Size and Material Effects on Flow Boiling Enhancement in Microchannels With Diffusion-Brazed Wire Mesh

Abstract

This paper focuses on flow boiling enhancement in microchannels using a surface enhancement technique based on the diffusion-brazing of a mesh to the channel's inner surface. Both qualitative flow boiling visualization using a high-speed camera and quantitative local variable measurements were carried out. Good agreement was obtained from the qualitative and quantitative results. After validation of single-phase flow in the current test setup, two-phase flow boiling tests for bare channels were used as the basis for comparison with mesh channels. Reasonably good agreement was obtained with two classic saturation flow boiling correlations. Both the flow boiling curves and heat transfer coefficient plots have shown significant enhancement of flow boiling for the mesh channels. Surprisingly, the 100-mesh channel outperformed the 200-mesh channel. The high-speed camera provided clear pictures of the processes occurring in the channels and helped elucidate the nucleation process taking place inside each channel. This provided the means to validate the hypothesis that the diffusion-brazed meshes introduce a significant amount of additional active nucleation sites on the channels' heating surface.