Tianjin urban region (TUR), which happened at some distance from the shear line at lower level and the preexisting convection to the South, analyzed by using ERA5 reanalysis data and observations from surface weather stations, and a S-band radar. The results show that, 42 min before the initiation of the convection, the atmospheric thermodynamic conditions around TUR were favorable for the initiation of the isolated convection, although the southerly and vertical shear of the horizontal wind at the lower level was weak. A sea-breeze front approached the TUR and continued to move West, leading to the triggering of the isolated convection in the context of the urban humid heat island (UHHI) effect. Subsequently, the gust front, which was formed between the cold pool away from the TUR and the warm and humid air of the UHHI, moved northward, approached the convection, and collided with sea breeze front, resulting in five reflectivity centers of isolated convection being merged and the convection’s development. Finally, the isolated convection split into two convections that moved away from the TUR and disappeared at 20:36 Beijing Time. The isolated convection was initiated and developed by the interaction of the sea breeze front and gust front in the context of the UHHI effect. The sea breeze front triggered the isolated convection around TUR in the context of the UHHI effect, and the gust front produced by the early convective storms to the south played a vital role in the development of the isolated convection.
7
Rivera-Salinas, Jorge-Enrique, Karla-Monzerratt Gregorio-Jáuregui, Heidi-Andrea Fonseca-Florido, Carlos-Alberto Ávila-Orta, Eduardo Ramírez-Vargas, José-Antonio Romero-Serrano, Alejandro Cruz-Ramírez, Víctor-Hugo Gutierréz-Pérez, Seydy-Lizbeth Olvera-Vazquez, and Lucero Rosales-Marines. "Numerical Study Using Microstructure Based Finite Element Modeling of the Onset of Convective Heat Transfer in Closed-Cell Polymeric Foam." Polymers 13, no. 11 (May 28, 2021): 1769. http://dx.doi.org/10.3390/polym13111769.
Full textAbstract:
The thermal performance of closed-cell foams as an insulation device depends on the thermal conductivity. In these systems, the heat transfer mode associated with the convective contribution is generally ignored, and studies are based on the thermo-physical properties that emerge from the conductive contribution, while others include a term for radiative transport. The criterion found in the literature for disregarding convective heat flux is the cell diameter; however, the cell size for which convection is effectively suppressed has not been clearly disclosed, and it is variously quoted in the range 3–10 mm. In practice, changes in thermal conductivity are also attributed to the convection heat transfer mode; hence, natural convection in porous materials is worthy of research. This work extends the field of study of conjugate heat transfer (convection and conduction) in cellular materials using microstructure-based finite element analysis. For air-based insulating materials, the criteria to consider natural convection (Ra=103) is met by cavities with sizes of 9.06 mm; however, convection is developed into several cavities despite their sizes being lower than 9.06 mm, hence, the average pore size that can effectively suppress the convective heat transfer is 6.0 mm. The amount of heat transported by convection is about 20% of the heat transported by conduction within the foam in a Ra=103, which, in turn, produces an increasing average of the conductivity of about 4.5%, with respect to a constant value.
8
Ecke, Robert E., Hans Haucke, and John Wheatley. "Convectively driven superfluid turbulence in dilute solutions of 3He in superfluid 4He." Canadian Journal of Physics 65, no. 11 (November 1, 1987): 1322–27. http://dx.doi.org/10.1139/p87-208.
Full textAbstract:
A dilute solution of 3He in superfluid 4He usually behaves as a single-component classical fluid in the context of thermal convection. However, certain convective states can be excited that do not seem to exist in classical convection. These states are characterized by noisy temperature fluctuations and a pronounced decrease in heat transport relative to the classical convecting states. Critical convective-flow fields are observed analogous to critical velocities for superfluid turbulence in pipes. The magnitudes of the average critical velocities for these two types of superfluid turbulence are in good agreement. Also, a quantitative estimate of energy dissipation due to the interaction of normal fluid and quantized vortex lines is consistent with the large decrease in heat transport for the turbulent states. These states are identified as states of convectively driven superfluid turbulence.
9
Jani, Jaronie Mohd, Sunan Huang, Martin Leary, and Aleksandar Subic. "Analysis of Convective Heat Transfer Coefficient on Shape Memory Alloy Actuatorunder Various Ambient Temperatures with Finite Difference Method." Applied Mechanics and Materials 736 (March 2015): 127–33. http://dx.doi.org/10.4028/www.scientific.net/amm.736.127.
Full textAbstract:
The demand for shape memory alloy (SMA) actuators for technical applications is steadily increasing; however SMA may have poor deactivation time due to relatively slow convective cooling. Convection heat transfer mechanism plays a critical role in the cooling process, where an increase of air circulation around the SMA actuator (i.e. forced convection) provides a significant improvement in deactivation time compared to the natural convection condition. The rate of convective heat transfer, either natural or forced, is measured by the convection heat transfer coefficient, which may be difficult to predict theoretically due to the numerous dependent variables. In this work, a study of free convective cooling of linear SMAactuators was conducted under various ambient temperatures to experimentally determine the convective heat transfer coefficient. A finite difference equation (FDE) was developed to simulate SMA response, and calibrated with the experimental data to obtain the unknown convectiveheat transfer coefficient, h. These coefficients are then compared with the available theoretical equations, and it was found that Eisakhaniet. almodel provides good agreement with the Experiment-FDE calibrated results. Therefore, FDE is reasonably useful to estimate the convective heat transfer coefficient of SMA actuator experiments under various conditions, with a few identified limitations (e.g. exclusion of other associative heat transfer factors).
10
Castro-Tapia, Matias, Andrew Cumming, and J. R. Fuentes. "Fast and Slow Crystallization-driven Convection in White Dwarfs." Astrophysical Journal 969, no. 1 (June 21, 2024): 10. http://dx.doi.org/10.3847/1538-4357/ad4152.
Full textAbstract:
Abstract We investigate crystallization-driven convection in carbon–oxygen white dwarfs. We present a version of the mixing length theory that self-consistently includes the effects of thermal diffusion and composition gradients, and provides solutions for the convective parameters based on the local heat and composition fluxes. Our formulation smoothly transitions between the regimes of fast adiabatic convection at large Peclet number and slow thermohaline convection at low Peclet number. It also allows for both thermally driven and compositionally driven convection, including correctly accounting for the direction of heat transport for compositionally driven convection in a thermally stable background. We use the MESA stellar evolution code to calculate the composition and heat fluxes during crystallization in different models of cooling white dwarfs, and determine the regime of convection and the convective velocity. We find that convection occurs in the regime of slow thermohaline convection during most of the cooling history of the star. However, at the onset of crystallization, the composition flux is large enough to drive fast overturning convection for a short time (∼10 Myr). We estimate the convective velocities in both of these phases and discuss the implications for explaining observed white dwarf magnetic fields with crystallization-driven dynamos.
11
Kiran, Palle, and S. H. Manjula. "Weakly Nonlinear Double-Diffusive Oscillatory Magneto-Convection Under Gravity Modulation." Sensor Letters 18, no. 9 (September 1, 2020): 725–38. http://dx.doi.org/10.1166/sl.2020.4281.
