Artículos de revistas: "Heat transfer limit"

1

Li, Xi Bing, Shi Gang Wang, Jian Hua Guo y Dong Sheng Li. "A Mathematical Modeling Method on Micro Heat Pipe with a Trapezium-Grooved Wick Structure". Applied Mechanics and Materials 29-32 (agosto de 2010): 1686–94. http://dx.doi.org/10.4028/www.scientific.net/amm.29-32.1686.

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With heat flux increasing and cooling space decreasing in the products in microelectronics and chemical engineering, micro heat pipe has become an ideal heat radiator for products with high heat flux. Through analyzing the factors influencing the structure, strength and heat transfer limits of circular micro heat pipe with trapezium-grooved wick structure, the heat transfer models are established in this paper, including the models of viscous limit, sonic limit, entrainment limit, capillary limit, condensing limit, boiling limit, continuous flow limit and frozen startup limit. The study lays a powerful theoretical foundation for the design and manufacture of circular micro heat pipe with a trapezium-grooved wick structure.

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2

Dobran, Flavio. "Suppression of the Sonic Heat Transfer Limit in High-Temperature Heat Pipes". Journal of Heat Transfer 111, n.º 3 (1 de agosto de 1989): 605–10. http://dx.doi.org/10.1115/1.3250725.

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The design of high-performance heat pipes requires optimization of heat transfer surfaces and liquid and vapor flow channels to suppress the heat transfer operating limits. In the paper an analytical model of the vapor flow in high-temperature heat pipes is presented, showing that the axial heat transport capacity limited by the sonic heat transfer limit depends on the working fluid, vapor flow area, manner of liquid evaporation into the vapor core of the evaporator, and lengths of the evaporator and adiabatic regions. Limited comparisons of the model predictions with data of the sonic heat transfer limits are shown to be very reasonable, giving credibility to the proposed analytical approach to determine the effect of various parameters on the axial heat transport capacity. Large axial heat transfer rates can be achieved with large vapor flow cross-sectional areas, small lengths of evaporator and adiabatic regions or a vapor flow area increase in these regions, and liquid evaporation in the evaporator normal to the main flow.

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3

Martin, Michael J. y Iain D. Boyd. "Stagnation-Point Heat Transfer Near the Continuum Limit". AIAA Journal 47, n.º 1 (enero de 2009): 283–85. http://dx.doi.org/10.2514/1.39789.

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4

Bertoli, Sávio L., José Alexandre B. Valle, Antônio G. Gerent y Juliano de Almeida. "Heat transfer at pneumatic particle transport — Limit solutions". Powder Technology 232 (diciembre de 2012): 64–77. http://dx.doi.org/10.1016/j.powtec.2012.07.050.

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5

Kashi, Barak y Herman D. Haustein. "Microscale sets a fundamental limit to heat transfer". International Communications in Heat and Mass Transfer 104 (mayo de 2019): 1–7. http://dx.doi.org/10.1016/j.icheatmasstransfer.2019.02.003.

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6

Li, Xi Bing, Chang Long Yang, Gong Di Xu, Wen Yuan y Shi Gang Wang. "A Mathematical Modeling Method for Capillary Limit of Micro Heat Pipe with Sintered Wick". Solid State Phenomena 175 (junio de 2011): 335–41. http://dx.doi.org/10.4028/www.scientific.net/ssp.175.335.

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With heat flux increasing and cooling space decreasing in microelectronic and chemical products, micro heat pipe has become an ideal heat dissipation device in high heat-flux products. Through the analysis of its working principle, the factors that affect its heat transfer limits and the patterns in which copper powders are arrayed in circular cavity, this paper first established a mathematical model for the crucial factors in affecting heat transfer limits in a circular micro heat pipe with a sintered wick, i.e. a theoretical model for capillary limit, and then verified its validity through experimental investigations. The study lays a powerful theoretical foundation for designing and manufacturing circular micro heat pipes with sintered wicks.

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7

OGUSHI, Tetsuro y Goro YAMANAKA. "Heat transfer performance of axial grooved heat pipes. The capillary pumping limit." Transactions of the Japan Society of Mechanical Engineers Series B 53, n.º 486 (1987): 600–607. http://dx.doi.org/10.1299/kikaib.53.600.

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8

Williams, Richard R. y Daniel K. Harris. "The heat transfer limit of step-graded metal felt heat pipe wicks". International Journal of Heat and Mass Transfer 48, n.º 2 (enero de 2005): 293–305. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2004.08.024.

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9

Michiyoshi, I., O. Takahashi y Y. Kikuchi. "Heat transfer and the low limit of film boiling". Experimental Thermal and Fluid Science 2, n.º 3 (julio de 1989): 268–79. http://dx.doi.org/10.1016/0894-1777(89)90016-2.

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10

Arpacı, V. S. y S. H. Kao. "Thermocapillary Driven Turbulent Heat Transfer". Journal of Heat Transfer 120, n.º 1 (1 de febrero de 1998): 214–19. http://dx.doi.org/10.1115/1.2830044.

