Mixing Chamber Diameter Research Articles

Numerical studies on structure optimization and flow characteristics of a hydrogen recirculation ejector under multiple load conditions

Ejectors are ideal hydrogen recirculation devices for PEMFC systems but typically exhibit poor recirculation performance at low loads. For purpose of extending ejector's operating range in vehicular applications, the entraining performance across multiple loads should be focused. In this study, A 40 kW ejector was designed with a 1D theory and optimized using a 2D CFD model. Simulations were conducted to study the influence of various diameter and axial dimensions on the ejector's performance and flow characteristics. The results reveal that as the load increases from 20% to 100%, the suboptimal diffuser exit diameter decreases from 2.5 to 1.5 times the mixing chamber diameter, the optimal nozzle exit position increases from 0.59 to 0.63 times, and the optimal mixing chamber length increases from 2.2 to 4.3 times. A convergent nozzle with a short throat significantly improves low-load entraining performance and achieves the highest performance growth in the variable-nozzle design. Additionally, an optimization method for axial dimensions based on the proposed parameter flow uniformity was established, allowing for precise determination of the optimal dimensions through a few simulations.

Effect of jet ejector geometry on the supply of a pumping unit preventing wax-deposit

Relevance. Today oil production by installations of electric centrifugal pumps is one of the leading methods of mechanized oil production. The mechanized operation of hard-to-recover oil objects is complicated by the high viscosity of reservoir oil, the formation of wax-deposits in the wellbore. This leads to an increase in hydraulic resistances due to a decrease in the flow section of pipes and other pumping equipment components, a decrease in the productivity of wells and the efficiency of pumping production. In this regard, an urgent task is to develop and improve methods and devices for preventing deposits of wax-deposits in wells. Object. Downhole pumping unit for dosing reagent (inhibitor of wax-deposits) into the well, which is a combination of two technical devices – a pump dosing the reagent and a jet pump. Aim. To analyze the influence of the design parameters of the dosing unit on the efficiency of its operation (reagent consumption, liquid cavitation coefficient in the jet pump). Methods. Mathematical modeling of the operation of a downhole dosing unit for the supply of reagent, based on the application of the laws of conservation of mass and quantity of motion, as well as Bernoulli's law for a moving flow in a jet pump. Results. Based on the simulation results, the nature of the influence of the design parameters of the developed installation on the reagent consumption is established. It is established that the maximum flow rate of the reagent is achieved with a mixing chamber diameter of about 22 mm; an increase in diameter relative to the specified value leads to a decrease in the degree of local pressure reduction, a decrease in the diameter of the mixing chamber – a drop in flow due to an increase in the flow rate in the chamber and an increase in hydraulic resistance. It was found that an increase in the supply of electric centrifugal pumps in the considered range of 100–200 m3 per day has practically no effect on the reagent consumption when the mixing chamber diameter is more than 30 mm. It was found that at confuser length values exceeding 210 mm, the cavitation coefficient, regardless of the mixing chamber diameter, exceeds one, which indicates a smooth and uniform pressure reduction in the device body. In general, it is shown that by regulating the design parameters of a downhole metering unit, it is possible to ensure the required reagent consumption at a known electric centrifugal pump supply (well flow rate).

Performance prediction and geometry optimization of ejector in PEMFC system using coupled CFD-BPNN and genetic algorithm

The ejector is a promising hydrogen recirculation device in proton exchange membrane fuel cell (PEMFC) systems. However, the limited entrainment performance of the ejector at wide operating conditions hinders its development and widespread application in PEMFC systems. To address this challenge and design a high-performance ejector adapted to the wide power range of PEMFC systems, a backpropagation neural network (BPNN) model with computational fluid dynamics (CFD) simulation data is developed. The sensitivity analysis of geometric parameters based on the CFD model reveals that the nozzle throat diameter and the mixing chamber diameter exert the most pronounced impact on the entrainment performance, with average influence rates of 24% and 57%, respectively. Furthermore, two advanced multi-objective genetic algorithms are applied to improve ejector performance. The linear weighted genetic algorithm (LWGA) method proves effective in elevating the overall ejector performance, achieving a remarkable enhancement in entrainment performance of up to 7.9%. On the other hand, the non-dominated sorting genetic algorithm (NSGA- II) method is favorable for expanding the operational power range of the ejector by 30%, as well as a 4.5% increase in overall ejector performance. This work provides a robust framework for designing and optimizing high-performance ejectors in high-power PEMFC systems.

