Journal articles: 'Thermodynamically and hydrodynamically developing flow'

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Altaç, Zekeriya, and Özge Altun. "Hydrodynamically and thermally developing laminar flow in spiral coil tubes." International Journal of Thermal Sciences 77 (March 2014): 96–107. http://dx.doi.org/10.1016/j.ijthermalsci.2013.10.020.

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Kumar Parwani, Ajit, Prabal Talukdar, and P. M. V. Subbarao. "Estimation of transient boundary flux for a developing flow in a parallel plate channel." International Journal of Numerical Methods for Heat & Fluid Flow 24, no. 3 (April 1, 2014): 522–44. http://dx.doi.org/10.1108/hff-01-2012-0020.

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Purpose – The purpose of this paper is to develop a numerical model for estimating the unknown boundary heat flux in a parallel plate channel for the case of a hydrodynamically and thermally developing laminar flow. Design/methodology/approach – The conjugate gradient method (CGM) is used to solve the inverse problem. The momentum equations are solved using an in-house computational fluid dynamics (CFD) source code. The energy equations along with the adjoint and sensitivity equations are solved using the finite volume method. Findings – The effects of number of measurements, distribution of measurements and functional form of unknown flux on the accuracy of estimations are investigated in this work. The prediction of boundary flux by the present algorithm is found to be quite reasonable. Originality/value – It is noticed from the literature review that study of inverse problem with hydrodynamically developing flow has not received sufficient attention despite its practical importance. In the present work, a hydrodynamically and thermally developing flow between two parallel plates is considered and unknown transient boundary heat flux at the upper plate of a parallel plate channel is estimated using CGM.

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Thompson, B. R., D. Maynes, and B. W. Webb. "Characterization of the Hydrodynamically Developing Flow in a Microtube Using MTV." Journal of Fluids Engineering 127, no. 5 (May 5, 2005): 1003–12. http://dx.doi.org/10.1115/1.1989368.

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Micro-molecular tagging velocimetry (μMTV) has been used to characterize the hydrodynamic developing flow in a microtube inlet with a nominal inner diameter of 180μm. Velocity profile data at 11 axial locations within the hydrodynamic developing region were acquired using the μMTV approach and the results represent the first characterization of hydrodynamically developing pipe flow at the microscale. The uncertainty in measurements of time-averaged velocity profiles ranged from 6% to 7% of the centerline velocity. The uncertainty in instantaneous measurements is in the range 8%–16% of the peak maximum velocity. Data were taken at Reynolds numbers of 60, 100, 140, 290, and 350. The data suggest the formation of a vena contracta with either locally turbulent flow or unsteady laminar flow separation early in the tube for the larger Reynolds (Re) numbers, which is quite different from macroscale experiment or numerical simulation where a vena-contracta is not observed for Re<500. The velocity profiles obtained very near the tube entrance exhibited a uniform velocity core flow surrounded by regions of relatively stagnant fluid in the near wall regions. The size of the inferred recirculation zones, measured velocity rms, and maximum shear rates all exhibit increasing magnitude with increasing Reynolds number. The velocity profiles were observed to evolve in the downstream direction until the classical parabolic distribution existed. The total hydrodynamic entry length agrees well with values published in the literature for laminar flow with a uniform inlet velocity, despite the existence of the observed vena contracta.

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Selimli, Selcuk, Ziyaddin Recebli, and Erol Arcaklioglu. "MHD numerical analyses of hydrodynamically developing laminar liquid lithium duct flow." International Journal of Hydrogen Energy 40, no. 44 (November 2015): 15358–64. http://dx.doi.org/10.1016/j.ijhydene.2015.02.020.

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Na, Y., and J. Y. Yoo. "Numerical simulation of the hydrodynamically developing flow of a viscoelastic fluid." KSME Journal 4, no. 1 (March 1990): 54–61. http://dx.doi.org/10.1007/bf02953391.

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Fann, Shin, and Wen-Jei Yang. "HYDRODYNAMICALLY AND THERMALLY DEVELOPING LAMINAR FLOW THROUGH ROTATING CHANNELS HAVING ISOTHERMAL WALLS." Numerical Heat Transfer, Part A: Applications 22, no. 3 (October 1992): 257–88. http://dx.doi.org/10.1080/10407789208944768.

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Hwang, T. H. "Laminar droplet flow in combined hydrodynamically and thermally developing region of circular tubes." International Communications in Heat and Mass Transfer 17, no. 6 (November 1990): 703–10. http://dx.doi.org/10.1016/0735-1933(90)90017-e.

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Almalowi, Saeed J., and Alparslan Oztekin. "Flow Simulations Using Two Dimensional Thermal Lattice Boltzmann Method." Journal of Applied Mathematics 2012 (2012): 1–12. http://dx.doi.org/10.1155/2012/135173.

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Lattice Boltzmann method is implemented to study hydrodynamically and thermally developing steady laminar flows in a channel. Numerical simulation of two-dimensional convective heat transfer problem is conducted using two-dimensional, nine directional D2Q9 thermal lattice Boltzmann arrangements. The velocity and temperature profiles in the developing region predicted by Lattice Boltzmann method are compared against those obtained by ANSYS-FLUENT. Velocity and temperature profiles as well as the skin friction and the Nusselt numbers agree very well with those predicted by the self-similar solutions of fully developed flows. It is clearly shown here that thermal lattice Boltzmann method is an effective computational fluid dynamics (CFD) tool to study nonisothermal flow problems.

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Chen, X. Y., K. C. Toh, C. Yang, and J. C. Chai. "Numerical Computation of Hydrodynamically and Thermally Developing Liquid Flow in Microchannels With Electrokinetics Effects." Journal of Heat Transfer 126, no. 1 (February 1, 2004): 70–75. http://dx.doi.org/10.1115/1.1643909.

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Developing fluid flow and heat transfer with temperature dependent properties in microchannels with electrokinetic effects is investigated numerically. The electrokinetic effect on liquid flow in a parallel slit is modeled by the general Nernst-Planck equation describing anion and cation distributions, the Poisson equation determining the electrical potential profile, the continuity equation, and the modified Navier-Stokes equation governing the velocity field. A Finite-Volume Method is utilized to solve the proposed model.

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Papadopoulos, P. K., and P. M. Hatzikonstantinou. "Numerical Investigation of the Thermally Developing Flow in a Curved Elliptic Duct With Internal Fins." Journal of Heat Transfer 129, no. 6 (October 17, 2006): 759–62. http://dx.doi.org/10.1115/1.2717254.

