Experimental analysis of the R744 vapour compression rack equipped with the multi-ejector expansion work recovery module

Abstract

Aim of this thesis is to present an experimental investigation of standard R744 supermarket refrigeration system, with the high-pressure electronic valve (HPV), and refrigeration system with multi-ejector expansion pack on the same vapour compression rack. Comparison of the R744 multi-ejector refrigeration system, was carried out based on energy performance characteristics: refrigeration capacity, power consumption, COP, and exergy efficiency. Apart from the system performance comparison, influence of the pressure level in the flash tank on the system performance for both alternatives was analysed.The experimental results indicated COP and exergy efficiency improvement of the multiejector refrigeration system up to 7% and 13.7%, respectively. The multi-ejector system was able to operate in smaller range of the tanks pressure lift than the standard system dependent on the refrigeration load and the exit gas cooler section parameters. The highest values of COP and exergy efficiency were obtained by the multi-ejector refrigeration system for the tanks pressure lift value close to the limit value. The values of the overall compressor efficiencies were significantly differentiated, dependent on the operation module (cooling load and heat rejection conditions), which strongly influenced the values of COP and exergy efficiency. Therefore, it was not possible to clearly define the optimum pressure in the flash tank. It was concluded that improvement of compressors efficiencies utilized in the multiejector system will indicate high energy performance of the refrigeration system.

Energy Evaluation of Multiple Stage Commercial Refrigeration Architectures Adapted to F-Gas Regulation

“…The booster system with gas ejectors and parallel compression, Figure 4, incorporates ejectors in combination with parallel compressors. Ejectors reduce the mass flow rate through the medium temperature compressors [42] and reduce the exergy losses incrementing the specific cooling capacity in the evaporators.…”

Transient model of an RSW system with CO2 refrigeration – A study of overall performance

“…That is, the evaporator's heat transferring area could be reduced, or used more efficiently, if a suction gas heat exchanger is included (Boewe et al, 2001). Ejectors can also be included to reduce throttling loss (Lucas and Koehler, 2012;Haida et al, 2016). A CO2 cycle with few components was modeled with the aim of creating a basis that was simple and transparent and provided a consistent basis to illustrate general trends in RSW system performance.…”

CO2 Refrigeration and Heat Pump Systems—A Comprehensive Review

“…The three vapour ejectors E1, E2 and E3 have different mass flow rates, designed in such a way that the mass flow rate through E3 is twice that which flows through E2 and four times that which flows through E1. From an experimental analysis [50], it was found that the system COP improved by 7% and the exergy efficiency by 13.7% compared to that of the parallel compression system. It was also observed that the compression efficiency is affected by the cooling load and heat rejection.…”

“…To ensure the gas enters the suction line of the low pressure compressor in the dry state, the gas exiting the evaporator is usually superheated by absorbing some heat from the outlet of the gas cooler through an IHX (see Section 4.1). From an experimental analysis [50], it was found that the system COP improved by 7% and the exergy efficiency by 13.7% compared to that of the parallel compression system. It was also observed that the compression efficiency is affected by the cooling load and heat rejection.…”

“…The various constraints of a single ejector system can be overcome by the multi-ejector concept discussed by Hafner et al [48] and later developed by Banasiak et al [49], experimentally analysed by Haida et al, [50] and numerically studied by Body et al [51]. The multi-ejector system discussed in these studies consists of a pack of ejectors placed in parallel as shown in Figure 15.…”