Full textAbstract:
An imposed time-periodic gravity field effect on double-diffusive magneto-convection for oscillatory mode has been investigated. The gravity field consisting of steady and periodic modes. A layer is confined with an electrically conducting fluid with Boussines q approximation and heated from below cooled from above. While using the perturbation technique we study nonlinear double-diffusive convection just above the critical state of the onset convection. The growth rate of the disturbances is confined with a critical Rayleigh number to investigate oscillatory convection. Analysis of finite- amplitude convection has been derived through the complex Ginzburg-Landau equation (CGLE). The convective heat and mass transfer obtained through CGLE at third-order under solvability conditions. This convective amplitude is required to estimate heat and mass transfer in terms of the Nusselt and Sherwood numbers. It is found that increasing the frequency of modulation causes diminishing heat and mass transfer. The effect of Prandtl number Pr, magnetic Prandtl number Pm, and amplitude δ enhances heat/mass transfer. It is found that an oscillatory mode of convection enhances the heat and mass transfer than the stationary mode. Further, streamlines, isotherms, and isohalines have their usual nature on double-diffusive magnetoconvection.
12
Rahman, M. M., M. M. Billah, and M. A. Alim. "Effect of Reynolds and Prandtl Numbers on Mixed Convection in an Obstructed Vented Cavity." Journal of Scientific Research 3, no. 2 (April 28, 2011): 271–81. http://dx.doi.org/10.3329/jsr.v3i2.4344.
Full textAbstract:
A numerical investigation is conducted to analyze the steady flow and thermal fields as well as heat transfer characteristics in a vented square cavity with a built-in heat conducting horizontal solid circular obstruction. Hydrodynamic behavior, thermal characteristics and heat transfer results are obtained by solving the couple of Navier-Stokes and energy equations by using a weighted residuals Finite element method. The computation was made for different Reynolds number, Prandtl number ranging from 50 to 200 and from 0.71 to 7.1 at the three different convective regimes. Three different regimes are observed with increasing Ri: forced convection (with negligible free convection), mixed convection (comparable free and forced convection) and free convection dominated region (with higher free convection). The results are presented to show the effects of the Reynolds number, Prandtl number on flow pattern, thermal field and heat transfer characteristics at the three convective regimes. It is found that the flow and thermal field strongly depend on the Reynolds number, Prandtl number as well as Richardson number. As the Reynolds number and Prandtl number increase, the heat transfer rate increases but average fluid temperature in the cavity and temperature at the cylinder center decrease at the three convective regimes.Keywords: Mixed convection; Finite element method; Obstructed vented cavity; Prandtl number.© 2011 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi:10.3329/jsr.v3i2.4344 J. Sci. Res. 3 (2), 271-281 (2011)
13
Shen, Xiang Yang, Jing Ding, and Jian Feng Lu. "Turbulent Convective Heat Transfer in a Transversely Grooved Tube with Natural Convection Effect." Applied Mechanics and Materials 741 (March 2015): 458–61. http://dx.doi.org/10.4028/www.scientific.net/amm.741.458.
Full textAbstract:
The turbulent convective heat transfer in a transversely grooved tube of molten salt with natural convection effect has been numerically investigated. In general, the average Nusselt number with and without considering natural convection in transversely grooved tube was almost equal. According to the simulated results, the heat transfer coefficient of transversely grooved tube in upside region was lower than that of downside region. The effect of natural convection on unilateral heat transfer in transversely grooved tube was more obvious with lower Reynolds number and higher inlet temperature, and the effect of natural convection on unilateral heat transfer was lower with bigger groove deep.
14
Kumar, Mahesh, Pankaj Khatak, Ravinder Kumar Sahdev, and Om Prakash. "The effect of open sun and indoor forced convection on heat transfer coefficients for the drying of papad." Journal of Energy in Southern Africa 22, no. 2 (May 1, 2011): 40–46. http://dx.doi.org/10.17159/2413-3051/2011/v22i2a3214.
Full textAbstract:
In this research paper, a simulation study has been carried out for the determination of convective heat transfer coefficients of papad under open sun drying and indoor forced convection drying modes. Experimental data obtained from open sun and indoor forced convection drying modes for papad were used to determine the values of the constants (C and n) in Nusselt number expression by using linear regression analysis, and consequently convective heat transfer coefficients were evaluated. The average values of convective heat transfer coefficients were found to be 3.54 and 1.56 W/m2 oC under open sun drying and indoor forced convection drying modes respectively. The experimental errors in terms of percent uncertainty were also evaluated.
15
Syaiful, Imam Syarifudin, Maria F. Soetanto, and Myung-whan Bae. "Numerical simulation of heat transfer augmentation in fin-and-tube heat exchanger with various number of rows of concave rectangular winglet vortex generator." MATEC Web of Conferences 159 (2018): 02012. http://dx.doi.org/10.1051/matecconf/201815902012.
Full textAbstract:
The passive method by using a vortex generator (VG) is an effective method for the improvement of convective heat transfer. This study is focused on usage of concave rectangular winglet vortex generator (CRW VG) for improving convective heat transfer in a fin-and-tube heat exchanger using numerical simulation. Concave rectangular winglet pairs (CRWP) and rectangular winglet pairs (RWP) VGs were mounted inside the gap between fins (gas side) with variations of the number of VG pairs of rows. Inlet air velocity variations expressed by the Reynolds numbers were ranged from 364 to 689. Augmentation of heat transfer is indicated by the ratio value of heat transfer convection coefficient between cases using VG and that without using VG (baseline). The results show that the convection heat transfer coefficient for cases using CRWP VG is higher than that using RWP VG. Convection heat transfer coefficient increases up to 102% by mounting CRWP VG at Re = 364. However, the increase in convection coefficient is accompanied by a rise in pressure drop to 216.8%.
16
Колчанова, Екатерина Андреевна, and Рафиль Вафавич Сагитов. "Modeling of heat transfer at local convection over a vertical throughflow in a two-layered air-heat generating porous system." Computational Continuum Mechanics 16, no. 4 (December 1, 2023): 445–58. http://dx.doi.org/10.7242/1999-6691/2023.16.4.37.
Full textAbstract:
Convective heat transfer in an air layer partially filled with a heat-generating granular porous medium is studied. There is a slow seepage of air through the layer in the vertical direction with a constant velocity. Equal temperatures are maintained at the outer solid permeable boundaries, and the heat source strength is constant within the porous sublayer and is proportional to the solid volume fraction. The permanent heat generation within the porous sublayer, combined with the vertical throughflow, causes a nonlinear thermal profile which is conducive for convection to occur. The Boussinesq approximation and Darcy's law are used to describe this convection. Numerical solution of the nonlinear convective problem is obtained on the basis of Newton's method. In the limiting case, the numerical data for the onset of convection are compared with the results of the earlier paper of the authors, where a linear stability theory and a method for constructing of the fundamental system of partial solution vectors have been applied, and with the data by other authors. The stationary regimes of local convection, which occurs in an “air – heat-generating porous medium-air” system over the basic vertical throughflow, and its effect on the heat transfer from the porous air sublayer with the growth of supercriticality are studied. It is shown that, depending on the velocity of the basic throughflow (the Peclet number), convection excitation can be both soft (due to supercritical pitchfork bifurcation) and hard (when the loss of stability of the basic throughflow is accompanied by subcritical pitchfork bifurcation that gives rise to an unstable secondary convective regime). This secondary regime is replaced by a stable tertiary convective regime with increasing supercriticality. It has been found that the total heat transfer rate for the upward basic throughflow exceeds that for the downward basic throughflow significantly, and that local convection at any direction of this throughflow increases the heat transfer rate in the system. An increase in the Nusselt number with the growth of supercriticality is recorded. However, a noticeable contribution of local convection to the total heat transfer is observed only when all values of the Pecklet number are negative and its positive values are lower than 2.