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The hydrodynamically fully developed and thermally developing flow inside a curved elliptic duct with internal longitudinal fins is studied numerically. The duct is subjected to the uniform temperature boundary condition on its wall and fins. The local and mean Nusselt numbers are examined for various values of the Dean and Prandtl numbers, the cross-sectional aspect ratio, and the fin height. The characteristics of the optimum duct, which achieves enhanced heat transfer rates combined with low friction losses, are determined in terms of the aspect ratio and the fin height.

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Yu, Shiping, and Timothy A. Ameel. "Slip Flow Convection in Isoflux Rectangular Microchannels." Journal of Heat Transfer 124, no. 2 (June 28, 2001): 346–55. http://dx.doi.org/10.1115/1.1447932.

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Laminar forced convection in thermally developing slip flow through isoflux rectangular microchannels is analytically investigated. Local and fully developed Nusselt numbers, fluid temperatures, and wall temperatures are obtained by solving the continuum energy equation for hydrodynamically fully developed slip flow with the velocity slip and temperature jump condition at the walls. It is found that heat transfer may increase, decrease, or remain unchanged, compared to nonslip flow conditions, depending on aspect ratios and two-dimensionless variables that include effects of the microchannel size or rarefaction and the fluid/wall interaction. The transition points that separate heat transfer enhancement from reduction are acquired for different aspect ratios.

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Min, Taegee, Hyoung Gwon Choi, Jung Yul Yoo, and Haecheon Choi. "Laminar convective heat transfer of a Bingham plastic in a circular pipe—II. Numerical approach hydrodynamically developing flow and simultaneously developing flow." International Journal of Heat and Mass Transfer 40, no. 15 (October 1997): 3689–701. http://dx.doi.org/10.1016/s0017-9310(97)00004-5.

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Cheng, K. C., and F. P. Yuen. "Flow Visualization Experiments on Secondary Flow Patterns in an Isothermally Heated Curved Pipe." Journal of Heat Transfer 109, no. 1 (February 1, 1987): 55–61. http://dx.doi.org/10.1115/1.3248067.

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Secondary flow patterns at the exit of a 180 deg bend (tube inside diameter d = 1.99 cm, radius of curvature Rc = 10.85 cm) are presented to illustrate the combined effects of centrifugal and buoyancy forces in hydrodynamically and thermally developing entrance region of an isothermally heated curved pipe with both parabolic and turbulent entrance velocity profiles. Three cases of upward, horizontal, and downward-curved pipe flows are studied for constant wall temperatures Tw=55–91°C, Dean number range K=22–1209 and ReRa=1.00×106–8.86×107. The flow visualization was realized by the smoke injection method. The secondary flow patterns shown are useful for future comparison with numerical predictions and confirming theoretical models. The results can be used to assess qualitatively the limit of the applicability of the existing correlation equations for laminar forced convection in isothermally heated curved pipes without buoyancy effects.

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Thomson, D. L., Y. Bayazitoglu, and A. J. Meade. "Low Dean Number Convective Heat Transfer in Helical Ducts of Rectangular Cross Section." Journal of Heat Transfer 120, no. 1 (February 1, 1998): 84–91. http://dx.doi.org/10.1115/1.2830069.

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Flow in a torroidal duct is characterized by increased convective heat transfer and friction compared to a straight duct of the same cross section. In this paper the importance of the nonplanarity (torsion) of a helical duct with rectangular cross section is investigated. A previously determined low Dean number velocity solution is used in the decoupled energy equation for the hydrodynamically fully developed, thermally developing case. Torsion, known to increase the friction factor, is found to cause a decrease in the fully developed Nusselt number compared to pure torroidal flow. Therefore, it is recommended that torsion be minimized to enhance heat transfer.

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Su, Duan, He, Ma, and Xu. "Thermally Developing Flow and Heat Transfer in Elliptical Minichannels with Constant Wall Temperature." Micromachines 10, no. 10 (October 21, 2019): 713. http://dx.doi.org/10.3390/mi10100713.

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Laminar convective heat transfer of elliptical minichannels is investigated for hydrodynamically fully developed but thermal developing flow with no-slip condition. A three-dimensional numerical model is developed in different elliptical geometries with the aspect ratio varying from 0.2 to 1. The effect of Reynolds number (25 ≤ Re ≤ 2000) on the local Nusselt number is examined in detail. The results indicate that the local Nusselt number is a decreasing function of Reynolds number and it is sensitive to Reynolds number especially for Re less than 250. The effect of aspect ratio on local Nusselt number is small when compared with the effect of Reynolds number on local Nusselt number. The local Nusselt number is independent of cross-section geometry at the inlet. The maximum effect of aspect ratio on local Nusselt number arises at the transition section rather than the fully developed region. However, the non-dimensional thermal entrance length is a monotonic decreasing concave function of aspect ratio but a weak function of Reynolds number. Correlations for the local Nusselt number and the thermal developing length for elliptical channels are developed with good accuracy, which may provide guidance for design and optimization of elliptical minichannel heat sinks.

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Talukdar, Prabal, and Carey J. Simonson. "Effect of Axial Radiation on Heat Transfer in a Thermally and Hydrodynamically Developing Flow between Parallel Plates." Numerical Heat Transfer, Part A: Applications 52, no. 10 (September 14, 2007): 911–34. http://dx.doi.org/10.1080/10407780701348307.

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Vandadi, V., A. Vandadi, H. Niazmand, and C. Aghanajafi. "Entropy Generation Analysis for Microscale Forced Convection in Thermal Entrance Region." Journal of Mechanics 28, no. 1 (March 2012): 71–76. http://dx.doi.org/10.1017/jmech.2012.7.

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ABSTRACTAn analytical study on entropy generation considering viscous dissipation effect in the circular microchannel is reported. The fluid flow is steady, laminar, hydrodynamically fully developed and thermally developing. In the first law analysis, appropriate dimensionless variables are applied to solve the energy equation in the thermal entrance region of microchannel. Subsequently the obtained temperature field is used to derive an expression for entropy generation rate. The effect of Knudsen number and Brinkman number on the entropy generation rate and Bejan number in different axial location is presented.

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Sakalis, V. D., and P. M. Hatzikonstantinou. "Laminar Heat Transfer in the Entrance Region of Internally Finned Square Ducts." Journal of Heat Transfer 123, no. 6 (May 15, 2001): 1030–34. http://dx.doi.org/10.1115/1.1404118.

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The laminar, incompressible, hydrodynamically fully developed and thermally developing flow is studied in straight ducts of square cross section, containing four equal, symmetrical, straight, thin and with 100 percent efficiency internal fins. Both the duct wall and the fins are subjected successively to constant temperature boundary condition. Numerical results are obtained using an iterative ADI scheme for the friction number, the temperature distribution and the Nusselt number for the thermally developing and developed regions as functions of axial distance and fin height. Results obtained are in good agreement with the corresponding literature values. In the thermally developing region a high heat transfer coefficient is obtained. Friction number and Nusselt number in the thermally developed limit increase as the fin height increases until they reach their critical values at fin heights near 0.85 and 0.73 respectively.

