Evaluation of axial conduction effects and heat losses in counter-flow microscale heat exchangers

A gas to gas counter flow micro Heat Exchanger (HE) made of an array of microchannels and fabricated using a combination of silicon and glass wafers is studied. A divergence of the experimental results from the classical heat exchanger theory is observed due to discernible axial conduction effects and heat loss to the environment. Hence, device performance is evaluated using a modified NTU approach that includes also non-negligible axial conduction effects due to the relatively thick and thermally conductive separating wall. This along with replacement of the adiabatic boundary conditions at the separating wall ends with proper temperature conditions enables to evaluate the heat losses to the environment and to reduce the average error between theoretical model and experimental data by 56%.