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Volume 128 (2015)

CONTENTS

No. 128, 2015, 97–118

A study of flow boiling heat transfer in a rectangular minichannel using liquid crystal and infrared thermography
KINGA STRĄK, MAGDALENA PIASECKA

Abstract

This paper presents results of flow boiling heat transfer in two parallel asymmetrically heated vertical minichannels. The heating element for Fluorinert FC-72 flowing in the minichannels was a thin foil with an enhanced surface on the side in contact with the fluid. The channels were observed from both sides through glass panes. Two of the panes allowed us to observe the two phase flow patterns on the enhanced surface of the foil, while the other two panes were used for simultaneous measurement of temperature on the smooth side of the foil. The temperature was measured by applying two contactless methods. One was liquid crystal thermography (LCT), which required treating the foil surface with thermochromic liquid crystals (TLCs), and the other was infrared thermography (IRT), which required coating the foil surface with black paint. Calculations were performed on the basis ofa one-dimensional model to determine the heat transfer coefficient at the foil-fluid interface from the Robin boundary condition. The experimental results were graphically represented as the foil temperature and the heat transfer coefficient against the distance from the minichannel inlet and as LCT and IRT images obtained for saturated boiling.

Keywords:

flow boiling heat transfer, rectangular minichannel, enhanced foil surface, liquid crystal thermography, infrared thermography
DO GÓRY