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Cheng, P., C. T. Hsu, and A. Chowdhury. "Forced Convection in the Entrance Region of a Packed Channel With Asymmetric Heating." Journal of Heat Transfer 110, no. 4a (November 1, 1988): 946–54. http://dx.doi.org/10.1115/1.3250597.

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The problem of a thermally developing forced convective flow in a packed channel heated asymmetrically is analyzed in this paper. The flow in the packed channel is assumed to be hydrodynamically fully developed and is governed by the Brinkman–Darcy–Ergun equation with variable porosity taken into consideration. A closed-form solution based on the method of matched asymptotic expansions is obtained for the axial velocity distribution, and the wall effect on pressure drop is illustrated. The energy equation for the thermally developing flow, with transverse thermal dispersion and variable stagnant thermal conductivity taken into consideration, was solved numerically. To match the predicted temperature distributions with existing experimental data, it is found that a wall function must be introduced to model the transverse thermal dispersion process in order to account for the wall effect on the lateral mixing of fluid. The variations of the local Nusselt number along the streamwise direction in terms of the appropriate parameters are illustrated. The thermal entrance length effect on forced convection in a packed channel is discussed.

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DiBenedetto, Michelle, Zhipeng Qin, and Jenny Suckale. "Crystal aggregates record the pre-eruptive flow field in the volcanic conduit at Kīlauea, Hawaii." Science Advances 6, no. 49 (December 2020): eabd4850. http://dx.doi.org/10.1126/sciadv.abd4850.

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Developing reliable, quantitative conduit models that capture the physical processes governing eruptions is hindered by our inability to observe conduit flow directly. The closest we get to direct evidence is testimony imprinted on individual crystals or bubbles in the conduit and preserved by quenching during the eruption. For example, small crystal aggregates in products of the 1959 eruption of Kīlauea Iki, Hawaii contain overgrown olivines separated by large, hydrodynamically unfavorable angles. The common occurrence of these aggregates calls for a flow mechanism that creates this crystal misorientation. Here, we show that the observed aggregates are the result of exposure to a steady wave field in the conduit through a customized, process-based model at the scale of individual crystals. We use this model to infer quantitative attributes of the flow at the time of aggregate formation; notably, the formation of misoriented aggregates is only reproduced in bidirectional, not unidirectional, conduit flow.

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Arslan, Kamil. "Three-dimensional computational fluid dynamics modeling of TiO2/R134a nanorefrigerant." Thermal Science 21, no. 1 Part A (2017): 175–86. http://dx.doi.org/10.2298/tsci140425002a.

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In this study, numerical investigations were carried out for R134a based TiO2 nanorefrigerants. Forced laminar flow and heat transfer of nanorefrigerants in a horizontal smooth circular cross-sectioned duct were investigated under steady-state condition. The nanorefrigerants consist of TiO2 nanoparticles suspended in R134a as a base fluid with four particle volume fractions of 0.8, 2.0 and 4.0%. Numerical studies were performed under laminar flow conditions where Reynolds numbers range from 8?102 to 2.2?103. Flow is flowing in the duct with hydrodynamically and thermally developing (simultaneously developing flow) condition. The uniform surface heat flux with uniform peripheral wall heat flux (H2) boundary condition was applied on the duct wall. Commercial CFD software, Ansys Fluent 14.5, was used to carry out the numerical study. Effect of nanoparticle volume fraction on the average convective heat transfer coefficient and average Darcy friction factor were analyzed. It is obtained in this study that increasing nanoparticle volume fraction of nanorefrigerant increases the convective heat transfer in the duct; however, increasing nanoparticle volume fraction does not influence the pressure drop in the duct. The velocity and temperature distribution in the duct for different Reynolds numbers and nanoparticle volume fractions were presented.

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Zhao, T. S., and P. Cheng. "Oscillatory Heat Transfer in a Pipe Subjected to a Laminar Reciprocating Flow." Journal of Heat Transfer 118, no. 3 (August 1, 1996): 592–97. http://dx.doi.org/10.1115/1.2822673.

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An experimental and numerical study has been carried out for laminar forced convection in a long pipe heated by uniform heat flux and subjected to a reciprocating flow of air. Transient fluid temperature variations in the two mixing chambers connected to both ends of the heated section were measured. These measurements were used as the thermal boundary conditions for the numerical simulation of the hydrodynamically and thermally developing reciprocating flow in the heated pipe. The coupled governing equations for time-dependent convective heat transfer in the fluid flow and conduction in the wall of the heated tube were solved numerically. The numerical results for time-resolved centerline fuid temperature, cycle-averaged wall temperature, and the space-cycle averaged Nusselt number are shown to be in good agreement with the experimental data. Based on the experimental data, a correlation equation is obtained for the cycle-space averaged Nusselt number in terms of appropriate dimensionless parameters for a laminar reciprocating flow of air in a long pipe with constant heat flux.

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Alhusseny, Ahmed, Ali Turan, Adel Nasser, and Faiza Hidri. "Hydrodynamically and thermally developing flow in a rectangular channel filled with a high porosity fiber and rotating about a parallel axis." International Communications in Heat and Mass Transfer 67 (October 2015): 114–23. http://dx.doi.org/10.1016/j.icheatmasstransfer.2015.07.012.

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Veloso, Dhiego Andrade, Carlos Antônio Cabral, and Fabio Araújo Lima. "Análise do campo de temperatura e do número de Nusselt local na convecção forçada assimétrica de fluidos não-newtonianos." Revista Principia - Divulgação Científica e Tecnológica do IFPB 1, no. 49 (June 2, 2020): 68. http://dx.doi.org/10.18265/1517-03062015v1n49p68-79.

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<p class="Normal1">The present work aims at analyzing the heat transfer in a flow inside a channel of parallel flat plates, hydrodynamically developed and thermally developing. It is considered that flat plates to have distincts thermophysical properties and that they are in contact with thermal reservoirs with different temperatures, in which guarantees an asymmetry in the problem studied. The flowing fluid is considered non-Newtonian of power law type. The Classical Integral Transformation Technique (CITT) was used to solve the energy equation. The temperature field and the local Nusselt numbers in the upper and lower plates are evaluated for several values of the power law index and the Biot number. The obtained results were confronted with existing ones in the open literature in order to validate the presented model.</p>

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Arslan, Kamil. "Three-dimensional numerical investigation of turbulent flow and heat transfer inside a horizontal semi-circular cross-sectioned duct." Thermal Science 18, no. 4 (2014): 1145–58. http://dx.doi.org/10.2298/tsci110724065a.