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A dimensionless number depending on the usual Prandtl and Marangoni numbers, Πs ∼ Ma/(1 + Pr1) = Ma Pr/(1 + Pr), is introduced for thermocapillary driven flows. Three heat transfer models are proposed in terms of Πs. The first model on laminar flow, using some dimensional arguments with a flow scale and the boundary layer concept, leads to Nu ∼ Πs1/4, Nu being the usual Nusselt number. The second model on transition flow, extending Landau’s original idea on the amplitude of disturbances past marginal stability of isothermal flow, leads to Nu − 1 ∼ (ΠS−ΠSc)1/2, ΠSc corresponding to the critical value of Πs for the marginal state. The third model on turbulent flow, introduces a thermal microscale ηθ ∼ (1 + Pr-1)1/4(να2/Ps)1/4 = (1 + Pr)1/4 (α3/Ps)1/4, with ν and α, respectively, being kinematic and thermal diffusivities, and Ps the production rate of thermocapillary energy. The first expression relating ηθ to Prandtl number explicitly includes its limit for Pr → ∞, ηθB ∼ (να2/ε)1/4, which is a Batchelor scale, and the second one explicitly includes its limit for Pr → 0, ηθC ∼ (α3/ε)1/4, which is an Oboukhov-Corrsin scale. In terms of ηθ and an integral scale l, the model leads to Nu ∼ l/ηθ ∼ Πs1/3. Recent experimental literature are interpreted by special cases of the foregoing models corresponding to Pr > 1.

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11

Ma, H. B. y G. P. Peterson. "The Influence of the Thermal Conductivity on the Heat Transfer Performance in a Heat Sink". Journal of Electronic Packaging 124, n.º 3 (26 de julio de 2002): 164–69. http://dx.doi.org/10.1115/1.1478058.

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An extensive numerical analysis of the temperature distribution and fluid flow in a heat sink currently being used for cooling desktop computers was conducted, and demonstrated that if the base of a heat sink was fabricated as a heat pipe instead of a solid material, the heat transfer performance could be significantly increased. It was shown that as the heat sink length increases, the effect of the thermal conductivity of the base on the heat transfer performance increases to be a predictable limit. As the thermal conductivity is increased, the heat transfer performance of heat sinks is enhanced, but cannot exceed this limit. When the thermal conductivity increases to 2,370 W/m-K, the heat transfer performance of the heat sinks will be very close to the heat transfer performance obtained assuming a base with infinite thermal conductivity. Further increases in the thermal conductivity would not significantly improve the heat transfer performance of the heat sinks.

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12

Andrews, M. J. y L. S. Fletcher. "Comparison of Several Heat Transfer Enhancement Technologies for Gas Heat Exchangers". Journal of Heat Transfer 118, n.º 4 (1 de noviembre de 1996): 897–902. http://dx.doi.org/10.1115/1.2822586.

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A comparative study about the performance of several enhanced heat transfer technologies for gas heat exchangers is presented. A Reynolds number range from 100 to 50,000 is considered for plate heat exchangers and the tube side of shell-and-tube heat exchangers. A volumetric performance measure has been adopted to evaluate the comparative performance of widely different technologies. The performance parameter, based on the heat transfer rate per unit pumping power, is suitable for different geometries, Reynolds numbers, and fluid properties. Modern technologies can achieve significant heat transfer enhancement, but comparison reveals that recent advances offer only marginal improvements that are often associated with more complex technology. Care must be exercised in choosing a technology because the best performing one is not necessarily the preferred choice since construction, retrofit, and maintenance costs may significantly alter the economic viability. However, there is an intrinsic interest in the comparative performance of very different technologies. Our performance evaluation indicates an upper limit may exist for single-mode convective heat transfer enhancement and compound enhancement may exceed this limit.

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13

Shang, Fumin, Shilong Fan, Qingjing Yang, Chaoyue Liu y Jianhong Liu. "Study on heat transfer characteristics of single-layer double-row pulsating heat pipe". Thermal Science, n.º 00 (2021): 253. http://dx.doi.org/10.2298/tsci210226253s.

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The structure and inclination angle of a pulsating heat pipe are critical factors influencing the heat transfer performance and operation mode. In this work, a single-layer double-row pulsating heat pipe is designed, and the start-up and heat transfer characteristics of pulsating heat pipe at limit angles (0?,90?, and 180?) are experimentally investigated. Also, the operation mode and heat transfer characteristics are studied through IR imager and temperature profiles. The study highlighted that the pulsating heat pipe has excellent operation characteristics in the limit angle. When the inclination angle is 0?, the double-row structure improves the start-up performance; at 90? inclination, the pulsating heat pipe starts the fastest, and the heat transfer resistance keeps the smallest in the whole test. When the inclination angle is 180?, the pulsating heat pipe has the best thermal sensitivity but weak working fluid flow capacity during operation.

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14

NODA, Hidehiko, Keisuke YOSHIOKA y Toshiro HAMATAKE. "A model for the heat transfer limit of a screen wick heat pipe." Transactions of the Japan Society of Mechanical Engineers Series B 53, n.º 494 (1987): 3118–23. http://dx.doi.org/10.1299/kikaib.53.3118.

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15

Wang, Shi Gang, Xi Bing Li, Bai Rui Tao y Hong Xia Zhang. "An Experimental Investigation on Micro Heat Pipe with a Trapezium-Grooved Wick Structure". Applied Mechanics and Materials 29-32 (agosto de 2010): 1695–700. http://dx.doi.org/10.4028/www.scientific.net/amm.29-32.1695.

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Through combination of experimental investigation with theoretical optimum design, this paper determined the crucial factors in affecting the heat transfer capacity in micro heat pipes with a trapezium-grooved wick structure are capillary limit and entrainment limit, and verified the validity of the heat transfer models thus built.

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16

Ito, Kota, Kazutaka Nishikawa, Atsushi Miura, Hiroshi Toshiyoshi y Hideo Iizuka. "Dynamic Modulation of Radiative Heat Transfer beyond the Blackbody Limit". Nano Letters 17, n.º 7 (12 de junio de 2017): 4347–53. http://dx.doi.org/10.1021/acs.nanolett.7b01422.

