Experimental Study on Gas Cooling Heat Transfer for Supercritical CO2 in Microchannels

Abstract

The conventional refrigerants have considerable ozone depleting effect (CFC/HCFC) and global warming impact (HFC). 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, when used with micro channels CO2 heat exchangers provide additional advantage of high compaction, low weight/low volume, while yielding excellent thermal performance. The objective of the present work was to study the heat transfer and pressure drop characteristics of supercritical CO2 gas cooling process in microchannels. A 10 ports microchannels tube with ID of 0.79mm was tested for the pressure range of 8 to 10MPa and mass flux range of 300 to 1200 kg/m2 s. As expected, mass flux has a significant influence both on the supercritical heat transfer and pressure drop coefficients. Pseudo-critical temperature (temperature at which the specific heat has maximum value for the given pressure) is found to play an important role in the CO2 heat exchanging process as well. Conventional forced convection heat transfer correlations fail to accurately predict the heat transfer coefficients of supercritical CO2 with deviations as much as 50% from experimental data, especially near pseudo-critical temperature. As the gas cooling pressure increases, the pressure drop decreases, which is due to the lower viscosity & higher density. Employing average specific heat along the entire tube length, a semi-empirical correlation was developed to predict the supercritical gas cooling process of CO2 in microchannels, within an error of 20%.

Semi-Empirical Correlation of Gas Cooling Heat Transfer of Supercritical Carbon Dioxide in Microchannels

“…A detailed introduction of experimental apparatus and the data reduction and experimental procedure, along with the experimental results of heat transfer coefficient and pressure drop, are reported elsewhere (Kuang et al 2004) and will not be repeated here.…”

A Review of Flow and Heat Transfer Characteristics of Supercritical Carbon Dioxide under Cooling Conditions in Energy and Power Systems

“…Under different flow rate conditions, the heat transfer coefficient oscillates near the peak. Liao and Zhao [22], Pitla et al [23], Yoon et al [24], Dang and Hihara [25], Kuang et al [26], Huai et al [27], Son and Park [28], Jing et al [31], Oh and Son [32], Eldik et al [33], Liu et al [34], Ding and Li [35], Zhang et al [37], Wahl et al [39], Dong et al [53], Huai and Koyama [54], and Lv et al [55] all experimentally investigated heat transfer characteristics influenced by mass flow with various parameter ranges and drew the consistent conclusions.…”

Modeling of the Flow and Heat Transfer of Supercritical Co2 Flowing in Serpentine Tubes

“…The main factors (physical properties, buoyancy, flow acceleration, inlet conditions, flow direction, and tube diameter) affecting the turbulent flow and heat transfer of ScCO2 in tubes have been extensively studied, especially for straight round tubes (Kuang et al, 2004;Liu et al, 2017;Shiralkar and Peter, 1970;Zhang et al, 2016). The results from these studies have shown that turbulent heat transfer to ScCO2 is very complex because of the extreme property variations.…”