An experimentally validated model for microchannel heat exchanger incorporating lubricant effect

Abstract

Please cite this article as: Huize Li, Pega Hrnjak, An experimentally validated model for microchannel heat exchanger incorporating lubricant effect, International Journal of Refrigeration (2015), http://dx.doi.org/Highlights  A heat exchanger model comprehensively considering lubricant effect was developed.  An infrared thermography based method was integrated in the heat exchanger model.  New model showed superiority over models that ignore or overly simplify lubricant effect. ABSTRACT This paper presents the further development of Li and Hrnjak's (2013) microchannel heat exchanger model which includes the thermodynamic and transport properties of refrigerant-oil mixture. Effect of lubricant is accounted in boiling heat transfer, pressure drop and refrigerant distribution. A newly proposed infrared thermography based method is implemented in the model to describe the liquid refrigerant distribution in the inlet header of the microchannel heat exchanger. The new model is validated against experimental results (R134a-PAG 46 oil) at various oil circulation ratios (0.1%-8.3%). Simulation results also indicate that lubricant addition improves refrigerant distribution which is in agreement with experiments and the infrared thermography based method enables the model capture lubricant effect on capacity more comprehensively.

Effect of Lubricating Oil on Refrigerant Distribution in Microchannel Heat Exchangers: A Review

“…2, the flow state of pure R134a is agitated flow at low quality. When OCR=0.5%, the oil has little effect on the flow state of the header, and when the OCR is increased to 2.5% and 4.7%, there will be too many small bubbles or bubbles in the header sometimes, and it is difficult for even light to pass through [22]. This makes the two-phase flow more uniform and the distribution more uniform.…”

Control of flash gas bypass MAC system with emphasis on start-ups and transients

“…There was numerous research in the last decade on how to quantify refrigerant maldistribution (Vist and Pettersen, 2004;Kim and Kim, 2011;Zou and Hrnjak, 2013;Li and Hrnjak, 2015a) and its effect on cooling capacity (Kulkarni et al, 2004;Zou et al, 2014;Li and Hrnjak, 2015b).…”

Experimental analysis and modeling of lubricant effects in microchannel evaporators working with low global warming potential refrigerants

“…Authors' previous work (Yatim et al, 2015) reported that if the OMF increased then the oil retained in a microchannel condenser also increased and the thermal performance of the condenser were degraded. Hrnjak and coworkers (Li and Hrnjak, 2013, 2014aand 2014band Zou et al 2014) carried out both numerical and experimental studies about the effect of oil on microchannel evaporator for a R134a and PAG oil working pair. They found that the mixture higher viscosity is detrimental for refrigerant distribution and that the refrigerant distribution becomes worse at oil mass fraction lower than 3 wt% but it becomes better at very higher OMF.…”