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17

Park, Hansaem y Min Soo Kim. "Theoretical Limit on COP of a Heat Pump from a Sequential System". International Journal of Air-Conditioning and Refrigeration 23, n.º 04 (diciembre de 2015): 1550029. http://dx.doi.org/10.1142/s2010132515500297.

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The theoretical limit on Coefficient of performance (COP), which is maximum and ideal one, is investigated with a sequential Carnot heat pump where multiple Carnot heat pumps are interconnected in parallel. Using fundamental relations from thermodynamics and heat transfer, the performance of a sequential Carnot heat pump is obtained analytically. The effect of major parameters of the system, such as the number of individual heat pumps in a sequential system, the number of transfer unit of heat exchangers, and temperatures of heat sources, on the performance is researched. Also, expressions for ideal COP derived by limit calculation when the system has an infinite number of Carnot heat pumps or infinite number of transfer unit are suggested. For example, the most ideal COP is the ratio of the final heat source temperature to the difference between the initial and final heat source temperature. To support the result of theoretical analysis, a simple simulation of sequential Carnot heat pumps is carried out with thermodynamic properties of real refrigerants. The result of a simulation quite accords with that of theoretical analysis.

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18

Nicoli, C. y P. Pelcé. "One-dimensional model for the Rijke tube". Journal of Fluid Mechanics 202 (mayo de 1989): 83–96. http://dx.doi.org/10.1017/s0022112089001102.

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We develop a simple model in which longitudinal, compressible, unsteady heat transfer between heater and gas is computed in the small-Mach-number limit. This calculation is used to determine the transfer function of the heater, which plays an important role in the stability limits of the thermoacoustic instability of the Rijke tube. The transfer function is determined analytically in the limit of small expansion parameter γ, and numerically for γ of order unity. In the case ρμ/cp = constant, an analytical solution can be found.

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19

Li, Xi Bing, Z. M. Shi, S. G. Wang, Q. M. Hu, L. Bao y H. J. Zhang. "Analysis of Structural Parameters of Grooved-Wicksin Micro Heat Pipes Based on Capillary Limits". Key Engineering Materials 499 (enero de 2012): 21–26. http://dx.doi.org/10.4028/www.scientific.net/kem.499.21.

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For great progress in heat pipe technology, a micro heat pipe has become an ideal heat dissipating device in high heat-flux electronic products, and capillary limit is the main factor affecting its heat transfer performance. Based on analyses of capillary limit and currently commonly-used groove structures, this paper built capillary limit models for micro heat pipes with dovetail-groove, rectangular-groove, trapezoidal-groove and V-groove wick structures respectively for theoretical analyses. The analysis results show that better heat transfer performances can be obtained in micro heat pipes with small-angle dovetail (i.e. a sector structure), rectangular and small-angle trapezoidal grooved wick structures when groove depth is 0.2-0.3mm and top-width-to-depth ratio is 1.2-1.5.

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20

Hui, C. Y. y K. S. Cheng. "Anisotropic Heat Transfer Inside Rotating Neutron Stars". Symposium - International Astronomical Union 218 (2004): 39–40. http://dx.doi.org/10.1017/s0074180900180520.

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We have developed the anisotropic heat transport equation for rotating neutron stars. With a simple model of neutron star, we also model the propagation of heat pulses resulting from transient energy releases inside the star. Even in the slow rotation limit, the results with rotational effects involved could differ significantly from those obtained with a spherically symmetric metric in the timescale of the thermal afterglow.

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21

Subramanian, Rajkumar y M. A. Jog. "Enhancement of Heat Transfer by an Electric Field for a Drop Translating at Intermediate Reynolds Number". Journal of Heat Transfer 127, n.º 10 (5 de mayo de 2005): 1087–95. http://dx.doi.org/10.1115/1.2033906.

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The enhancement of heat transfer by an electric field to a spherical droplet translating at intermediate Reynolds number is numerically investigated using a finite volume method. Two heat transfer limits are considered. The first limit is the external problem where the bulk of the resistance is assumed to be in the continuous phase. Results show that the external Nusselt number significantly increases with electric field strength at all Reynolds numbers. Also, the drag coefficient increases with electric field strength. The enhancement in heat transfer is higher with lower ratio of viscosity of the dispersed phase to the viscosity of the continuous phase. The second heat transfer limit is the internal problem where the bulk of the resistance is assumed to be in the dispersed phase. Results show that the steady state Nusselt number for a combined electrically induced and translational flow is substantially greater than that for purely translational flow. Furthermore, for a drop moving at intermediate Reynolds number, the maximum steady state Nusselt number for a combined electrically induced and translational flow is slightly greater than that for a purely electric field driven motion in a suspended drop.

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22

Guillemette, Christina U., Quinn E. Fletcher, Stan Boutin, Ryan M. Hodges, Andrew G. McAdam y Murray M. Humphries. "Lactating red squirrels experiencing high heat load occupy less insulated nests". Biology Letters 5, n.º 2 (16 de diciembre de 2008): 166–68. http://dx.doi.org/10.1098/rsbl.2008.0592.

