Horizontal Nucleate Flow Boiling Heat Transfer Coefficient Measurements andVisual Observations for R12, R134a, and R134a/Ester Lubricant Mixtures

摘要

The paper presents a calorimetric and visual investigation of horizontal nucleateflow boiling of five different fluids: (1) dichlorodifluoromethane (R12), (2) 1,1,1,2-tetrafluoroethane (R134a), (3) R134a/1.7% proprietary polyol ester lubricant, (4) R134a/0.9% neopentyle polyol ester lubricant, and (5) R134a/2.3% neopentyle polyol ester lubricant. The calorimetric aspect of the study concentrates on the measurement of the local two-phase heat transfer coefficient (h(sub 2 phi)). The visual measurements obtained from high-speed 16 mm film of the boiling were taken simultaneously with the calorimetric measurements. The bubble diameters (D(sub b)), and the bubble density were derived from over 50 high-speed films. The purpose of the study is to provide a source of heat transfer information for the boiling of R12 and R134a/ester lubricant mixtures. Automotive and supermarket companies have begun to manufacture original air conditioning/refrigeration equipment with R134a as the operating fluid. The evaporator predominantly utilized by these industries is the in-tube heat exchanger. Naturally, designers of such evaporators require heat transfer coefficients for the horizontal flow boiling of R134a/ester mixtures. Only the nucleate flow boiling regime was investigated in the study with the aim of furthering the understanding of the fundamental heat transfer mechanisms responsible for the phenomenon.