Experimental investigation of a novel steam ejector refrigerator suitable for solar energy applications

The paper presents the results of an experimental investigation of a novel steam jet refrigerator suitable for solar energy applications. The primary flow of the ejector is controlled using a spindle in order to provide fine tuning and for ejector operation as well as optimum coefficient of performance. The influence of the spindle position, and the boiler temperature, as well as that of evaporating temperature which denotes the cooling load temperature, on the performance of the ejector is assessed.     

Steam jet ejector cooling powered by waste or solar heat

A small scale steam jet ejector experimental setup was designed and manufactured. This ejector setup consists of an open loop configuration and the boiler operate in the temperature range of T_b = 85–140 °C. The typical evaporator liquid temperatures range from T_e = 5 °C to 10 °C while the typical water-cooled condenser pressure ranges from P_c = 1.70 kPa to 5.63 kPa (T_c = 15–35 °C). The boiler is powered by two 4 kW electric elements while a 3 kW electric element simulates the cooling load in the evaporator. The electric elements are controlled by means of variacs.Primary nozzles with throat diameters of 2.5 mm, 3.0 mm and 3.5 mm are tested while the secondary ejector throat diameter remains unchanged at 18 mm. These primary nozzles allow the boiler to operate in the temperature range of T_b = 85–110 °C. When the nozzle throat diameter is increased, the minimum boiler temperature decreases. A primary nozzle with a 3.5 mm throat diameter was tested at a boiler temperature of T_b = 95 °C, an evaporator temperature of T_e = 10 °C and a critical condenser pressure of P_crit = 2.67 kPa (22.6 °C). The system's COP is 0.253.In a case study the experimental data of a solar powered steam jet ejector air conditioner is investigated. Solar powered steam ejector air conditioning systems are technical and economical viable when compared to conventional vapour compression air conditioners. Such a system can either utilise flat plate or evacuated tube solar thermal collectors depending on the type of solar energy available.     

Performance of ejector cooling system with thermal pumping effect using R141b and R365mfc

The ejector cooling system (ECS) is suitable for solar cooling application due to its simple design and low cost. An ECS using a multi-function generator (ECS/MFG) as a thermal pumping device without rotating machines for refrigerant circulation has been designed and tested. The experiment of an ECS/MFG operating at full-cycle while using R141b has shown that the COP_o can reach 0.225 and cooling capacity of 0.75 kW at generator temperature 90 °C, condenser temperature 37 °C, and evaporator temperature 8.5 °C. The present study also redesigned the ejector for working fluid R365mfc in order to replace R141b. This study has shown that R365mfc can replace R141b as the working fluid of ECS/MFG at no payoff of system performance as long as the ejector design is optimized.     

An experimental investigation of steam ejector refrigeration system powered by extra low temperature heat source

A steam ejector refrigeration system is a low capital cost solution for utilizing industrial waste heat or solar energy. When the heat source temperature is lower than 80 °C, the utilization of the thermal energy from such a low-temperature heat source can be a considerable challenge. In this investigation, an experimental prototype for the steam ejector refrigeration system was designed and manufactured, which can operate using extra low-temperature heat source below 80 °C. The effects of the operation temperature, the nozzle exit position (NXP) and the diameter of the constant area section on the working performance of the steam ejector were investigated at generating temperatures ranging from 40 °C to 70 °C. Three ejectors with a same de Laval nozzle for the primary nozzle and three different constant-area sections were designed and fabricated. The experimental results show that a steam ejector can function for a certain configuration size of the steam ejector with a generating temperature ranging from 40 °C to 70 °C and an evaporating temperature of 10 °C. For a given NXP, the system COP and cooling capacity of the steam ejector decreased until inoperative as the diameter of the constant area section reduced. The results of this investigation provided a good solution for the refrigeration application of the steam ejector refrigeration system powered by an extra low-temperature heat source.     

Evaluation of a variable flow ejector for anode gas circulation in a 50-kW class SOFC

Solid oxide fuel cells (SOFC) are highly efficient in terms of converting hydrogen's chemical energy into electrical energy through electrochemical reactions and for generating power in the range of several kW to several tens of kW. A variable flow ejector equipped with an adjustable recirculating flow rate mechanism was designed for this investigation. A prototype was manufactured to control the circulation of anode exhaust gas for a 50-kW class SOFC system. The ejector performance was evaluated using SOFC simulator equipment that simulated the pressure and temperature environment of a 50-kW SOFC system. In the heating simulation experiment, the mass flow rate ratio of the driving gas to the suction gas could be controlled from 3.7 to 5.4 under conditions simulating 100% of the rated load operation and from 4 to 7.5 when simulating 30%–50% of the partial load conditions. A simple heat transfer model for the motive nozzle was used in the ejector analysis, and issues for improving the ejector recirculation performance in the high-temperature field were identified.     