17
Schutzeichel, Maximilian Otto Heinrich, Thorben Strübing, Ozan Tamer, Thomas Kletschkowski, Hans Peter Monner, and Michael Sinapius. "Experimental and Numerical Investigation of a Multifunctional CFRP towards Heat Convection under Aircraft Icing Conditions." Applied Mechanics 3, no. 3 (August 3, 2022): 995–1018. http://dx.doi.org/10.3390/applmech3030056.
Full textAbstract:
A combined experimental and numerical approach for the analysis of convective heat transfer from a multifunctional flat plate specimen under aircraft icing conditions is presented. The experimental setup including a heat control and measurement system that is installed in a de-icing test bed. The ambient temperature (θa=[253,283]K), air velocity (va={0,15,30}ms), and angle of attack (α={10,30}∘) are varied, and their influence on heat transfer during local Joule heating is discussed. The numerical approach utilises the results to compute the convective heat transfer coefficients (HTC) based on Newton’s convective heat transfer condition. Results indicate that the numerical model represents the heat transfer behaviour with high accuracy. The HTC for free convection was found to hold h¯≈2.5Wm2K and h¯≈[10,40]Wm2K for forced convection conditions with minor scattering. The increase in HTC under forced convection conditions has a significant effect on the overall heat transfer behaviour, resulting in high temperature gradients within the material. The functional optimisation of multifunctional structures will benefit from including application related convection conditions, dealing with resulting temperature fields by structural design. It is expected that multifunctional structures for de-icing as well as for structural energy storage, morphing structures, or stiffness adaptive structures with similar material constituents will benefit from this recognition.
18
Čorný, Ivan. "Aspects of Determination of Convective Coefficients." Advances in Thermal Processes and Energy Transformation 1, no. 2 (2018): 31–33. http://dx.doi.org/10.54570/atpet2018/01/02/0031.
Full textAbstract:
The paper deals with selected aspects in the determination of convective coefficients and the formation of air convection models on solid surfaces. The goal is to assess the suitability of individual approaches for application in specific situations, considering that convective heat transfer coefficients have a significant impact on the resulting accuracy of the facilities/process design. Convection is a dynamic phenomenon, its exact physical description is complex, convection coefficients cannot be measured directly. Correct determination of convective coefficients is therefore very important in various areas where thermal energy is transmitted in this way. The paper gives an overview of selected aspects of various methods for determining convective heat transfer parameters.
19
Bergles, A. E. "Heat Transfer Enhancement—The Encouragement and Accommodation of High Heat Fluxes." Journal of Heat Transfer 119, no. 1 (February 1, 1997): 8–19. http://dx.doi.org/10.1115/1.2824105.
Full textAbstract:
This review considers the many techniques that have been developed to enhance convective heat transfer. After introducing the techniques, the applications to most of the modes of heat transfer (single-phase forced convection, including compound techniques, pool boiling, convective boiling/evaporation, vapor-space condensation, and convective condensation) are described. Comments are offered regarding commercial introduction of this technology and the generations of heat transfer technology; advanced enhancement represents third-generation heat transfer technology.
20
Mathuriya, Goldi. "Analysis Effects of Average Value of Convective and Evaporative Heat Transfer Coefficient on Solar Cabinet Dryer for Reduction of Mass of Papad." International Journal for Research in Applied Science and Engineering Technology 9, no. 12 (December 31, 2021): 1511–23. http://dx.doi.org/10.22214/ijraset.2021.39522.
Full textAbstract:
Abstract: In this research paper, the behavior of heat and mass transfer phenomenon during greenhouse papad drying under forced convection mode has been investigated. Various experiments were performed during the month of April 2020 at SRCEM Banmore, morena (26o 34’13” N 78o 10’48” E). Experimental data obtained for forced convection greenhouse drying of papad were used to determine the constants in the Nusselt number expression by using the simple linear regression analysis and, consequently, the values of convective and evaporative heat transfer coefficients were evaluated. The average values of experimental constants C and n were determined as 0.9714 and 0.0129 respectively. The average values of convective and evaporative heat transfer coefficients were determined as 0.0886 W/m2 oC and 6.7583 W/m2 oC respectively. The experimental error in terms of percentage uncertainty was also evaluated. Keywords: Papad, Papad drying, Heat transfer coefficient, Convective, Evaporative, Forced convection greenhouse
21
Tewari, S. S., and Y. Jaluria. "Mixed Convection Heat Transfer From Thermal Sources Mounted on Horizontal and Vertical Surfaces." Journal of Heat Transfer 112, no. 4 (November 1, 1990): 975–87. http://dx.doi.org/10.1115/1.2910509.
Full textAbstract:
An experimental study is carried out on the fundamental aspects of the conjugate, mixed convective heat transfer from two finite width heat sources, which are of negligible thickness, have a uniform heat flux input at the surface, and are located on a flat plate in the horizontal or the vertical orientation. The heat sources are wide in the transverse direction and, therefore, a two-dimensional flow circumstance is simulated. The mixed convection parameter is varied over a fairly wide range to include the buoyancy-dominated and the mixed convection regimes. The circumstances of pure natural convection are also investigated. The convective mechanisms have been studied in detail by measuring the surface temperatures and determining the heat transfer coefficients for the two heated strips, which represent isolated thermal sources. Experimental results indicate that a stronger upstream heat source causes an increase in the surface temperature of a relatively weaker heat source, located downstream, by reducing its convective heat transfer coefficient. The influence of the upstream source is found to be strongly dependent on the surface orientation, especially in the pure natural convection and the buoyancy dominated regimes. The two heat sources are found to be essentially independent of each other, in terms of thermal effects, at a separation distance of more than about three strip widths for both the orientations. The results obtained are relevant to many engineering applications, such as the cooling of electronic systems, positioning of heating elements in furnaces, and safety considerations in enclosure fires.
22
Vairavan, Rajendaran, Vithyacharan Retnasamy, Zaliman Sauli, Hussin Kamarudin, Muammar Mohamad Isa, and Steven Taniselass. "Heat Sink Cooling Fan and Rotation Speed Effect Analysis on Heat Dissipation of High Power GaN LED Package." Advanced Materials Research 1082 (December 2014): 315–18. http://dx.doi.org/10.4028/www.scientific.net/amr.1082.315.
