Axial Wall Conduction in Pulsating Laminar Flow in a Microtube

A two-dimensional numerical analysis is carried out to understand the effect of pulsation on the axial wall conduction in simultaneously developing single phase laminar flow in a microtube with constant heat flux boundary condition imposed on its outer surface and while the cross-sectional solid faces exposed to the surrounding are kept adiabatic. Water is used as the working fluid and enters the microtube at 300K with a slug velocity that varying with time sinusoidally, thus causing pulsating flows in the microtube. The inlet velocity thus consists of a fixed component and a fluctuating component which varies sinusoidally with time. For this simulation conductivity ratio is considered at a wide range (k_sf 2.26–703) while the thickness ratio (δ_sf), amplitude (A), and flow rate (Re) remain constant. To understand effect of pulsation, frequency of oscillation (f) is changed by taking four different Womersley numbers (1.414, 2, 2.45, and 3.163). Based on the numerical simulation, it is concluded that for a particular pulsation frequency (Wo) there exists an optimum value of k_sf at which overall Nusselt number (Nu) is maximum. Effect of pulsation frequency on heat transfer is found to be very small. Heat transfer is found to be increasing at lower thermal conductive microtube wall material (or k_sf) while it is decreasing at higher k_sf compared to steady flow in microtube. Existing studies do indicate that pulsation (i) increases heat transfer (ii) decreases heat transfer, or (iii) no effect. The researchers actually failed to observe the present overall trend as none of the existing studies considered a widely varying thermal conductive wall material.