Discrete ejector control solution design,characterization, and verification in a 5 kW PEMFC system

An ejector primary gas flow control solution based on three solenoid valves is designed, implemented and tested in a 5 kW proton exchange membrane fuel cell (PEMFC) system with ejector-based anode gas recirculation. The robust and cost effective combination of the tested flow control method and a single ejector is shown to achieve adequate anode gas recirculation rate on a wide PEMFC load range.In addition, the effect of anode gas inert content on ejector performance in the 5 kW PEMFC system is studied at varying load and anode pressure levels. Results show that increasing the inert content increases recirculated anode gas mass flow rate but decreases both the molar flow rate and the anode inlet humidity.Finally, the PEMFC power ramp-rate limitations are studied using two fuel supply strategies: 1) advancing fuel supply and venting out extra fuel and 2) not advancing fuel supply but instead using a large anode volume. Results indicate that the power of the present PEMFC system can be ramped from 1 kW to 4.2 kW within few hundred milliseconds using either of these strategies.     

Optimal design of a novel nested-nozzle ejector for PEMFC's hydrogen supply and recirculation system

The ejector-based hydrogen supply and recirculation system (HSRS) for a Proton Exchange Membrane Fuel Cell (PEMFC) system has the advantages of compact size and zero power consumption, compared with the HSRS using a recirculation pump. However, the conventional ejector with a single venturi nozzle can only function within a narrow power range of the PEMFC system due to its restricted primary inlet pressure. This study proposed a novel ejector design with nested nozzles to solve this problem. The key geometric parameters, including the nozzle diameters of a large nozzle (BN), a small nozzle (SN), and the axial distance between two nozzles, were optimized using CFD simulations to obtain the maximum entrainment capability. The BN mode is responsible for the stack's higher load operations, while the SN mode supports the lower power operations. Additionally, a bypass was used parallel to the nested-nozzle ejector in the HSRS to extend the ejector operating range further. The consistent CFD simulation and testing results of the nested-nozzle ejector showed effective hydrogen entrainment capability between 9% and 100% of power output for a 150 kW PEMFC stack. Moreover, the new nested-nozzle ejector HSRS showed much-reduced anode inlet pressure fluctuation compared to the HSRS using two conventional ejectors.     

Numerical Simulation of the Performance of a Capillary Thermal Driven Ejector Refrigerator

A capillary driven ejector refrigerator is a new refrigeration system that can use solar energy and other low-grade heat sources. In this paper, the performance of the refrigeration system is simulated numerically by use of an iteration algorithm and block exchanging technology for all unit models. The flow and heat transfer characteristics in a solar collector, generator, ejector, condenser, and evaporator are analyzed and calculated. The results show that when the generating temperature is higher than 75–80°C and the environmental temperature is lower than 35°C, the system can work normally; the coefficient of performance of this refrigeration system is in the range of 0.05–0.15 by use of water as a refrigerant. The cooling capacity and COP increase with an increasing generative temperature and decreasing condensing pressure.     

A solar ejector air‐conditioning system using environment‐friendly working fluids

In this paper, the performance of the solar‐driven ejector air conditioning with several environment‐friendly working fluids is studied. The effect of the fluid nature and operating conditions on the ejector performance is examined. This performance is calculated using an empirical correlation. Thermodynamic properties of functioning fluids are obtained with a package REFPROP7. It appears that the refrigerant R717 offers the highest coefficient of performance (COP). For generator temperature T_B = 90°C, condenser temperature T_C = 35°C and evaporator temperature T_E = 15°C and with R717, the COP of ejector air‐conditioning system is 0.408. Using a meteorological data for the city of Tunis, the system performance is computed for three collector types. The air‐conditioning season and period were taken for six months from April to September. The daily period is between 8 and 17 h. For the solar air‐conditioning application, the COP of the overall system varied from 0.21 to 0.28 and the exergy efficiency varied from 0.14 to 0.19 with the same working conditions and total solar radiation (351–875 Wm^?2) in July. Copyright © 2008 John Wiley & Sons, Ltd.     

