Mechanics, Materials Science & Engineering, May 2017
ISSN 2412-5954
A Study on the COP of CO2 Air Conditioning System with Minichannel Evaporator Using Subcooling Process26 Thanhtrung Dang1,a, Chihiep Le2,b, Tronghieu Nguyen1,c, Minhhung Doan1,d 1
Department of Thermal Engineering, HCMC University of Technology and Education, Vietnam
2
Department of Heat and Refrigeration Engineering, HCMC University of Technology, Vietnam
a
trungdang@hcmute.edu.vn
b
lechihiep@gmail.com
c
hieunt@hcmute.edu.vn
d
hungdm@hcmute.edu.vn DOI 10.2412/mmse.46.29.103 provided by Seo4U.link
Keywords: air conditioning, CO2 refrigerant, subcooling, minichannel, evaporator, heat transfer.
ABSTRACT. Experimental studies on a CO 2 air conditioning system with minichannel evaporator using subcooling process are presented in this paper. Without subcooling process, the COP obtained for this case is nearly 1.59; it is lower than that of conventional air conditioning systems. But, with subcooling process, the COP strongly increases as the gas cooler outlet temperature is lower than 30 C which confirms the need of subcooling CO 2 used in air conditioners. In subcooling process, the COP of 4.97 was achieved for the gas cooler pressure of 77bar and the evaporating temperature of 15 C, it is higher than those obtained by other published results. It is suggested that the CO 2 air conditioning system should be operated corresponding to the case where the gas cooler pressure ranges from 74-77bar and the evaporating temperature ranges from 10-15 C in transcritical mode for high effectiveness and safety.
Introduction. Scientists working in air conditioning engineering have been interested in problems such as environmentally friendly refrigerants and high effectiveness heat exchangers. In these fields, CO2 is considered as a good candidate in order to replace HCFCs and compact heat exchangers would be used widely in the future. Regarding to CO2 and compact heat exchangers, an overview of the flow boiling heat transfer characteristics and the special thermo-physical properties of CO2 in a horizontal tube was investigated by Zhao and Bansal [1]. Due to the large surface tension, the boiling heat transfer coefficient of CO2 was found to be much lower at low temperatures but it increased with vapor quality (until dryout). However, this study was only reviewed for horizontal tube. Baheta el at. [2] simulated performance of transcritical carbon dioxide refrigeration cycle by using EXCEL program. In this study, the highest Coefficient of Performace (COP) was 3.24 at 10MPa gas cooler pressure. The results indicated that COP increases as rising the evaporative temperature. Using numerical simulation, Cheng and Thome [3] studied on cooling of microprocessors using flow boiling of CO2 in a micro-evaporator. Based on the analysis and comparison, CO2 appeared to be a promising coolant for microprocessors at low operating temperatures but also presented a great technological challenge like other new cooling technologies. However, the investigations in [2, 3] did not experimentally perform. A comprehensive review of flow boiling heat transfer and two-phase flow of CO2 covers both macrochannel tests and micro-channel investigations was presented Thome and Ribatski [4]. The results showed that CO2 gives higher heat transfer coefficients than those of conventional refrigerants. Ducoulombier et al. [5] studied carbon dioxide two-phase flow pressure drops in a single horizontal -NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/
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