Effect of mixing chamber structure on the performance of adjustable ejector

The study employs numerical simulation method to analyze performance of an adjustable ejector, with a specific focus on the influence of the structure dimension of mixing chamber. R41/R1234yf refrigerant is used as the working medium in the study. The primary and secondary flow inlets are set at the pressure of 1.4 MPa and 0.2 MPa, respectively, along with temperature of 353.15 K and 288.15 K corresponding. The outlet pressure of the ejector is 0.3 MPa. The simulation results show that optimal mixing chamber diameter within a range from 14.7mm to 18.7mm exists for obtaining peak adjustable ejector performance. Maximum entrainment ratio of 0.59 is obtained when cone diameter ratio is 65% and diameter of the mixing chamber is 15.7mm. Furthermore, the optimal mixing chamber length within range from 24mm to 220mm exists for obtaining peak adjustable ejector performance. Maximum entrainment ratio of 0.624 is obtained when cone diameter ratio is 76% and length of the mixing chamber is 88 mm. Therefore, it is crucial during designing process of the mixing chamber to ensure the complete fluid mixture and minimal flow resistance.

Optimization and performance investigation of confocal twin-nozzle ejector for PEMFC hydrogen supply and recirculation system under actual variable operating conditions

The actual operating boundary conditions under different Proton Exchange Membrane Fuel Cell (PEMFC) power outputs are considered to evaluate the performance of a confocal twin-nozzle ejector and optimize its geometric parameters through the experimentally verified 3D Computational Fluid Dynamics model. The effects of primary and outlet pressures, anode gas relative humidity (RH), and nitrogen mole fraction (XN2) on its recirculation ratio are investigated. Besides, two key geometric parameters, mixing chamber diameter Dm and length Lam, are optimized under variable operating conditions. The results show that the two-nozzle (TN) mode can operate over a wider range of outlet pressure variation than single-nozzle (SN) mode, and an optimum primary pressure exists for both two modes. Considering the overall performance of SN and TN modes over the entire investigated PEMFC power range, the optimal Dm and Lam are 5.50 and 22.00 mm, respectively. The recirculation ratio at the rated power of 84 kW is improved by 14.10% compared to the initial structure. The ejector's total recirculation capability is positively correlated with both RH and XN2, while the hydrogen recirculation capability is negatively correlated with them. The impact of RH on the recirculation ratio of confocal twin-nozzle ejector is consistent with that of the conventional nozzle ejector. This work may provide useful ways for designing novel-type nozzle ejectors to expand the narrow operating range of ejectors used for PEMFC hydrogen supply and recirculation systems.

A novel dual-nozzle ejector for enhancement of hydrogen recirculation applied to proton exchange membrane fuel cell system

The ejector enables hydrogen recycling, offering advantages of non-parasitic power and low noise. However, traditional ejector falls short in operating the proton exchange membrane fuel cell(PEMFC) system across various operating points efficiently. To overcome this limitation, a novel dual-nozzle ejector is proposed for optimal hydrogen recirculation at different power. The computational fluid dynamics(CFD) method is utilized to simulate and verified by experimental results. Firstly, nozzle structure is optimized to address unstable flow phenomena such as vortex generated at nozzle outlet. Subsequently, analysis of flow field is conducted by different structure under idle and full-load conditions. Results show that initial optimization resulted in an 18.8% increase of recirculation ratio under idle condition. Overall performance of constant-section mixing chamber diameter (Dm) of 6.5 is optimal within the output current range from 31.1A to 559.8A. Under idle condition, highest recirculation ratio is achieved when constant-section mixing chamber length is 4Dm, nozzle exit position is at 1.1Dm, diffuser chamber angle is 3°. While under full-load condition, the energy loss caused by wall flow resistance is more significant. By exploring the mechanism of different structure changes under two conditions, particularly under idle condition, this study provides a reference for optimization of ejectors in the future.

