Effect of Flow Regime in the Horizontal Inlet Header on Refrigerant-Oil Mixture Distribution in a MAC Microchannel Evaporator

An experimentally validated model for microchannel heat exchanger incorporating lubricant effect

“…The lubricant influences on pressure drop, heat transfer, distribution were all included in the model. That study only considered the effect of lubricant within parallel microchannel tubes and the effect in the inlet header is ignored which is proved to be very important by Zou and Hrnjak (2014) and Li and Hrnjak (2014b). This paper presents the improvement of the Li and Hrnjak's (2013) model by incorporating the lubricant effect in the inlet header by using a newly developed infrared (IR) thermography based method (Li and Hrnjak 2015).…”

“…Foam was formed after a large amount of oil (2.5% and 4.7%) was introduced, making the flow regime more homogeneous. Li and Hrnjak (2014b) filmed the flow regime of R134a and PAG46 mixture in the horizontal inlet header of a microchannel exchanger under the Oil Circulation Ratio (OCR, which is defined as the oil mass flow rate divided by the total mass flow rate) ranging from 0.1% to 8.3%. They found that higher oil addition contributed to more foaming, which improved refrigerant distribution.…”

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

“…The presence of lubricants will also affect the refrigerant distribution, which is the result of the combined effect of the oil effect in the header and the microchannel tube. In summary, the presence of lubricating oil in the microchannel heat exchanger will affect the distribution of refrigerant in two ways [18]: (1) The addition of lubricating oil can change the flow resistance of each microchannel tube to varying degrees, thereby affecting the mass flow of refrigerant distribution between parallel tubes. Lubricating oil affects the flow resistance by changing the heat transfer and pressure drop characteristics of the working fluid.…”

“…This is because foam is formed after introducing a large amount of oil (2.5% and 4.7%) to make the flow pattern more uniform. The study by H. Li et al [18] showed that the addition of lubricating oil will significantly affect the flow state in the horizontal inlet header. When the OCR is 0.1%, a very small amount of foam is formed, and most of the pipe inlet is exposed to the vapor phase, especially when the minimum liquid level is reached.…”

Effect of row-crossing header configuration on refrigerant distribution in a two row/four pass parallel flow minichannel heat exchanger

“…Mass flux was varied from 73 to 143 kg/m 2 s. They reported that, in the intermediate header, more liquid was forced downstream as mass flux or quality increased. Li and Hrnjak [17] and Zou et al [18] investigated the effect of oil on two-phase distribution in an evaporator for upward flow of R-134a. It was found that small amount of oil (0.5% by mass) worsen the flow distribution.…”