Convection microscale heat transfer

Bayazitoglu, Y., Tunc, G., Wilson, K., and Tjahjono, I., (2005) Convective Heat Transfer for Single-Phase Gases in MicroChannel Slip Flow Analytical Solutions, presented at NATO Advanced Study Institute, Microscale Heat Transfer - Fundamentals and Applications in Biological and Microelectromechanical Systems, July 18-30, Altin Yunus - Qe me, Izmir, Turkey. 

Yener, Y., Kaka9, S., and Avelino, M. R. (2005) Single-Phase Convective Heat Trmsfer in Microchannels — The State-of-the-Art Review, NATO Advanced Study Institute on Microscale Heat Transfer, Cesme, Tiukey, July 18-30. 

Y. Yener, S. Kakac, M. Avehno, and T. Okutucu, Single phase forced convection in microchannels - State-of art-review, Microscale Heat Transfer-Fundamentals and Applications in Biological Systems and MEMS, edited by... 

R.M. Cotta, M.D. Mikhailov, and S. Kakag, Steady and Periodic Forced Convection in Microchannels, NATO Science Series II Microscale Heat Transfer Fundamentals and Applications, V. 193, S. Kakag et al. (eds.), pp. 49-74 (2005). 

V. S. Arpaci, Two thermal microscales for natural convection and heat transfer correlations," Significant Questions in Buoyancy Affected Enclosure or Cavity Flows, ASME HTD-60,117,1986b. 

Convection and conduction are the two major heat transfer mechanisms that have been investigated at microscale. Convective heat transfer in microchannels has been intensively analyzed by both experimental and analytical means. Conduction studies have focused mostly on thin films in recent years to address such questions as How is the heat transferred How does it differ from large-scale conduction ... 

CONVECTIVE HEAT TRANSFER IN MICROSCALE SLIP FLOW... 

In this lecture, the effects of the abovementioned dimensionless parameters, namely, Knudsen, Peclet, and Brinkman numbers representing rarefaction, axial conduction, and viscous dissipation, respectively, will be analyzed on forced convection heat transfer in microchannel gaseous slip flow under constant wall temperature and constant wall heat flux boundary conditions. Nusselt number will be used as the dimensionless convection heat transfer coefficient. A majority of the results will be presented as the variation of Nusselt number along the channel for various Kn, Pe, and Br values. The lecture is divided into three major sections for convective heat transfer in microscale slip flow. First, the principal results for microtubes will be presented. Then, the effect of roughness on the microchannel wall on heat transfer will be explained. Finally, the variation of the thermophysical properties of the fluid will be considered. 

Bayazitoglu Y, Tunc G, Wilson K, Tjahjono I (2005) Convective heat transfer for single-phase gases in microchannel slip flow analytical solutions. In Kakac S, Vasiliev L, Bayazitoglu Y, Yenta- Y (eds) Microscale heat transfca-fundamentals and applications. Kluwer Academic Publishers, The Netherlands... 

The heat transfer in microchannels is expected to agree with conventional theory provided that the discussed continuum assumptions can be made. For example, under fully developed laminar flow conditions at low Re, Nu is constant. However, many experimental data show large deviations between each other and inconsistency with classical theory exists. There is an increase in Nu with increasing Re measured. According to Herwig and Hausner [37], a common theoretical basis on forced convection for macro- and microchannels can be used to describe forced convection of liquids in the laminar regime. However, there are effects which are more pronounced and which are of more importance on the microscale, such as surface tension, viscous forces and electrostatic forces [38]. These effects are called scaling effects with respect to standard macroscale analysis. 

Q is the amount of heat in Joules that is transferred from surroundings into the system. Although the temperature difference is the driving force, the energy transfer is Q in Joules of energy. The heat transfer is transient in nature. The study of heat transfer is a separate subject in itself and is discussed in detail elsewhere [7] and in Chapter 11. The modes of heat transfer, conduction, convection, and radiation and of late microscale mechanisms such as wave heat conduction is discussed in Chapter 9. 

Peles et al. [22] investigated heat transfer and pressure drop phenomena over a bank of micro-pin fins in a micro-heat sink. The dimensionless total thermal resistance was expressed as a function of Re)molds number, Prandtl number and the geometrical configuration of the pin-fin microheat sink. They compared their theoretical model with their experimental results and concluded that very high heat fluxes can be dissipated at a low wall terr5>erature rise using a microscale pin-fin heat sink. Thus, forced convection over shrouded pin-fin arrays is a very effective cooling device. In many cases, the primary cause for the rise in wall temperature is the increase of the fluid tempera-... 

The Reynolds number in microreaction systems usually ranges from 0.2 to 10. In contrast to the turbulent flow patterns that occur on the macroscale, viscous effects govern the behavior of fluids on the microscale and the flow is always laminar, resulting in a parabolic flow profile. In microfluidic reaction systems, where the characteristic length is usually greater than 10 pm, a continuum description can be used to predict the flow characteristics. This allows commercially written Navier-Stokes solvers such as FEMLAB and FLUENT to model liquid flows in microreaction channels. However, modeling gas flows may require one to take account of boundary sUp conditions (if 10 < Kn < 10 , where Kn is the Knudsen number) and compressibility (if the Mach number Ma is greater than 0.3). Microfluidic reaction systems can be modeled on the basis of the Navier-Stokes equation, in conjunction with convection-diffusion equations for heat and mass transfer, and reaction-kinetic equations. 

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