Full textAbstract:
In this work, thermal simulation analysis on high power LED is reported where the effect of the heat sink cooling fan and its rotation speed on the heat dissipation of the high power LED was evaluated. Ansys version 11 was utilized for the simulation. The thermal performance of the high power LED package was assessed in terms of operating junction temperature, von Mises stress and thermal resistance. The heat dissipation analysis was done under four types of convection condition:one natural convection conditionthree forced convection condition,. The forced convection condition was used to replicate the effect of a fan with various rotation speeds placed under the heat sink to increase the convective heat transfer coefficient. Results of the analysis showed that that the junction temperature, von Mises stress and thermal resistance of the GaN chip reduces with the increase of the fan rotation speed.
23
Zhang, Jian, Liang Wang, Yu Jie Xu, Yi Fei Wang, Zheng Yang, and Hai Sheng Chen. "Natural Convective Heat Transfer Characteristics of the Bundle Heat Exchanger in the Latent Heat Microcapsulated Phase Change Material Slurry." Materials Science Forum 852 (April 2016): 969–76. http://dx.doi.org/10.4028/www.scientific.net/msf.852.969.
Full textAbstract:
As a novel latent functionally thermal fluid, microcapsulated phase change material slurry (MPCMS) has many potential applications in the fields of energy storage, air-conditioning, refrigeration and heat exchanger, etc. In order to investigate the heat storage and heat transfer performance of MPCMS, natural convection in a rectangular enclosure heated by bundle heat exchanger has been studied numerically in this paper. The effects of mass concentration (Cm) of MPCMS, the vertical spaces of bundle heat exchanger on the natural convective heat transfer are investigated. The results indicate that, MPCMS with Cm=30% shows the best natural convectionperformance, and a lower position of bundle heat exchanger can strengthen the natural convection.
24
Vreugdenhil, Catherine A., and Bishakhdatta Gayen. "Ocean Convection." Fluids 6, no. 10 (October 12, 2021): 360. http://dx.doi.org/10.3390/fluids6100360.
Full textAbstract:
Ocean convection is a key mechanism that regulates heat uptake, water-mass transformation, CO2 exchange, and nutrient transport with crucial implications for ocean dynamics and climate change. Both cooling to the atmosphere and salinification, from evaporation or sea-ice formation, cause surface waters to become dense and down-well as turbulent convective plumes. The upper mixed layer in the ocean is significantly deepened and sustained by convection. In the tropics and subtropics, night-time cooling is a main driver of mixed layer convection, while in the mid- and high-latitude regions, winter cooling is key to mixed layer convection. Additionally, at higher latitudes, and particularly in the sub-polar North Atlantic Ocean, the extensive surface heat loss during winter drives open-ocean convection that can reach thousands of meters in depth. On the Antarctic continental shelf, polynya convection regulates the formation of dense bottom slope currents. These strong convection events help to drive the immense water-mass transport of the globally-spanning meridional overturning circulation (MOC). However, convection is often highly localised in time and space, making it extremely difficult to accurately measure in field observations. Ocean models such as global circulation models (GCMs) are unable to resolve convection and turbulence and, instead, rely on simple convective parameterizations that result in a poor representation of convective processes and their impact on ocean circulation, air–sea exchange, and ocean biology. In the past few decades there has been markedly more observations, advancements in high-resolution numerical simulations, continued innovation in laboratory experiments and improvement of theory for ocean convection. The impacts of anthropogenic climate change on ocean convection are beginning to be observed, but key questions remain regarding future climate scenarios. Here, we review the current knowledge and future direction of ocean convection arising from sea–surface interactions, with a focus on mixed layer, open-ocean, and polynya convection.
25
Pitchurov, George T., Detelin Markov, and Emanuil Georgiev. "Verification of the capacity of lubricating oil cooler system of turbine bearings." IOP Conference Series: Earth and Environmental Science 1128, no. 1 (January 1, 2023): 012019. http://dx.doi.org/10.1088/1755-1315/1128/1/012019.
Full textAbstract:
Abstract The capacity to cool the lubrication oil of hydraulic turbine bearings by submerged water heat exchangers has been verified. Calculations are done for existing heat exchangers and for retrofit ones. Input data from on-site measurements was used, as well as data for the physical constants. The goal of the study was to prove that the new heat exchangers’ efficiency is not less than that of the existing heat exchangers. The method of analysis elaborated on calculation of convective heat transfer coefficient. This was done for both a forced convection and an inhibited convection setup. It was debated that only the forced convection setup was a factor affecting the difference between both designs.
26
Nakagawa, Takashi, and Shun-ichiro Karato. "Influence of realistic rheological properties on the style of mantle convection: roles of dynamic friction and depth-dependence of rheological properties." Geophysical Journal International 226, no. 3 (May 11, 2021): 1986–96. http://dx.doi.org/10.1093/gji/ggab197.
Full textAbstract:
SUMMARY In order to generate plate tectonics, the near surface layer should not be too strong, but the causes for not-so-strong near surface layer remains unclear. We conduct mantle convection modelling in the spherical geometry to investigate the influence of the strength of the near surface layer. We explore a range of friction coefficients including the static high friction coefficient (∼0.6) as well as the reduced friction coefficients by fast fault motion in earthquakes. When the friction coefficient is low enough (<0.03), the surface layer is yielded by the convective stress, and the style of mantle convection appears the mobile-lid mode (plate tectonics style of convection). This style is relevant for the Earth where fault motion is unstable because of the low surface temperature. In contrast, for a high friction coefficient, the surface layer is too strong, generating the stagnant-lid mode. This case corresponds to Venus where fault motion is stable because of high surface temperature. Our calculations show that, in plate tectonic style of convection, the mantle convection is likely to be more vigorous, inducing the high convective stress that helps the operation of plate tectonics. In contrast, when stagnant-lid mode of convection appears, the convective vigor is likely to be low, inducing the low convective stress. Therefore, in each case, the interplay between the surface strength and convective stress tends to maintain the same mode of convection in a self-consistent way. We also investigate the relationship between mantle temperature and heat flux for two different modes of convection upon a change in friction coefficient. We found that the heat flow associated with mobile lid convection caused by low friction is less sensitive to the mantle temperature compared to a conventional mantle convection model, where the heat flow is highly sensitive to mantle temperature. This provides a possible mechanism to solve the thermal runaway paradox.
27
Kumar, Mahesh. "Experimental study on natural convection greenhouse drying of papad." Journal of Energy in Southern Africa 24, no. 4 (November 1, 2013): 37–43. http://dx.doi.org/10.17159/2413-3051/2013/v24i4a3144.
Full textAbstract:
In this paper, the convective heat transfer coefficients of papad for greenhouse drying under a natural convection mode are reported. Various experiments were conducted during the month of April 2010 at Guru Jambheshwar University of Science and Technology Hisar, India (29o5’5” N 75o45’55” E). Experimental data obtained for the natural convection greenhouse drying of papad was used to evaluate the constants in the Nusselt number expression by using simple linear regression analysis. These values of the constant were used further to determine the values of the convective heat transfer coefficient. The average value of a convective heat transfer coefficient was determined as 1.23 W/m2 oC. The experimental error in terms of percent uncertainty was also evaluated.
