A study of working fluids for heat driven ejector refrigeration using lumped parameter models

This paper studies the influence of working fluids over the performance of heat driven ejector refrigeration systems performance by using a lumped parameter model. The model used has been selected after a comparison of different models with a set of experimental data available in the literature. The effect of generator, evaporator and condenser temperature over the entrainment ratio and the COP has been investigated for different working fluids in the typical operating conditions of low grade energy sources. The results show a growth in performance (the entrainment ratio and the COP) with a rise in the generator and evaporator temperature and a decrease in the condenser temperature. The working fluids have a great impact on the ejector performance and each refrigerant has its own range of operating conditions. R134a is found to be suitable for low generator temperature (70–100 °C), whereas the hydrocarbons R600 is suitable for medium generator temperatures (100–130 °C) and R601 for high generator temperatures (130–180 °C).     

Design aspects of ejectors: Effects of suction chamber geometry

Ejector loop reactors are appealing devices for two fluids mixing. The high interfacial area produced in such reactors gives them an advantage over the conventional contactors. Suction chamber where the two streams of the primary and secondary fluid meet is an important part of the overall ejector geometry. The present work deals with optimization of the geometry of the suction chamber using computational fluid dynamics (CFD). The effect of (i) projection ratio (L_TN/D_T), i.e., ratio of the distance between the nozzle tip and throat (L_TN) to the throat diameter (D_T), (ii) the diameter of the suction chamber (D_S) and (iii) the angle of the converging section (θ) on the entrainment rate of the secondary fluid have been studied. It was observed that for low values of projection ratio the entrainment rate was low. It increased with an increase in the projection ratio; however, became constant beyond a particular value of this ratio. The effect of D_S on the rate of entrainment was observed to be more complex. The entrainment rate showed a maximum value when D_S was varied over a wide range. The results obtained for different values of θ suggest that the optimum lies in the range of 5°-15°. The results have been explained on the basis of flow patterns produced.     

Flow visualization in supersonic ejectors using laser tomography techniques

This paper presents flow imaging techniques developed for investigating flow in ejectors. These visualization techniques use the laser sheet method but differ from each other by the kind of the illumination source, the polarization direction of the incident light and the type of the scattering tracers. Each of these methods enables the visualization of specific phenomena (shock structure, flow instabilities, mixing process). Although the flow visualizations are primarily qualitative, they allow the determination of the flow regime, the measurement of the non-mixing length, can indicate suggestions for the design of ejectors and provide the possibility to validate numerical simulations.     

具有自适应弹射机制的粒子群算法

针对粒子群算法容易陷入局部最优和停滞的问题,提出自适应弹射机制的粒子群算法.为了保持粒子群的活力,在算法内引入弹射操作.当粒子满足条件,当前位置赋予很大的速度,使其飞到很远的区域.弹射方式可以选择全维弹射和概率弹射.为了配合弹射操作,提出粒子优劣的判断机制,使粒子可以被弹射飞出可行域.在算法中设定自适应判别函数,当粒子满足该判别函数,对粒子实施弹射.数值实验表明,文中算法具有较强的全局搜索能力和较快的搜索速度.     

Anode recirculation behavior of a solid oxide fuel cell system: A safety analysis and a performance optimization

Anode recirculation, which is generally driven by an ejector, is commonly used in solid oxide fuel cell (SOFC) systems that operate with natural gas. Alternative fuels such as gasification syngas from biomass have been proposed for potential use in the SOFC systems because of the fuel flexibility of SOFCs and the sustainability of biomass resources. Because the ejector was initially designed to use natural gas, its recirculation behavior when using alternative fuels is not well understood. The aim of this research work is to study anode recirculation behavior and analyze its effect on safety issues regarding carbon deposition and nickel oxidation and the performance of an SOFC system fed with gasification syngas under steady state operation. We developed a detailed model including a recirculation model and an SOFC stack model for this study, which was well validated by experimental data. The results show that the entrainment ratio with the gasification syngas is much smaller than that with the natural gas, and the gasification syngas does not have the tendency toward carbon deposition or nickel oxidation under the operating conditions studied. In addition, the recirculation affects the performance of the SOFC, especially the net electrical efficiency, which could be promoted by 160%.     

