Nozzle Throat Diameter Research Articles

Gas jet target with controllable density via throat diameter of conical nozzle

A supersonic gas jet has been a special target in the ultraintense laser interaction field due to its controllable atomic density distribution. This work investigates the spatial atomic density distribution in argon gas jets ejected from conical nozzles with different throat diameters. Both experiment and simulation results show that the atomic density and its distribution can be controlled by changing the throat diameter of the conical nozzle. The quantitative dependence of atomic density on the throat diameter under different backing pressures is obtained. It also agrees with that from the one-dimensional gas dynamics model. However, it is noted that for a large throat diameter at a high gas backing pressure, a radial saddle-shaped atomic density profile is demonstrated experimentally within a few millimeters away from the nozzle outlet. The results are helpful to optimize the density profile in gas-jet targets and to understand the effect of the throat diameter of the conical nozzle on cluster size in Hagena scaling law.

Parametric study of a vortex-enhanced supersonic inductive plasma torch

The feed gas injection configuration in radio-frequency (RF) inductively coupled plasma (ICP) torches plays a critical role in discharge stability, gas heating, and device thermal management: particularly if a supersonic nozzle is used to subsequently accelerate the hot gas. A novel injection configuration is the bidirectional vortex, which segments the internal ICP flow field into two counter-propagating vortices that can significantly enhance gas heating and reduce heat losses. The diameter of the interface between the vortices (known as the mantle) is expected to be an important dimensional parameter affecting torch operation, especially relative to the nozzle size. In this work, we investigate the effect of nozzle throat diameter on the behaviour and performance of a vortex-enhanced supersonic ICP torch. The system is operated at RF powers and argon mass flow rates between 200–1000 W and 0–400 mg s−1 respectively, and different nozzle diameters ranging from 1.5 to 4 mm are explored. Because of the high-temperature environment, and to prevent disruption of the vortex flow fields, non-invasive diagnostics are used to measure the gas temperature and plasma density, and to infer the torch thermal efficiency and achievable gas specific enthalpy change. The maximum temperature is between 8500–9500 K with the 1.5 mm nozzle giving the highest temperature for a given power and mass flow rate, while plasma densities vary between 1020–1021 m−3 depending on the operating conditions. The thermal efficiency increases from 29% for the 1.5 mm nozzle to just above 70% for the 4 mm nozzle with a similar maximum specific enthalpy of around 1.5 MJ kg−1. These results demonstrate the important coupling between torch properties, and how system optimization can lead to tailored performance of potential interest to several ground and space-based applications.

Performance Analysis of an Ejector-Enhanced Heat Pump System for Low-Temperature Waste Heat Recovery Using UHVDC Converter Valves

This article proposes a heating method based on heat pump technology to address the large amount of low-grade waste heat generated by a certain type of ultra-high voltage direct current (UHVDC) converter valve. Thermal performance calculations for two systems, a basic vapor compression heat pump system (BVCHPS) based on thermal expansion valve throttling and an ejector-enhanced heat pump system (EEHPS) are analyzed. The research results show that the EEHPS exhibits superior COP and exergy efficiency when generating hot water above 80 °C using a heat source below 50 °C. Additionally, mathematical modeling analysis identifies optimal structural parameters such as nozzle throat diameter, throat area ratio, and nozzle outlet diameter for the ejector in its design state. The low-temperature waste heat recovered from the UHVDC converter valves can be further used in engineering applications such as heating, refrigeration, seawater desalination, and sewage treatment.

Theoretical studies on wide-operating-range ejector based on operating conditions and multi-parameter coupling effect in proton exchange membrane fuel cell system

