太阳能两级喷射式制冷系统性能的分析

在特定工况下对太阳能两级喷射式制冷系统进行了分析,计算了系统中各个设备的损失,讨论了发生温度和蒸发温度的变化对制冷子系统中各个设备的损失的影响。结果表明,太阳能集热器的损失最大,为47.67%;其次为冷凝器,损失为21.15%。在冷凝温度、蒸发温度条件一定的情况下,系统存在一个最佳的发生温度使得系统的总损失最小。     

Performance characteristics of a two-stage irreversible combined refrigeration system at maximum coefficient of performance

A general cycle model of a two-stage combined refrigeration system is established and used for analizing the influence of multi-irreversibilities, such as finite rate heat transfer, heat leak between the heat reservoirs and internal dissipation of the working fluid, on the performance of the refrigeration system. The coefficient of performance is taken as an objective function for optimization. The maximum coefficient of performance is calculated, and other corresponding performance parameters, such as the temperatures of the working fluid in the isothermal processes, the optimal distribution of the heat transfer areas and the power input of the refrigeration system, are determined. The results obtained here are more general than those obtained from a two-stage endoreversible combined refrigeration system and can guide the optimal design and operation of real combined refrigerator systems.     

非共沸混合工质压缩制冷循环的不可避免(火用)损失

以非共沸混合工质替代 CFCS是比较有效的替代方案。通过对给定节点温差下的蒸发器和冷凝器内的温度匹配分析 ,提出利用调节非共沸混合工质的配比来优化蒸发器和冷凝器内的温度匹配 ,并可计算出循环的实际不可避免灯用损失 ,从而提出采用非共沸混合工质的蒸气压缩制冷循环的实际不可避免灯用损失的计算方法 ,并提出利用最佳配比和实际不可避免的灯用损失的计算 ,对各种非共沸混合工质对进行筛选 ,以进一步减少循环可避免的灯用损失 ,为优化蒸气压缩制冷循环 ,提高循环的性能奠定基础。     

非共沸混合工质压缩制冷循环的不可避免Yong损失

以非共沸混合工质替代CFC5是比较有效的替代方案。通过对给定节点温差下的蒸发器和冷凝器内的温度匹配分析，提出利用调节非共沸混合工质的配比来优化蒸发器和冷凝器内的温度匹配，并可计算出循环的实际不可避免炯损失，从而提出采用非共沸混合工质的蒸气压缩制冷循环的实际不可避免炯损失的计算方法，并提出利用最佳配比和实际不可避免的Yong损失的计算，对各种非共沸混合工质对进行筛选，以进一步减少循环可避免的炯损失，为优化蒸气压缩制冷循环，提高循环的性能奠定基础。     

Global sensitivity analysis of two-stage thermoelectric refrigeration system based on response variance

In this paper, a mathematical model of two-stage thermoelectric refrigeration system is established considering the influence of external heat transfer and its performance is analysed based on finite-time thermodynamics and Newton's heat transfer law. Taking the cooling capacity and coefficient of performance of the two-stage thermoelectric refrigeration system as separate objective functions, the general relationship between cooling capacity, coefficient of performance, and working design parameters of the system is determined. The influence of the fluctuation of the input design parameters on the output performance parameters is studied using a global sensitivity analysis based on the variance response. The main and total Global sensitivity indices of input parameters that affect the output performance are calculated, and the related sensitivity ranking are obtained. The results can be used to guide the performance analysis and parameter optimization of two-stage thermoelectric refrigeration system in application.     

Numerical investigation of a two-stage air-cooled absorption refrigeration system for solar cooling: Cycle analysis and absorption cooling performances

Two-stage air-cooled ammonia–water absorption refrigeration system could make good use of low-grade solar thermal energy to produce cooling effect. The system simulation results show that thermal COP is 0.34 and electrical COP is 26 under a typical summer condition with 85 °C hot water supplied from solar collector. System performances under variable working conditions are also analyzed. Circular finned tube bundles are selected to build the air-cooled equipment. The condenser should be arranged in the front to get an optimum system performance. The mathematical model of the two-stage air-cooled absorber considering simultaneous heat and mass transfer processes is developed. Low pressure absorber should be arranged in front of middle pressure absorber to minimize the absorption length. Configuration of the air-cooled equipment is suggested for a 5 kW cooling capacity system. Temperature and concentration profiles along the finned tube length show that mass transfer resistance mainly exists in liquid phase while heat transfer resistance mainly exists in cooling air side. The impacts on system refrigeration capacities related to absorption behaviors under variable working conditions are also investigated. Both cycle analysis and absorption performances show that two-stage air-cooled ammonia–water absorption chiller is technically feasible in practical solar cooling applications.     

