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

    Authors

    A. Miglani; D. Joo; S. Basu;R. Kumar

    Comments

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    Abbreviated Journal Title

    Int. J. Heat Mass Transf.

    Keywords

    Nucleate pool boiling; Thermochromic liquid crystal; Area of influence; Ebullition frequency; ANNULAR 2-PHASE FLOW; HEAT-TRANSFER; VELOCITY-MEASUREMENTS; SATURATED; R-134A; VERTICAL DUCT; NARROW DUCT; BUBBLE; THERMOGRAPHY; MICROLAYER; TUBE; Thermodynamics; Engineering, Mechanical; Mechanics

    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. (C) 2013 Elsevier Ltd. All rights reserved.

    Journal Title

    International Journal of Heat and Mass Transfer

    Volume

    60

    Publication Date

    1-1-2013

    Document Type

    Article

    Language

    English

    First Page

    188

    Last Page

    200

    WOS Identifier

    WOS:000317534500023

    ISSN

    0017-9310

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