When the ejector in a fuel cell system operates under off-design conditions, its performance will significantly decrease. To improve the performance of the ejector under all operating conditions, this paper proposes a theoretical model for predicting performance and optimizing the structure of the ejector that has not been studied before. Based on the jet theory, a two-dimensional three-segment velocity distribution is established, and the exponent of the velocity function is modified by simulation and experimental data, reducing the model’s calculation error from 15% to 6.5%. By combining the Lagrange algorithm, we investigate the influence of operating conditions and multi-parameter coupling effects on ejector performance, obtaining optimal values for structural parameters under different load conditions. The results show that the optimal value of main nozzle exit position (Lx) increases with increasing current and the optimal value ranges from 0.5 to 6 mm. The influence of dimensionless parameter (λc), dimensionless parameter (λd) and diffusion angle (αd) on ejector performance is significant and optimal values exist. Reducing the nozzle throat diameter (dnt) can effectively promote the entrainment performance at low power, and four adjustment conditions are proposed. When dnt decreases from 3.2 to 2.0 mm, the operating range of the current is increased by 38.42%, the power range is increased by 42.12%, and the pressure drop of the ejector (pd) decreased by 9.66 bar. The theoretical model not only improves the accuracy of predicting the entrainment ratio, but also realizes the study of the influence of multi-structural parameter coupling effect on the performance of the ejector, which leads to a significant improvement in the optimization accuracy and efficiency, and extends the applicable power range of the ejector. This provides a new direction for the future performance optimization of wide operating range ejectors considering multi-parameter coupling effects.

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.

STUDY OF THE PROCESS OF PLANT RAW MATERIAL EXTRACTION IN A STATIC-TYPE CAVITATION INLINE MIXER

Abstract. The flowering heads of calendula have a significant content of biologically active substances (BAS) with a wide range of pharmacological activities. Traditional methods for obtaining their aqueous extracts include maceration or percolation. However, these methods have significant drawbacks. The rational choice of equipment and the study of the influence of thermophysical conditions on the extraction process of specific plant raw materials to intensify mass transfer processes are relevant. The aim of the study is to investigate the transition of solid substances of calendula flowers into a soluble state in a flow cavitation mixer of a static type to intensify mass transfer processes in obtaining aqueous extracts. For the research, previously ground dry calendula flower heads, swollen in distilled water at a hydro module of 1:15 and reduced to 0,1-2 mm, were used. The work was carried out on an experimental cavitation mixer of the Venturi tube type with a variable cavitation reactor with a nozzle throat diameter ranging from 0,006 m to 0,12 m. The efficiency of extraction was determined by the amount of water-soluble substances, and the cavitation phenomenon was characterized by the cavitation number. Results: The overall design of the cavitation apparatus, the profile and geometric parameters of the nozzle, the flow parameters, as well as the properties of the plant material, significantly affect the hydrodynamic conditions and the development of cavitation effects during processing. The Venturi-type flow cavitation mixer used in the research showed high efficiency in processing mass transfer processes during the extraction of a water suspension of calendula flower heads. The results obtained indicate that the most significant impact of cavitation effects is observed at nozzle throat diameters of 0,08 m and 0,10 m, with cavitation numbers χ = 0,53 and χ = 0,84, respectively. In this case, the process duration can be limited to 60 seconds. The obtained conclusions are confirmed by microstructure studies.

Multifactor response-based optimization for enhancing cavitation performance of short injection self-priming pumps

As the heart of the water supply systems, the energy conversion efficiency of the self-priming pumps with built-in injection system under overload conditions is extremely affected by cavitation problems. This study focuses on a typical short-type injection self-priming pump devoted to improve the pump performance, especially to solve the cavitation problem under overload conditions. Through a two-factor, five-level orthogonal test that combines numerical simulation and experimental validation, the influence of key structural parameters within the ejector on cavitation performance and energy characteristics are analyzed. The results demonstrate the high level accuracy of numerical simulation, as indicated by the consistency and small error between the numerical results and the experimental results for head, efficiency, and power under full flow conditions. Regression analysis based on the orthogonal test results reveals significant correlations between the hydraulic performance of the pump and the nozzle throat diameter and nozzle outlet diameter. Under overload conditions, the high-speed jet generated by the injector induces a negative pressure at the effuser and nozzle, leading to cavitation at the effuser throat and nozzle outlet. Employing appropriate structural parameters, particularly the effuser throat diameter and nozzle outlet diameter, proves effective in increasing the operating flow range. This in turn improves the energy characteristics of the entire hydraulic system. The optimal combination identified for the ejector's structural parameters in this study is a nozzle outlet diameter of 8.2 mm and a throat diameter of 18 mm. This provides theoretical insights for the optimal design of short-type jet self-priming pumps, holding practical significance in engineering applications.

