Abstract

A computational study, based on exact solutions for transient laminar flow in pipes and on an empirical correlation for transition to turbulence in the presence of temporal acceleration, shows that, provided certain conditions are met, pumping an incompressible fluid at a prescribed flow rate by a series of consecutive pressure gradient pulses may require less mechanical power consumption than pumping the same flow rate under steady-state turbulent flow conditions. The reason is that, in the former case, the fluid is pumped under conditions of accelerated laminar flow, for which the onset of turbulence occurs at Reynolds numbers much larger than the steady-state critical value of about 2100. The conclusions of this study rest crucially on the exact criterion for transition to turbulence in accelerated laminar flow, for which, unfortunately, existing experimental results exhibit a large scatter and general consensus is still lacking. Also, the present study adopts a simplified description of the problem, and further model refinements, design efforts, and supporting experimental tests will have to be performed before the hypothesis that pulsed pumping can provide energetic advantages can be demonstrated in "real-world" situations.

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