Convection heat transfer in concentric micro annular tubes with constant wall temperature

Heat transfer characteristics of gaseous flows in concentric micro annular tubes with constant wall temperature whose temperature is lower or higher than the inlet temperature were numerically investigated. The slip velocity, temperature jump and shear stress work were considered on the slip boundary. The numerical methodology was based on the Arbitrary–Lagrangian–Eulerian (ALE) method. The computations were performed for two thermal cases. This is, the wall temperature was constant at the outer wall and inner wall was adiabatic (Case i) and the wall temperature was constant at the inner wall and the outer wall was adiabatic (Case ii). The stagnation temperature was fixed at 300 K and the computations were done for the wall temperature which ranges from 250 K to 350 K. The outer tube radius ranged from 20 to 150 μm with the radius ratio 0.02, 0.05, 0.1, 0.25 and 0.5 and the ratio of length to hydraulic diameter was 100. The stagnation pressure was chosen in such a way that the exit Mach number ranged from 0.1 to 0.8. The outlet pressure was fixed at the atmospheric pressure. The heat transfer characteristics in concentric micro annular tubes were obtained. The bulk temperature and the total temperature are compared with those of both cooled and heated cases and also compared with those of the simultaneously developing incompressible flow obtained by SIMPLE algorithm. The results show that the compressible slip flow static bulk temperature along the length is different from that of incompressible flow. Therefore heat transfer characteristics of the gaseous flow are different from those of the liquid flow and also have different trends whether the wall temperature is lower or higher than the inlet temperature. A correlation for the prediction of the heat transfer rate of gas slip flow in concentric micro annular tubes is proposed.