Experimental and numerical study on low-temperature supersonic ejector

Ejectors have emerged as a viable solution for handling Boil-Off-Gas (BOG) generated by cryogenic storage tanks. The efficiency of ejector-based systems plays is highly dependent on the ejector's performance which is influenced by various factors including the geometry of the ejector and the boundary conditions. In this study, an axisymmetric supersonic ejector was designed, optimized, and evaluated for BOG removal. The baseline geometric dimensions design of the ejector was obtained via theoretical analysis. Subsequently, computational fluid dynamics (CFD) simulations were employed to optimize the boundary conditions and geometrical parameters. Experimental investigations were conducted to validate the design and evaluate the ejector's performance. The results highlighted the significant influence of two key parameters, namely, the mixing chamber diameter (Dm) and the nozzle exit position (NXP), on the ejector's performance. Optimized Dm showed an increase of about 12.5% compared with the baseline geometry. By operating the ejector within its on-design geometric and boundary conditions, the maximum entrainment ratio (ER) was achieved. The CFD models successfully identified and validated various flow phenomena, including double choke, single choke, and backflow, which were consistent with the experimental observations. Both the numerical models and experimental findings demonstrated that the modified ejector achieved an entrainment ratio of 1.06 under its design condition showing a 33.66% increase compared with that obtained using the baseline geometry. These results indicate the potential of the supersonic ejector as an alternative solution for BOG applications, emphasizing its efficacy in handling this industrial challenge.

Optimization of geometric parameters of ejector for fuel cell system based on multi-objective optimization method

ABSTRACT In this study, the multi-objective orthogonal experiment is employed to optimize the geometric parameters of the ejector. The optimization objective is determined by applying linear weighting to the entrainment ratios for 100 SLPM and 990 SLPM operating conditions. Four geometric parameters are optimized, including the nozzle exit diameter, nozzle exit position, mixing chamber length, the mixing chamber diameter. Moreover, Computational Fluid Dynamics simulations are performed, and the effects of each geometric parameter and the interaction between parameters on the performance of the ejector are ranked by range analysis. The results show that the mixing chamber diameter has the most significant impact on the optimization objective, and the degree of influence of the other factors and interactions on the entrainment ratio varies for different operating conditions. Compared with the initial parameters, the parameters obtained by the multi-objective optimization method have an average improvement of 96% in entrainment ratio over the full operating range, and the experimental results are in general agreement with the simulation results. The adaptability analysis of the ejector performance indicates that the ejector optimized by the multi-objective optimization method can meet the hydrogen excess ratio requirements for the full operating range of the fuel cell system.

FLUID BEHAVIOR INVESTIGATION ON A SINGLE-PHASE EJECTOR USING NUMERICAL APPROACH

This study aims to determine fluid flow behaviors and its property inside of an ejector for a single-phase system. Numerical simulation has been employed to investigate the efficiency of the ejector. The numerical process begins with model creation, mesh sensitivity study, turbulent model selection and validation study. Seven parts of ejector that can be optimized to achieve the objectives namely nozzle diameter, venturi tube neck diameter, nozzle distance, venturi tube neck length, straight pipe length, mixing chamber diameter, and mixing chamber length. Through these seven aspects, a total of 82 design points has been generated by CFD software and have obtained a candidate that provides optimized parameters that are 2.12mm, 18.93mm, 3.12mm, 80.71mm, 195.9mm, 138.63mm and 165.64mm. These parameters that contribute to the optimized output have contributed 0.0462% efficiency than before. This also shows that this ejector model does not require significant changes because this model is said to be close to the optimized ejector. Through these seven modifiable parameters, a total of 82 design points has been generated by MOGA algorithm and have obtained a candidate that provides optimized parameters that are 2.12mm, 18.93mm, 3.12mm, 80.71mm, 195.9mm, 138.63mm and 165.64mm. These parameters that contribute to the optimized output have contributed 0.0462% efficiency.

Influence of geometric parameters on the performance of ejector used in aeroengine air system

By using an ejector to draw low-pressure, low-temperature air into the aeroengine's air system, it is possible to significantly enhance the cooling effect of the hot component of the engine. It is very necessary to clarify the sensitivity of ejector performance to different geometric parameters, especially the receiving chamber height, mixing chamber diameter, and diffuser diameter, which are of great significance to improve ejector performance and save limited aeroengine space. Therefore, this paper investigated the effects of these three geometric parameters on the ejector's performance by numerical simulation. The results show that increasing the mixing chamber diameter can significantly improve ejector performance. When the compression ratio is 1.17 and the mixing chamber diameter is increased from 3 mm to 9 mm, the entrainment ratio and the total pressure recovery coefficient are increased by 23.1 % and 7 %, respectively. Especially when the compression ratio is 1, simultaneously increasing the size of the receiving chamber, mixing chamber, and diffuser can greatly improve the ejector's performance. When the diameter of the mixing chamber is increased from 6 mm to 27 mm, the entrainment ratio and the total pressure recovery coefficient are increased by 211 % and 39 %, respectively. The change in ejector structure will influence its flow field and then affect the mixing process. When the size of the ejector is too small, the strong background shock wave suppresses the mixing of the primary flow and the secondary flow, which then causes an increase in the total pressure loss. When the size of the ejector is too large, the eddy current loss leads to ejector performance reduction.