Dynamic Modelling and Simulation of Industrial Plant Fire and Gas Detection Systems; Parametric Analysis of Nozzle Flow

Industrial plant safety is of paramount importance, and the effective operation of Fire and Gas Detection Systems (FGDS) plays a critical role in preventing and mitigating incidents. This study presents a comprehensive parametric computational fluid dynamics (CFD) analysis of nozzle flow, aimed at enhancing our understanding of the complex fluid dynamics within nozzle geometries. Nozzles find wide applications in industries ranging from aerospace propulsion systems to industrial processes. The analysis employs CFD simulations with varying geometric parameters, such as nozzle shape, throat diameter, and expansion ratio, to investigate their influence on flow characteristics, including velocity profiles, pressure distributions, and shock formations. The parametric study involves systematic variations of these geometric parameters, allowing for the identification of optimal configurations for specific applications. The results shed light on the intricate interplay between nozzle geometry and flow behavior, providing valuable insights for nozzle design and optimization.

Numerical and experimental research on axial injection end-burning hybrid rocket motors with polyethylene fuel

This study investigates the end-burning hybrid rocket motors with polyethylene fuel by the numerical simulation and experiment. Based on computational fluid dynamics, a numerical model is developed. The model is validated by two firing tests in this hybrid rocket motor, which uses oxygen and polyethylene as propellants. The results show that the numerical and experimental data are in good agreement, and the error of the chamber pressure is less than 2.63%. Based on the simulation mode, the blowoff limit of the end-burning hybrid rocket motors is investigated. When the nozzle throat diameter and the inner diameter of grain are large, it is more difficult for the hybrid rocket motor to achieve end-burning mode, i.e., the flame spreading is prevented in the narrow duct. The main reason is that when the nozzle throat and the grain port are large, chamber pressure and oxidizer flow velocity are low. Therefore, the friction velocity considering the pressure and flow velocity is proposed. The critical friction velocity is about 4.054–4.890 m/s in the hybrid rocket motors. When the friction velocity exceeds the critical friction velocity, the combustion mode in hybrid rocket motors changes from the flame spreading mode to the end-burning mode. Moreover, the regression rate formula is obtained by fitting, which shows that the regression rate has a good correlation with combustion chamber pressure. The critical friction velocity and regression rate formula can provide an important reference for end-burning hybrid rocket motors.

Simulation and Experimental Investigation of Performance and Flow Behavior for Steam Ejector Refrigeration System

The ejector refrigeration system is a desirable choice to reduce energy consumption. A Computational Fluid Dynamics CFD simulation using the ANSYS package was performed to investigate the flow inside the ejector and determine the performance of a small-scale steam ejector. The experimental results showed that at the nozzle throat diameter of 2.6 mm and the evaporator temperature of 10oC, increasing boiler temperature from 110oC to 140oC decreases the entrainment ratio by 66.25%. At the boiler temperature of 120oC, increasing the evaporator temperature from 7.5 to 15 oC increases the entrainment ratio by 65.57%. While at the boiler temperature of 120oC and the evaporator temperature of 10oC, increasing the nozzle throat diameter from 2.4 to 2.8 mm decreases the entrainment ratio by 40%. The numerical results showed that reducing the condenser back pressure or increasing the primary fluid temperature, secondary fluid temperature, and nozzle throat diameter moves the second shock waves in the downstream direction. It could be concluded that the second shock series position detects the ejector operation mode. The ejector runs in critical mode if the second shock series position is close to the diffuser. In contrast, if the second shock series position moves toward the upstream, the ejector runs in subcritical mode.

Numerical Analysis on Effect of Structural Parameters on Flow Field and Internal Trajectory in Gas–Steam Ejection Systems

This paper aims to study the influence of the structure of spray holes and throats on the flow field and the internal trajectory of the gas–steam ejection device. The compressible Navier–Stokes equations, discrete ordinate methods and RNG k-ε turbulence model are utilized to simulate the two-phase flow of the rocket gas with multispecies and the water sprays. The comparison between numerical results and experimental data confirms the accuracy and effectiveness of this model. The simulation analysis on the cases of the ejection process with multiple spray hole diameters, number of spray holes, total spray area, and throat diameter are conducted. The shock wave structure inside the gas–steam ejection device is examined. The simulation results show that, instead of the spray hole diameter and number, the total spray area and secondary nozzle throat diameter are the key factors that affect the flow field and internal trajectory of the gas–steam ejection device. Under the existing spray structure, the maximum number of spray holes is 300 to achieve the stability of the flow field and internal ballistic trajectory of gas–steam ejection devices. By comparing the throat diameters of multiple secondary nozzles, it was found that the minimum throat diameter of the secondary nozzles should be no less than 100 mm. The results could be valuable for the design of gas–steam ejection devices.

