Heat-driven Ejector Refrigeration Research Articles

Numerical investigation in effects of refrigerants’ thermodynamic properties on performance of supersonic ejector

ABSTRACT Using zeotropic mixtures with unique temperature glide characteristics as the working medium in heat-driven ejector refrigeration system will potentially reduce the irreversible losses in heat exchange process. However, the intrinsic link between the pure/mixture refrigerants’ thermophysical properties and the entrainment performance of supersonic ejector has not yet been elucidated. In this study, a novel ejector CFD model is established by coupling the real-gas thermodynamic equation and species transport equation, then the relationships between thermophysical properties of pure/mixture refrigerants and ejector’s dimensionless operational parameters were thoroughly investigated. The results indicated that the ejector expansion ratio rises as primary flow inlet temperature or refrigerant’s normal boiling point increases, while the dimensionless parameters of primary nozzle are relatively insensitive to the variation of primary flow inlet temperature and refrigerant’s boiling point, resulted in changes of supersonic jet expansion behaviour. Moreover, the specific volume and adiabatic index change characteristics resulted in minor fluctuations of primary nozzle’s dimensionless parameters. When the bubble point temperature is fixed at 30℃ in the condenser, the saturated vapor/liquid phase pressure glide characteristics of R600a/R1234ze mixture may lead to an increasement of ejector’s compression ratio.

Techno-economic assessment of low-grade geothermal heat-driven ejector refrigeration cycle with a flash chamber and a booster compressor

Techno-economic assessment of low-grade geothermal heat-driven ejector refrigeration cycle with a flash chamber and a booster compressor

A new variable mixing chamber ejector: CFD assessment

• A new variable mixing chamber ejector is proposed for waste-heat driven chillers. • The mixing chamber cross-sectional area can be increased or reduced. • The cooling capacity increased by up to 120%. • The backflow condensing temperature increased by almost 8 °C. Research on the reduction of refrigeration systems energy consumption is a topic in which popularity benefits from the contextual growth of the refrigeration market. Solar or waste heat-driven ejector refrigeration systems are very promising in this context. However, the lack of operational flexibility of ejectors penalizes the performance of such systems. Since the mixing chamber has a fixed cross-section, for condensation temperatures above critical, the cooling capacity vanishes and, for temperatures lower than critical, the cooling capacity stagnates. The paper proposes a new variable mixing chamber solution that overcomes these limitations. It is a range extender that allows ejectors to operate at high cooling capacity all over the operation range of the system. This range extender is based on the concept of lateral cylindrical moving slots. The paper compares the new ejector to a reference ejector from the literature. First, the Computational Fluid Mechanics (CFD) model viability is evaluated thanks to the experimental measurements on the reference ejector. Then, the new system’s performance is evaluated. The results show that the adaptation of the mixing chamber section to the condensation temperature allows increasing the cooling capacity without supplementary motive energy. That leads to an increase of up to 120% of the cooling capacity at low condensation temperatures and a shifting of 8 °C of the critical temperature. Such extension of the operational range was never obtained before. That means that an ejector stalling at 33 °C could operate at 41 °C using the proposed range extender.

A Study on the Combined Driven Refrigeration Cycle Using Ejector

The rising need for thermal comfort has resulted in a rapid increase in refrigeration systems’ usage and, subsequently, the need for electricity for air-conditioning systems. The ejector system can be driven by a free or affordable low-temperature heat source such as waste heat as the primary source of energy instead of electricity. Heat-driven ejector refrigeration systems become a promising solution for reducing energy consumption to conventional compressor-based refrigeration technologies. An air-conditioning system that uses the ejector achieves better performance in terms of energy-saving. This paper presents a study on the combined driven refrigeration cycle based on ejectors to maximize cycle performance. The experimental setup is designed to determine the coefficient of performance (COP) with ejector nozzle sizes 1.8, 3.6, and 5.4[Formula: see text]mm, respectively. In this system, the R-134a refrigerant is considered as a working fluid. The results depict that the efficiency is higher than that of the conventional refrigeration method due to comparing the performance of the conventional refrigeration cycle and the combined driven refrigeration cycle. The modified cycle efficiency is better than the vapor compression cycle below 0∘C, which implies sustainability at low temperatures by using low-grade thermal energy. For the improvement of mechanical efficiency, proposed cycle can be easily used.

A performance evaluation of the ejector refrigeration system based on thermo-economic criteria through multi-objective approach

This work investigates an exhaust heat-driven ejector refrigeration system with the thermo-economic considerations. The system is thermally modelled and is optimized considering the performance coefficient and the total annual cost as two objectives using heat transfer search algorithm. Generator temperature, evaporator temperature and condenser temperature are considered as design variables. A 2-D shock circle model is used to simulate the ejector component with R245fa refrigerant. The results of multi-objective optimization are discussed using the Pareto frontier obtained between both conflicting objective functions. The effect of varying the nozzle throat diameter and the ecological function on the thermo-economic objectives is presented and discussed. The sensitivity analysis of the objective functions to the decision variables is investigated. Further, the exergo-economic results at the optimal point are also presented and discussed. The results reveal that the ejector and the generator are the leading contributors to the exergy destruction and hence to the total annual cost. The coefficient of performance and total annual cost at the best optimal point are 0.3 and 25,903 $/year, respectively. The optimized product unit cost of the system is 53.8 $/GJ with 10.5% exergy efficiency.

Numerical investigation of the flow structures inside mixing section of the ejector

In this study, the effect of the position of the primary nozzle and the converging angle of the mixing section is investigated numerically for a vapor jet ejector to be used in a heat-driven ejector refrigeration cycle. Entrainment ratio is reported as one of the global performance parameters which is affected sensitively by the nozzle position and converging angle of the mixing section. Furthermore, the effect of the geometric parameters is also explained using Mach number distributions throughout the ejector. Mach contours and the shadowgraphs of the ejector as well are displayed comparatively. The influence of the secondary flow effective area is discussed for better comprehension of the ejector performance by means of the aforecited geometrical parameters. The importance of this study is that the results can lead to the design of the mixing chamber of the ejector for the heat-driven ejector refrigeration systems. ANSYS Fluent software package is used for computational fluid dynamics simulations taking real gas thermodynamic properties into account and the numerical model was validated using the experimental data from the literature.