理论[火用]分析在冷冻厂高温库中的应用

通过对一定环境温度条件下的高温冷库中的氨蒸汽压缩系统进行[火用]分析,利用线性拟合的方法对氨的物性进行模拟,并对定冷凝温度和变冷凝温度时,制冷系统的各部件的炯损失和系统的[火用]效率进行计算分析,得出在冷库氨蒸汽压缩系统中的蒸发器中的[火用]损失最大,压缩机和冷凝器次之的结果。提出要对冷库氨蒸汽压缩系统的性能进行改进,必须首先考虑提高其蒸发器、压缩机和冷凝器的[火用]效率着手;认为在一定环境温度条件下,降低冷凝温度是提高[火用]效率的较好的改进措施之一．     

理论(焩)分析在冷冻厂高温库中的应用

通过对一定环境温度条件下的高温冷库中的氨蒸汽压缩系统进行(焩)分析,利用线性拟合的方法对氨的物性进行模拟,并对定冷凝温度和变冷凝温度时,制冷系统的各部件的(焩)损失和系统的(焩)效率进行计算分析,得出在冷库氨蒸汽压缩系统中的蒸发器中的(焩)损失最大,压缩机和冷凝器次之的结果.提出要对冷库氨蒸汽压缩系统的性能进行改进,必须首先考虑提高其蒸发器、压缩机和冷凝器的(焩)效率着手;认为在一定环境温度条件下,降低冷凝温度是提高(焩)效率的较好的改进措施之一.     

R134a/R134a复叠式空气源热泵系统性能分析

介绍了能够替代我国北方燃煤锅炉的R134a/R134a复叠式空气源热泵系统,分析其热力循环过程,并进行了复叠式热泵循环的热力学理论分析。通过计算,得出不同蒸发温度、冷凝温度以及冷凝蒸发器传热温差下,系统COP随蒸发冷凝温度的变化情况,从而得出系统最优低温级冷凝温度和最佳质量流量比。根据理论计算分析得出的结论对复叠式空气源热泵系统进行设计优化。     

R245fa传热性能实验研究

蒸发器和冷凝器的传热性能是影响制冷机组和双工质发电机组做功效率的关键因素,为了提高中低温余热在热泵机组和地热双工质发电系统中的利用效率,本文选用R245fa循环工质,对满液式蒸发器和冷凝器进行实验研究,分别讨论热水温度进口温度对蒸发器和冷凝器的传热系数、蒸发压力和冷凝压力的影响。研究结果表明,在工质流量和冷却水流量保持不变的条件下,蒸发器传热系数随着热水进口温度和温差的增大而减小,冷凝器的传热系数随着热水进口温度的增加先增大后减小,蒸发器传热系数可以达到2500 W/(m2·℃);蒸发器压力和汽轮机前后的压差随着热水出口温度的增加而增加,热水流量对蒸发压力和冷凝压力的变化浮动较小。     

R245fa传热性能实验

蒸发器和冷凝器的传热性能是影响制冷机组和双工质发电机组做功效率的关键因素,为了提高中低温余热在热泵机组和地热双工质发电系统中的利用效率,本文选用R245fa循环工质,对满液式蒸发器和冷凝器进行实验研究,分别讨论热水温度进口温度对蒸发器和冷凝器的传热系数、蒸发压力和冷凝压力的影响。研究结果表明,在工质流量和冷却水流量保持不变的条件下,蒸发器传热系数随着热水进口温度和温差的增大而减小,冷凝器的传热系数随着热水进口温度的增加先增大后减小,蒸发器传热系数可以达到2500 W/(m2?℃);蒸发器压力和汽轮机前后的压差随着热水出口温度的增加而增加,热水流量对蒸发压力和冷凝压力的变化浮动较小。     

强化传热技术在空调中的应用

众所周知,提高空调机热力循环过程中制冷剂的蒸发温度、降低其冷凝温度均能提高空调器的制冷系数。但是随着冷凝温度的降低和蒸发温度的提高,空调器的传热温差将会随之降低,蒸发器和冷凝器的传热条件恶化。虽然增大蒸发器、冷凝器的换热面积能解决这一矛盾,但是由此必然导致空调器体积增大、能重比降低。解决这一矛盾最为明智的方法就是利用现有的传热强化技术、强化冷凝器和蒸发器的传热实现空调机蒸发器、冷凝器的低温差传热。本文将简要介绍强化传热技术及几种能在空调设计中应用的强化传热管。     

定环境温度下冷库的氨蒸汽压缩制冷系统的火用分析

本文通过对定环境温度条件下的冷库中的氨蒸汽单级压缩系统进行火用分析,利用线性拟合的方法对氨的物性进行模拟,并对定蒸发温度和变蒸发温度时,制冷系统的各部件的火用损失和系统的火用效率进行计算分析,得出在冷库氨蒸汽压缩系统中的蒸发器中的火用损失最大,压缩机和冷凝器次之的结果。提出要对冷库氨蒸汽压缩系统的性能进行改进,必须首先考虑提高其蒸发器、压缩机和冷凝器的火用效率着手;从而提出定环境温度条件下,提高蒸发温度是提高系统火用效率的较好的改进措施之一。     

