Effect of wall proximity on convective heat transfer from a heated block in a pulsating channel flow

Experiments are carried out to investigate heat transfer enhancement from a heated square cylinder in a channel by pulsating flow. For all the experiments, the amplitude of the pulsating flow is fixed at A = 0.05. The vortex shedding frequency and the time-averaged Nusselt number are measured for various gap height (S/D = 3.5, 2.0, 1.5, 1.0 and 0.75) at Reynolds number Re = 700. The influences of the pulsating frequency (0 Hz ≤ fp ≤ 90 Hz) and the gap height on convective heat transfer as well as on the lock-on regime are examined. The measured Strouhal numbers as function of the gap height for non-pulsating (A = 0.0) steady inlet flow are compared with the previously published data, and good agreement is found. The lock-on phenomenon is observed in the present flow pulsation for various gap heights. When the pulsating frequency is within the lock-on regime, heat transfer from the square cylinder is significantly enhanced. It is also revealed that as the gap height decreases, the heat transfer enhancement factor E is increased and lock-on regime shrinks.