Axial wall conduction in cryogenic fluid microtube

Abstract

Axial wall conduction plays a crucial role in the thermal performance of micro device. In this background a numerical investigation is carried out to understand the effect of axial wall conduction in a microtube at low temperature. Helium at 100 K enters a microtube of inner diameter of 0.4 mm and length of 60 mm and subjected to constant wall heat flux while the microtube cross-sectional faces are considered insulated. Temperature varying thermophysical property of helium is considered in the analysis as the value of properties changes appreciably with temperature. Simulations have been carried out for varying flow Re =1, 100, 500, solid wall to fluid conductivity ratio ksf =1.71-2822.3, and microtube wall thickness to inner radius ratio δsf =1-2. The result shows that conductivity ratio and wall thickness play dominant role in conjugate heat transfer process. It is found that there exist an optimum ksf at which Nuavg is maximum when other parameters are kept constant. Nuavg is found to be lower for higher wall thickness (δsf). When Helium flow rate is increased, it is found that Nuavg increases.