Experimental Study of Miscible and Immiscible Oil Effects on Heat Transfer Coefficients and Pressure Drop in Microchannel Gas Cooling of Supercritical CO2

Abstract

Carbon Dioxide (CO2) is being investigated as an alternative refrigerant for vapor compression systems. In addition to its environmental benefits, Carbon Dioxide offers certain attractive thermal characteristics such as small surface tension, small liquid viscosity and large refrigerant capacity. Furthermore, combination with microchannels provides CO2 heat exchangers that have low weight, high compaction and high heat transfer coefficient. But certain oil (e.g., lubricate oil for compressor) will be carried into the vapor compression system, which usually has negative effect on heat transfer and pressure drop. The objective of the present paper is to study the effect of oil addition on heat transfer coefficient and pressure drop in supercritical gas cooling process in microchannels. Experiments addressed effect of three different types of oil (two immiscible and one miscible) at various oil concentrations ranging from 0% (no oil) to 5% by weight. As expected, oil addition has significant negative effect on heat transfer coefficients. At higher oil concentrations the heat transfer coefficients are substantially lower and the pressure drops are higher. As far the type of oil is concerned, the immiscible oil demonstrated more negative influence on the heat transfer and pressure drops than the miscible oil.

Development and validation of static simulation model for CO2 heat pump

“…Cheng et al [12] reviewed the studies on the cooling heat transfer of supercritical CO 2 . Among them, Mori et al [13], Kuang et al [14], Yun et al [15], and Dang et al [16] deal with the effect of lubricant oil. In our experiment, the oil type is PAG, the tube diameter is 4.8 mm, the mass flux is from 1250 to 1859 kg Á m 2 s, and the pressure is about 12 Mpa.…”

The Effect of Lubricant Oil Concentration on the Performance of a Gas Cooler Using Carbon Dioxide

“…The gas cooling heat transfer coefficient decreased by maximum of 20.4% and the pressure drop increased by an average of 4.8 times as the concentration of lubricating oil increased from 0 to 4 wt%. Kuang et al (8) performed a gas cooling experiment by mixing CO 2 with lubricating oils of various concentrations in a mini-channel. When the concentration of the lubricating oil was 5 wt%, the heat transfer coefficient decreased by 57% but the pressure drop increased by 44%.…”

Investigating the effect of dry cooling system design on the performance of supercritical CO2 cycle in concentrated solar power application

“…In Figure 2-2(b), when the operating pressure was increased from the critical pressure (7.5 MPa to 8 MPa) with the same mass flux, the pressure drop decreased due to less variation of properties away from the critical region. The influence of mass velocity on the pressure drop was also experimentally investigated with different diameters of a circular pipe by Son and park [30], Yoon et al [31], Pettersen [37], Kuang et al [42], Yun et al [44], Zingerli and Groll [50], Liu et al [1] and Fang et al [77] and reached similar findings.…”

“…[31], Pettersen [37], Olson [39], Kuang et al [42], Liao and Zhao [25], Kim et al [73] and many more.…”