Effect of Compressibility on Heat Transfer in Microchannels

In this paper an experimental investigation of convective heat transfer is presented for laminar gas flow through a microchannel. A test stand was setup to impose thermal boundary conditions of constant temperature gradient along the microchannel length. Additionally, thin film temperature sensors were developed and used to directly measure the microchannel surface temperature. Heat transfer experiments were conducted in the laminar flow regime with the outlet Ma between 0.10 and 0.42. The experimental measurements of inlet and outlet gas temperature and the microchannel wall temperature were used to validate a 2D numerical model for gaseous flow in microchannel. The model was then used to determine bcal values of Ma, Re, and Nu. The numerical results show that after the entrance region, Nu approaches 8.23, the fully developed value of Nu for incompressible flow for constant wall heat flux if Nu is defined based on (T_w-T_aw) and plotted as a function of the new dimensionless axial length, X* = (x/2H)(Ma²)/(RePr).