Geometrical investigation of microchannel with two trapezoidal blocks subjected to laminar convective flows with and without boiling

Elizaldo Domingues dos Santos,Sylvie Lorente,Ana Pavlovic,Luiz Alberto Oliveira Rocha,Bruno Costa Feijó,Liércio André Isoldi

doi:10.31181/rme200103020f

Abstract

Microchannels are important devices to improve the heat exchange in several engineering applications as heat, ventilation and air conditioning, microelectronic cooling, power generation systems and others. The present work performs a numerical study of a microchannel with two trapezoidal blocks subjected to laminar flows, aiming to analyze the influence of the boiling process on the geometric configuration of the microchannel. Constructal Design and Exhaustive Search are used for the geometrical evaluation of the blocks. The Mixture multi-phase model and the Lee phase change model were both employed for the numerical simulation of the boiling process. In this study, the influence of the height and higher width of the first block (H11/L11) over the heat transfer rate and pressure drop for different magnitudes of the ratio between the lower width and higher width (L12/L11) was investigated. It is considered water in monophase cases and water/vapor mixture for multiphase flow. Two different Reynolds numbers (ReH = 0.1 and 10.0) were investigated. Results indicated that, for the present thermal conditions, the consideration of boiling flows were not significant for prediction of optimal configurations. Results also showed that in the cases where the boiling process was enabled, the multi-objective performance was higher than in the cases without boiling, especially for ReH = 0.1.

Highlights

Microchannels usually have diameters between 0.01 and 0.2 mm (Kandlikar & Grande, 2003) and differ significantly to conventional channels
The main purpose of the present study is to investigate the influence of the height and higher width of the first block (H11/L11) over the heat transfer rate (q) and over the pressure drop (ΔP) for different magnitudes of the ratio between the lower width and higher width (L12/L11)
It is shown the influence of the geometry (H11/L11 and L12/L11) over the defined performance indicators, for ReH = 0.1 and 10.0, and it is shown the comparison between the approaches with and without boiling

Summary

Introduction

Microchannels usually have diameters between 0.01 and 0.2 mm (Kandlikar & Grande, 2003) and differ significantly to conventional channels (those with a diameter larger than 3.0 mm). The boiling process happens in a microchannel when its walls are at a temperature higher than the saturation temperature, causing the formation of vapor bubbles on the liquid. This is a process that can lead to an increase in the heat transfer coefficient (Collier & Thome, 1994; Rohsenow et al, 1998) and for that reason is a desired situation in many applications that have high rates of heat dissipation. There is strong evidence from single phase studies that the microchannels geometry can have a very important effect over the overall performance of the system (Ghani et al, 2017)

Objectives

Results

Conclusion