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In this study, steady-state turbulent forced flow and heat transfer in a horizontal smooth semi-circular cross-sectioned duct was numerically investigated. The study was carried out in the turbulent flow condition where Reynolds numbers range from 1?104 to 5.5?104. Flow is hydrodynamically and thermally developing (simultaneously developing flow) under uniform surface heat flux with uniform peripheral wall heat flux (H2) boundary condition on the duct?s wall. A commercial CFD program, Ansys Fluent 12.1, with different turbulent models was used to carry out the numerical study. Different suitable turbulence models for fully turbulent flow (k-? Standard, k-? Realizable, k-? RNG, k-? Standard and k-? SST) were used in this study. The results have shown that as the Reynolds number increases Nusselt number increases but Darcy friction factor decreases. Based on the present numerical solutions, new engineering correlations were presented for the average Nusselt number and average Darcy friction factor. The numerical results for different turbulence models were compared with each other and similar experimental investigations carried out in the literature. It is obtained that, k-? Standard, k-? Realizable and k-? RNG turbulence models are the most suitable turbulence models for this investigation. Isovel contours of velocity magnitude and temperature distribution for different Reynolds numbers, turbulence models and axial stations in the duct were presented graphically. Also, local heat transfer coefficient and local Darcy friction factor as function of dimensionless position along the duct were obtained in this investigation.

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Duan, Zhipeng, Hao Ma, Boshu He, Liangbin Su, and Xin Zhang. "Pressure Drop of Microchannel Plate Fin Heat Sinks." Micromachines 10, no. 2 (January 24, 2019): 80. http://dx.doi.org/10.3390/mi10020080.

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The entrance region constitutes a considerable fraction of the channel length in miniaturized devices. Laminar slip flow in microchannel plate fin heat sinks under hydrodynamically developing conditions is investigated semi-analytically and numerically in this paper. The semi-analytical model for the pressure drop of microchannel plate fin heat sinks is obtained by solving the momentum equation with the first-order velocity slip boundary conditions at the channel walls. The simple pressure drop model utilizes fundamental solutions from fluid dynamics to predict its constitutive components. The accuracy of the model is examined using computational fluid dynamics (CFD) simulations and the experimental and numerical data available in the literature. The model can be applied to either apparent liquid slip over hydrophobic and superhydrophobic surfaces or gas slip flow in microchannel heat sinks. The developed model has an accuracy of 92 percent for slip flow in microchannel plate fin heat sinks. The developed model may be used to predict the pressure drop of slip flow in microchannel plate fin heat sinks for minimizing the effort and expense of experiments, especially in the design and optimization of microchannel plate fin heat sinks.

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Ahuja, V. R., J. van der Gucht, and W. J. Briels. "Hydrodynamically Coupled Brownian Dynamics: A coarse-grain particle-based Brownian dynamics technique with hydrodynamic interactions for modeling self-developing flow of polymer solutions." Journal of Chemical Physics 148, no. 3 (January 21, 2018): 034902. http://dx.doi.org/10.1063/1.5006627.

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Throckmorton, A. L., J. Kapadia, and D. Madduri. "Mechanical axial flow blood pump to support cavopulmonary circulation." International Journal of Artificial Organs 31, no. 11 (November 2008): 970–82. http://dx.doi.org/10.1177/039139880803101107.

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We are developing a collapsible, percutaneously inserted, axial flow blood pump to support the cavopulmonary circulation in infants with a failing single ventricle physiology. An initial design of the impeller for this axial flow blood pump was performed using computational fluid dynamics analysis, including pressure-flow characteristics, scalar stress estimations, blood damage indices, and fluid force predictions. A plastic prototype was constructed for hydraulic performance testing, and these experimental results were compared with the numerical predictions. The numerical predictions and experimental findings of the pump performance demonstrated a pressure generation of 2–16 mm Hg for 50–750 ml/min over 5,500–7,500 RPM with deviation found at lower rotational speeds. The axial fluid forces remained below 0.1 N, and the radial fluid forces were determined to be virtually zero due to the centered impeller case. The scalar stress levels remained below 250 Pa for all operating conditions. Blood damage analysis yielded a mean residence time of the released particles, which was found to be less than 0.4 seconds for both flow rates that were examined, and a maximum residence time was determined to be less than 0.8 seconds. We are in the process of designing a cage with hydrodynamically shaped filament blades to act as a diffuser and optimizing the impeller blade shape to reduce the flow vorticity at the pump outlet. This blood pump will improve the clinical treatment of patients with failing Fontan physiology and provide a unique catheter-based therapeutic approach as a bridge to recovery or transplantation.

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Duan, Zhipeng, Peng Liang, Hao Ma, Niya Ma, and Boshu He. "Numerical simulation of pressure drop for three-dimensional rectangular microchannels." Engineering Computations 35, no. 6 (August 6, 2018): 2234–54. http://dx.doi.org/10.1108/ec-07-2017-0275.

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Purpose The purpose of this paper is to numerically investigate the flow characteristics and extend the data of friction factor and Reynolds number product of hydrodynamically developing laminar flow in three-dimensional rectangular microchannels with different aspect ratios. Design/methodology/approach Using a finite-volume approach, the friction factor characteristics of Newtonian fluid in three-dimensional rectangular ducts with aspect ratios from 0.1 to 1 are conducted numerically under no-slip boundary conditions. A simple model that approximately predicts the apparent friction factor and Reynolds number product fappRe is referenced as a semi-theoretical fundamental analysis for numerical simulations. Findings The accurate and reliable results of fappRe are obtained, which are compared with classic numerical data and experimental data, and the simple semi-theoretical model used and all comparisons show good agreement. Among them, the maximum relative error with the classic numerical data is less than 3.9 per cent. The data of fappRe are significantly extended to other different aspect ratios and the novel values of fappRe are presented in the tables. The characteristics of fappRe are analyzed as a function of a non-dimensional axial distance and the aspect ratios. A more effective and accurate fourth-order fitting equation for the Hagenbach's factor of rectangular channels is proposed. Originality/value From the reliable data, it is shown that the values of fappRe and the model can be references of pressure drop and friction factor for developing laminar flow in rectangular channels for researchers and engineering applications.

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Everts, Marilize, and Josua P. Meyer. "Laminar hydrodynamic and thermal entrance lengths for simultaneously hydrodynamically and thermally developing forced and mixed convective flows in horizontal tubes." Experimental Thermal and Fluid Science 118 (October 2020): 110153. http://dx.doi.org/10.1016/j.expthermflusci.2020.110153.

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Parsons, J. R., and M. L. Arey. "Development of Convective Heat Transfer Near Suddenly Heated, Vertically Aligned Horizontal Wires." Journal of Heat Transfer 109, no. 4 (November 1, 1987): 912–18. http://dx.doi.org/10.1115/1.3248203.