28
Zakharov N.S., Pokusaev B.G., Vyazmin A.V., Nekrasov D.A., Sulyagina O.A., and Moshin A.A. "Research of heat transfer processes in hydrogels by holographic interferometry and gradient thermometry." Technical Physics Letters 48, no. 5 (2022): 7. http://dx.doi.org/10.21883/tpl.2022.05.53551.19058.
Full textAbstract:
The study of natural convection in structured optically transparent materials using pure and combined agarose-gelatin gels was carried out by optical holography. The article presents data on visualization of the occurrence and development of convective flows in such gels with non-stationary conductive heating from below. The similarities and differences of the conditions of heat transfer and the occurrence of convection in structured materials and droplet liquids are analyzed. For the first time experimentally obtained data on the effect of two interpenetrating and interacting structured media on the transition from conductive to convective heat transfer. Keywords: natural convection in gels, optical holography, hydrogels, three-dimensional bioprinting.
29
Ma, Nancy, John Walker, David Bliss, and George Bryant. "Forced Convection During Liquid Encapsulated Crystal Growth With an Axial Magnetic Field." Journal of Fluids Engineering 120, no. 4 (December 1, 1998): 844–50. http://dx.doi.org/10.1115/1.2820749.
Full textAbstract:
This paper treats the forced convection, which is produced by the rotation of the crystal about its vertical centerline during the liquid-encapsulated Czochralski or Kyropoulos growth of compound semiconductor crystals, with a uniform vertical magnetic field. The model assumes that the magnetic field strength is sufficiently large that convective heat transfer and all inertial effects except the centripetal acceleration are negligible. With the liquid encapsulant in the radial gap between the outside surface of the crystal and the vertical wall of the crucible, the forced convection is fundamentally different from that with a free surface between the crystal and crucible for the Czochralski growth of silicon crystals. Again unlike the case for silicon growth, the forced convection for the actual nonzero electrical conductivity of an indium-phosphide crystal is virtually identical to that for an electrically insulating crystal. The electromagnetic damping of the forced convection is stronger than that of the buoyant convection. In order to maintain a given balance between the forced and buoyant convections, the angular velocity of the crystal must be increased as the magnetic field strength is increased.
30
Yu, D., T. A. Ameel, R. O. Warrington, and R. F. Barron. "Conjugate Heat Transfer With Buoyancy Effects From Micro-Chip Sized Repeated Heaters." Journal of Electronic Packaging 119, no. 4 (December 1, 1997): 275–80. http://dx.doi.org/10.1115/1.2792249.
Full textAbstract:
Laminar mixed convection heat transfer across five in-line microchipsized heaters, surface mounted on printed circuit board (PCB), was investigated by the weighted residual finite element method. The effects of axial heat conduction within the PCB for both mixed convection and pure forced convection are reported. The flow regime considered was 200 ≤ Re ≤ 800 and 0 ≤ Gr ≤ 58,000. Internal heat generation was included in the microchip-sized blocks in order to accurately model the thermal response to predict the maximum temperature rise. On the outer PCB walls, convective heat transfer conditions were given. Thermophysical and transport properties based on materials used in the electronics industry, including orthotropic thermal conductivity in PCB, were used. The flow and solid domains were solved simultaneously. A sensitivity study of PCB heat transfer coefficients, isotropic thermal conductivity, thermal conductivity variations, and spacing effects was performed. The mixed convection transient heating process was compared with the steady-state formulation to estimate the influence of flow oscillation in heat transfer. It was found that the maximum temperature rise in the microchips predicted by pure forced convection was, at most, 10 percent higher than that predicted by mixed convection. The difference in maximum temperature between the trailing and leading chips in the array was 30 percent.
31
BURR, ULRICH, and ULRICH MÜLLER. "Rayleigh–Bénard convection in liquid metal layers under the influence of a horizontal magnetic field." Journal of Fluid Mechanics 453 (February 25, 2002): 345–69. http://dx.doi.org/10.1017/s002211200100698x.
Full textAbstract:
This article presents an analytical and experimental study of magnetohydrodynamic Rayleigh–Bénard convection in a large aspect ratio, 20[ratio ]10[ratio ]1, rectangular box. The test fluid is a eutectic sodium potassium Na22K78 alloy with a small Prandtl number of Pr≈0:02. The experimental setup covers Rayleigh numbers in the range 103< Ra<8×104 and Chandrasekhar numbers 0[les ]Q[les ]1.44×106 or Hartmann numbers 0[les ]M[les ]1200, respectively.When a horizontal magnetic field is imposed on a heated liquid metal layer, the electromagnetic forces give rise to a transition of the three-dimensional convective roll pattern into a quasi-two-dimensional flow pattern in such a way that convective rolls become more and more aligned with the magnetic field. A linear stability analysis based on two-dimensional model equations shows that the critical Rayleigh number for the onset of convection of quasi-two-dimensional flow is shifted to significantly higher values due to Hartmann braking at walls perpendicular to the magnetic field. This finding is experimentally confirmed by measured Nusselt numbers. Moreover, the experiments show that the convective heat transport at supercritical conditions is clearly diminished. Adjacent to the onset of convection there is a significant region of stationary convection with significant convective heat transfer before the flow proceeds to time-dependent convection. However, in spite of the Joule dissipation effect there is a certain range of magnetic field intensities where an enhanced heat transfer is observed. Estimates of the local isotropy properties of the flow by a four-element temperature probe demonstrate that the increase in convective heat transport is accompanied by the formation of strong non-isotropic time-dependent flow in the form of large-scale convective rolls aligned with the magnetic field which exhibit a simpler temporal structure compared to ordinary hydrodynamic flow and which are very effective for the convective heat transport.
32
Alsulaiei, Zaher Mohammed Abed, Haider Jabaur Abid, R. Shakir, and Hawra Salah Hamid Ajimi. "Forecast Study on the Overall Coefficient for Passage of Single-Phase and Passage of Single-Phase in an Annular to Plain Tubes Heat Stream." IOP Conference Series: Earth and Environmental Science 1223, no. 1 (August 1, 2023): 012028. http://dx.doi.org/10.1088/1755-1315/1223/1/012028.
Full textAbstract:
Abstract To prevent buoyancy effects from increasing the overall heat transfer coefficient due to low heat flux, smooth vertical circular tubes require forced convection conjectures. Previous research has focused on mixed convection in turbulent regions and has limited studies on forced convective heat transfer. This study aims to investigate the predictable overall coefficients of heat transfer performance under specific conditions of forced convection, considering both vertical up flow and down flow through the smooth circular test section. The recommended Reynolds numbers for water are (7201.6–14577.4) and (3186.7–6396.75) for single-phase and single-phase annular passages, respectively, with a heat application range of (50–500 W). The overall coefficient of heat transfer is (333.91 - 432.95 W/m2.K) and (169.76 - 251.20 W/m2.K) for single-phase and single-phase annular passages, respectively. The flow was turbulent for all heat fluxes.
33
Jacobs, Harold R. "Convection heat transfer." International Journal of Heat and Fluid Flow 8, no. 1 (March 1987): 15. http://dx.doi.org/10.1016/0142-727x(87)90045-2.