A Simple Design Approach of Two-Phase Ejectors for CO2 Transcritical Heat Pumps

Integrating a two-phase ejector in mechanical vapor compression heat pumps is a practical and low-cost solution for improving performance and reducing energy consumption. Typically, using an ejector to recover part of the important pressure expansion losses in CO2 systems may improve the operating conditions of the compressor. One of the prerequisites for the success of such an application is the proper design of the ejector. This study is mainly dedicated to developing a simple approach for CO2 ejector design. The advantage of using the ejector as an expander in a transcritical CO2 heat pump is first introduced. Compressor operation is particularly improved. The development of an ejector design model for CO2 expanding from transcritical to two-phase conditions is presented. Validation of the thermodynamic model with experimental results from the literature shows the predictions to be within an acceptable range of discrepancy. The primary nozzle throat diameter calculations do not exceed ±8% of error for transcritical conditions. The error of the predicted pressure at the outlet of the ejector is in the limit of -15% to +3%. A practical design example for estimating the transcritical CO2 ejectors geometry integrated in a heat pump is presented. The results show the important decrease of primary nozzle diameters with the drop of Tevap, especially for the throat. A decrease of Dmix also occurs with Tevap and an optimal diameter is obtained for each condition considered. The design of the diffuser is based on a compromise between the outlet velocity and the length of the diffuser. The detailed design procedure with the proposed model, complemented with data from the literature, is a valuable tool for rapidly generating useful results and obtaining preliminary designs transcritical CO2 ejector.

Optimization of the ejector parameters for anodic recirculation systems in high-performance dual-stack proton-exchange membrane fuel cells

The anodic recirculation system (ARS) is critical in designing modern proton-exchange membrane fuel cells (PEMFC). Although the flow-through approach can outperform the dead-end approach, it yields excess residual hydrogen during the operation of the fuel-supply system. This residue can reduce the fuel mileage and be explosive when discharged into the environment, particularly in the multi-stack configuration where multiple PEMFCs are connected for high-power purposes. Therefore, it is desirable to develop an appropriate ARS design that facilitates the recycling of this excess hydrogen. This study aimed to develop a one-dimensional ARS model for dual-stack PEMFCs to optimize the recirculation performance, as well as analyze the effect of ARS on fuel cell (FC) stacks. Subsequently, the dual-ejector concept was adopted, having demonstrated higher efficiency than the single-ejector concept in high-performance PEMFCs. In the designing step, ejector geometries were determined based on the sensitivity analysis of the nozzle throat and mixing chamber diameters. The filtering conditions were set for four parameters: hydrogen unrecoverable percentage (4,1% and 5%), stoichiometry (1.5–3), recirculation ratio, and anode inlet pressure (<1.5 bar). Hence, the minimum hydrogen unrecoverable value the system can achieve by optimization was 4.073%. Due to other filtering conditions being close to the upper limit of the requirements, expanding the unrecoverable condition was recommended despite higher hydrogen emissions. Additionally, the performed methodology demonstrated great potential in providing benefits related to simulation speed, accuracy, and the mapping of system-level interrelationships. Through this method, the optimized geometries ensured that filtering parameters were under control during operation. Moreover, this concept could reveal the direct effect of the anode inlet on the working pressure of each FC stack during dynamic simulation with changes in the Nernst voltage and losses.

Investigation on the influence of geometric parameters on two-phase ejector performance with R290

In this paper, the effect of geometric parameters on a two-phase ejector performance was experimentally studied, and the R290 was used as the working fluid. The four geometric parameters of the ejector were discussed in detail, including the diameter of the nozzle throat (Dt), the nozzle exit position (NXP), the diameter of the mixing section (Dm) and the length of the mixing section (Lm). The experimental results indicated that the pressure lift ratio (rp) of the ejector was sensitive to Dt and NXP. Within the increase of Dt and NXP discussed in this paper, the rp of the ejector varied from 1.13 to 1.33 and 1.32 to 1.07, respectively. In addition, a maximum rp of the ejector could be obtained when Dm was 3 mm to 4 mm under different nozzle throat diameter. When the Dt was 0.7 mm, the entrainment ratio of the ejector varied from 0.402 to 1.406 as the Dm varied from 2 mm to 6 mm. The Lm of the ejector diffuser had little effect on the ejector performance. Moreover, the empirical correlations for the efficiencies of R290 two-phase ejector components were summarized based on the experimental result and ejector model.