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Experiments have been performed which describe the transient development of natural convective flow from both a single and two vertically aligned horizontal cylindrical heat sources. The temperature of the wire heat sources was monitored with a resistance bridge arrangement while the development of the flow field was observed optically with a Mach–Zehnder interferometer. Results for the single wire show that after an initial regime where the wire temperature follows pure conductive response to a motionless fluid, two types of fluid motion will begin. The first is characterized as a local buoyancy, wherein the heated fluid adjacent to the wire begins to rise. The second is the onset of global convective motion, this being governed by the thermal stability of the fluid layer immediately above the cylinder. The interaction of these two motions is dependent on the heating rate and relative heat capacities of the cylinder and fluid, and governs whether the temperature response will exceed the steady value during the transient (overshoot). The two heat source experiments show that the merging of the two developing temperature fields is hydrodynamically stabilizing and thermally insulating. For small spacing-to-diameter ratios, the development of convective motion is delayed and the heat transfer coefficients degraded by the proximity of another heat source. For larger spacings, the transient behavior approaches that of a single isolated cylinder.

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Sitkowski, Matthew, James P. Kossin, Christopher M. Rozoff, and John A. Knaff. "Hurricane Eyewall Replacement Cycle Thermodynamics and the Relict Inner Eyewall Circulation." Monthly Weather Review 140, no. 12 (December 1, 2012): 4035–45. http://dx.doi.org/10.1175/mwr-d-11-00349.1.

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Abstract Flight-level aircraft data are used to examine inner-core thermodynamic changes during eyewall replacement cycles (ERCs) and the role of the relict inner eyewall circulation on the evolution of a hurricane during and following an ERC. Near the end of an ERC, the eye comprises two thermodynamically and kinematically distinct air masses separated by a relict wind maximum, inside of which high inertial stability restricts radial motion creating a “containment vessel” that confines the old-eye air mass. Restricted radial flow aloft also reduces subsidence within this confined region. Subsidence-induced warming is thus focused along the outer periphery of the developing post-ERC eye, which leads to a flattening of the pressure profile within the eye and a steepening of the gradient at the eyewall. This then causes a local intensification of the winds in the eyewall. The cessation of active convection and subsidence near the storm center, which has been occurring over the course of the ERC, leads to an increase in minimum pressure. The increase in minimum pressure concurrent with the increase of winds in the developing eyewall can create a highly anomalous pressure–wind relationship. When the relict inner eyewall circulation dissipates, the air masses are free to mix and subsidence can resume more uniformly over the entire eye.

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Aydin, Orhan. "“Effects of viscous dissipation on the heat transfer in forced pipe flow. Part 1: Both hydrodynamically and thermally fully developed flow [Energy Conv. Manage. 2005; 46; 757–769] and Part 2: Thermally developing flow [Energy Conv. Manage. 2005; 3091–3102]” by Orhan Aydin." Energy Conversion and Management 47, no. 18-19 (November 2006): 3499–500. http://dx.doi.org/10.1016/j.enconman.2006.02.023.

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Liu, Meishen, and Greeshma Gadikota. "Phase Evolution and Textural Changes during the Direct Conversion and Storage of CO2 to Produce Calcium Carbonate from Calcium Hydroxide." Geosciences 8, no. 12 (November 30, 2018): 445. http://dx.doi.org/10.3390/geosciences8120445.

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The increasing use of energy resources recovered from subsurface environments and the resulting carbon imbalance in the environment has motivated the need to develop thermodynamically downhill pathways to convert and store CO2 as water-insoluble calcium or magnesium carbonates. While previous studies extensively explored aqueous routes to produce calcium and magnesium carbonates from CO2, there is limited scientific understanding of the phase evolution and textural changes during the direct gas–solid conversion routes to produce calcium carbonate from calcium hydroxide, which is one of the abundant constituents of alkaline industrial residues. With increasing interest in developing integrated pathways for capturing, converting, and storing CO2 from dilute flue gases, understanding the composition of product phases as they evolve is essential for evaluating the efficacy of a given processing route. Therefore, in this study, we investigate the phase evolution and the corresponding textural changes as calcium hydroxide is converted to calcium carbonate under the continuous flow of CO2 at an ambient pressure of 1 atm with continuous heating from 30 °C to 500 °C using in-operando wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS), and ultrasmall angle X-ray scattering (USAXS) measurements.

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35

Nield, D. A., and K. Hooman. "Comments on “Effects of viscous dissipation on the heat transfer in forced pipe flow. Part 1: Both hydrodynamically and thermally fully developed flow [Energy Conv. Manage. 2005; 46: 757–769] and Part 2: Thermally developing flow [Energy Conv. Manage. 2005; 46: 3091–3202]” by O. Aydin." Energy Conversion and Management 47, no. 18-19 (November 2006): 3501–3. http://dx.doi.org/10.1016/j.enconman.2006.02.020.

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Nguyen, Giang Dinh, Alexander M. Korsunsky, and Jonathan Belnoue. "Coupled Damage-Plasticity Modelling of Ductile Failure in an Aluminium Alloy." Applied Mechanics and Materials 784 (August 2015): 266–73. http://dx.doi.org/10.4028/www.scientific.net/amm.784.266.

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The ductile failure of metallic alloys is characterized by the long plateau of the stress-strain response during plastic deformation. In aluminium alloys this complex process is principally mediated by crystal slip associated with dislocation nucleation, motion, interaction, and locking. This results in hardening, i.e. the increase in the flow stress and progressive exhaustion of ductility, eventually leading to damage. Therefore, in the advanced stages of deformation the strength increase at the material level competes with overall stiffness and strength decrease due to effective cross-section reduction by decohesion and voiding. Capturing the complex hierarchical failure of these materials requires developing sophisticated concurrent constitutive descriptions of both plastic deformation and damage at different stages of failure. In the present study the modelling of aluminium alloy failure is accomplished using a plasticity-based model with nonlinear hardening coupled with isotropic damage in a thermodynamically consistent framework. The model developed in this way is enhanced with nonlocal regularization to deal with material instabilities issues due to softening. Emphasis is placed on the correspondence between experimental measurements of the essential work of fracture and the non-essential work of fracture, and both local and spatial sets of model parameters. This approach is the key to assuring a constitutive response consistent with experimental observations, an issue usually overlooked in nonlocal constitutive modelling. Numerical examples are used to demonstrate the features of the new approach.

