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首页> 外文期刊>International Journal of Heat and Mass Transfer >Nucleation dynamics and pool boiling characteristics of high pressure refrigerant using thermochromic liquid crystals
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Nucleation dynamics and pool boiling characteristics of high pressure refrigerant using thermochromic liquid crystals

机译：热致变色液晶的高压制冷剂成核动力学和池沸腾特性

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摘要

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 ℃ in the local excess temperature at the nucleation site, which results in momentary augmentation (~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 dimen-sionless bubble generation frequency in terms of modified boiling number.
机译：本文报告了一项基于无创TLC（热致变色液晶）的热成像技术对单个孤立成核位点以下振荡温度场的实验研究。提出了经验相关性，以证明在制冷剂R-134a的核池沸腾状态下，系统压力和壁热通量对不同沸腾特性的影响。使用同步的高分辨率成像捕获TLC瞬态响应和两相流结构。观察到，成核位点的影响区域在气泡生长期间表现出两部分不同的瞬时行为，并且在气泡离开的瞬间扩大到最大为气泡直径的1.57倍。这伴随着成核位置局部过高温度急剧下降2.5℃，这导致了成核起源处局部传热系数的瞬时增加（〜40％）。在气泡剥离事件期间观察到的提高的传热速率主要归因于后退气泡后的瞬态微对流。此外，结果表明，系统压力从813.6 kPa略微增加到882.5 kPa对壁过热或整体传热系数和沸腾频率均无显着影响。另外，已经获得了气泡雷诺数，Jackob数和无量纲气泡产生频率的相关性，以修正的沸腾数表示。

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