Primary Fluid Pressure Research Articles

Optimum Efficiency of a Steam Ejector for Fire Suppression Based on the Variable Mixing Section Diameter.

The steam ejector is valuable and efficient in the fire suppression field due to its strong fluid-carrying capacity and mixing ability. It utilizes pressurized steam droplets generated at the exit to extinguish the fire quickly and the steam droplet strategy allows for an expressive decrease in water consumption. In this regard, the fire suppression process is influenced by the steam ejector efficiency, the performance of the pressurized steam, and the ejector core geometry, which controls the quality of the extinguishing mechanisms. This study investigated the impact of different mixing section diameters on the pumping performance of the ejector. The results showed that change in the diffuser throat diameter was susceptible to the entrainment ratio, which significantly increased, by 4 mm, by increasing the throat diameter of the diffuser and improved the pumping efficiency. Still, the critical back pressure of the ejector reduced. In addition, the diameter effect was studied and analyzed to evaluate the ejector performance under different operating parameters. The results revealed a rise in the entrainment ratio, then it diminished with increasing primary fluid pressure. The highest entrainment ratio recorded was 0.5 when the pressure reached 0.36 MPa at the critical range of back pressure, where the entrainment ratio remained constant until a certain back pressure value. Exceeding the critical pressure by increasing the back pressure to 7000 Pa permitted the entrainment ratio to reduce to zero. An optimum constant diameter maximized the ejector pumping efficiency under certain operating parameters. In actual design and production, it is necessary to consider both the exhaust efficiency and the ultimate exhaust capacity of the ejector.

Experimental investigation of a double-slider adjustable ejector under off-design conditions

• A double-slider adjustable ejector was proposed and verified experimentally. • Pressure and flow adjustment experiments of the primary flow were investigated. • Critical pressure and the optimal flow range of the primary flow were presented. • Entrainment ratio of double-slider ejector was 0.23–0.29 in the optimal range. • Contrastive analyses of single and double slider ejectors performance were studied. An undesirable working performance and relatively narrow operating conditions range restrict the ejector popularization and application in the industry. In this study, a novel double-slider adjustable ejector was proposed, which can adjust the throat diameters of the primary nozzle and mixing section synchronously so as to achieve its continuous and smooth operation with a high entrainment ratio in a wide operation condition. Firstly, mathematical model of the adjustable mechanism was developed, and the test device of the ejector performance was established. Secondly, the experiments of the primary flow pressure and the reduction rate of the primary mass flow rate as variables were investigated for the double-slider adjustable ejector. The results indicated the critical adjustment range of the primary flow pressure was 0.7–1.0 MPa. Within the range, the critical adjustment range of the reduction rate of the primary mass flow rate should be lower than 42.27%, and the optimal range should be within 31.27%. In this optimal range, the entrainment ratio was 0.23–0.29. Finally, the performance of the single-slider and double-slider adjustable ejectors was compared, and it was concluded that the double-slider ejector had a higher entrainment ratio and a more stable working range, the maximum increment in average entrainment ratio of the double-slider adjustable ejector was 34.5% than that of the single-slider adjustable ejector. But the critical backpressure of the double-slider adjustable ejector was lower, the phenomenon was more prominent when the reduction rate of the primary mass flow rate exceeded 42.27% and the primary fluid pressure was lower than 0.8 MPa. This study can provide a beneficial reference for the further design of adjustable ejectors under off-design conditions.

Characterization of choking flow behaviors inside steam ejectors based on the ejector refrigeration system

Abstract In order to maximize the working potential of a steam ejector, aside from experiment testing of various design parameters, it is also important to understand the involved thermal fluid mixing behaviors. In this study, an ejector refrigeration experimental system was established, and a numerical model was developed to comprehend the complex and non-linear flow characteristic using an ideal gas model which is more consistent with the experimental data compared with the wet steam model. Herein, it was discovered that the choking flow and the occurrence locations of this phenomenon played an essential role in the system efficiency. For the first time, three choke behaviors modes were characterized by means of numerical investigations: “fit-choked flow mode”, “sub-choked flow mode” and “super-choked flow mode”. The relationship between the choke and the normal shock wave was revealed to analyze the two mixing fluids flow conditions. The influence of primary fluid pressure and the back pressure on the ejector performance under three choke flow modes were comprehensively discussed. The simulation results indicated that the choking flow was a critical factor in affecting the performance of the steam ejector, and the performance optimizes at “fit-choked flow mode” when the primary fluid pressure was 0.36 MPa with a remarkable entrainment ratio of 0.525.

A Steam Ejector Refrigeration System Powered by Engine Combustion Waste Heat: Part 2. Understanding the Nature of the Shock Wave Structure

In general, engine fuel combustion generates 30% waste heat, which is disposed to the environment. The use of the steam ejector refrigeration to recycle the waste heat and transfer them to useful energy source could be an environmentally friendly solution to such an issue. The steam ejector is the main component of the ejector refrigeration system, which can operate at a low-temperature range. In this article, the internal shock wave structure of the ejector is comprehensively studied through the computation fluid dynamics (CFD) approach. The shock wave structure can be subdivided into two regions: firstly the pseudo-shock region consisting of shock train and co-velocity region; secondly the oblique-shock region composed of a single normal shock and a series of oblique shocks. The effect of the shock wave structure on both pumping performance and the critical back pressure were investigated. Numerical predictions indicated that the entrainment ratio is enhanced under two conditions including (i) a longer pseudo-shock region and (ii) when the normal shock wave occurs near the outlet. Furthermore, the system is stabilized as the back pressure and its disturbance is reduced. A critical range of the primary fluid pressure is investigated such that the pumping is effectively optimized.