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Xavier, Prince, See Yee Lim, Muhammad Firdaus Ammar Bin Abdullah, Michael Bala, Sheeba Nettukandy Chenoli, Asteria S. Handayani, Charline Marzin, et al. "Seasonal Dependence of Cold Surges and their Interaction with the Madden–Julian Oscillation over Southeast Asia." Journal of Climate 33, no. 6 (March 15, 2020): 2467–82. http://dx.doi.org/10.1175/jcli-d-19-0048.1.

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AbstractNortheasterly cold surges strongly influence the rainfall patterns over the Malay Peninsula during the northeast monsoon season. This study looks at the changes in the cold surges and Madden–Julian oscillation (MJO) characteristics through the northeast monsoon season and their interaction. Nearly 75% of the cold surge events tend to cross the equator around the Java Sea area (100°–110°E) in February–March with drier conditions prevailing over the Malay Peninsula and increased rainfall over Java. Both the cold surges and the MJO undergo seasonal variations with well-defined regional features. Wavelet analysis shows that MJO amplitude and high-frequency rainfall variations over Southeast Asia peak in November–December. MJO amplitude is suppressed during February and March. This is linked to the high-frequency surges of meridional winds that are prominent during the early part of the season, but February–March is dominated by low-frequency (~20–90 days) cross-equatorial monsoon flow. These prolonged periods of strong meridional flow at the equator interact with the MJO both dynamically and thermodynamically and act as a barrier for convection from propagating from the Indian Ocean to the Maritime Continent (MC). These interactions may have implications for weather and seasonal forecasting over the region. An evaluation of the properties of cold surges and their interaction with the seasonal cycle in the Met Office Unified Model is performed. The atmosphere–ocean coupled model performs better in representing the pattern of influence of the cold surges despite the biases in intensity and spatial distribution of rainfall extremes. These diagnostics are presented with the aim of developing a set of model evaluation metrics for global and regional models.

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MILLER, R. S., and J. BELLAN. "Direct numerical simulation of a confined three-dimensional gas mixing layer with one evaporating hydrocarbon-droplet-laden stream." Journal of Fluid Mechanics 384 (April 10, 1999): 293–338. http://dx.doi.org/10.1017/s0022112098004042.

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Direct numerical simulations are performed of a confined three-dimensional, temporally developing, initially isothermal gas mixing layer with one stream laden with as many as 7.3×105 evaporating hydrocarbon droplets, at moderate gas temperature and subsonic Mach number. Complete two-way phase couplings of mass, momentum and energy are incorporated which are based on a thermodynamically self-consistent specification of the vapour enthalpy, internal energy and latent heat of vaporization. Effects of the initial liquid mass loading ratio (ML), initial Stokes number (St0), initial droplet temperature and flow three-dimensionality on the mixing layer growth and development are discussed. The dominant parameter governing flow modulation is found to be the liquid mass loading ratio. Variations in the initial Stokes number over the range 0.5[les ]St0[les ]2.0 do not cause significant modulations of either first- or second-order gas phase statistics. The mixing layer growth rate and kinetic energy are increasingly attenuated for increasing liquid loadings in the range 0[les ]ML[les ]0.35. The laden stream becomes saturated before evaporation is completed for all but the smallest liquid loadings owing to: (i) latent heat effects which reduce the gas temperature, and (ii) build up of the evaporated vapour mass fraction. However, droplets continue to be entrained into the layer where they evaporate owing to contact with the relatively higher-temperature vapour-free gas stream. The droplets within the layer are observed to be centrifuged out of high-vorticity regions and to migrate towards high-strain regions of the flow. This results in the formation of concentration streaks in spanwise braid regions which are wrapped around the periphery of secondary streamwise vortices. Persistent regions of positive and negative slip velocity and slip temperature are identified. The velocity component variances in both the streamwise and spanwise directions are found to be larger for the droplets than for the gas phase on the unladen stream side of the layer; however, the cross-stream velocity and temperature variances are larger for the gas. Finally, both the mean streamwise gas velocity and droplet number density profiles are observed to coincide for all ML when the cross-stream coordinate is normalized by the instantaneous vorticity thickness; however, first-order thermodynamic profiles do not coincide.

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McTaggart-Cowan, Ron, Eyad H. Atallah, John R. Gyakum, and Lance F. Bosart. "Hurricane Juan (2003). Part I: A Diagnostic and Compositing Life Cycle Study." Monthly Weather Review 134, no. 7 (July 1, 2006): 1725–47. http://dx.doi.org/10.1175/mwr3142.1.

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Abstract A detailed analysis of the complex life cycle of Hurricane Juan (in 2003) is undertaken to elucidate the structures and forcings that prevailed over the period leading up to the hurricane’s landfall in Halifax, Nova Scotia, Canada. Despite the presence of easterly wave precursors, Hurricane Juan’s initial development is shown to occur in a baroclinic environment beneath a low-latitude potential vorticity streamer. This feature interacts with a lower-level shear line as the incipient vortex begins to effectively focus ascent and convection. The system undergoes a slow tropical transition over a period of several days as the deep-layer shear over the developing storm decreases. The hurricane is repeatedly perturbed by subsynoptic-scale waves traveling along the leading edge of a large upstream trough. However, Hurricane Juan maintains its tropical structure despite its relatively high formation latitude (28°N) and its northward trajectory. The unusual persistence of the storm’s tropical nature as it propagates northward is of primary interest in this study. In particular, the role of persistent ridging along the east coast of North America is investigated both in high-resolution analyses for Hurricane Juan and in a compositing framework. Dynamic tropopause, quasigeostrophic, and modified Eady model diagnostics are used to elucidate the interactions between Hurricane Juan and this amplified midlatitude flow. Given the strength and persistence of the anomalous ridge–trough couplet both in the case diagnosis and in the composite fields, the study concludes that the presence of prestorm, high-amplitude ridging along the east coast likely reinforced by diabatic ridging downshear of the storm itself produces an environment both dynamically and thermodynamically conducive to the high-latitude landfall of hurricanes still in the tropical phase.

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Bennett, T. D. "Correlations for Convection in Hydrodynamically Developing Laminar Duct Flow." Journal of Heat Transfer 141, no. 11 (September 27, 2019). http://dx.doi.org/10.1115/1.4044390.

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Abstract A generalized correlation for combined entry convection in ducts of arbitrary cross section has been developed. The correlation is constructed for the average Nusselt number using knowledge of fully developed transport constants. The general correlation reproduces the first principle solutions for the well-established round and parallel plate duct geometries to within ±5% for both constant temperature and constant heat flux wall conditions when Pr ≥ 0.7. A survey of the literature demonstrates that the new generalized correlation performs as well or better than existing correlations, which are expressed for specific geometries and wall conditions. The new correlation is generally in good agreement with the first principle solutions of less common duct geometries so long as the duct has a convective surface equal to the wetted perimeter. The new correlation is not recommended for ducts having small aspect ratios that pinch the flow when convection is prescribed by the H2 constant heat flux wall condition.