Design and characterization of an electronically controlled variable flow rate ejector for fuel cell applications

A variable flow ejector is presented to address the challenge of providing cost-effective recirculation of hydrogen in fuel cell systems. The ejector uses supersonic flow to provide sufficient pressure rise for the Ballard Mark 9 SSL stack used in the University of Delaware’s fuel cell hybrid buses. Details of geometry optimization via computational fluid dynamic simulation, control system design, electronic control implementation, and mechanical design are discussed. Results from testing in the final application are included, showing the ejector’s excellent performance compared to Ballard’s specifications for recirculation flow rate.     

First and second law investigation of waste heat based combined power and ejector-absorption refrigeration cycle

In the proposed cogeneration cycle, a LiBr-H₂O absorption refrigeration system is employed to the combined power and ejector refrigeration system which uses R141b as a working fluid. Estimates for irreversibilities of individual components of the cycle lead to possible measures for performance improvement. Results of exergy distribution of waste heat in the cycle show that around 53.6% of the total input exergy is destroyed due to irreversibilities in the components, 22.7% is available as a useful exergy output, and 23.7% is exhaust exergy lost to the environment, whereas energy distribution shows 44% is exhaust energy and 19.7% is useful energy output. Results also show that proposed cogeneration cycle yields much better thermal and exergy efficiencies than the previously investigated combined power and ejector cooling cycle. Current investigation clearly show that the second law analysis is quantitatively visualizes losses within a cycle and gives clear trends for optimization.     

Experimentelle Untersuchung einer Dampfstrahlkälteanlage mit einem alternativen Treibmedium

In order to determine the increase in efficiency of n‐octane compared to water as a propellant in ejector refrigeration systems, a pilot plant with a cooling capacity of up to 1.5 kW was set up. In both cases, water was used as the suction medium, the so‐called cooling medium. From the pressure and temperature measurement data, the two mass flows, the so‐called motive and suction flow, and from this the mass flow ratios could be obtained. Subsequently, a comparison of the theoretical coefficient of performance for the two propellants was carried out in the case of closed‐loop operation.     

A theoretical study of an innovative ejector enhanced vapor compression heat pump cycle for water heating application

This study presents a novel vapor compression heat pump cycle in which an ejector associated with a subcooler is applied to enhance the heating performance for air-source heat pump water heater application. The heating coefficient of performance (COP_h) and heating capacity of the novel cycle using the non-azeotropic mixture refrigerant R417A are theoretically investigated, for the ranges of evaporating temperature (−15 to 10 °C) and condensing temperature (55-60 °C). The theoretical results show that the COP_h and volumetric heating capacity of the novel cycle are better than that of the conventional heat pump cycle. It is found that for the operating conditions considered, the maximum COP_h and volumetric heating capacity can be improved by up to 1.62-6.92% and 15.20-37.32% over the conventional heat pump cycle, respectively. The performance characteristics of the novel cycle show its promise in air-source heat pump water heater applications.     

The first and second law analysis on an organic Rankine cycle with ejector

In consideration of the low efficiency of the organic Rankine cycle (ORC) with low-grade heat source (LGHS), an organic Rankine cycle with ejector (EORC) and a double organic Rankine cycle (DORC) based on the ORC is introduced in this paper. The thermodynamic first law and second law analysis and comparison on the ORC, EORC and DORC cycles are conducted on the cycle’s power output, thermal efficiency, exergy loss and exergy efficiency. Water is chosen as the LGHS fluid, and the same temperature and mass flow rate of the water is the standard condition for the comparative analysis on the cycles. The emphasis is on the thermodynamic performance at the maximum net power output of the cycles. The results show the power output is higher in the EORC and DORC compared to the ORC. And the cycle’s exergy efficiency could be ranked from high to low: DORC > EORC > ORC.