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The heat dissipation limit hypothesis suggests that the capacity for lactating mammals to transfer energy to their offspring through milk may be constrained by limits on heat dissipation, particularly in species that raise offspring in well-insulated nests. We tested a prediction of this hypothesis by evaluating whether lactating free-ranging red squirrels ( Tamiasciurus hudsonicus ) occupy less insulated nests when experiencing conditions that increase heat load. In support of the hypothesis, when climate normal ambient temperatures were warm, squirrels supporting large litter masses of furred offspring occupied nests of lower insulative value. These results support the heat dissipation limit hypothesis and suggest that free-ranging mammals may select nests based on their insulative value, not only to reduce heat loss in cold conditions but also to dissipate heat during periods of heat stress.

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23

Yuan, Suo Xian, Ming Hu y Guang Qi Cai. "Research on the Heat Partition Ratios in Grinding Area". Advanced Materials Research 76-78 (junio de 2009): 72–75. http://dx.doi.org/10.4028/www.scientific.net/amr.76-78.72.

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Grinding temperature is the main factor to limit the improvement of grinding efficiency. The main reason of grinding temperature rise is amount of heat transfer into the workpiece in grinding process. How to determine the proportion ratio, which heat transfers into the workpiece, is the main research issue to the precise machining scholars. In this paper, the heat resistance model is used to analyze the proportional coefficient about how much heat transfer into the grinding wheel, and the factors which to influence this coefficient are discussed. The moving heat source method is used to calculate the temperature field caused by single grain heat source, and the heat integral method is used to calculate the heat contains by the grinding chip, and then the heat proportional coefficients transferring into the chip and workpiece are determined respectively.

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24

Huda, Hairul, Renanto Handogo, Totok Ruki Biyanto, Wei Wu y Vincentius Surya Kurnia Adi. "Oil Refinery Heat Exchanger Network Cleaning Scheduling Strategy with Unit Cleanability Consideration". ASEAN Journal of Chemical Engineering 20, n.º 1 (29 de junio de 2020): 31. http://dx.doi.org/10.22146/ajche.51880.

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Heat exchanger networks (HENs) play an important role in the chemical industries. Unfortunately, fouling is inevitable in heat exchangers operation. Therefore, the optimal cleaning procedure is required to restore heat exchangers' performance periodically. A systematic cleaning scheduling strategy for the heat exchanger network in an oil refinery is proposed in this work. There are 11 operating heat exchangers in an oil refinery to be reviewed. Different cleaning decision scenarios based on the overall heat transfer coefficient are explored for optimal cleaning schedule performance. The daily number of exchangers available to be cleaned i.e., the unit cleanability, is investigated while minimizing the energy consumption and the additional heat requirement due to the offline heat exchanger under cleaning procedure. The HEN performance and the energy-saving from the cleaning procedures are benchmarked with the uncleaned HEN. The results indicate that the cleaning procedure significantly increases the HEN performance and simultaneously reduces the heat requirement if compared to the untreated HEN benchmark. The possible conflicting situation is discussed when some heat exchangers are waiting to be cleaned due to the unit cleanability restriction, which allows the overall heat transfer coefficient to be below the allowed limit. Therefore, nonconflicting cleaning scheduling is also addressed in this work by relaxing the unit cleanability limit. Furthermore, the optimal cleaning schedule is also suggested for user reference. In this work, the optimum cleaning schedule with minimum energy consumption and maximum energy saving could be achieved when cleaning decision limit is set at 40% decrease of overall heat transfer coefficient. In the contrast, the lowest number of cleaning procedures is associated with 90% decrease in the overall heat transfer coefficient as the cleaning decision limit.

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25

Shih, Tom I. P., Yu-Liang Lin y Mark A. Stephens. "Fluid Flow and Heat Transfer in an Internal Coolant Passage". International Journal of Rotating Machinery 7, n.º 5 (2001): 351–64. http://dx.doi.org/10.1155/s1023621x0100029x.

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Computations were performed to study the three-dimensional flow and heat transfer in a U-shaped duct of square cross section with inclined ribs on two opposite walls under rotating and non-rotating conditions. Two extreme limits in the Reynolds number (25,000 and 350,000) were investigated. The rotation numbers investigated are 0, 0.24, and 0.039. Results show rotation and the bend to reinforce secondary flows that align with it and to retard those that do not. Rotation was found to affect significantly the flow and heat transfer in the bend even at a very high Reynolds number of 350,000 and a very low Rotation number of 0:039. When there is no rotation, the flow and heat transfer in the bend were dominated by rib-induced secondary flows at the high Reynolds number limit and by bend-induced pressure-gradients at the low Reynolds number limit. Long streaks of reduced surface heat transfer occur in the bend at locations where streamlines from two contiguous secondary flows merge and then flow away from the surface. The location and size of these streaks varied markedly with Reynolds and rotation numbers.This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy. Turbulence is modelled by the low-Reynolds shear-stress transport (SST) model of Menter. Solutions were generated by using a cell-centered, finite-volume method, that is based on second-order accurate flux-difference splitting and a diagonalized alternating-direction implicit scheme with local time-stepping and V-cycle multigrid.

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26

Schwarz, Florian, Vladimir Danov, Alexander Lodermeyer, Alexander Hensler y Stefan Becker. "Thermodynamic Analysis of the Dryout Limit of Oscillating Heat Pipes". Energies 13, n.º 23 (1 de diciembre de 2020): 6346. http://dx.doi.org/10.3390/en13236346.

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The operating limits of oscillating heat pipes (OHP) are crucial for the optimal design of cooling systems. In particular, the dryout limit is a key factor in optimizing the functionality of an OHP. As shown in previous studies, experimental approaches to determine the dryout limit lead to contradictory results. This work proposes a compact theory to predict a dryout threshold that unifies the experimental and analytical data. The theory is based on the influence of vapor quality on the flow pattern. When the vapor quality exceeds a certain limit (x = 0.006), the flow pattern changes from slug flow to annular flow and the heat transfer decreases abruptly. The results indicate a uniform threshold value, which has been validated experimentally and by the literature. With that approach, it becomes possible to design an OHP with an optimized filling ratio and, hence, substantially improve its cooling abilities.