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41

Rastogi, Pallavi, and Shripad P. Mahulikar. "Entropy Generation and Poiseuille Number Link in Developing Isothermal Laminar Micro-Flow." Journal of Energy Resources Technology 144, no. 4 (July 15, 2021). http://dx.doi.org/10.1115/1.4051621.

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Abstract It is well-known that Poiseuille number (Po, hitherto viewed mainly as a fluid mechanics parameter) decreases along a hydrodynamically developing flow, from infinity at inlet to a fixed value downstream. This study reveals that the dimensionless entropy generation rate per unit length due to fluid friction (S˙¯′gen,fr) varies exactly the same way; hence, Po and S˙¯gen,fr′ are jointly studied for their dependence. Laminar hydrodynamic development of isothermal flow of incompressible fluid (water) in a circular micro-tube (diameter, D) is examined. Results are obtained for a given flow velocity for different D, and then, numerical experiments are conducted for different flow velocities for the same D-values. Striking similarity in trends of Po and S˙¯gen,fr′ shows a unique linear relation between them for the hydrodynamically developing region. It is theoretically shown that Po is a direct measure of entropy generation due to fluid friction, which explains its numerically obtained linear relation with S˙¯gen,fr′. It is found that in hydrodynamically developing region, both Po and S˙¯gen,fr′, decrease with decreasing D, which is the identified micro-effect.

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Özdemir, Mehmed Rafet, and Ali Koşar. "Thermally Developing Single-Phase Flows in Microtubes." Journal of Heat Transfer 135, no. 7 (June 6, 2013). http://dx.doi.org/10.1115/1.4023881.

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The pressure drop and heat transfer due to the flow of de-ionized water at high mass fluxes in microtubes of ∼ 254 μm and ∼ 685 μm inner diameters is investigated in the laminar, transition and the turbulent flow regimes. The flow is hydrodynamically fully developed and thermally developing. The experimental friction factors and heat transfer coefficients are respectively predicted to within ±20% and ±30% by existing open literature correlations. Higher single phase heat transfer coefficients were obtained with increasing mass fluxes, which is motivating to operate at high mass fluxes and under thermally developing flow conditions. The transition to turbulent flow and friction factors for both laminar and turbulent conditions were found to be in agreement with existing theory. A reasonable agreement was present between experimental results and theoretical predictions recommended for convective heat transfer in thermally developing flows.

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Kolade, Babajide, Kenneth E. Goodson, and John K. Eaton. "Convective Performance of Nanofluids in a Laminar Thermally Developing Tube Flow." Journal of Heat Transfer 131, no. 5 (March 19, 2009). http://dx.doi.org/10.1115/1.3013831.

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While many of the published papers on nanofluids focus on measuring the increased thermal conductivity of the suspension under static conditions, the convective performance of these fluids has received relatively little attention. The present work measures the effective thermal conductivity of nanofluids under developing convective boundary layer conditions in tubes of diameter 5 mm. The experiments use a hydrodynamically fully developed laminar tube flow in the range 500≤Re≤1600 with constant wall heat flux. The experiments were validated through measurements on pure de-ionized (DI) water, which results in a thermal conductivity value that agrees within 0.4% of handbook value. The increase in effective thermal conductivity for DI-water/Al2O3 nanofluids is 6% for 2% volume concentration of Al2O3, which is consistent with the previously reported conductivity values for this sample. For a suspension of multiwall carbon nanotubes in silicone oil, the thermal conductivity is increased by 10% over that of the base fluid for a concentration of 0.2% by volume. Scanning electron microscopy was utilized to examine the structure of the dry state of the nanotubes and elucidate the performance differences of carbon nanomaterials.

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Angeneh, Saeid R., and Murat K. Aktas. "Oscillatory Flow Induced Developing Convection in a Shallow Enclosure: Effect of Sinusoidal Bottom Wall Temperature." Journal of Heat Transfer 142, no. 3 (January 13, 2020). http://dx.doi.org/10.1115/1.4045749.

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Abstract The influence of hydrodynamically developing nonzero mean acoustic streaming motion on transient convective heat transfer in an air-filled rectangular enclosure is studied numerically. The enclosure is two-dimensional with sinusoidal bottom wall spatial temperature distribution. The oscillatory flow under relatively large Womersley number regime conditions is actuated by the periodic vibrations of the enclosure side wall. The side walls of the enclosure are adiabatic, while the top wall is isothermal. The compressible form of the Navier–Stokes equations is considered to predict the oscillatory- and time-averaged mean flow fields. A control-volume method based explicit computational scheme is used to simulate the convective transport in the enclosure. The longitudinal and the transverse temperature gradients strongly affect the flow structure in the enclosure. The mean fluid motion alters the heat transfer behavior compared to the pure conduction.

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Kondle, Satyanarayana, Jorge L. Alvarado, and Charles Marsh. "Laminar Flow Forced Convection Heat Transfer Behavior of a Phase Change Material Fluid in Microchannels." Journal of Heat Transfer 135, no. 5 (April 11, 2013). http://dx.doi.org/10.1115/1.4023221.

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In this paper, a phase change material (PCM) fluid (N-eicosane) is compared with pure water as heat transfer fluid. The heat transfer behavior of PCM fluid under laminar flow conditions (Reynolds number of 700) in circular and rectangular microchannels was studied numerically. In the numerical study, an effective specific heat model was used to take into account the phase change process. Heat transfer results for circular and rectangular microchannels with PCM fluid were obtained under hydrodynamically and thermally fully developed conditions. A PCM fluid in microchannels with aspect ratios of 1 to 2, 1 to 4, and 1 to 8 was found to enhance the thermal behavior of microchannels which can be beneficial in a host of cooling applications. The flow was assumed to be hydrodynamically fully developed at the inlet and thermally developing inside the microchannel. Heat transfer characteristics of PCM slurry flow in microchannels have been studied under three types of wall boundary conditions including constant axial heat flux with constant peripheral temperature (H1), constant heat flux with variable peripheral temperature (H2), and constant wall temperature (T) boundary condition. The fully developed Nusselt number was found to be higher for H1 than for H2 and T boundary conditions for all the geometries. Moreover, Nusselt number also increased with aspect ratio and was sensitive to the variations in effective specific heat.

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46

Dominic, A., J. Sarangan, S. Suresh, and V. S. Devah Dhanush. "An Experimental Investigation of Wavy and Straight Minichannel Heat Sinks Using Water and Nanofluids." Journal of Thermal Science and Engineering Applications 7, no. 3 (September 1, 2015). http://dx.doi.org/10.1115/1.4030104.