新型可调式喷射器性能的计算与分析

提出在喷射器喷嘴内插入喷针来调节喷射器工作参数的方案,建立了可调武喷射器性能计算模型,分析了喷嘴截面积变化对喷射系数、气体压力、气体流量等参数的影响。结果表明,通过对喷射器喉口面积的调节,可以实现把出口流量控制在一个稳定的区域内,从而减小喷射器入口参数对出口参数以至整个系统的影响。可调式喷嘴可拓宽喷射器的有效工作范围。     

Experiments on vapour jet refrigeration system suitable for solar energy applications

Experiments are carried out on a R11 vapour jet refrigeration system (VJRS) to study the influence of ejector configuration and operating conditions on the performance. Eight ejector configurations, formed out of five nozzles and seven diffusers are investigated. The influence of boiler temperature, which represents the solar energy collection temperature, and that of evaporating temperature, which denotes the cooling load temperature, are studied. Overall COPs in the range of 0.08-0.33 and evaporating temperatures in the range of −3–18°C are obtained for boiler temperatures from 75 to 85°C. Ejector configuration has significant influence in deciding the operating range.     

斯特林发动机小空间燃气引射特性仿真研究

采用FLUENT软件对应用于斯特林发动机小空间燃烧室的不同类型的引射器的引射特性进行了计算研究.研究结果表明:在一次流体总质量流量和喷嘴总流通面积相同的条件下,多孔式喷嘴引射器的速度、温度及浓度分布均匀性明显优于中心、环形式喷嘴引射器,喷孔数量越多均匀性越好;多孔式喷嘴引射器的引射系数明显大于中心、环形式喷嘴引射器,喷孔数量越多引射系数越大.     

CFD modelling and experimental investigation of an ejector refrigeration system using methanol as the working fluid

This paper presents results of computational fluid dynamic (CFD) analysis and experimental investigation of an ejector refrigeration system using methanol as the working fluid. The CFD modelling was used to investigate the effect of the relative position of the primary nozzle exit within the mixing chamber on the performance of the ejector. The results of the CFD were used to obtain the optimum geometry of the ejector, which was then used to design, construct and test a small‐scale experimental ejector refrigeration system. Methanol was used as the working fluid, as it has the advantage of being an ‘environmentally friendly’ refrigerant that does not contribute to global warming and ozone layer depletion. In addition, use of methanol allows the ejector refrigeration system to produce cooling at temperatures below the freezing point of the water, which of course would not be possible with a water ejector refrigeration system. CFD results showed that positioning the nozzle exit at least 0.21 length of the mixing chamber throat's diameter upstream of the entrance of the mixing chamber gave better performance than pushing it into the mixing chamber. Experimental values of coefficient of performance (COP) between 0.2 and 0.4 were obtained at operating conditions achievable using low‐grade heat such as solar energy and waste heat. Copyright © 2001 John Wiley & Sons, Ltd.     

Experimental investigation of an ejector refrigerator: Effect of mixing chamber geometry on system performance

This paper describes an experimental study of an ejector refrigeration cycle using R11 as the working fluid. The system was tested with boiler temperature from 100 to 110°C, the condenser temperature from 35 to 41°C, and the evaporator temperature up to 12°C. Two different mixing chambers with throat diameter of 8 mm were used. Choking of the fluid was always found in the first mixing chamber, but not in the second one. The system was more flexible to operate when there was no choking in the mixing chamber. A cooling temperature as low as ?5°C could be obtained with COP between 0.1 and 0.25 and cooling capacity between 500 and 1700 W. Copyright © 2001 John Wiley & Sons, Ltd.     

太阳能喷射式制冷系统喷射器性能的三维数值模拟

利用FLUENT软件对太阳能喷射式制冷系统中的喷射器进行三维数值模拟,从影响喷射器性能的主要工作参数和喷射器的主要尺寸、结构等方面进行了数值计算。从数值模拟的研究中得出：流线型结构的喷射器能减弱混合过程中的回流现象;在超过某一值时继续增加工作流体的压力对喷射器性能没有改善;喷嘴出口和扩压管入口存在一定的距离会提高喷射器的性能;收缩段采用流线型的喷射器性能很接近四段都采用流线型的喷射器的性能,并且都能提高喷射器的性能。     

Performance of ejector heat pumps

An ejector-compression heat pump can use low-grade thermal energy in the neighbourhood of 93.3°C (200°F) to provide space cooling and heating. This paper applies the existing ejector theory to estimate the performance of an ejector heat pump system at various operating conditions. The study includes parametric, sensitivity and off-design analyses of the heat pump performance. The performance enhancement options and desired ejector geometry are also examined. Refrigerants 11, 113 and 114 are three of the halocarbons most suitable for the ejector heat pump system. The estimated coefficients of performance for a simple ejector heat pump are 0.3 for the cooling mode and 1.3 for the heating mode at a sample operating condition in which the refrigerant (R-11) boiling temperature is 93.3°C (200°F), condensing temperature 43.3°C (110°F) and evaporating temperature 10°C (50°F). A 24 per cent performance improvement is predicted for a heat pump with two-stage ejectors and regenerative heat exchangers. The off-design performance is relatively insensitive to the evaporator temperature variations.     