Simulation of an integrated hybrid desiccant vapor-compression cooling system

The performance of a desiccant, integrated, hybrid, vapor-compression cooling system is modeled numerically. The concept of hybrid cooling investigated in this paper utilizes the waste heat rejected from a vapor-compression cycle to activate a desiccant dehumidification cycle. The hybrid system consists of 4 major components: a compressor, an evaporator and 2 desiccant, integrated condensers/dehumidifiers. The equations governing the transport of heat and mass in the desiccant, integrated condenser/dehumidifiers are formulated considering air as the working fluid in the process stream and a refrigerant stream, which is cooled from superheated vapor to subcooled liquid, as the heat source during desorption; a water stream is used to remove the heat generated during adsorption. The governing equations are nondimensionalized and solved for both sorption processes using an explicit finite-difference scheme. The performance of a first generation prototype desiccant, integrated, hybrid, vapor-compression cooling system is then evaluated at ARI conditions.     

Experimental study on two-stage compression refrigeration/heat pump system with dual-cylinder rolling piston compressor

A thermodynamically analytical model on the two-stage compression refrigeration/heat pump system with vapor injection was derived. The optimal volume ratio of the high-pressure cylinder to the low-pressure one has been discussed under both cooling and heating conditions. Based on the above research, the prototype was developed and its experimental setup established. A comprehensive experiments for the prototype have been conducted, and the results show that, compared with the single-stage compression heat pump system, the cooling capacity and cooling COP can increase 5%–15% and 10–12%, respectively. Also, the heating capacity with the evaporating temperature ranging from 0.3 to 3 °C is 92–95% of that under the rate condition with the evaporating temperature of 7 °C, and 58% when the evaporation temperature is between −28 °C and −24 °C.     

太阳能低温储粮吸附制冷系统

低温储粮是一种具有广阔应用前景及实用价值的科学储粮方法。从降低能耗的角度出发,设计并建造了一种用于低温储粮的太阳能吸附制冷系统,测试分析了系统的热性能。试验测试结果表明：通过合理配置集热器面积,太阳能制冷系统能够满足低温储粮对冷负荷的需求。     

Design and development of a refrigeration system energized with hydrogen produced from scrap aluminum

Hydrogen holds out great promise as an energy source whose use does not pollute the environment. In this context, methods of hydrogen production which do not involve formation of carbon dioxide are especially attractive. The present work describes a cheap and versatile prototype of an alkaline hydrolyser which efficiently produces hydrogen from aluminum scrap and aqueous sodium hydroxide, the hydrogen produced being used directly to energize, by combustion, a refrigerator working on the ammonia–water principle, which was also designed and developed in our laboratory. A direct comparison of the system when energized by liquid-propane flame and by hydrogen flame shows a clearly better performance in the latter case, which produces a temperature of −20 °C after about 2 h of operation.     

Comparison of the optimal performance of single- and two-stage thermoelectric refrigeration systems

The cycle models of a single-stage and a two-stage semiconductor thermoelectric refrigeration system are established, based on non-equilibrium thermodynamics. They are used to derive the general expressions of three important performance parameters, such as the coefficient of performance (COP), the rate of refrigeration, and the power input. By using these expressions, the performance of the two-stage thermoelectric refrigeration system is discussed in detail. The maximum COP and rate of refrigeration are calculated, the internal structure parameter of the thermoelectric device is optimized, and the reasonable ranges of some parameters are determined. The results obtained here are compared with those of a single-stage thermoelectric refrigeration system, and consequently the advantages of two-stage thermoelectric refrigerators are expounded.     

Computer-aided conceptual thermodynamic design of a two-stage dual fluid absorption cycle for solar refrigeration

This communication presents thermodynamic assessment of a two-stage dual fluid absorption refrigeration system using H₂O---LiBr and NH₃---H₂O as working fluids at the first and second stage, respectively. Both stages are assumed to be operated with hot water available from separate solar collectors. In the cascading of two-stage absorption systems, the evaporator of the first stage produces cooling water which is circulated in the absorber of the second stage. It is found that two-stage systems can be used for the production of very low temperatures using moderate generator temperatures at the first stage. The effects of generator temperature, absorber temperature and condenser temperature on the coefficient of performance, minimum evaporator temperature and effective refrigeration produced are also presented.     

Thermodynamic study of a two-stage vapour absorption refrigeration system using NH3 refrigerant with liquid/solid absorbents

A systematic investigation is made of the two-stage vapour absorption refrigeration system employing the refrigerant absorbent combinations of NH₃---H₂O and NH₃---LiNO₃. The system consists of coupling two conventional absorption cycles so that the first-stage evaporator produces cooling water to circulate in the absorber of the second stage. The effect of operating variables such as generator temperature, evaporator temperature, absorber temperature and condenser temperature on the coefficient of performance (COP), heat transfer rates and relative circulation have been studied for both single-stage and two-stage absorption refrigeration systems. It is found that the COP is higher for NH₃---LiNO₃ than for NH₃---H₂O, in both single-stage and two-stage absorption systems, especially at higher generator temperatures. Furthermore, the minimum evaporator temperature achieved is lower for NH₃---LiNO₃, and the system can be operated at lower generator temperatures.     