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An experimental investigation on the heat transfer performance and pressure drop characteristics of thermally developing and hydrodynamically developed laminar flow of de-ionized (DI) water and 0.1%, 0.5%, and 0.8% concentrations of Al2O3/water nanofluid in wavy and straight minichannels was conducted. Reynolds number was varied from 700 to 1900 and two different heat fluxes of 45 kW/m2 and 65 kW/m2 were applied. The performance factor (PF) of water in wavy minichannels over their straight counterparts was higher than the nanofluids. Temperature distributions and general correlations of these minichannels are also presented.

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47

Ramadan, K. M., Mohammed Kamil, and M. S. Bataineh. "Conjugate Heat Transfer in a Microchannel Simultaneously Developing Gas Flow: A Vorticity Stream Function-Based Numerical Analysis." Journal of Thermal Science and Engineering Applications 11, no. 6 (May 15, 2019). http://dx.doi.org/10.1115/1.4043468.

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A simultaneously developing microchannel gas flow is analyzed numerically, using the vorticity–stream function form of the Navier–Stokes equation, together with the fluid energy equation and the solid wall heat conduction equation. Rarefaction, shear work, viscous dissipation, pressure work, axial conduction, and conjugate effects on heat transfer characteristics are investigated. The shear work contribution to the wall heat flux is evaluated in both the developing and the fully developed flow regions and compared with the conductive wall heat flux. The assumption of hydrodynamically fully developed, thermally developing flow—normally used in the analysis of channel heat transfer—is assessed and compared with the simultaneously developing flow case. Analytical expressions for the fluid flow and heat transfer parameters under fully developed conditions are also derived and compared with the numerical results for verification. The analysis presented shows that the shear work and the combined viscous dissipation and pressure work result in extending the thermal entrance length by far. Heat conduction in the wall also contributes to increase the thermal entry length. The results presented also demonstrate the shear work contribution to heat transfer in the slip flow regime, although minor in the very first portion of the thermal entrance length, and it becomes progressively more significant as the flow thermal development conditions are approached and turns out to be exactly equal in magnitude to the conductive wall heat flux in the thermally fully developed region, resulting in a zero Nusselt number, as verified by both the exact and numerical solutions.

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Karamanis, Georgios, Marc Hodes, Toby Kirk, and Demetrios T. Papageorgiou. "Solution of the Graetz–Nusselt Problem for Liquid Flow Over Isothermal Parallel Ridges." Journal of Heat Transfer 139, no. 9 (May 2, 2017). http://dx.doi.org/10.1115/1.4036281.

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We consider convective heat transfer for laminar flow of liquid between parallel plates that are textured with isothermal ridges oriented parallel to the flow. Three different flow configurations are analyzed: one plate textured and the other one smooth; both plates textured and the ridges aligned; and both plates textured, but the ridges staggered by half a pitch. The liquid is assumed to be in the Cassie state on the textured surface(s), to which a mixed boundary condition of no-slip on the ridges and no-shear along flat menisci applies. Heat is exchanged with the liquid either through the ridges of one plate with the other plate adiabatic, or through the ridges of both plates. The thermal energy equation is subjected to a mixed isothermal-ridge and adiabatic-meniscus boundary condition on the textured surface(s). Axial conduction is neglected and the inlet temperature profile is arbitrary. We solve for the three-dimensional developing temperature profile assuming a hydrodynamically developed flow, i.e., we consider the Graetz–Nusselt problem. Using the method of separation of variables, the thermal problem is essentially reduced to a two-dimensional eigenvalue problem in the transverse coordinates, which is solved numerically. Expressions for the local Nusselt number and those averaged over the period of the ridges in the developing and fully developed regions are provided. Nusselt numbers averaged over the period and length of the domain are also provided. Our approach enables the aforementioned quantities to be computed in a small fraction of the time required by a general computational fluid dynamics (CFD) solver.

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Raghavan, V., and B. Premachandran. "Microscale Flow Through Channels With a Right-Angled Bend: Effect of Fillet Radius." Journal of Fluids Engineering 130, no. 10 (September 12, 2008). http://dx.doi.org/10.1115/1.2969455.

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Microscale gas flow through channels with a right-angled bend has been numerically analyzed to study the effect of the fillet radius on flow characteristics. The flow is assumed to be incompressible, laminar, and hydrodynamically developing. The fillet radius has been varied from zero, representing a sharp corner, to 0.6 times the height of the channel. The Knudsen number has been varied from zero, representing no-slip at the boundary, to 0.1, which is the limiting case for the slip-flow regime. A low Reynolds number of value 1 has been considered in the present study, which makes the flow to be within the incompressible slip-flow regime. The flow characteristics in terms of velocity profiles, velocity vectors, and the pressure ratio between the inlet and outlet of the channel have been presented for several cases. Results show that for the case of the fillet radius equal to zero, the flow separation occurs after the bend and due to this, the exit velocity profile changes significantly. The highest pressure ratio between the inlet and the outlet is required to maintain a specific mass flow rate for this case. The cases with a nonzero fillet radius exhibit exit velocity profiles identical to that of a straight channel. The pressure ratio decreases when the fillet radius and the Knudsen number are increased.

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Azari, Milad, Arman Sadeghi, and Morteza Dejam. "Liquid Flow Forced Convection in Rectangular Microchannels With Nonuniform Heating: Toward Analytical Modeling of Hotspots." Journal of Heat Transfer 142, no. 8 (June 23, 2020). http://dx.doi.org/10.1115/1.4047148.

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Abstract The heat generated by microprocessors has an extremely nonuniform spatial distribution with hotspots that have heat fluxes several times larger than the background flux. Hence, for an accurate design of microchannel heat sinks used for cooling of micro-electronic devices, models are required that can take such a nonuniform distribution of wall heat flux into account. In this study, analytical solutions are obtained for hydrodynamically fully developed but thermally developing mixed electro-osmotic and pressure-driven (PD) flow in a rectangular microchannel with a peripherally uniform but axially nonuniform distribution of the wall heat flux. It is assumed that the heat flux is applied over a finite length, to mimic a physically more realistic situation, and the Péclet number is small so that lateral temperature variations are negligible as compared to the axial variations of temperature. By comparing the results with those of full numerical simulations for exponential (EHF), sinusoidal (SHF), and stepwise (STHF) distributions of wall heat flux, it is demonstrated that the solutions obtained are accurate up to a Péclet number of 10. Fortunately, this value is larger than the maximum Péclet number of electro-osmotic microflows. Furthermore, it is shown that smoother distributions of wall heat flux give rise to higher heat transfer rates. The model developed in this study can pave the way for modeling of hotspots in more complicated microfluidic devices.

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Journal articles on the topic 'Thermodynamically and hydrodynamically developing flow'

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