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27

Kim, Kyung Mo y In Cheol Bang. "Heat transfer characteristics and operation limit of pressurized hybrid heat pipe for small modular reactors". Applied Thermal Engineering 112 (febrero de 2017): 560–71. http://dx.doi.org/10.1016/j.applthermaleng.2016.10.077.

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28

Wang, Chenglong, Xiao Liu, Minghao Liu, Simiao Tang, Zhixing Tian, Dalin Zhang, Wenxi Tian, Suizheng Qiu y Guanghui Su. "Experimental study on heat transfer limit of high temperature potassium heat pipe for advanced reactors". Annals of Nuclear Energy 151 (febrero de 2021): 107935. http://dx.doi.org/10.1016/j.anucene.2020.107935.

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29

Shang, Fumin, Qingjing Yang, Chaoyue Liu, Shilong Fan y Jianhong Liu. "An experimental study on heat transfer performance of a pulsating heat pipe radiator for CPU heat dissipation". E3S Web of Conferences 165 (2020): 06035. http://dx.doi.org/10.1051/e3sconf/202016506035.

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To meet the requirement of electronic heat dissipation with high heat flux, a kind of heat dissipation device using pulsating heat pipe (PHP) for CPU heat dissipation was put forward. The heat transfer performance and surface temperature distribution of the radiator are analyzed by analyzing the wall temperature distribution and the distribution of the evaporator and condenser of the PHP. The experimental results show that the change of wind speed has obvious influence on the operation of the PHP radiator. The surface temperature distribution of the PHP radiator is very uniform, which is especially beneficial for CPU cooling. The heat transfer performance of the PHP is better, and the minimum average thermal resistance is 0.19 k/W. In addition, there is no drying phenomenon when the temperature reaches about 120 °C, which indicates that the pulsating heat pipe has a very high heat transfer limit.

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30

Silaipillayarputhur, Karthik y Tawfiq Al-Mughanam. "Performance of Pure Crossflow Heat Exchanger in Sensible Heat Transfer Application". Energies 14, n.º 17 (2 de septiembre de 2021): 5489. http://dx.doi.org/10.3390/en14175489.

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All process industries involve the usage of heat exchanger equipment and understanding its performance during the design phase is very essential. The present research work specifies the performance of a pure cross flow heat exchanger in terms of dimensionless factors such as number of transfer units, capacity rate ratio, and heat exchanger effectiveness. Steady state sensible heat transfer was considered in the analysis. The matrix approach that was established in the earlier work was used in the study. The results were depicted in the form of charts, tables, and performance equations. It was observed that indeterminately increasing the number of transfer units past a threshold limit provided very marginal improvement in the performance of a pure cross flow heat exchanger. Likewise, flow pattern in a heat exchanger is usually assumed either as mixed or unmixed. However, due to various operating conditions, partially mixed conditions do exist. This work considers partially mixed conditions in the tube side of the heat exchanger. The correction factor for heat exchanger effectiveness was developed to accommodate partially mixed flow conditions in the pure cross flow heat exchanger.

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31

Williams, Richard R. y Daniel K. Harris. "A device and technique to measure the heat transfer limit of a planar heat pipe wick". Experimental Thermal and Fluid Science 30, n.º 3 (enero de 2006): 277–84. http://dx.doi.org/10.1016/j.expthermflusci.2005.07.008.

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32

Nellis, Gregory F. y John M. Pfotenhauer. "Effectiveness-NTU Relationship for a Counterflow Heat Exchanger Subjected to an External Heat Transfer". Journal of Heat Transfer 127, n.º 9 (11 de noviembre de 2004): 1071–73. http://dx.doi.org/10.1115/1.2010496.

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This paper presents the analytical solution for the effectiveness of a counterflow heat exchanger subjected to a uniformly distributed, external heat flux. The solution is verified against conventional ε-NTU relations in the limit of zero external heat flux. This situation is of interest in applications such as cryogenic and process engineering, and the analytical solution provides a convenient method for treating differential elements of a heat exchanger in a numerical model.

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33

Kiwan, S. y M. A. Al-Nimr. "Using Porous Fins for Heat Transfer Enhancement". Journal of Heat Transfer 123, n.º 4 (14 de julio de 2000): 790–95. http://dx.doi.org/10.1115/1.1371922.

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This work introduces a novel method that enhances the heat transfer from a given surface by using porous fins. The thermal performance of porous fins is estimated and compared with that of the conventional solid fins. It is found that using porous fin of porosity ε may enhance the performance of an equal size conventional solid fin and, as a result, save 100 ε percent of the fin material. The effect of different design and operating parameters on the porous fin thermal performance is investigated. Examples of these parameters are Ra number, Da number, and thermal conductivity ratio. It is found that more enhancement in the porous fin performance may be achieved as Ra increases especially at large Da numbers. Also, it is found that there is an optimum limit for the thermal conductivity ratio beyond which there is no further improvement in the fin performance.

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34

Salmi, Mohamed, Abdelhakim Boursas, Mederreg Derradji, Giulio Lorenzini, Hijaz Ahmad, Younes Menni, Houari Ameur y Rachid Maoudj. "Improved Heat Transfer in W-Baffled Air-Heat Exchangers with Upper-Inlet and Lower-Exit". Mathematical Modelling of Engineering Problems 8, n.º 1 (28 de febrero de 2021): 1–9. http://dx.doi.org/10.18280/mmep.080101.

