Performance Evaluation Of The Booster-assisted Ejector Refrigeration System

With the rapid development of economy and industry, people’s living standards is improving, as well as the energy consumption for refrigeration. All kinds of refrigerating processes are consuming huge energy, for example, the storage and transportation of fresh food, the environment control of industrial process and air conditioning refrigeration in buildings and vehicles. The international Institute of Refrigeration (IIR) has estimated that the energy needed to run all refrigerating machines, including air-conditioning plants and heat pumps, accounts for between 10 and 20% of world-wide electricity consumption. The energy conservation of refrigeration is meaningful.Ejector refrigeration system (ERS) studied in this paper has attracted many researchers due to its advantages. The characteristics of ERS:1. the ejector as the key component of an ERS is widely known as a pump device without moving-part requiring no maintenance and no lubrication; 2. Environmental-friendly refrigerant can be used in ERS, such as water, CO2. It can reduce environment pollution in the process of production and transportation of traditional refrigerants; 3. The ERS provides a promising way to utilize sustainable energy like solar energy, geothermal energy, and low grade heat energies, which are easily available from sources such as automobiles and industrial processes. It is meaningful to the shortage of normal energy and environmental protection. But ERS also has disadvantages. The flow field inside the ejector is very complicated, and what’s more, phase transition is happening inside the ejectors in many cases. Researchers have done many investigations and presented a lot of ejector models, but none of them is widely recognized. Compared to the other refrigeration systems, ERS has poor refrigeration effect and needed to be improved. This paper has two targets to analyze:1D ejector model and Booster-assisted ejector refrigeration system (BERS).1D ejector model is widely investigated and used. This paper presented a novel mathematical model to predict the optimum performance of an ejector, on the foundation of constant-pressure mixing model and hypothetical throat model. And then, use published experimental data to verify this mathematical model. The verification results show that the new-proposed model is correct. Based on the first and second laws of thermodynamics, theoretical analyses on the performance characteristics of the BERS were carried out to study the effects of pressure of secondary flow, evaporating temperature, and condensing temperature on COP of the system, and also on entrainment ratio and exergy destruction rates. The results show that the entrainment ratio increases and exergy destruction decreases with secondary flow pressure, but the COP first increases and then decreases as the pressure of secondary flow increases. That is to say, there exists an optimal pressure for maximum COP. The effect of evaporating temperature of secondary flow on entrainment ratio is negligible, but the increase of evaporating temperature can improve the COP and decrease the exergy destruction. Both of the COP and entrainment ratio follow the same trend, and COP and entrainment ratio decrease as the condensing temperature increases. The results of analysis of exergy destruction show that the main irreversibility of a BERS occurs in the condenser, evaporator and ejector. Additionally, about a half of the exergy destruction occurs in the ejector. And then a BERS test bench is designed and built.This paper presented a novel mathematical ejector model, and carried out investigation of the BERS. All the studies can provide the guidance on ejector refrigeration system.