Effect of Periodic Pulsations on Heat Transfer in Simultaneously Developing Laminar Flows: A Numerical Study

Heat transfer in the channels and ducts are well understood in the steady laminar flows for engineering applications. In contrast, unsteady flows have potential for research as many aspects of such flows are still unclear. Periodic pulsating flow in a channel is a kind of unsteady flow which requires further investigation because (i) many upcoming applications, especially in mini-micro scale engineering domain e.g. enhanced mixing, MEMS applications, bio-fluidic devices and thermal management of electronics etc. (ii) critical review of literature reveals that there is prevailing confusion related to the species transport coefficients. Thus, need for a systematic parametric study, both numerical and experimental, cannot be overemphasized. In this paper, two different configurations of laminar pulsatile internal flow, i.e. Case (i): unidirectional flow with axial superimposed pulsations (flow in circular axisymmetric tube) and, Case (ii) unidirectional flow with superimposed transverse pulsations (parallel plates) have been numerically scrutinized. Effect of frequency (Womersley number, Wo), Prandtl number (Pr), Reynolds number (Re) and amplitude ratio, on the instantaneous and time averaged heat transfer and friction factor (Poiseuille number) is studied. It is found that the change in species transport is either marginal or highly limited and is primarily occurring in the developing length of the channel/ plate. Nusselt number under pulsating conditions in the fully developed flow regime is not very different from its steady counterpart. Enhancement of species transport due to such periodic pulsatile internal flows, over and above the non-pulsatile regular flow conditions, is questionable, and at best, rather limited. Enhancement in heat transfer is seen in Case (ii) under certain operating conditions. This latter configuration is more attractive than the former and further optimization studies are required to improve understanding.