Enhanced single- and two-phase transport phenomena using flow separation in a microgap with copper woven mesh coatings

摘要

The temperature difference on a heating wall between the inlet and outlet is usually large during the convective heat transfer in microgaps or microchannels due to the subcooling of the liquid and the entrance effects. In this study, a flow separation technique was developed to experimentally demonstrate that the overall transport processes including pressure drop and heat transfer could be significantly improved. "Flow separation" denotes routing of a portion of the incoming flow through a passive microjet. This flow arrangement was observed to effectively reduce the temperature difference along the flow direction, interrupt the growth of boundary layer in the single-phase regime, as well as to introduce mixing and manage the bubble expansion rate in the two-phase regime. The primary reasons for the pressure drop reduction could be the increased flow area because of the additional auxiliary channel and the effective management of the bubble expansion rate. Specifically, compared with a conventional microgap in the similar working conditions, the average wall temperature during convective boiling was reduced by 2.9 ± 0.6℃ in the steady state at a mass flux of 83 kg/(m~2 s) with a 60.4% reduction in the pressure drop. Moreover, CHF in the two-phase regime reached 311 W/cm~2 at a mass flux of 373.5 kg/(m~2 s).