Optimization of the primary nozzle for design a high entrainment ejector in spacesuit portable life support system

In looking forward to the future of human space exploration, it is increasingly stringent for the ventilation circuit subsystem in terms of reliability, simplicity and energy-efficient. Considering this requirement, the ejector, with the advantages of miniature size, no parasitic energy consumption and high reliability, is considered an appropriate alternative to the ventilation fan because it simultaneously implements the functions of mixing, entraining, and lifting pressure. This paper proposed a high entrainment ejector for application in spacesuit portable life support systems. The optimizations of the ejector nozzle geometrical parameters and nozzle exit position (NXP) were performed using a validated three-dimensional numerical model under various operating conditions. The results show that the NXP has a more significant effect on entrainment performance than other geometrical parameters in spacesuit portable life support systems, and the optimum NXP are not impacted by changes of the primary flow pressure and mixing chamber diameter, which similarly obtained the optimal entrainment ratio at the nozzle exit position of 2 mm. The maximum increments of entrainment ratio with the NXP varying from −4 mm to 8 mm are 0.2945 and 0.7664 under different primary flow pressures and mixing chamber diameters, respectively. Compared with the nozzle exit position, the most effects of nozzle converging angle and length on entrainment ratio are just 0.0864 and 0.0445. The optimum ejector extends the oxygen service duration by 12 min compared to the original one for the same volume of an oxygen tank, which is vital for the astronauts to conduct extravehicular activities in outer space.

Numerical analysis of key structural parameters of ejector for PEMFC system under low power conditions

In this study, a three-dimensional numerical model of an ejector is established, which is based on a 40 W power proton exchange membrane fuel cell (PEMFC) system. Computational Fluid Dynamics (CFD) technique is used to analyze the ejector in low power condition. The effects of two key structural parameters (distance from the mixing chamber to the nozzle and the mixing chamber diameter) on the ejector performance at different currents are investigated. It is found that ejector entrainment ratio changes slightly with the distance from mixing chamber to nozzle. The ejector entrainment ratio increases first and then decreases with the mixing chamber diameter. Moreover, with the increase of mixing chamber diameter, the turbulent kinetic energy and turbulent dissipation rate decrease obviously.

Optimization of three key ejector geometries under fixed and varied operating conditions: A numerical study

In this paper, as for an ejector utilized in a carbon capture system, by using CFD simulation, its three key geometries such as length of constant-pressure mixing chamber (XL3), length and diameter of constant-area mixing chamber (XL5 and D5) were first optimized individually. Then, the relative sensitivity of ejector performance to the three geometries was identified. Next, the effect of six optimization sequences (S1: XL3 → D5 → XL5, S2: XL3 → XL5 → D5, S3: XL5 → D5 → XL3, S4: XL5 → XL3 → D5, S5: D5 → XL3 → XL5, S6: D5 → XL5 → XL3) of the three geometries on entrainment ratio (ER) was evaluated. And then, the ER under varied working conditions was analyzed. Finally, four typical working conditions were selected for doing re-optimization to check whether the ejector performance can be significantly improved and how big difference of the optimized geometries with re-optimization can be generated. The results showed that: (1) the relative sensitivity of ER to D5 is greater than XL3, and that to XL5 is the least; (2) Among six optimization sequences of three geometries, S2 offers the best ejector performance, both S5 and S6 generate the equal and lowest ER; (3) The change of ER with the primary flow pressure is largely related to the back pressure; (4) Re-optimization under four typical operating conditions can improve ejector performance by 4.3% ∼ 128.8%, and optimum D5 and XL3 increases evidently as compared to that without re-optimization. The research results would enhance the application of ejector in carbon capture and relevant chemical fields.

