Optimization of pulsating heaters in forced convection

This is a theoretical, numerical and experimental study that shows how to optimize the performance of on and off pulsating heaters in forced convection. Scale analysis shows that there exists an optimal heat pulse interval or frequency that maximizes the overall thermal conductance between the heater and the free stream U ∝. Numerical results for a flat plate heater and experimental results for a cylinder in cross-flow validate the theory. Numerically it is shown that the optimal pulsating regime can be identified accurately by using a complete simulation of the flow and temperature field around the heater. Boundary layer simplified numerical methods fail to simulate the short-times (high frequency) range of the process. The maximized overall conductance of a pulsating heater does not exceed the conductance associated with a steady (continuous) heater. The experimental and numerical results are nondimensionalized and correlated by using the scales recommended by theory. When the ‘on’ and ‘of’ intervals are comparable, the optimal heat pulse interval is approximately 0.1 L U∝ , where L is the scale of the swept length of the heater shape. This conclusion also applies to a pulsating heater embedded in a porous medium with uniform flow.