Full text
34
Palotai, Csaba, Shawn Brueshaber, Ramanakumar Sankar, and Kunio Sayanagi. "Moist Convection in the Giant Planet Atmospheres." Remote Sensing 15, no. 1 (December 30, 2022): 219. http://dx.doi.org/10.3390/rs15010219.
Full textAbstract:
The outer planets of our Solar System display a myriad of interesting cloud features, of different colors and sizes. The differences between the types of observed clouds suggest a complex interplay between the dynamics and chemistry at play in these atmospheres. Particularly, the stark difference between the banded structures of Jupiter and Saturn vs. the sporadic clouds on the ice giants highlights the varieties in dynamic, chemical and thermal processes that shape these atmospheres. Since the early explorations of these planets by spacecrafts, such as Voyager and Voyager 2, there are many outstanding questions about the long-term stability of the observed features. One hypothesis is that the internal heat generated during the formation of these planets is transported to the upper atmosphere through latent heat release from convecting clouds (i.e., moist convection). In this review, we present evidence of moist convective activity in the gas giant atmospheres of our Solar System from remote sensing data, both from ground- and space-based observations. We detail the processes that drive moist convective activity, both in terms of the dynamics as well as the microphysical processes that shape the resulting clouds. Finally, we also discuss the effects of moist convection on shaping the large-scale dynamics (such as jet structures on these planets).
35
Siebers, D. L., R. F. Moffatt, and R. G. Schwind. "Experimental, Variable Properties Natural Convection From a Large, Vertical, Flat Surface." Journal of Heat Transfer 107, no. 1 (February 1, 1985): 124–32. http://dx.doi.org/10.1115/1.3247367.
Full textAbstract:
Natural convection heat transfer from a vertical, 3.02 m high by 2.95 m long, electrically heat surface in air was studied. The air was at the ambient temperature and the atmospheric pressure, and the surface temperature was varied from 60 C to 520 C. These conditions resulted in Grashof numbers up to 2 × 1012 and surface-to-ambient temperature ratios up to 2.7. Convective heat transfer coefficients were measured at 105 locations on the surface by an energy balance. Boundary layer mean temperature profiles were measured with a thermocouple. Results show that: (1) the turbulent natural convection heat transfer data are correlated by the expression Nuy=0.098Gry1/3TwT∞−0.14 when all properties are evaluated at T∞; (2) variable properties do not have a significant effect on laminar natural convection heat transfer; (3) the transition Grashof number decreases with increasing temperature; and (4) the boundary layer mean temperaturue profiles for turbulent natural convection can be represented by a “universal” temperature profile.
36
Goluskin, David, Hans Johnston, Glenn R. Flierl, and Edward A. Spiegel. "Convectively driven shear and decreased heat flux." Journal of Fluid Mechanics 759 (October 31, 2014): 360–85. http://dx.doi.org/10.1017/jfm.2014.577.
Full textAbstract:
AbstractWe report on direct numerical simulations of two-dimensional, horizontally periodic Rayleigh–Bénard convection between free-slip boundaries. We focus on the ability of the convection to drive large-scale horizontal flow that is vertically sheared. For the Prandtl numbers ($\mathit{Pr}$) between 1 and 10 simulated here, this large-scale shear can be induced by raising the Rayleigh number ($\mathit{Ra}$) sufficiently, and we explore the resulting convection for $\mathit{Ra}$ up to $10^{10}$. When present in our simulations, the sheared mean flow accounts for a large fraction of the total kinetic energy, and this fraction tends towards unity as $\mathit{Ra}\rightarrow \infty$. The shear helps disperse convective structures, and it reduces vertical heat flux; in parameter regimes where one state with large-scale shear and one without are both stable, the Nusselt number of the state with shear is smaller and grows more slowly with $\mathit{Ra}$. When the large-scale shear is present with $\mathit{Pr}\lesssim 2$, the convection undergoes strong global oscillations on long timescales, and heat transport occurs in bursts. Nusselt numbers, time-averaged over these bursts, vary non-monotonically with $\mathit{Ra}$ for $\mathit{Pr}=1$. When the shear is present with $\mathit{Pr}\gtrsim 3$, the flow does not burst, and convective heat transport is sustained at all times. Nusselt numbers then grow roughly as powers of $\mathit{Ra}$, but the growth rates are slower than any previously reported for Rayleigh–Bénard convection without large-scale shear. We find that the Nusselt numbers grow proportionally to $\mathit{Ra}^{0.077}$ when $\mathit{Pr}=3$ and to $\mathit{Ra}^{0.19}$ when $\mathit{Pr}=10$. Analogies with tokamak plasmas are described.
37
Journal, IJSREM. "HEAT TRANSFER ANALYSIS ON BASE OF HEAT SINK WITH UNIFORM HEAT GENERATION." INTERANTIONAL JOURNAL OF SCIENTIFIC RESEARCH IN ENGINEERING AND MANAGEMENT 08, no. 03 (March 1, 2024): 1–13. http://dx.doi.org/10.55041/ijsrem28936.
Full textAbstract:
The present work describes the important results of problem of combined conduction, convection and radiation from a rectangular heat sink base subjected to uniform internal heat generation in its base. The governing equations for temperature distribution within the base are obtained by a relevant energy balance between rate of heat generation, heat conducted, convected and radiated. The derived non-linear partial differential equations are converted into algebraic form using finite difference method with 2nd order accuracy. The obtained algebraic equations have been solved simultaneously by Gauss-siedel iterative method with stringent convergence criteria and a C code has been written for above purpose. The computational domain has been discretized uniformly in all directions. A grid convergence test has been carried out to optimize the size of element. A complete parametric study has been carried out to study the effect of material of heat sink, regime of convection and role of radiation on local temperature distribution and maximum heat sink base temperature. It has been observed that material with high conductivity decreases the local temperature gradient and thus the maximum temperature. The regime of convection has a great influence on maximum temperature of heat sink with 15K of drop in Tmax. for a change in flow regime from free convection to forced convection. A special study on exclusive role of convection on maximum temperature reveals that one should not ignore the role forced convection in heat dissipation. Key Words: Heat generation, Multimode heat transfer, Radiation
38
Lawrence, Jino, and Vanav Kumar Alagarsamy. "Fluid Flow and Heat Transfer Analysis of Quadratic Free Convection in a Nanofluid Filled Porous Cavity." International Journal of Heat and Technology 39, no. 3 (June 30, 2021): 876–84. http://dx.doi.org/10.18280/ijht.390322.
Full textAbstract:
The involvement of non-linear convection effects in a natural convective fluid flow and heat transfer along with the effects of magnetic field in a porous cavity is studied numerically. Cu-water filled cavity of higher temperature at the left wall and lower temperature at the right wall. The governing equations are organized to achieve the required flow by using two-dimensional equations of energy, continuity and momentum. Vorticity-stream function based dimensionless equations are solved using the finite difference techniques. The results are discussed for various dimensionless parameters such as the Darcy number, non-linear convection parameter, Hartmann number, Rayleigh number and solid volume fraction of the nanoparticles. An augment in streamline velocity and convection heat transfer are observed by increasing the Rayleigh number, non-linear convection parameter and Darcy number. The non-linear convection parameter has a lesser effect on the lower Rayleigh numbers. Diminished streamline intensity and reduction in convection heat transfer are noted for an increase in the strength of the applied magnetic field irrespective of the non-linear convection parameter.
