Experimental study of flow boiling heat transfer in rectangular ribbed micro-channels with rectangular cavities

Abstract

The flow boiling heat transfer in the RRM (i.e. ribbed micro-channel with aligned side-wall rectangular cavities), ORM (i.e. ribbed micro-channel with offset side-wall rectangular cavities), and ORMB (i.e. ribbed micro-channel with offset side-wall and bottom rectangular cavities) were experimentally investigated at a range of heat fluxes and mass fluxes. Combined with the visualization technology, the influences of offset rectangular cavities on the heat transfer and pressure drop penalty were revealed. The results showed that the existence of offset rectangular cavities enhances the heat transfer performance of micro-channels in both single-phase and two-phase regions. The bottom rectangular cavities in the ORMB enhances the disturbance to the main stream, thus further enhancing the heat transfer performance in the single-phase region and shifting from laminar to transitional flow earlier compared to the ORM. The capillary effect provided by the bottom cavities intensifies the heat transfer in the two-phase region, resulting in a significant increase in the critical heat flux in the ORMB. Compared to the ORM, the maximum increase of critical heat flux in the ORMB reaches 22.3 % (17.57 W·cm−2). The existence of offset rectangular cavities causes alternating resistance forces to the main stream, which increases the pressure drop in the ORM by 8–32.2 % compared to the RRM. The capillary effect provided by the bottom cavities to the liquid-phase in the ORMB is beneficial for the alleviation of vapor blockage and expansion. Hence the pressure drop in the ORMB is reduced by 82.3 % at most compared to the ORM in the two-phase region.