Flow Field and Gas Field Distribution of Non-Submerged Cavitation Water Jet Based on Dual-Nozzle with Concentric Configuration

Cavitation water jet peening is an efficient and green surface treatment technology. The dual-nozzle can realize a cavitation water jet in air (non-submerged condition), which can be used for the surface treatment of large structures. The flow field characteristics of the dual-nozzle determine the cavitation effect. In this paper, the simulation of a cavitation water jet in air is carried out using Fluent software. The flow field characteristics containing velocity distribution, impact pressure, and gas phase volume fraction distribution are studied in detail. Furthermore, the effects of the nozzle structure parameters and incidence pressure on flow field characteristics are discussed. It was found that the structure parameters of the inner nozzle have a great influence on the flow field characteristics. Setting a contraction segment and expansion segment can improve the impact pressure and increase the intensity of the cavitation jet. Increasing the throat diameter and incidence pressure of the internal nozzle is also beneficial to improve the impact pressure and cavitation intensity. In order to assure a good cavitation effect, nozzle optimization should be performed. This study has guiding significance for the design of the dual-nozzle for a non-submerged cavitation water jet.

Experimental Firing Test Campaign and Nozzle Heat Transfer Reconstruction in a 200 N Hybrid Rocket Engine with Different Paraffin-Based Fuel Grain Lengths

Firing test campaigns were carried out on a 200 N thrust-class hybrid rocket engine, using gaseous oxygen as an oxidizer and a paraffin-wax-based fuel. Different fuel grain lengths were adopted to extend the fuel characterization under different operating conditions, and to evaluate rocket performances and internal ballistics in the different configurations. In addition to data collected under a 220 mm propellant grain length, two further test campaigns were carried out considering 130 mm and 70 mm grain lengths. Two different injector types were adopted in the 130 mm configuration; in particular, a showerhead injection system was used with the aim to contain high-amplitude pressure oscillations observed during some firing tests in this engine configuration. Parameters such as the chamber pressure and temperature inside the graphite nozzle, space-averaged fuel regression rate and nozzle throat diameter were measured. The results allowed for the investigation of different issues related to hybrid rockets (e.g., fuel regression rate, engine performance, nozzle ablation under different conditions). The focus was mainly directed to the nozzle heat transfer, through the reconstruction of the convective heat transfer coefficient for different tests in the 70 mm grain length engine configuration. The reconstruction took advantage of the experimental data provided by the nozzle embedded thermocouple. Then, the experimental convective heat transfer coefficient was used to validate the results from some empirical correlations. The results showed significant differences between the experimental convective heat transfer coefficients when considering tests with different oxidizer mass flow rates. Furthermore, the predictions from the empirical correlations proved to be more reliable only in cases characterized by oxidizer-rich conditions.

Design, fabrication, and investigations of prototype supersonic micro-ejector for innovative cooling system of electronic components

Innovative approach for electronics cooling was proposed, i.e. heat generated by a part of electronic equipment, e.g. CPU, is absorbed by heat driven micro-ejector refrigeration system that can provide cooling of other electronic components, e.g. GPU. It was demonstrated the procedure of design, fabrication, and experimentation on the supersonic micro-ejectors for the case of isobutane as a working fluid for such system. It was demonstrated that it possible to design and fabricate the micro-ejector of cooling capacity in the range 3 W suitable for cooling of electronic equipment. For the discussed micro-ejector entrainment ratio obtained was app. 0.20 under conditions of the motive heat source temperature app. 60 °C and evaporation temperature app. 22 °C. There were demonstrated difficulties in fabrication of the supersonic ejector due to small dimensions of the motive nozzle as well as mixing chamber. Required throat diameter of the motive nozzle was less than 200 μm and the diameter of the mixing chamber was 260 μm. For reported tests conditions the boundary temperature of the on-design operation condition was between 21 – 25 °C. However, the operation of the micro-ejector under off-design operation regime was stable and repeatable. Micro-ejector tests required an indirect method of measurement of critical motive mass flow rate to be applied. The performance line of tested ejector fits to ejectors theory and meet the basic assumptions in terms of thermal capacity and operating temperature. CFD technique used for numerical predictions of the ejector performance fits to experimental measured values with acceptable accuracy.

