Nucleation dynamics and pool boiling characteristics of high pressure refrigerant using thermochromic liquid crystals

Miglani, Ankur and Joo, Daniel and Basu, Saptarshi and Kumar, Ranganathan (2013) Nucleation dynamics and pool boiling characteristics of high pressure refrigerant using thermochromic liquid crystals. In: International Journal of Heat and Mass Transfer, 60 . pp. 188-200.

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Abstract

This paper reports an experimental investigation of oscillating temperature field beneath a single isolated nucleation site using a non-invasive TLC (thermochromic liquid crystal) based thermography technique. Empirical correlations are presented to demonstrate the influence of system pressure and wall heat flux on different ebullition characteristics in the nucleate pool boiling regime of refrigerant R-134a. TLC transient response and two-phase flow structure are captured using synchronized, high resolution imaging. It is observed that the area of influence of nucleation site exhibits a two-part distinct transient behavior during the bubble growth period and broadens to a maximum of 1.57 times the bubble diameter at the instant of bubble departure. This is accompanied by a sharp fall of 2.5 degrees C in the local excess temperature at the nucleation site, which results in momentary augmentation (similar to 40%) in the local heat transfer coefficient at the nucleation origin. The enhanced heat transfer rate observed during the bubble peel-off event is primarily due to transient micro-convection in the wake of the retreating bubble. Further, the results indicate that a slight increase in system pressure from 813.6 to 882.5 kPa has no considerable effect on either the wall superheat or the overall heat transfer coefficient and ebullition frequency. In addition, correlations have been obtained for bubble Reynolds number, Jackob number and the dimensionless bubble generation frequency in terms of modified boiling number.

Item Type:	Journal Article
Publication:	International Journal of Heat and Mass Transfer
Publisher:	Elsevier Science
Additional Information:	Copyright of this article belongs to Elsevier Science.
Keywords:	Nucleate Pool Boiling; Thermochromic Liquid Crystal; Area of Influence; Ebullition Frequency
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	28 May 2013 05:48
Last Modified:	28 May 2013 05:48
URI:	http://eprints.iisc.ac.in/id/eprint/46565

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