Numerical Study Of Axial Back Conduction In Microtubes

Abstract

A two dimensional numerical simulation is carried out to study the effect of axial wall conduction in a microtube in conjugate heat transfer situations. Both, constant wall heat flux and constant wall temperature, at the outer surface of the tube are analyzed while flow of fluid through the microtube is laminar, simultaneously developing in nature. The cross-sectional solid faces are considered adiabatic. A microtube of length 120 mm and internal radius 0.2 mm is considered while the thickness of the tube wall is varied. Simulations have been performed for a wide range of tube wall to convective fluid conductivity ratio (ksf ≈ 0.33 - 702), tube thickness to inner radius ratio (δsf ≈ 1, 16), and flow Reynolds number (Re ≈ 100, 1000). The results show that ksf plays a dominant role in the conjugate heat transfer process. For constant heat flux applied on the outer surface of the microtube, there exists an optimum value of ksf at which the average Nusselt number (Nu) over the microtube length is maximum; it decreases with departure from this optimum ksf value. However, for constant wall temperature on the outer surface of the microtube, no such optimum ksf value is observed at which Nu is maximum. The value of Nu is found to be increasing with decreasing value of ksf. Secondly, thicker wall leads to higherNu.