Trains of Taylor bubbles over hot nano-textured mini-channel surface

Abstract

To enhance heat transfer in forced convective boiling the mini-channel bottom was amended by nano-textured structures - periodic rectangular mats of electrospun polymer nanofibers. The fibers were about several hundreds of nanometer in diameter. The test fluid was FC-72. The flow in mini-channels contained trains of the Taylor bubbles. The role of the nanofibers was to retain the warm mini-channel bottom wetted, to prevent dry-out and thus to enhance the heat removal rate. In the present experiments the time-average heat flux at the nanofiber-coated domains was found to be 1.6 times higher than that at the uncoated ones. Accordingly, a significant decrease (by 5-8 K) in the superheat was observed. The heat transfer coefficient at the nanofiber mat-coated domains was found to be an order of magnitude higher than that at the uncoated domains. Such significant enhancement of heat transfer results from the fact that nanofiber mats facilitate wetting of the surface under the passing Taylor bubbles, thus delaying formation of vapor layer at the channel bottom. (C) 2015 Elsevier Ltd. All rights reserved.