Effect of Suction Nozzle Pressure Drop on the Performance of an Ejector-Expansion Transcritical CO2 Refrigeration Cycle

Zhenying Zhang,Lili Tian

doi:10.3390/e16084309

Zhenying Zhang, Lili Tian

Open Access

https://doi.org/10.3390/e16084309

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Abstract

The basic transcritical CO2 systems exhibit low energy efficiency due to their large throttling loss. Replacing the throttle valve with an ejector is an effective measure for recovering some of the energy lost in the expansion process. In this paper, a thermodynamic model of the ejector-expansion transcritical CO2 refrigeration cycle is developed. The effect of the suction nozzle pressure drop (SNPD) on the cycle performance is discussed. The results indicate that the SNPD has little impact on entrainment ratio. There exists an optimum SNPD which gives a maximum recovered pressure and COP under a specified condition. The value of the optimum SNPD mainly depends on the efficiencies of the motive nozzle and the suction nozzle, but it is essentially independent of evaporating temperature and gas cooler outlet temperature. Through optimizing the value of SNPD, the maximum COP of the ejector-expansion cycle can be up to 45.1% higher than that of the basic cycle. The exergy loss of the ejector-expansion cycle is reduced about 43.0% compared with the basic cycle.

Highlights

Among the natural refrigerants, the carbon dioxide (CO2) has received extensive attention owing to its zero ozone depletion potential, very low global warming potential, safety, and admirable thermalEntropy 2014, 16 physical properties
The reference transcritical CO2 refrigeration cycle suffers from the defect of its low energy efficiency due to the large throttling loss [1]
The refrigerated object temperature is set at 20 °C, the reference state is defined as the environment temperature, 35 °C, the gas cooler outlet temperature is set at 40 °C, the evaporation temperature is set at 5 °C, and the ejector is assumed to have the following efficiencies: ηmot = 0.9, ηsuc = 0.9, ηdif = 0.8

Summary

Introduction

The carbon dioxide (CO2) has received extensive attention owing to its zero ozone depletion potential, very low global warming potential, safety, and admirable thermal. The reference transcritical CO2 refrigeration cycle suffers from the defect of its low energy efficiency due to the large throttling loss [1] This loss can be reduced by using a two-phase ejector to replace the throttling valve [2]. Developed a thermodynamic model of the ejector-expansion transcritical CO2 refrigeration cycle, and concluded that its COP was 22% better than that of the reference system. Sun and Ma [10] investigated the ejector-expansion transcritical CO2 refrigeration cycle based on the first and second laws of thermodynamics, and stated that the replacement of throttling valve by an ejector could decrease more than 25% exergy loss and increase COP by over 30%. The effect of SNPD on the performance of ejector-expansion refrigeration cycle was discussed. The effect of SNPD on the transcritical CO2 ejector-expansion cycle performance is analyzed

Thermodynamic Modeling

Energy Analysis

Exergy Analysis

Results and Discussion

Conclusions

Conflicts of Interest