Influence of secondary fluid on the performance of indirect refrigeration system

Abstract This paper proposes solutions to address the issues of traditional refrigerant substitution and the compatibility between secondary fluid and indirect refrigeration system. By using heat balance test method, the performance of three new different secondary fluids, LM-1, LM-4, LM-8, is compared with ethylene glycol at different flow rates. The secondary fluid with the best performance and its optimal working parameters are obtained. Furthermore, the Reynolds and Prandtl numbers corresponding to the optimal working parameters are derived, which provides theoretical basis for the design of intermediate heat exchanger in indirect refrigeration systems. The test results show that in the cold storage temperature of −18 °C, compared to the aqueous solution of ethylene glycol, the coefficient of performance (COPc) of LM-8, LM-1, and LM-4 is higher by 12.3%, 3.9%, and 1.7%, respectively. When the cold storage temperature of is 0 °C, compared to that of ethylene glycol solution, the COPc of LM-1 and LM-8 increases by 9.3% and 6.1%, respectively, while the COPc of LM-4 decreases by 0.9%. Therefore, these three secondary fluids can be used as potential alternatives for ethylene glycol, but LM-1 has a low flash point and certain risk, so it is not recommended to use. LM-8 exhibits the best performance, but the price is more expensive. The LM-4 is less expensive and has the closest performance to ethylene glycol. In the existing systems, considering cost and safety, LM-4 secondary fluid can be used to directly replace ethylene glycol.