Effects of operating conditions and geometries on the performance of nitrogen ejectors for Joule–Thomson cooling

Ejectors in Joule–Thomson (JT) cooling cycles can reduce the evaporator pressure and the compressor power consumption, achieving lower temperatures and higher efficiencies. The ejector, being a major component of a JT cooling cycle with an ejector, is critical to overall cooling performance. In this study, the effects of inlet pressures, outlet pressures, inlet temperatures, nozzle, and mixing geometries on the performance of nitrogen ejectors are investigated experimentally and numerically. The critical back pressure of the ejector increases as the primary and secondary inlet pressures increase. Depending on the working mode, the entrainment ratio varies with the ejector inlet temperature. The clogging due to the deposition of water molecules as impurities occurs when the ejector inlet temperature is below 222 K, resulting in the rapid reduction of mass-flow rates. For nitrogen ejector designs, the following ratios are recommended: constant-area mixing chamber diameter to nozzle outlet diameter, constant-area mixing chamber diameter to nozzle throat diameter, nozzle exit position to constant-area mixing chamber diameter, constant-area mixing chamber length to constant-area mixing chamber diameter. The results of this study will be beneficial in promoting the use of ejectors in JT cooling cycles.

Optimized mixing chamber length and diameter of a steam ejector for the application of gas turbine power plant: a computational approach

Optimized mixing chamber length and diameter of a steam ejector for the application of gas turbine power plant: a computational approach

Multi-round optimization of an ejector with different mixing chamber geometries at various liquid volume fractions of inlet fluids

• Two inlet fluids of the ejector have four liquid volume fraction combinations. • Multi-round optimization with six sequences of three geometries is conducted. • Optimal three geometries and ER under six optimization sequences are obtained. • Recommended sequence for each liquid volume fraction combination is presented. • Ultimate optimal three parameters and ER largely depend on inlet fluid states. The performance of the ejector relies on the geometrical parameters and the fluid phase state. Although the optimization of geometries of the ejector has been conducted in previous studies, the influence of different optimization sequence of geometric parameters was ignored in previous literatures. To close the knowledge gap, the goal of this paper is to investigate whether different optimization sequences affect the ejector performance and whether the ejector performance is the same under different optimization sequences after multiple rounds of optimization. Therefore, three geometrical parameters, namely the constant-pressure mixing chamber length (L pm ), the constant-area mixing chamber length (L am ) and diameter (D am ), are selected for the optimization study; besides, multi-round optimization with six optimization sequences of these three parameters is conducted by CFD simulations under four different combinations of primary flow liquid volume fraction (LVF 1 ) and secondary flow liquid volume fraction (LVF 2 ) (LVF 1 = 0 plus LVF 2 = 0, LVF 1 = 0 plus LVF 2 = 0.06, LVF 1 = 0.06 plus LVF 2 = 0, LVF 1 = 0.06 plus LVF 2 = 0.06) for the first time. The results showed that: (1) for each LVF combination, the three optimal parameters and corresponding maximum ER produced by one round optimization of six different optimization sequences are evidently different; (2) after multiple rounds of optimization, for LVF 1 = 0 plus LVF 2 = 0 or LVF 1 = 0.06 plus LVF 2 = 0.06, ultimate optimal geometrical parameters and maximum ER are the same with each other for six optimization sequences, however, for LVF 1 = 0 plus LVF 2 = 0.06 or LVF 1 = 0.06 plus LVF 2 = 0, each of them still has two different ultimate maximum ER; (4) for those four combinations, different sequence takes different optimization rounds, recommended sequences are D am → L am → L pm (S6), L pm → L am → D am (S1) or L pm → D am → L am (S2), and L am → L pm → D am (S3) and D am → L am → L pm , respectively; and (5) the ultimate optimal parameters and maximum ER in four combinations differ significantly because they are largely dependent on the inlet fluid states.

Experimental investigation on the influence of ejector geometry on the pull-down performance of an ejector-enhanced auto-cascade low-temperature freezer

