Flow boiling study in mini-channels
Résumé
The use ofmini-channel heat exchangers (hydraulic diameter about 1 mm) in compact heat exchangers improves heat transfer coefficients, and thermal efficiency while requiring a lower fluid mass. They are widely used in condensers for automobile air-conditioning and are now being used in evaporators, as well as in other applications such as domestic air-conditioning systems. However, more general use requires a better understanding of boiling heat transfer in confined spaces. Many definitions of micro and minichannel hydraulic diameter are used throughout the literature. Kandlikar and Grande (2003) proposed the following classification: conventional channels (Dh > 3 mm), minichannels (200 μm < Dh < 3 mm), micro-channels (Dh < 200 μm), that will be used throughout this paper. These definitions rely upon the molecular mean free path in a single-phase flow, surface tension effectsand flow patterns in two-phase flow applications. In recent studies in minichannels the hydraulic diameter ranges from 100 μm to 2–3 mm. The channel cross sections were either circular or rectangular and much of the research concerned boiling. Commonly, classical correlations have been used with or without modifications to predict flow boiling results in minichannels. However agreement was poor and the need for new correlations was evident.
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