Convective Heat Transfer in Microchannels

The use of convective heat transfer in microchannels to cool microchips has been proposed over the last two decades. Many analytical and experimental studies, involving both liquids and gases, have been carried out to gain a better understanding of huid how and heat transfer phenomena at the micro level. 

Convective heat transfer in microchannels is significantly enhanced, depending on the values of the Knudsen, the Prandtl and the Brinkman numbers and the aspect ratio. Heat transfer characteristics can be significantly different from conventionally sized channels. 

Tunc, G (2002) Convective Heat Transfer in MicroChannel Gaseous Slip Flow, PhD. Thesis, Rice University, Houston, TX. 

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 ... 

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. 

G.L. Morini, Single-phase convective heat transfer in microchannels A review of experimental results. International Journal of Thermal Sciences 43, 631-651 (2004). 

Convective heat transfer in microchannels is a process involving a forced mass movement of... 

Convective Heat Transfer in Microchannels, Fig. 1 Sketch of a straight microchannel with constant crosssection and Cartesian coordinate system... 

Convective Heat Transfer in MicroChannel, Fig. 4 Combination of heated and adiabatic walls considered for each geometry investigated... 

Convective Heat Transfer in Microchannels, Table 3 Nusselt numbers Nut3 for laminar fully developed flow as a fimction of the dimensionless wall thermal resistance and of the Peclet number for the T3 honndary condition... 

Convective Heat Transfer in Microchannels, Tabie 5 Nusselt numbers Nuhs for laminar fully developed flow as a function of the m parameter defined by Eqs. 18 and 31 for the H5 boundary emidition ... 

Convective Heat Transfer in Microchannels, Table 11 Nusselt numbers Nuhi for laminar fully developed flow for a KOH-etched trapezoidal cross section with three (3hc) and four (4bc) heated sides as a function of the aspect ratio 5 for the HI boundary condition... 

Convective heat transfer in microchannels has been studied extensively in the last decade both experimentally and theoretically. From a chronological analysis of these experimental works it is possible to note that the discrepancy between the experimental data obtained for microchannels and the predictions of the conventional theory is decreasing. This fact can be partially explained by considering the dramatic improvements in microfabrication techniques with the consequent more appropriate control of... 

Nonnegligible wall-fluid conjugate heat transfer when the conduction heat transfer at the walls of a microcharmel is comparable to the wall-fluid convection heat transfer (see Convective Heat Transfer in Microchannels ), thermally fully developed conditions cannot be reached along the microchannel. 

On the contrary, under the H boundary condition (see Convective Heat Transfer in Microchannels ) with a fully developed velocity profile hydrodynamically fully developed and thermally developing flow Fig. 3), the mean Nusselt number for circular microtubes as a functitMi of the dimensionless axial coordinate z for laminar flows can be calculated as follows ... 

For laminar flows, the value of the mean Nusselt number depends on the thermal boundary condition considered a description of the most common thermal boundary conditions for microchannels can be found in convective heat transfer in microchannels (i.e., T, HI, H2 boundary conditions). 

In the Hausen correlation, the Nusselt number is calculated as a sum of two terms the first term (Nu) is the fully developed value of the Nusselt number its value can be found in convective heat transfer in microchannels for the most common microchannel cross sections. The second term takes into account the effects of... 

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