Flow Boiling of Water in a Rectangular Metallic Microchannel

Mehmed Rafet Özdemir,Mohamed M Mahmoud,Tassos G Karayiannis

doi:10.1080/01457632.2019.1707390

Mehmed Rafet Özdemir, Mohamed M Mahmoud + Show 1 more

Open Access

https://doi.org/10.1080/01457632.2019.1707390

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Abstract

The article presents the experimental results of flow boiling of water in single rectangular microchannels. Three rectangular copper microchannels having the same hydraulic diameter (0.56 mm) and length (62 mm) but different aspect ratios (width/height, 0.5, 2.56, and 4.94) were investigated using de-ionized water as the working fluid. The experiments were conducted over the experimental range of mass flux 200–800 kg/(m2s), heat flux 4–1350 kW/m2 and inlet subcooling of ∼14 K. The results showed that the channel with smaller aspect ratio exhibited better heat transfer performance up to certain heat fluxes (∼480–500 kW/m2), whilst the effect of channel aspect ratio became insignificant for higher heat fluxes. The flow boiling patterns were observed and the main flow regimes were bubbly, slug, churn, and annular flow. Flow reversal was also observed that caused a periodic flow in the two microchannels having smaller aspect ratio. A comparison of the experimental results with widely used macro and micro-scale heat transfer correlations is presented. The macro-scale correlations failed to predict the experimental data while some micro-scale correlations could predict the data reasonably well.

Highlights

The rapid developments in miniaturization of novel electronic equipment and the improvements in their performance have resulted in a big challenge in their thermal management
Yen et al [3] tested smooth Pyrex glass circular and square microchannels with the same hydraulic diameter (Dh 1⁄4 0.21 mm) and concluded that the heat transfer coefficient was higher for the square microchannel
The flow patterns were captured at three locations

Summary

Introduction

The rapid developments in miniaturization of novel electronic equipment and the improvements in their performance have resulted in a big challenge in their thermal management. Flow boiling in microchannels is regarded as a promising solution for cooling such electronic equipment and high heat flux devices. This is based on the fact that flows with phase change can achieve high heat transfer rates and better axial temperature uniformity than single phase flow-based cooling schemes. Yen et al [3] tested smooth Pyrex glass circular and square microchannels with the same hydraulic diameter (Dh 1⁄4 0.21 mm) and concluded that the heat transfer coefficient was higher for the square microchannel They attributed this to the sharp edges of the square microchannel, which behaved as effective nucleation sites that enhance the heat transfer rate.

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