CFD Simulation of Ejector in Steam Jet Refrigeration

In this study CFD technique was employed to investigate the effect of divergent angle of primary nozzle, NXP (NXP = Distance between the nozzle exit to mixing chamber inlet) and throat of the ejector on the performance of ejector using the steam jet refrigeration cycle. In all these cases, only one fixed mixing chamber with different divergent primary nozzle, NXP and throat of an ejector was investigated numerically using the commercial CFD package, the effect of primary fluid pressure mass flow rate and mach numbers were observed and analyzed. The velocity contour lines were used to explain the happening of process inside the ejector it was found that the throat diameter, NXP and diverging angle of primary nozzle plays a crucial role in the steam jet refrigeration.

Experimental investigations on a R134a ejector applied in a refrigeration system

An experimental investigation on the performance of an ejector applied in a refrigeration system is conducted. The system uses R134a as a working fluid. The experimental results indicate that back pressure plays an important role in the entrainment ratio of an ejector because this parameter determines the operation mode of an ejector under certain primary fluid pressure and secondary fluid pressure. Increasing in the primary fluid pressure can improve the critical back pressure while deteriorate the best performance of an ejector. Moreover, an optimal value of the primary fluid pressure exists corresponding to a maximum value of the entrainment ratio under a given condition. A logarithmic relation is developed to predict the critical back pressure and to determine operating conditions in a R134a ejector refrigeration system. The research findings will be meaningful for researchers to have a better understanding of the R134a ejector applied in a refrigeration system.

Experimental investigation on two-phase driven ejector performance in a novel ejector enhanced refrigeration system

This paper presents an experimental investigation on two-phase driven ejector performance characteristics in a novel ejector enhanced refrigeration system (NERC). An experimental setup using refrigerant R600a is designed and built based on the NERC system. In the experimental setup, the ejector uses two-phase refrigerant coming from the high-temperature evaporator as the primary fluid. The experiments are carried out to examine the influences of the main operational and geometric parameters, including the primary fluid pressure, the secondary fluid pressure, the NXP and the nozzle throat diameter. The results show that the entrainment ratio, the pressure lift ratio and the overall ejector efficiency of the two-phase driven ejector are strongly affected by those parameters. Additionally, the effect of the quality of the two-phase primary fluid is also experimentally investigated. The meaningful results obtained here may serve as good guidelines for further improving the two-phase driven ejector performance and providing promising use of the two-phase driven ejector in the ejector-expansion technology.

A Numerical Study on the Supersonic Steam Ejector Use in Steam Turbine System

Supersonic steam ejector is widely used in steam energy systems such as refrigeration, wood drying equipment, papermaking machine, and steam turbine. In this paper the Computational Fluids Dynamics (CFD) method was employed to simulate a supersonic steam ejector, SST k-w turbulence model was adopted, and both real gas model and ideal gas model for fluid property were considered and compared. The mixing chamber angle, throat length, and nozzle exit position (NXP) primary pressure and temperature effects on entrainment ratio were investigated. The results show that performance of the ejector is underestimated using ideal gas model, and the entrainment ratio is 20%–40% lower than that when using real gas model. There is an optimum mixing chamber angel and NXP makes the entrainment ratio achieve its maximum; as throat length is decreased within a range, the entrainment ratio remains unchanged. Primary fluid pressure has a critical value, and the entrainment ratio reaches its peak at working critical pressure; when working steam superheat degree increases, the entrainment ratio is increased.

CFD simulation on the effect of primary nozzle geometries for a steam ejector in refrigeration cycle

In this study, the CFD technique was employed to investigate the effect of the primary nozzle geometries on the performance of an ejector used in the steam jet refrigeration cycle. In all cases, only one fixed-geometry mixing chamber together with eight different primary nozzles was investigated numerically using the commercial CFD package, FLUENT 6.3. The effects on the primary fluid pressure, mass flow rate and Mach number were observed and analyzed. The Mach number contour lines were used to explain the mixing process occurring inside the ejector. It was found that shock's position of the mixed fluid and the expansion angle of the primary fluid jet stream within the mixing chamber played a very important role in the ejector performance.

Numerical and experimental investigation of performance of the liquid–gas and liquid jet pumps in desalination systems

The present work described experimental and numerical investigations of ejectors using water as the motive fluid and water and gas as the entrained fluid. These ejectors are used in low temperature thermal desalination systems to entrain the brine and non-condensable gases to keep the desalination systems operating on condition of the vacuum. The numerical simulations were based on the Euler–Euler multiphase model, with a simplified slip velocity ratio, determined by comparing the experimental and the simulation results. The simulations showed that the slip velocity between phases is 11% and 12%. The simulations examined the influence of several variables, including the primary fluid pressure, the suction fluid pressure and the discharge pressure, on the volumetric entrainment ratio and efficiency. The results show that, if the structural variables are fixed, the volumetric entrainment ratio is determined by the pressure ratio ΔPp/ΔPc with the maximum efficiency obtained for a pressure ratio equal to the throat aspect ratio (DT/DN)2.