Thermo-hydrodynamics of pulsating laminar flow in a microtube: a numerical study

Abstract

A two dimensional numerical analysis is carried out to understand the thermo- hydrodynamics of single phase pulsating laminar flow in a microtube with constant flux boundary condition imposed on its outer surface while the cross-sectional solid faces exposed to the surrounding are insulated. The inlet velocity to the tube is the combination of a fixed component of velocity and fluctuating component of velocity which varies sinusoidally with time, thus causing pulsatile velocity at the inlet. The working fluid is water and enters the tube at 300K. Simulations have been carried out at a range of pulsating frequency between 2-10 Hz and amplitude ratio (A) equals to 0.2. To study the effect of axial wall conduction microtube, wall to fluid conductivity ratio is taken in a very wide range (ksf = 0.344 – 715) at a flow Reynolds number of 100. 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 ksf) while it is decreasing at higher ksf compared to steady flow in microtube. Again, for a particular pulsating frequency (Wo), with very low ksf leads to lower the overall Nusselt number while the time averaged relative Nusselt number remains almost constant through the entire length of microtube and it is less than the corresponding steady state Nusselt number. Higher ksf with a particular frequency again lowers overall Nusselt number slightly due to severe back conduction. From this, it is confirmed that for a particular pulsating frequency, there exist an optimum value of ksf which maximizes the overall Nusselt number while all other parameters like flow Reynolds number, microtube thickness to inner radius ratio (äsf) remaining the same.