Design and performance simulation of a new solar continuous solid adsorption refrigeration and heating hybrid system

In this paper, the design of a new continuous solid adsorption refrigeration and heating hybrid system driven by solar energy was proposed, and its performance simulation and analysis were made under the normal working conditions. Some performance parameters of the system were obtained, and the effects of water mass in water tank on the system's COP_cooling, COP_heating etc. were discussed. The simulation indicated: the system could refrigerate continuously with such a design, and at the conditions of that the daily sun-radiation is 21.6 MJ, the mean ambient temperature is 29.9°C, the evaporating temperature is 5°C, the heat-collecting coefficient of upper bed η is 60%, and the heat-transfer coefficient between lower bed and ambient α is 2 W/m² K, by day a hybrid system of single combined bed could furnish 30 kg hot water of 47.8°C, and had a mean COP_cooling of 0.18, a mean COP_heating of 0.34, a continuous mean SCP_a of 17.6 W/kg, a continuous mean SCP_c of 87.8 W/m², and a continuous mean SHP_c of 165.9 W/m²; and at night it had a cooling capacity of 0.26 MJ/kg of adsorbent, and a cooling capacity of 1.3 MJ/m² of heat-collecting area.     

渔船发动机废热驱动的两级复叠吸收制冷循环性能分析

针对传统吸收式制冷无法达到较低温度以及自复叠吸收制冷在制得较低温度时系统性能系数过小的缺点,提出发动机废热驱动的两级复叠式吸收制冷循环用于捕获海产品的速冻保鲜。首先采用SRK方程获得了该循环高、低温级工质对R134a/DMF和R23/DMF的热力学性质参数,进而对循环进行了建模分析。通过直接搜索法得到了在不同工况下的最优高温级发生温度。发现在当吸收温度为30℃,冷凝温度为35℃,制冷温度在-40℃以上时,循环最佳蒸发冷凝温度和高、低温级发生温度分别为-3℃、106℃和140℃,此时循环COPint 可达到0.143。但该循环性能受吸收、冷凝温度影响较大,因此不太适合在海水温度过高的海域使用。     

太阳能烟囱制冷系统的研究

通过分析制冷系统和太阳能烟囱热气流发电系统的技术和特点,提出了太阳能烟囱制冷系统.将太阳能烟囱系统与制冷系统相结合进行制冷,可实现制冷不用电.该系统由烟囱、集热棚、蓄热层、涡轮机、开启式制冷压缩机、冷凝器和变速器等组成.介绍了太阳能烟囱制冷系统的结构特点、工作原理以及系统相关参数的计算方法.分析结果表明,太阳能烟囱制冷系统结构简单,运行维护方便,制冷不用电,无污染,具有良好的环境效应,可根据环境温度改变压缩机运行转速调节供冷负荷,能有效解决热带及沙漠地区的供冷及供电问题.     

Design and optimisation of an absorption refrigeration system operated by solar energy

A general theoretical study on design and optimisation of the water-lithium bromide and the ammonia-water absorption refrigeration cycles has been undertaken. The results of this study show that in general for fixed initial conditions and given system refrigeration capacity higher generator temperature causes higher cooling ratio with smaller heat exchange surfaces and consequently lower cost. A comparison of the two cycles also indicate that the water-lithium bromide system is simpler than the ammonia-water system and operates at a higher cooling ratio and smaller heat exchange surfaces for the same conditions.     

Performance analysis and optimization of a new two-stage ejector-expansion transcritical CO2 refrigeration cycle

In this paper, a new two-stage configuration of ejector-expansion transcritical CO₂ (TRCC) refrigeration cycle is presented, which uses an internal heat exchanger and intercooler to enhance the performance of the new cycle. The theoretical analysis on the performance characteristics was carried out for the new cycle based on the first and second laws of thermodynamics. Based on the simulation results, it is found that, compared with the conventional two-stage transcritical CO₂ cycle, the COP and second law efficiency of the new two-stage cycle are about 12.5–21% higher than that of conventional two-stage cycle. It is also concluded that, the performance of the new two-stage transcritical CO₂ refrigeration can be significantly improved based on the presented new two-stage cycle. Hence the new two-stage refrigeration cycle is a promising refrigeration cycle from the thermodynamically and technical point of views. A regression analysis in terms of evaporator and gas cooler exit temperatures has been used, in order to develop mathematical expressions for maximum COP, optimum discharge and inter-stage pressures and entrainment ratio.     

Performance of a solar LiBr-water absorption refrigeration system

This paper describes the performance of a nonstorage, continuous, solar operated absorption refrigeration cycle. The solar collectors and the refrigeration experimental unit are manufactured locally. The results presented in this paper are based on the operation of the unit when there was enough solar energy to power its generator. This amounted to 4–5 h per day during the months of August and September in Amman, Jordan. These results include the variation of both the generator and evaporator temperatures during the test periods, the performance of the unit as a function of these temperatures and available solar intensity, and the ideal performance of the unit based on the measured temperatures. The maximum ideal coefficient of performance was determined as being equal to 1.6, while the peak actual coefficient of performance was determined to be equal to 0.55. These values are very close to published values.