R290直接接触冷凝制冷循环性能分析对比

本文分析了R290直接接触冷凝(DCC)制冷循环的性能,并与R290常规单级压缩制冷循环的热力性能进行对比,得出:在最佳主循环冷凝温度下,R290直接接触冷凝制冷循环可获得最大性能系数和最低冷凝器热负荷。主循环过冷液体的过冷度增大,最优性能系数降低、最低冷凝器热负荷增加、蒸发器的制冷剂质量流量减少,同时,获得最优性能系数和最低冷凝器热负荷的最佳主循环冷凝温度升高。当蒸发温度为-15～-6℃,R290直接接触冷凝制冷循环相比R290单级压缩制冷循环的性能系数提高了7.5%～14.9%,冷间供冷设备蒸发器的制冷剂质量流量减少了26.5%～36.7%,冷凝器热负荷减少了1.5%～3.7%。结果表明R290直接接触冷凝制冷循环具有很好的发展前景。     

杭氧与西交大联合课题“大型制氧装置高效冷凝蒸发器”通过鉴定

20 0 3年 2月 2 6日 ,浙江省科技厅组织的杭州制氧机集团有限公司和西安交通大学联合课题“大型制氧装置高效冷凝蒸发器”的鉴定会在杭州举行。鉴定委员会听取了联合课题组所作的“新型高效冷凝蒸发器及其相关新技术”研究开发报告、研制报告、性能测试报告、用户使用情况报告、科技查新报告等。经过认真讨论 ,一致认为 :(1 )该项目首创特殊通道比例作为基本换热单元 ,构成双沸腾型冷凝蒸发器 ,使冷凝蒸发器的总传热温差得到大幅度降低 ;首创冷凝通道的结构方案 ,显著降低了冷凝蒸发器液氧的平均饱和沸腾温度 ,使主冷传热温差降低到0 6 0K…     

CO_2-C_3H_8复叠低温预冷系统的理论分析及优化设计

设计了一个低温级带回热器的CO2-C3H8复叠制冷循环低温预冷系统(213 K),并进行了低温预冷系统的参数选择和优化设计.该系统高温级循环采用CO2、低温级循环采用C3H8作为循环工质.通过对该系统的理论计算,得出了中间温度、复叠温差及低温级蒸发器冷端温差对系统性能系数的影响曲线;通过进一步的优化分析获得了系统最佳中间温度及对应的系统性能系数COP与复叠温差-低温级蒸发器冷端温差以及制冷温度-冷凝温度的关联式.     

Exergy analysis of R1234yf and R1234ze as R134a replacements in a two evaporator vapour compression refrigeration system

Exergy analysis is a useful way for determining the real thermodynamic losses and optimising environmental and economic performance in the systems such as vapour compression refrigeration systems. The present study deals with the exergy analysis on a two evaporator vapour compression refrigeration system using R1234yf, R1234ze and R134a as refrigerants. In the calculation of losses occurring in different system components, besides the exergy efficiency of the refrigeration cycle, a computer code was developed by using Engineering Equation Solver (EES-V9.172-3D) software package program. The effects of the evaporator and condenser temperatures on the exergy destruction and exergy efficiency of the system were investigated. R1234yf and R1234ze, which are good alternatives to R134a concerning their environmentally friendly properties and this is the most significant finding emerging from this study.     

Exergy analysis of gas turbine trigeneration system for combined production of power heat and refrigeration

A conceptual trigeneration system is proposed based on the conventional gas turbine cycle for the high temperature heat addition while adopting the heat recovery steam generator for process heat and vapor absorption refrigeration for the cold production. Combined first and second law approach is applied and computational analysis is performed to investigate the effects of overall pressure ratio, turbine inlet temperature, pressure drop in combustor and heat recovery steam generator, and evaporator temperature on the exergy destruction in each component, first law efficiency, electrical to thermal energy ratio, and second law efficiency of the system. Thermodynamic analysis indicates that exergy destruction in combustion chamber and HRSG is significantly affected by the pressure ratio and turbine inlet temperature, and not at all affected by pressure drop and evaporator temperature. The process heat pressure and evaporator temperature causes significant exergy destruction in various components of vapor absorption refrigeration cycle and HRSG. It also indicates that maximum exergy is destroyed during the combustion and steam generation process; which represents over 80% of the total exergy destruction in the overall system. The first law efficiency, electrical to thermal energy ratio and second law efficiency of the trigeneration, cogeneration, and gas turbine cycle significantly varies with the change in overall pressure ratio and turbine inlet temperature, but the change in pressure drop, process heat pressure, and evaporator temperature shows small variations in these parameters. Decision makers should find the methodology contained in this paper useful in the comparison and selection of advanced heat recovery systems.     

