Numerical investigation of an R744 liquid ejector for supermarket refrigeration systems

Abstract

This paper presents a numerical investigation of an R744 liquid ejector applied to a supermarket refrigeration system. The use of the liquid ejector enables the operation of the evaporator in a flooded mode and recirculates the R744 liquid phase, which improves the energy efficiency of the refrigeration system. The investigation was performed using two ejectors of different sizes installed in a multi-ejector block. The numerical model was formulated based on the homogenous equilibrium model and validated with the experimental results. The influence of the pre-mixer, mixer and diffuser dimensions on the ejector performance measured using the mass entrainment ratio is presented. The results show that the best liquid ejector performance was obtained for the short lengths of the pre-mixer and mixer compared to the broadly investigated two-phase ejectors connected to the evaporator port. In addition, wide diffuser angles improved the mass entrainment ratio of both liquid ejectors, which may lead to a reduction in the diffuser length.

Performance mapping of the R744 ejectors for refrigeration and air conditioning supermarket application: A hybrid reduced-order model

“…where u a (k) is the calculated snapshot based on the arbitrary parameter set k and f a (k) stands for vector of interpolation functions defined in Eq. (10). The implementation of RBF into the POD model reduces the dimensionality of ROM to the number of unknown parameters k. The unknown parameters are defined as the boundary conditions of the CO 2 two-phase ejector as follows:…”

“…This platform has been successfully used in several numerical investigations of the CO 2 ejector, i.e. parametrisation procedure of the R744 liquid ejectors [10], swirling of the motive and suction streams for ejector performance improvement [38], shape optimisation of the R744 twophase ejector [39] and numerical investigation of the multi-ejector module during single and parallel operation [40]. Therefore, the CFD results used to generate the hybrid ROM basis were obtained by use of the ejectorPL platform.…”

“…In the vapour ejector, the R744 vapour stream from the medium-temperature evaporator is compressed without any additional work [9]. The liquid ejector is utilised in the CO 2 refrigeration system to pump the liquid outside the medium-temperature evaporator to run the evaporator in flooded mode [10]. CO 2 supermarket refrigeration systems operate at different ambient temperatures and different cooling demands, which vary during the daytime.…”

Shape optimisation of a two-phase ejector for CO 2 refrigeration systems

“…The multi-ejector refrigeration system that was investigated by Haida et al (2016a) demonstrated that the application of ejectors provided significant COP improvements. Moreover, Haida et al (2016b) the liquid ejectors and performed a sensitivity analysis of the ejector shape on the ejector efficiency. However, in this study, only the vapour sucking ejectors were optimised.…”

The performance evaluation of R744 transcritical ejector and R290/R744 cascade refrigeration systems for Turkey

“…As known, an ejector used as an expansion device in R744 transcritical systems, has improved the COP [4,5]. Several theoretical and experimental investigations have been performed for different configurations using ejector [6][7][8][9]. Design of the ejector is revised to work at refrigeration systems with R744.…”