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In the current study, this way was adopted numerically in order to optimize the performance of a HEC through the use of extended solid sections in the form of 'W' (W-baffles: WBs). All limit conditions of the channel have been defined, with all the thermo-physical properties of the HTF (heat transfer fluid) used. The FVM (Finite-Volume-Method) has been adopted with some necessary numerical schemes in order to give the numerical solution, which allows us to visualize dynamically the flow filed and to deduce all the energetic characteristics contained by this HE. Dynamically, the HTF flow velocity at the HEC outlet section reached about 1.812 m/s, in the case of the lowest Re value. While, it passed 4.8 m/s in the case of the largest value of the same variable, i.e. 1.726 to 4.648 times better than the Uin within the limits of Re numbers used. Thermally, areas with very hight TGs (temperature gradients) were observed near the top deflector’s sides, which reflects the effect of the W-baffles. This highlights the importance of the adopted obstacles in changing characteristics of the HEC to the best.

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35

Sobral, R. L., J. M. Quirino, E. D. Correa y R. M. S. Gama. "NUMERICAL STUDY OF HEAT TRANSFER IN EXTENDED SURFACESWITH MUTUAL RADIATION BETWEEN PARALLEL FINS". Revista de Engenharia Térmica 17, n.º 1 (30 de junio de 2018): 80. http://dx.doi.org/10.5380/reterm.v17i1.62264.

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The present work shows the influence of the mutual heat transfer on the effectiveness of finned surfaces. Numerical simulations are carried out through a sequence of linear problems, possessing an equivalent minimum principle, that has as its limit the solution of the original problem. The original nonlinear problem is regarded as the limit (which always exists) of a sequence of linear problems like the classical conduction-convection ones. In this work the nonlinear conduction-radiation heat transfer process is considered and simulated by means of a finite difference linear scheme. Such a limit is reached in an easy way by means of standard procedures, allowing the employment of more realistic hypotheses, like some nonlinear boundary conditions, since the mathematical complexities are not a constraint for simulating the elliptic partial differential equation. This work accounts for the the steady state heat transfer process in rigid fins which experiences convective and radiative heat exchange. Some typical results are shown in order to illustrate the methodology. Results have shown both the relevance of the radiation and the importance of the thermal interaction between the fins, so that there is an effective and realistic thermal mapping. Neglecting the thermal interaction can lead to errors of up to 20 percent.

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36

Mekcem, Maroua. "Nanofluids and heat pipe limitations". Academic Perspective Procedia 1, n.º 1 (9 de noviembre de 2018): 298–304. http://dx.doi.org/10.33793/acperpro.01.01.58.

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Given the high efficiency of heat pipes as heat transfer devices, which work with phase changing principle (evaporation and condensation) and without requiring any external energy input, the heat pipes have been utilized for many years in several areas. However, heat transfer in heat pipes is limited by physical phenomena which appear during its operation, called heat pipe limitations; these can limit and reduce its performance. At this state, the use of nanofluids instead of conventional fluids come a solution after that Choi and Eastman (1995) confirmed the feasibility of enhancing the thermal conductivity of fluids by adding nanoparticles. This paper represents a general description of heat pipes, including a brief historical perspective, principle of operation and explanation of main heat transfer limitations. The work shows the contribution of nanofluids in pushing back the heat pipe limitations.

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37

Li, Yung-Ming, Jane-Sunn Liaw y Chi-Chuan Wang. "A Criterion of Heat Transfer Deterioration for Supercritical Organic Fluids Flowing Upward and Its Heat Transfer Correlation". Energies 13, n.º 4 (22 de febrero de 2020): 989. http://dx.doi.org/10.3390/en13040989.

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The main objective of this study was to develop the supercritical heat transfer correlation applicable for organic fluids when flowing upward in smooth tubes based on the available experimental data. The organic fluids contain R-22, R-134a, R-245fa and Ethanol and the associated heat transfer characteristics were compared with non-organic fluids like water and carbon-dioxide (CO2). It was found that the limit heat flux may result in heat transfer deterioration (HTD) of organic fluid and the corresponding values are much smaller than water or CO2. A new criterion to predict the HTD was developed and this criterion yields the best predictive ability against database. It was found that HTD occurs can be well described by the acceleration parameter evaluated at the wall condition rather than at bulk condition. For estimation of the supercritical heat transfer coefficient (HTC) for organic fluid, the present study proposes a new correlation with a physically based correction factor, which gives satisfactory predictions against the HTC of supercritical organic fluid. The new correlation can offer the smallest average deviation of 0.007 and standard deviation of 0.181 among the existing correlations.

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38

Kedia, R., M. L. Hunt y T. Colonius. "Transition of Chaotic Flow in a Radially Heated Taylor-Couette System". Journal of Heat Transfer 121, n.º 3 (1 de agosto de 1999): 574–82. http://dx.doi.org/10.1115/1.2826018.