Comparative study of irreversibilities in an aqua-ammonia absorption refrigeration system

Irreversibilities in components of an aqua-ammonia absorption refrigeratio system (ARS) have been determined by second law analysis. The components of the ARS are as follows: condenser, evaporator, absorber, generator, pump, expansion valves, mixture heat exchanger and refrigerant heat exchanger. It is assumed that the ammonia concentration at the generator exit is, independent of the other parameters, equal to 0.999 and at the evaporator exit the gas is saturated vapour. Pressrre losses between the generator and condenser, and the evaporator and absorber are taken into consideration. In the results the dimensionless exergy loss of each component, the exergetic coefficient of performance, the coefficient of performance and the circulation ratio are given graphically for each different generator, evaporator, condenser and absorber temperature.     

Exergetic analysis of a vapour compression refrigeration system with R134a, R143a, R152a, R404A, R407C, R410A, R502 and R507A

This communication deals with the exergetic analysis of a vapour compression refrigeration system with selected refrigerants. The various parameters computed are COP and exergetic efficiency in the system. Effects of degree of condenser temperature, evaporator temperature and sub-cooling of condenser outlet, supper-heating of evaporator out let and effectiveness of vapour liquid heat exchanger are also computed and discussed. In this study, it was found that R134a has the better performance in all respect, whereas R407C refrigerant has poor performance.     

A theoretical study on a novel combined power and ejector refrigeration cycle

A new combined power and refrigeration cycle is proposed for the cogeneration, which combines the Rankine cycle and the ejector refrigeration cycle by adding an extraction turbine between heat recovery vapor generator (HRVG) and ejector. This combined cycle could produce both power output and refrigeration output simultaneously, and could be driven by the flue gas from gas turbine or engine, solar energy, geothermal energy and industrial waste heats. Parametric analysis and exergy analysis are conducted to examine the effects of thermodynamic parameters on the performance and exergy destruction in each component for the combined cycle. The results show that the condenser temperature, the evaporator temperature, the turbine inlet pressure, the turbine extraction pressure and extraction ratio have significant effects on the turbine power output, refrigeration output, exergy efficiency and exergy destruction in each component in the combined cycle. It is also shown that the biggest exergy destruction occurs in the heat recovery vapor generator, followed by the ejector and turbine.     

Thermal and exergoeconomic analysis of a novel solar driven combined power and ejector refrigeration (CPER) system

In the present study, a novel solar driven combined power and ejector refrigeration system (CPER) of 50 kW power capacity composed of an ORC (organic Rankine cycle) and an ejector refrigeration system is investigated. Solar driven CPER system is composed of two main cycles: collector cycle and refrigeration cycle. The collector cycle is made of a U-tube ETC and circulation pump and the ejector refrigeration cycle consists of generator, turbine, ejector, heat exchanger, condenser, evaporator, expansion valve, and pump. Thermodynamic performance of the proposed CPER system is evaluated and a thermo-economic analysis is conducted using the SPECO (specific exergy costing) method. A parametric study showed the effects of condenser temperature, evaporator temperature, generator pressure, turbine back pressure and turbine extraction ratio. The genetic algorithm optimization analysis is conducted which shows 25.5% improvement in thermal energy, 21.27% in exergy efficiency, and 7.76% reduction in the total cost of the CPER system. The results reveal that the performance of the CPER system is considerably improved at higher temperatures of generator and evaporator.     

Computer-based refrigerant thermodynamic properties. Part 3: Use of the program in the computation of standard refrigeration cyclesPropriétés thermodynamiques des frigorifigènes calculées par ordinateur. 3e partie: utilisation du programme pour le calcul des cycles frigorifiques normaux

The first program listed in this paper provides for the user to call up the thermodynamic properties of one of the stored refrigerants at a specified temperature (and pressure) at a display terminal. The second program calculates the performance of a vapour compression refrigeration cycle for the specified refrigerant operating between given values of the evaporator and condenser temperatures.     

A novel linear electromagnetic-drive oil-free refrigeration compressor using R134a

A new type of oil-free moving magnet linear compressor with clearance seals and flexure springs has been designed for incorporation into a vapour compression refrigeration system with compact heat exchangers for applications such as electronics cooling. A linear compressor prototype was built with a maximum stroke of 14 mm and a piston diameter of 19 mm. An experimental apparatus was built to measure the compressor efficiencies and coefficient of performance (COP) of a refrigeration system with the linear compressor, using R134a. The resonant frequency for each operating condition was predicted using the discharge pressure, suction pressure and stroke. Refrigeration measurements were conducted for different strokes under each pressure ratio with a fixed condenser outlet temperature of 50 °C and evaporator temperature ranging from 6 °C to 27 °C. The results show that the COPs are around 3.0 for tests with a pressure ratio of 2.5 (evaporator temperature of 20 °C).     

Computer-based refrigerant thermodynamic properties. Part 3: Use of the program in the computation of standard refrigeration cycles

The first program listed in this paper provides for the user to call up the thermodynamic properties of one of the stored refrigerants at a specified temperature (and pressure) at a display terminal. The second program calculates the performance of a vapour compression refrigeration cycle for the specified refrigerant operating between given values of the evaporator and condenser temperatures.