39
Lv, Liugen, Yi Xiang, Zhipan Gu, and Chen Huang. "Dynamic characteristics of convection heat and radiation heat on building surfaces under cyclic heat flow." Science Progress 105, no. 1 (January 2022): 003685042210751. http://dx.doi.org/10.1177/00368504221075189.
Full textAbstract:
The dynamic heat transfer of building surfaces has thermal conduction, convection and radiation at the same time. It is the basis of building thermal environment simulation, air conditioning load calculation, building energy analysis and air conditioning system conservation operation. Under cyclic heat flow, the convection and radiation separating method was used to calculate the radiation heat and convection heat of building surfaces, and dynamic characteristics of convection heat and radiation heat on building surfaces was provided in this paper. For the dynamic heat transfer of building surfaces under cyclic heat flow, three indexes of peak error, mean error and average relative error were used to analyze dynamic heat transfer. The temperature distribution and dynamic heat transfer of convection heat and radiation heat of building surfaces were studied systematically. The separating cooling load and the room cooling load were basically consistent with each other, the convection and radiation separating method was reliable and available. The peak value of convection heat corresponded to the foot value of the radiation heat, and the relative error of them was 1.9%-2.2%. The dynamic characteristics of radiation heat and convection heat had important reference for the study of dynamic heat transfer of building surfaces under cyclic heat flow.
40
Giorgi, Claudio, and Federico Zullo. "Entropy Rates and Efficiency of Convecting-Radiating Fins." Energies 14, no. 6 (March 16, 2021): 1643. http://dx.doi.org/10.3390/en14061643.
Full textAbstract:
We present a novel indicator for the effectiveness of longitudinal, convecting-radiating fins to dissipate heat. Starting from an analysis of the properties of the entropy rate of the steady state, we show how it is possible to assess the efficiency of such devices by looking at the amount of entropy produced in the heat transfer process. Our study concerns both purely convective fins and convection-radiant fins and takes advantage of explicit expressions for the distribution of heat along the fin. It is shown that, in a suitable limit, the standard definition of efficiency and the entropic definition coincide. The role of the fluid temperature is explicit in the new definition and in the purely convective case. An application to an aluminium fin is given. Analytical and numerical results are discussed.
41
Turmukhambetov, A. Zh. "FRACTAL-STRUCTURAL ANALYSIS OF CONVECTION HEAT TRANSFER IN A TURBULENT MEDIUM." Eurasian Physical Technical Journal 17, no. 2 (December 24, 2020): 61–68. http://dx.doi.org/10.31489/2020no2/61-68.
Full textAbstract:
The features of convective heat transfer of bodies in a turbulent environment are considered. The results of experimental research by one of the authors are discussed. Experimental data show that the heat transfer of a spherical body is affected by natural convection, the thermo-physical properties of the medium, the tightness of the flow, the turbulent flow regime, etc. Due to these factors, the formula for calculating convective heat transfer, which includes many experimental constants, becomes cumbersome and inconvenient for practical application. The paper presents the results of applying fractal-structural analysis methods to describe experimental data on convective heat exchange of badly streamlined (cylinder and sphere) bodies in a channel. Quantitative relations are obtained that link the intensity of turbulent heat transfer with the criteria for the degree of self-organization.
42
Khaled, A. R. A. "Maximizing Heat Transfer Through Joint Fin Systems." Journal of Heat Transfer 128, no. 2 (September 14, 2005): 203–6. http://dx.doi.org/10.1115/1.2137764.
Full textAbstract:
Heat transfer through joint fins is modeled and analyzed analytically in this work. The terminology “joint fin systems” is used to refer to extending surfaces that are exposed to two different convective media from its both ends. It is found that heat transfer through joint fins is maximized at certain critical lengths of each portion (the receiver fin portion which faces the hot side and the sender fin portion that faces the cold side of the convective media). The critical length of each portion of joint fins is increased as the convection coefficient of the other fin portion increases. At a certain value of the thermal conductivity of the sender fin portion, the critical length for the receiver fin portion may be reduced while heat transfer is maximized. This value depends on the convection coefficient for both fin portions. Thermal performance of joint fins is increased as both thermal conductivity of the sender fin portion or its convection coefficient increases. This work shows that the design of machine components such as bolts, screws, and others can be improved to achieve favorable heat transfer characteristics in addition to its main functions such as rigid fixation properties.
43
Nigen, J. S., and C. H. Amon. "Time-Dependent Conjugate Heat Transfer Characteristics of Self-Sustained Oscillatory Flows in a Grooved Channel." Journal of Fluids Engineering 116, no. 3 (September 1, 1994): 499–507. http://dx.doi.org/10.1115/1.2910305.
Full textAbstract:
Convective heat transport in a grooved channel is numerically investigated using a time-dependent formulation. Conjugate conduction/convection and uniform heat-flux representations for the solid domain are considered. For the conjugate representation, the solid domain is composed of multiple materials and concentrated heat generation. The associated cooling flows include laminar and transitional regimes. Steady and time-dependent contours of the streamfunction and local skin-friction coefficients are presented. Additionally, local distributions of Nusselt number and surface temperature are displayed for both the conjugate and convection-only representations. These results are contrasted over the range of Reynolds numbers explored to demonstrate the significance of including time-dependency and conjugation in the study of convective heat transport. Such considerations are found to be important in the design and analysis of heat exchanger configurations with spatially varying material composition and concentrated heat generation.
44
Molinari, John, Jaclyn Frank, and David Vollaro. "Convective Bursts, Downdraft Cooling, and Boundary Layer Recovery in a Sheared Tropical Storm." Monthly Weather Review 141, no. 3 (March 1, 2013): 1048–60. http://dx.doi.org/10.1175/mwr-d-12-00135.1.
Full textAbstract:
Abstract Tropical Storm Edouard (2002) experienced episodic outbreaks of convection downshear within the storm core in the presence of 11–15 m s−1 of ambient vertical wind shear. These outbreaks lasted 2–6 h and were followed by long periods with no deep convection. Flights from U.S. Air Force reconnaissance aircraft within the boundary layer were used to investigate the cause of one such oscillation. Low equivalent potential temperature θe air filled the boundary layer as convection ceased, creating a 4–6-K deficit in θe within the convective region. Soundings within 110 km of the center were supportive of convective downdrafts, with midlevel relative humidity below 15% and large downdraft CAPE. Deep convection ceased within 75 km of the center for more than 8 h. Tangential velocity reached hurricane force locally during the convective outbreak, then became nearly symmetric after convection stopped, arguably as a result of axisymmetrization, and the storm weakened. Nevertheless, the corresponding lack of convective downdrafts during this period allowed surface heat and moisture fluxes to produce substantial increases in boundary layer entropy. A new burst of convection followed. Consistent with recent papers it is argued that tropical cyclone intensification and decay can be understood as a competition between surface heat and moisture fluxes (“fuel”) and low-entropy downdrafts into the boundary layer (“antifuel”).
