Heat and Mass Transfer Research Journal (HMTRJ)

Research Article

Applicability of Correlations for Boiling/Condensing in Macrochannels to Minichannels

Mirza M. Shah

Engineering Research Associates, 10 Dahlia Lane, Redding, CT 06896, USA

Submitted: October 3, 2017; Revised: February 4, 2018; Accepted: February 5, 2018

Abstract

Channels with small flow passages, commonly known as mini channels, are being widely used in heat exchangers for boiling and condensation. Correlations for heat transfer validated with macro channel data have been reported to sometimes fail for small diameter channels. Hence it is important to know the limits of applicability of such correlations. Many criteria have been proposed for boundary between macro and mini channels. The suitability of these criteria for determining the limits of applicability was evaluated by comparing wide ranging data for heat transfer during condensation, saturated boiling, subcooled boiling, film boiling, and with data for CHF (critical heat flux), with well-validated correlations for macro channels. The criteria based exclusively on diameter or Bond number and its equivalents were found inadequate. Satisfactory criteria for mini-macro boundary were identified for condensation and saturated boiling heat transfer. Macro channel correlations for subcooled and film boiling, and for CHF, were found to be satisfactory even for very small diameter channels.

Keywords

Channels; Mini/macro classification; boiling; condensation; heat transfer; correlations.

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