Validation of the thermal equilibrium assumption in the transient conjugated forced convection channel flow

The validity of the local thermal equilibrium assumption in the transient c onjugated forced convection channel flow is investigated analytically. Clos ed form expressions are presented for the temperatures of the fluid and sol id domains and for the criterion which insure the validity of the local the rmal equilibrium assumption. It is found that three dimensionless parameter s control the local thermal equilibrium assumption. These parameters are th e Biot number Bi, the dimensionless channel length xi (max) and the solid t o fluid total thermal capacity ratio C-R. The qualitative and quantitative aspects of the effects of these three parameters on the channel thermalizat ion time are investigated.