Investigation and development of improved methods for the design of ejector

The ejector is a simple mechanical device having no moving parts has the characteristics of being fixed, reliable, inexpensive, simple to keep up and handle. An ejector is a device that allows a fluid at low pressure flow (secondary fluid flow) by speed up some other fluid at high pressure flow (primary fluid flow) through nozzle. It is used in lot of industrial processes, particularly with air or steam as operating fluid. The ejector system has a vast range of applications. They reduce pollution compared to fossil fuel power plants. The geometry of the ejector has a remarkable impact on the performance of the ejector. A steam ejector can effectively make use of unused heat resources, which is mainly used in air conditioning, refrigeration, and seawater desalination sectors. The geometry of mixing chamber of the steam ejector features a critical effect on its outcome. The numerical simulation results shows that the entrainment ratio and critical back pressure of the steam ejector initially increases and then decreases with the increase in mixing chamber length for different mach numbers. Mixing chamber length of 40 mm to 80 mm and nozzle throat diameter 2.5 mm provides high performance of steam ejector for steam ejector refrigeration.Ejector with converging-area chamber has higher performance than ejector with constant area section. Hydrocarbon ejector cooling applications is highly recommended.

A study of the parameters affecting the particle velocity in cold-spray: Theoretical results and comparison with experimental data

Within coating applications, cold-spray is nowadays an extended technique commonly used in environments such as the additive manufacturing or repair industries. The differential factor that leads this approach to be chosen over others is its low deposition temperature. The need for ensuring the resistance and durability of the free-standing components has led to the development of models that can predict the kinetic energy of the particles, which is the main driving parameter affecting the deposit performance. In this study, an optimisation theoretical model, previously developed by the authors, is validated with the experimental exit particle velocity data taken from commercial geometries and using Fluent simulations available in literature. The aim of this work is to relate fundamental parameters in the cold-spray process such as the stagnation conditions, nozzle geometry, powder size or particle velocity. This objective is achieved by creating novel interdependent maps connecting these pivotal data by virtue of the model presented. Several graphs describing the final particle velocity depending on the stagnation pressure and temperature are obtained along with the optimal geometry for a wide range of materials (aluminium, titanium, steel, Inconel 625 and copper). In addition, the analytical model is able to hand over a deposition window of particle sizes and velocities that can be achieved using a specific cold-spray equipment. Both set of maps combined together can be a powerful tool which users and manufacturers can benefit from on the grounds that they do not only provide information about whether a deposition can be achieved or not with a cold-spray equipment but also about the stagnation conditions needed. The results obtained with this methodology reflect the limitations of low and medium-pressure equipment in terms of the maximum particle diameter that can be deposited and constitute a novel advance in the state of art of cold-spray. Moreover, the fundamental parameter regarding the geometry, namely the ratio between the nozzle exit and the nozzle throat diameters, is represented as a function of the above-mentioned parameters.

Study on the ejector-expansion refrigeration system for low-temperature freezer application: Experimental and exergetic assessments

In this study, the authors propose applying the ejector-expansion refrigeration system (ERS) to develop a -50 °C low-temperature freezer. The main performance of the ERS based prototype freezers were investigated by experimental and exegetic methods. The influences of nozzle throat diameter and compressor displacement on ejector performance were discussed in detail. The higher efficiency and transiting exergy efficiency of ejector could be obtained with a larger nozzle throat diameter and compressor displacement. When the nozzle throat diameter rises from 0.4 to 0.7, ejector efficiency and transiting exergy efficiency increase from 16.1% to 20.1% and 26.1% to 30.2%, respectively. Moreover, these results demonstrated that the ERS-based freezer could operate stably with appropriate nozzle throat diameter and compressor displacement. Compared with the conventional single-stage vapor compression refrigeration system (CVRS), the compression ratio of ERS was reduced by 15.8%. In addition, the system performance decreased with the increase of capillary tube length. When capillary tube length varied from 40 mm∼ 80 mm, the COP of the freezer decreased from 0.59 to 0.52, and the overall exergy efficiency of freezer decreased from 22.1% to 17.1%. This research confirms that the ERS could provide a novel way for developing a -50 °C low-temperature freezer.