Abstract
This paper investigates the thermohydraulic performance of finned-tube supercritical carbon dioxide (sCO2) gas coolers operating with refrigerant pressures near the critical point. A distributed modelling approach combined with the ε-NTU method has been developed for the simulation of the gas cooler. The heat transfer and pressure drop for each evenly divided segment are calculated using empirical correlations for Nusselt number and friction factor. The model was validated against test results and then used to investigate the influence of design and operating parameters on local and overall gas cooler performance. The results show that the refrigerant heat-transfer coefficient increases with decreasing temperature and reaches its maximum close to the pseudocritical temperature before beginning to decrease. The pressure drop increases along the flow direction with decreasing temperature. Overall performance results illustrate that higher refrigerant mass flow rate and decreasing finned-tube diameter lead to improved heat-transfer rates but also increased pressure drops. Design optimization of gas coolers should take into consideration their impact on overall refrigeration performance and life cycle cost. This is important in the drive to reduce the footprint of components, energy consumption, and environmental impacts of refrigeration and heat-pump systems. The present work provides practical guidance to the design of finned-tube gas coolers and can be used as the basis for the modelling of integrated sCO2 refrigeration and heat-pump systems.
Highlights
Due to growing environmental awareness and concerns, carbon dioxide (CO2 ) is becoming an important commercial and industrial fluid, profiting from its environmental credentials and its advantageous characteristics, such as being nontoxic and nonflammable and having low viscosity and a large refrigeration capacity
Among the air-coupled CO2 gas coolers, the finned-tube heat exchanger is generally considered to be potentially applicable to gas-cooling devices [6]
The sCO2 pressure drop increases with an increase of its inlet pressure, mass flow rate, and air inlet temperature, and decreases with an increase of frontal air velocity. These experimental data usually provide a better understanding of the performance of sCO2 gas coolers, but do not provide sufficient information on local thermohydraulic performance from measurements on full-scale gas coolers [11]
Summary
Due to growing environmental awareness and concerns, carbon dioxide (CO2 ) is becoming an important commercial and industrial fluid, profiting from its environmental credentials and its advantageous characteristics, such as being nontoxic and nonflammable and having low viscosity and a large refrigeration capacity. Since the early 1990s, when Lorentzen published a patent application for a transcritical CO2 automotive air conditioning system [1], researchers have paid much attention to the use of CO2 , a potential replacement of the nonenvironmentally friendly refrigerants such as chlorofluorocarbon and hydrochlorofluorocarbons, in refrigeration, air conditioning, and heat-pump systems [2,3,4,5]. The heat transfer of a gas cooler increases with the increase of sCO2 inlet pressure, mass flow rate, and air frontal velocity, and decreases with an increase of air inlet temperature. The sCO2 pressure drop increases with an increase of its inlet pressure, mass flow rate, and air inlet temperature, and decreases with an increase of frontal air velocity These experimental data usually provide a better understanding of the performance of sCO2 gas coolers, but do not provide sufficient information on local thermohydraulic performance from measurements on full-scale gas coolers [11]. Ge et al [9,12], Singh et al [13], Gupta et al [14], and Marcinichen et al [15]
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