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Numerical simulations have been performed to study the stability of heated, incompressible Taylor-Couette flow for a radius ratio of 0.7 and a Prandtl number of 0.7. As Gr is increased, the Taylor cell that has the same direction of circulation as the natural convection current increases in size and the counterrotating cell becomes smaller. The flow remains axisymmetric and the average heat transfer decreases with the increase in Gr. When the cylinder is impulsively heated, the counterrotating cell vanishes and n = 1 spiral is formed for Gr = 1000. This transition marks an increase in the heat transfer due to an increase in the radial velocity component of the fluid. By slowly varying the Grashof number, the simulations demonstrate the existence of a hysteresis loop. Two different stable states with same heat transfer are found to exist at the same Grashof number. A time-delay analysis of the radial velocity and the local heat transfer coefficient time is performed to determine the dimension at two Grashof numbers. For a fixed Reynolds number of 100, the two-dimensional projection of the reconstructed attractor shows a limit cycle for Gr = −1700. The limit cycle behavior disappears at Gr = −2100, and the reconstructed attractor becomes irregular. The attractor dimension increases to about 3.2 from a value of 1 for the limit cycle case; similar values were determined for both the local heat transfer and the local radial velocity, indicating that the dynamics of the temperature variations can be inferred from that of the velocity variations.

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39

Majumdar, A. "Microscale Heat Conduction in Dielectric Thin Films". Journal of Heat Transfer 115, n.º 1 (1 de febrero de 1993): 7–16. http://dx.doi.org/10.1115/1.2910673.

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Heat conduction in dielectric thin films is a critical issue in the design of electronic devices and packages. Depending on the material properties, there exists a range of film thickness where the Fourier law, used for macroscale heat conduction, cannot be applied. This paper shows that in this microscale regime, heat transport by lattice vibrations or phonons can be analyzed as a radiative transfer problem. Based on Boltzmann transport theory, an equation of phonon radiative transfer (EPRT) is developed. In the acoustically thick limit, ξL ≫ 1, or the macroscale regime, where the film thickness is much larger than the phonon-scattering mean free path, the EPRT reduces to the Fourier law. In the acoustically thin limit, ξL ≪ 1, the EPRT yields the blackbody radiation law q = σ (T14 − T24) at temperatures below the Debye temperature, where q is the heat flux and T1 and T2 are temperatures at the film boundaries. For transient heat conduction, the EPRT suggests that a heat pulse is transported as a wave, which becomes attenuated in the film due to phonon scattering. It is also shown that the hyperbolic heat equation can be derived from the EPRT only in the acoustically thick limit. The EPRT is then used to study heat transport in diamond thin films in wide range of acoustical thicknesses spanning the thin and the thick regimes. The heat flux follows the relation q = 4σT3ΔT/(3ξL/4 + 1) as derived in the modified diffusion approximation for photon radiative transfer. The thermal conductivity, as currently predicted by kinetic theory, causes the Fourier law to overpredict the heat flux by 33 percent when ξL ≪ 1, by 133 percent when ξL = 1, and by about 10 percent when ξL increases to 10. To use the Fourier law in both ballistic and diffusive transport regimes, a simple expression for an effective thermal conductivity is developed.

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40

Williams, T. M., D. Noren, P. Berry, J. A. Estes, C. Allison y J. Kirtland. "The diving physiology of bottlenose dolphins (Tursiops truncatus). III. Thermoregulation at depth". Journal of Experimental Biology 202, n.º 20 (15 de octubre de 1999): 2763–69. http://dx.doi.org/10.1242/jeb.202.20.2763.

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During diving, marine mammals initiate a series of cardiovascular changes that include bradycardia and decreased peripheral circulation. Because heat transfer from thermal windows located in peripheral sites of these mammals depends on blood flow, such adjustments may limit their thermoregulatory capabilities during submergence. Here, we demonstrate how the thermoregulatory responses of bottlenose dolphins (Tursiops truncatus) are coordinated with the diving response. Heart rate, skin temperature and heat transfer from the dorsal fin and flank were measured while dolphins rested on the water surface, stationed 5–50 m under water and floated at the surface immediately following a dive. The results showed that heat flow ranged from 42.9+/−7.3 to 126.2+/−23.1 W m(−)(2) and varied with anatomical site and diving activity. Upon submergence, heat flow declined by 35 % from the dorsal fin and by 24 % from the flank. An immediate increase in heat flow to levels exceeding pre-dive values occurred at both sites upon resurfacing. Changes in heart rate during diving paralleled the thermoregulatory responses. Mean pre-dive heart rate (102.0+/−2.6 beats min(−)(1), N=26) decreased by 63.4 % during dives to 50 m and immediately returned to near resting levels upon resurfacing. These studies indicate that heat dissipation by dolphins is attenuated during diving. Rather than challenge the diving response, heat transfer is delayed until post-dive periods when the need for oxygen conservation is reduced.

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41

Ju, Jian Liang, Zhi Gang Zhang y Wei Zhang. "Analysis on the Selection of Working Fluid in the Small Diameter Gravity Heat Pipe - Based on a New Passive Technology". Applied Mechanics and Materials 368-370 (agosto de 2013): 661–65. http://dx.doi.org/10.4028/www.scientific.net/amm.368-370.661.

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This paper discusses the suitable working fluid applying in small diameter (millimeter scale) gravity heat pipe theoretically. The working temperature, characteristics of material, heat transfer limit and thermal physical properties of working medium of the heat pipe were studied. It is concluded that each aspect capability of heat transfer of R717 is excellent, but its working pressure is a bit high; the synthesized capability of R134a is relatively ideal and can be chosen as the working medium.

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42

Wang, Chi-Chuan. "Extending the Limit of Direct Air-Cooling Heat Sink". Heat Transfer Engineering 29, n.º 11 (noviembre de 2008): 911–12. http://dx.doi.org/10.1080/01457630802185991.

