Ejector refrigeration is a promising technology to reduce primary energy consumption for building cooling. Unfortunately, a change in the design criteria (i.e., geometry, working fluid, operating conditions) influences the system performance owing to variations in the local fluid dynamic phenomena at the “local-scale”. For this reason, a general agreement on ejector performance is far from being reached. In addition, a general assessment of ejector performance is even more challenging when considering the recent regulations concerning the working fluids, which are going to phase-out most of the refrigerants commonly used in refrigeration and air conditioning systems. Despite there are different options to replace them, no refrigerant has yet imposed. This paper contributes to the discussion on the screening of working fluids, using a previouslyvalidated lumped parameter model. The modelling approach has been applied to sub-critic ejector refrigeration systems and some alternatives to high GWP refrigerants are considered. The influence of the generator, the evaporator and the condenser temperatures over the ejector performance, for the different working fluids, have been presented and commented. The results are comments in terms of entrainment ratio and coefficient of performance, to provide indications and guidelines for refrigerant selection in prospective ejector refrigeration systems

A screening of low-gwp refrigerant for ejector refrigeration

Two-dimensional Navier-Stokes equations were solved to simulate the insight complex flow field of the ejector. Considering the different steam phases in the steam ejector, real gas related expressions of steam properties were used. Different from ideal gas or isoentropic flow hypothesis, rational temperature profile, i.e., temperature decreases gradually in the nozzle and changes fluctuantly after the nozzle, was shown clearly with real gas properties. Phase transition phenomenon occurred in the steam ejector was obtained through calculating the percentage of saturated water in the ejector. A shock diamond pattern after the nozzle is clearly shown by observing velocity profile in the ejector gained by numerical simulation. An oblique shock occured at the upper section of the diffuser was observed.

Study on special phenomena in the ejector used in an steam ejector refrigeration system

The steam ejector, an essential auxiliary device, finds extensive use in various applications, including Multiple Effect Evaporation Desalination systems. The present study endeavored to evaluate the impact of different Converging-Diverging Nozzle placements. Initially, a vapor ejection was designed under certain conditions, utilizing one-dimensional compressible flow equations. Subsequently, the flow within the vapor ejection was simulated via a computational fluid dynamics (CFD) application, specifically the ANSYS program. The investigation entailed the selection of multiple nozzle locations and the examination of their effects under two scenarios: one with a constant back pressure for various suction pressures at each nozzle location, and the other with a fixed suction pressure coupled with several exit pressures. Results from the first scenario indicated that the optimal nozzle location was 5 mm from the commencement of the mixing area. For the second scenario, it was observed that closer proximity of the nozzle to the mixing area enhanced the performance of the steam ejector.

Supersonic Nozzle Location in Steam Ejector Effect on the Mass Fraction and Vacuum of Second Fluid

Steam ejectorsareused in many applications such as drying, cleaning, energy recovery, etc. Many papers have been published to investigate the structure configuration effects on the performance of the steam ejectors.Almost all these papers took the entrainment ratio, compressing ratio or energyefficiencyas the targets, and they concluded that the throat length of steam ejector has little influence on itsperformance. Though the operating flexibility is an important criterion of the steam ejector, few studies have taken it as a target. The main objective of this paper is to investigate the throat length effects on the operating flexibility of the steam ejector. In this study, the throat length of steam ejector was taken as a key parameterto be considered. CFD model under different grid density is established firstly and validated by literature’s data. Then several ejector geometries has been configured and tested under different working conditions. The result confirmed the conclusions of the literatures that throat length has little influence on the entrainment ratio. The detailed local information of the throat was analyzed to explain the conclusion: The contours of Mach number under different ejector’s throat length show that, diamond shock wave length and position basically remain nearly unchanged, so the ejector coefficient keepsunchanged accordingly. Though the throat length has little effect on the entrainment ratio, there is optimum throat length corresponding to biggest critical back pressure of ejectors and which is corresponding with theoperating flexibility of steam ejectors. In the case of this paper, the critical back pressure could improve almost 5.00kPa by changing ejector’s throat length. This change can enhance operating flexibility in actual process. So the throat length of ejectors has important effect on the operating flexibility of ejectors and cannot be overlooked during the design process of steam ejectors. Powered by TCPDF (www.tcpdf.org) PRES17 conference

Effect of throat length on steam ejector critical back pressure

The plain-orifice is the most common type of atomizer. The flow regime inside plain-orifice nozzle has a tremendous effect on the external spray. At present, the judgement method of the flow pattern is not uniform. The purpose of this study is to numerically investigate the relationship between the change of flow pattern, the ratio of nozzle length and nozzle diameter (L/d), the ratio of nozzle radius of the entrance and nozzle diameter (r/d) in plain-orifice nozzle. The computational fluid dynamics (CFD) code FLUENT was used to perform the numerical simulation of the cavitating flow and hydraulic flip in the nozzles. In this paper, the relationship between the change of flow pattern, r/d and L/d was obtained, and the relation curves between L/d and r/d were plotted, and a new model of flow pattern was obtained. The model established in this paper is more accurate than the empirical model to judge the change of flow pattern. The new model is helpful to modify the existing empirical model. According to the relationship, the researcher can use the method of reasonably adjusting the relationship between the nozzle structure and operating conditions to avoid the generation of hydraulic flip, and to get better atomization effect.

On flow regime inside plain-orifice nozzle

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Effect of throat length on steam ejector critical back pressure

On flow regime inside plain-orifice nozzle