Heat transfer enhancement on micro-pin-finned surfaces under high-frequency reciprocating flow

To further improve the flow boiling heat transfer performance, an experimental study was carried out to test the effect of high-frequency reciprocating flow on the heat transfer performance on micro-pin-finned surfaces. Three micro-pin-finned surfaces with different dimensions together with the smooth surface were tested. In the experiments, the inlet liquid subcooling was 35 K and the flow velocity varied from 0.25 to 0.75 m/s, with the reciprocating frequency varied from 1 to 10 Hz. The effects of flow velocity, reciprocating frequency and surface structure were tested. The results indicated that the forced convection was greatly intensified by the high-frequency flow reciprocation on micro-pin-finned surfaces with a maximum increase of heat transfer coefficient of 69.9%. The critical heat flux (CHF) of micro-pin-finned surfaces also got a further enhancement by the flow reciprocation and the mechanism of CHF improvement was analyzed. Under reciprocating flow conditions, the boiling crisis happens only when the duration of dryout exceeds a critical dryout time, where the former one is decided by the reciprocating frequency, the latter one relates to the evaporation time of the liquid sublayer and wicking effect of the surface structure.