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43

Tian, F. Z., G. M. Xin, Q. Hai y L. Cheng. "An Investigation of Heat Transfer Characteristic of Cross Internal Helical Microfin Gravity Heat Pipe with Self-Rewetting Fluid". Advanced Materials Research 765-767 (septiembre de 2013): 189–92. http://dx.doi.org/10.4028/www.scientific.net/amr.765-767.189.

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Gravity heat pipe has been widely used in many heat transfer devices due to its high thermal conductivity, low cost and sample structure. In the paper, an experimental investigation of the gravity heat pipe with cross internal helical microfin gravity with two kind of working fluid (water and butyl alcohol solution with 5% mass fraction) was presented from horizontal and vertical position. The experimental results showed that in the horizontal position, self-rewetting fluid can significant increases the GHPCIHMs drying limit, decreases the thermal resistance and improves the heat transfer performance. In the vertical position, gravity effect play main functions on fluid return, self-rewetting has not been proved to have played a positive role on the heat transfer performance.

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44

Focke, W. W. "Selecting Optimum Plate Heat Exchanger Surface Patterns". Journal of Heat Transfer 108, n.º 1 (1 de febrero de 1986): 153–60. http://dx.doi.org/10.1115/1.3246880.

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With appropriate simplifications, plate heat exchanger dimensions and performance can be described by suitable combinations of the base dimensionless groups: Colburn j factor, friction factor, and Reynolds number. Such combinations are used to construct graphic methods for finding optimum geometries (patterns that minimize the surface area required for heat transfer) subject to various constraints. It was found that the number of potentially optimum geometries increased with increasing number of constraints. In plate heat exchangers, the heat transfer performance is related to the pumping power expended. Therefore, in modular plate heat exchangers, the fixed plate lengths limit design flexibility in that heat transfer and pressure drop cannot be varied independently. This limitation can be partly overcome by using interchangeable chevron-type plates of different corrugation inclination angles in the same plate pack.

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45

Yuen, W. W. y E. E. Takara. "Analysis of Combined Conductive-Radiative Heat Transfer in a Two-Dimensional Rectangular Enclosure With a Gray Medium". Journal of Heat Transfer 110, n.º 2 (1 de mayo de 1988): 468–74. http://dx.doi.org/10.1115/1.3250509.

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Combined conductive–radiative heat transfer in a two-dimensional enclosure is considered. The numerical procedure is based on a combination of two previous techniques that have been demonstrated to be successful for a two-dimensional pure radiation problem and a one-dimensional combined conductive–radiative heat transfer problem, respectively. Both temperature profile and heat transfer distributions are generated efficiently and accurately. Numerical data are presented to serve as benchmark solutions for two-dimensional combined conductive–radiative heat transfer. The accuracy of two commonly used approximation procedures for multidimensional combined conductive–radiative heat transfer is assessed. The additive solution, which is effective in generating approximation to one-dimensional combined conductive–radiative heat transfer, appears to be an acceptable empirical approach in estimating heat transfer in the present two-dimensional problem. The diffusion approximation, on the other hand, is shown to be generally inaccurate. For all optical thicknesses and conduction-radiation parameters considered (including the optically thick limit), the diffusion approximation is shown to yield significant errors in both the temperature and heat flux predictions.

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46

Milanez, Fernando y Marcia B. H. Mantelli. "HEAT TRANSFER LIMIT DUE TO PRESSURE DROP OF A TWO-PHASE LOOP THERMOSYPHON". Heat Pipe Science and Technology, An International Journal 1, n.º 3 (2010): 237–50. http://dx.doi.org/10.1615/heatpipescietech.2011003082.

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47

Yadav, Mahesh Kumar y Vinod Yadav. "Time limit for using the semi-infinite heat transfer solutions: a novel approach". IOP SciNotes 1, n.º 2 (29 de agosto de 2020): 024402. http://dx.doi.org/10.1088/2633-1357/abaf67.

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48

Thompson, Dakotah, Linxiao Zhu, Rohith Mittapally, Seid Sadat, Zhen Xing, Patrick McArdle, M. Mumtaz Qazilbash, Pramod Reddy y Edgar Meyhofer. "Hundred-fold enhancement in far-field radiative heat transfer over the blackbody limit". Nature 561, n.º 7722 (septiembre de 2018): 216–21. http://dx.doi.org/10.1038/s41586-018-0480-9.

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49

Murugesan, Chandrasekar y Suresh Sivan. "Limits for thermal conductivity of nanofluids". Thermal Science 14, n.º 1 (2010): 65–71. http://dx.doi.org/10.2298/tsci1001065m.

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Nanofluids have offered challenges to thermal engineers and attracted many researchers over the past decade to determine the reasons for anomalous enhancement of thermal conductivity in them. Experiments on measurement of nanofluid thermal conductivity have ended in a large degree of randomness and scatter in their values. Hence in this paper, lower and upper limits for thermal conductivity of nanofluids are developed. The upper limit is estimated by coupling heat transfer mechanisms like particle shape, Brownian motion and nanolayer while the lower limit is based on Maxwell's equation. Experimental data from a range of independent published sources is used for validation of the developed limits.

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50

Choi, M., H. R. Baum y R. Greif. "The Heat Transfer Problem for the Modified Chemical Vapor Deposition Process". Journal of Heat Transfer 109, n.º 3 (1 de agosto de 1987): 642–46. http://dx.doi.org/10.1115/1.3248136.

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The heat transfer problem related to the modified chemical vapor deposition process has been analyzed in the high Peclet number limit. Variations in the axial, angular, and radial directions are presented. Of particular interest are the effects of tube rotation and variable properties on the temperature profiles.

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