• Effects of ejector geometry on EARC based low-temperature freezer were explored. • D t and L m are the critical parameters influencing the pull-down performances. • Malfunction of pressure lift at start-up phase was prone to occur at small D m . • NXP seriously affects ejector performance instead of the pull-down rate Employing an ejector to recover the expansion work of the auto-cascade refrigeration cycle is a feasible method to improve the system performance. The system operation characteristics are closely relevant to the ejector geometry parameters. In order to obtain the critical structure parameters influencing the freezer's pull-down performance, experimental research was conducted on an ejector-enhanced auto-cascade refrigeration cycle applied in a low-temperature freezer. The impacts of the ejector nozzle throat, mixing chamber diameter and length, and the nozzle exit position on the system's pull-down and steady operation characteristics were explored. The experimental results illustrated that the cooling rate and the attainable freezing temperature were mainly influenced by the nozzle throat and mixing chamber length instead of the nozzle exit position and mixing chamber diameter. The nozzle throat diameter of 0.52 mm and the mixing chamber length of 25 mm was optimal concerning the fastest cool-down rate and lowest freezing temperature of -61.2 °C. At the early phase of the pull-down process, a small mixing chamber diameter would cause the ejector malfunction of the pressure lift. There was a worst nozzle exit position of slowing down the pull-down speed, rising the freezing temperature, and reducing the system COP and exergy efficiency at the given operations. The ejector yielded the maximum pressure lift ratio of 1.196 and the entrainment ratio of 0.523 at the optimal ejector geometries. This work would be helpful to guide the ejector structure optimization for the ejector-enhanced auto-cascade low-temperature freezers.

Numerical Investigation on the Performance of Two-Throat Nozzle Ejectors with Different Mixing Chamber Structural Parameters

In this study, the effects of the mixing chamber diameter (Dm), mixing chamber length (Lm) and pre-mixing chamber converging angle (θpm) were numerically investigated for a two-throat nozzle ejector to be utilized in a CO2 refrigeration cycle. The developed simulated method was validated by actual experimental data of a CO2 ejector in heat pump water heater system from the published literature. The main results revealed that the two-throat nozzle ejectors can obtain better performance with Dm in the range of 8–9 mm, Lm in the range of 64–82 mm and θpm at approximately 60°, respectively. Deviation from its optimal value could lead to a poor operational performance. Therefore, the mixing chamber structural parameters should be designed at the scope around its optimal value to guarantee the two-throat nozzle ejector performance. The following research can be developed around the two-throat nozzle geometries to strengthen the ejector performance.

Experimental investigation on the dynamic characteristic of the direct expansion solar assisted ejector-compression heat pump cycle for water heater

A continuing research on the direct expansion solar assisted ejector-compression heat pump cycle for water heater is presented in this paper, aiming to reveal the system dynamic characteristic by experimental method. The performance advantage of the presented system is verified at first. According to the test results, under the considered condition, the presented system can outperform the traditional ejector enhanced heat pump system and the air-source heat pump system by 24.1% and 29% in the heating coefficient of performance aspect, 24.2% and 30.5% in the average heating capacity aspect. After that, the main parameters affecting the dynamic behavior of the presented system are examined, including the ejector nozzle exit position, ejector mixing chamber diameter and solar radiation intensity. According to the test results, the system achieves the maximum heating coefficient of performance and heating capacity under mixing chamber diameter of 4 mm and nozzle exit position of 6 mm. Note that the ejector malfunction phenomenon appears when the mixing chamber diameter is reduced to 3 mm, due to the blocked flow channel of the ejector secondary flow. Additionally, the experiment finds that enhancing the solar radiation can obviously improve the ejector pressure lift ratio and help the system achieve superior heating performance.

Numerical investigation into effects of ejector geometry and operating conditions on hydrogen recirculation ratio in 80 kW PEM fuel cell system

Ejectors play a crucial role in improving the fuel utilization efficiency of proton- PEMFC systems by recirculating the excess hydrogen discharged from the anode outlet side of the stack. This study has constructed a full MATLAB/Simulink model of an 80 kW PEMFC system consisting of an anode hydrogen gas supply system, a cathode oxygen gas supply system, a fuel cell stack, a terminal exhaust and drainage system, and an ejector-based anodic gas recirculation system. The model has been used to examine the effects of the ejector geometry and PEMFC operating conditions on the hydrogen recirculation ratio and hydrogen stoichiometric ratio. The results show that as the primary flow pressure increases, the primary mass flow rate increases, but the recirculation ratio and secondary mass flow decrease. By contrast, as the secondary pressure increases, the primary mass flow rate remains unchanged, but the secondary mass flow rate and recirculation ratio increase. For a constant primary flow pressure, the recirculation ratio increases with an increasing primary flow temperature. Conversely, for a constant secondary flow pressure, the recirculation ratio reduces slightly with an increasing secondary flow temperature. For a hydrogen stoichiometric ratio of 1.5, the optimal value of the mixing chamber diameter (D2) to nozzle throat diameter (Dt) is found to be D2/Dt = 2.2.