Theoretical study on an innovative ejector enhanced Joule‐Thomson cycle

This paper describes an innovative ejector enhanced Joule‐Thomson cycle for low‐temperature refrigerators. Since an ejector is introduced into the cycle, the cycle performance is profoundly affected by the pressure lift ratio and entrainment ratio of the ejector. As a case study, the performance characteristic of the novel cycle refrigerator using the non‐azeotropic refrigerant mixture R14/R23 with the molar fraction of 0.6/0.4 is theoretically investigated in detail. The theoretical results show that in a typical refrigeration temperature range from −65°C to −95°C, the novel cycle refrigerator has 24.4%–41.5% improvement in coefficient of performance and 60%–220% enhancement in refrigeration capacity when compared to a basic Joule‐Thomson cycle low‐temperature refrigerator. This achieves a significant advantage as the use of the novel cycle is applied to low‐temperature refrigerators for the medical and commercial applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Geometric optimization of an ejector for a 4 kW SOFC system with anode off-gas recycle

One of the important energy saving tools used in solid oxide fuel cell (SOFC) system is the anode off-gas recycling (AGR) via an ejector which allows the recirculation of the unused fuels in the anode exhaust gas including hot steam which is essential for the elimination of the carbon deposition and the initiation of the reactions in the reformer. In an ejector system developed for the SOFCs, the steam to carbon ratio (STCR) and entrainment ratio are the crucial parameters for the determination of the ejector performance. These parameters can be engineered by modifying the geometric dimensions and operation conditions. This study focuses on the determination of the maximum STCR value and entrainment ratio via numerical geometric analyses for a micro combined heat and power (μ-CHP) system based on 4 kW SOFC, utilizing methane. A detailed numerical procedure for designing an ejector is provided and the ejector performance is investigated for different critical dimensions (throat diameter, nozzle exit angle and nozzle position etc.). The results show that the nozzle position and the nozzle exit angle significantly affect STCR and the entrainment ratio. When the nozzle position increases and nozzle exit angle decreases, the entrainment ratio and STCR is found to increase. The entrainment ratio and STCR are determined as around 7.3 and 2.7, respectively for a specific design created in the study.     

Modeling analysis on solar steam generator employed in multi-effect distillation (MED) system

Recently the porous bilayer wood solar collectors have drawn increasing attention because of their potential application in solar desalination. In this paper, a thermodynamic model has been developed to analyze the performance of the wood solar collector. A modeling analysis has also been conducted to assess the performance and operating conditions of the multiple effect desalination (MED) system integrated with the porous wood solar collector. Specifically, the effects of operating parameters, such as the motive steam temperature, seawater flow rate, input solar energy and number of effects on the energy consumption for each ton of distilled water produced have been investigated in the MED desalination system combined with the bilayer wood solar steam generator. It is found that, under a given operating condition, there exists an optimum steam generation temperature of around 145°C in the wood solar collector, so that the specific power consumption in the MED system reaches a minimum value of 24.88 kWh/t. The average temperature difference is significantly affected by the solar heating capacity. With the solar capacity increasing from 50 kW to 230 kW, the average temperature difference increases from 1.88°C to 6.27°C. This parametric simulation study will help the design of efficient bilayer wood solar steam generator as well as the MED desalination system.     

Experimental investigations of a small-scale solar-assisted absorption cooling system

The present study deals with a small-scale solar-assisted absorption cooling system having a cooling capacity of 3.52 kW and was investigated experimentally under the climatic conditions of Taxila, Pakistan. Initially, a mathematical model was developed for LiBr/H₂O vapor absorption system alongside flat-plate solar thermal collectors to achieve the required operating temperature range of 75°C. Following this, a parametric analysis of the whole system was performed, including various design and climate parameters, such as the working temperatures of the generator, evaporator, condenser, absorber, mass flow rate, and coefficient of performance (COP) of the system. An experimental setup was coupled with solar collectors and instruments to get hot water using solar energy and measurements of main parameters for real-time performance assessment. From the results obtained, it was revealed that the maximum average COP of the system achieved was 0.70, and the maximum outlet temperature from solar thermal collectors was 75°C. A sensitivity analysis was performed to validate the potential of the absorption machine in the seasonal cooling demand. An economic valuation was accomplished based on the current cost of conventional cooling systems. It was established that the solar cooling system is economical only when shared with domestic water heating.