45
Musielak, Grzegorz, Dominik Mierzwa, and Joanna Łechtańska. "Experimental Investigation of Enhancement of Natural Convective Heat Transfer in Air Using Ultrasound." Applied Sciences 13, no. 4 (February 15, 2023): 2516. http://dx.doi.org/10.3390/app13042516.
Full textAbstract:
One of the methods to improve convective heat exchange is the application of ultrasound assistance. However, little is known about ultrasound application in the air. The main purpose of this study is to investigate the effect of ultrasound on natural convection cooling. The tests are based on the cooling of the metal samples (in four different shapes) preheated to a temperature of 60 °C. Cooling takes place in free convection without and with the use of ultrasound at different powers (50 W, 100 W, 150 W, and 200 W). The study uses a mathematical model based on a small Biot’s number assumption. The values of the convective heat exchange coefficients are determined by using an approximation of the experimental results. The coefficients obtained are an increasing exponential function of the applied ultrasound power. This study indicates the possibility of using ultrasound to improve heat transfer by free convection.
46
Motegi, Kosuke, Yasuteru Sibamoto, Takashi Hibiki, Naofumi Tsukamoto, and Junichi Kaneko. "Opposing Mixed Convection Heat Transfer for Turbulent Single-Phase Flows." International Journal of Energy Research 2024 (January 16, 2024): 1–22. http://dx.doi.org/10.1155/2024/6029412.
Full textAbstract:
Convection, wherein forced and natural convections are prominent, is known as mixed convection. Specifically, when a forced convection flow is downward, this flow is called opposing flow. The objectives of this study are to gain a comprehensive understanding of opposing flow mixed convection heat transfer and to establish the prediction methodology by evaluating existing correlations and models. Several heat transfer correlations have been reported related to single-phase opposing flow; however, these correlations are based on experiments conducted in various channel geometries, working fluids, and thermal flow parameter ranges. Because the definition of nondimensional parameters and their validated range confirmed by experiments differ for each correlation reported in previous studies, establishing a guideline for deciding which correlation should be selected based on its range of applicability and extrapolation performance is important. This study reviewed the existing heat transfer correlations for turbulent opposing flow mixed convection and the single-phase heat transfer correlations implemented in the thermal–hydraulic system codes. Furthermore, the authors evaluated the predictive performance of each correlation by comparing them with the experimental data obtained under various experimental conditions. The Jackson and Fewster, Churchill, and Swanson and Catton correlations can accurately predict all the experimental data. The effect of the difference in the thermal boundary conditions, i.e., uniform heat flux and uniform wall temperature, on the turbulent mixed convection heat transfer coefficient is not substantial. The authors confirmed that heat transfer correlations using the hydraulic-equivalent diameter as a characteristic length can be used for predictions regardless of channel-geometry differences. Furthermore, correlations described based on nondimensional dominant parameters can be used for predictions regardless of the differences in working fluids. The authors investigated the extrapolation performance of the mixed convection heat transfer correlations for a wide range of nondimensional parameters and observed that the Jackson and Fewster, Churchill, and Aicher and Martin correlations exhibit excellent extrapolation performance with respect to natural and forced convection flows, indicating that they can be applied beyond the parameter range validated experimentally.
47
Kladias, N., and V. Prasad. "Flow Transitions in Buoyancy-Induced Non-Darcy Convection in a Porous Medium Heated From Below." Journal of Heat Transfer 112, no. 3 (August 1, 1990): 675–84. http://dx.doi.org/10.1115/1.2910440.
Full textAbstract:
Thermoconvective instabilities in horizontal porous layers heated from below are studied numerically by employing the Brinkman-Forchheimer extended Darcy formulation. The onsets of stable and oscillatory convection are found to be strong functions of the governing parameters: fluid Rayleigh and Prandtl numbers, Darcy number, and conductivity ratio. The effects of porosity and specific heat ratio are pronounced only in the fluctuating convection regime. At the onset, the oscillatory convection is highly periodic, but with an increase in convective motions the disorder increases monotonically and the fluctuations become highly random. These results do not confirm the possibility of reverse transition from a more-disordered to a less-disordered state as predicted by the Darcy model (Kimura et al., 1986). The applicability of Darcy formulation is thus highly restricted in the case of a Be´nard convection problem. In a randomly oscillating convective state, the heat transfer rate varies substantially with time.
48
Zhang, Jianfei, Chu Zhao, Hongyan Li, and Wenquan Tao. "3D Numerical Simulation of Heat Transfer of a Heated Plate under the Electric Field Generated by a Needle Electrode." Mathematical Problems in Engineering 2014 (2014): 1–10. http://dx.doi.org/10.1155/2014/354180.
Full textAbstract:
A three-dimensional numerical model that couples the electric field, velocity field, and temperature field is developed based on the commercial code COMSOL Multiphysics. The influences of several factors on convective heat transfer on a heated plate in the electric field generated by a needle electrode are observed. The factors are the applied voltage, the distance between the two electrodes, and the size of the ground plate. The results show that applied voltage is one of the most important factors for the convection heat transfer. The convection heat transfer efficiency significantly increases with the improvement of the applied voltage. From the perspective of the model size, the decrease of the distance between two electrodes and the size of the plate could improve the average convection heat transfer coefficient. Smaller ionic wind device needs lower applied voltage and less electric energy to obtain the same average convection heat transfer coefficient as the bigger one, which provides the theoretical basis for the potential of miniaturizing the ionic wind cooling device.
49
Wang, Jian Sheng, and Yong Xu. "Effect of Surface Radiation on Conjugate Natural Convection in a Square Enclosure with a Tube at Different Locations." Applied Mechanics and Materials 281 (January 2013): 190–96. http://dx.doi.org/10.4028/www.scientific.net/amm.281.190.
Full textAbstract:
The conjugate natural convection heat transfer with and without the interaction of the surface radiation in a square enclosure was carried out by numerical simulation. The vertical walls of the square enclosure were heated with different temperatures, and the others were adiabatic. A circular tube was inserted into the square enclosure. It was observed that varied location of the tube center can lead to different motion and heat transfer intensities. In addition, surface radiation reduces the convective heat transfer in the square enclosure compared to the pure natural convection case and enhances the overall heat transfer performance.
50
Finn, D. P., P. F. Monaghan, and P. H. Oosthuizen. "Heat Transfer to Unfrosted Wind Convectors: Mathematical Modeling and Comparison With Experimental Results." Journal of Solar Energy Engineering 112, no. 4 (November 1, 1990): 280–86. http://dx.doi.org/10.1115/1.2929935.
Full textAbstract:
Wind convectors are an alternative air source evaporator system for heat pumps. This paper describes a mathematical model that calculates the heat transfer to wind convectors when forced convection conditions prevail and when wind convector surface frost and rainfall are absent. The mathematical model is validated and predicts heat transfer to within 8 percent of experimental data based on a root mean square difference estimation. Further simulation studies show that heat transfer to wind convectors is dominated by sensible convection and latent heat transfer, that longwave radiation contributes less than 5 percent of total heat transfer and that solar radiation can contribute up to 25 percent of total heat transfer under optimum conditions.