工质性质对有机朗肯循环低温发电系统影响的实验研究

在有机工质双循环朗肯发电系统中,循环工质的性质对电能输出量和低温热能的转化效率有重要影响。该研究设计搭建试验台,并对R142b、R152a和R134a 3种典型循环工质进行对比实验,分析压力、液体密度、潜热、气体比容、膨胀过程焓差等因素对低温热能发电系统的影响,并对系统优化和循环工质的选择提供依据。     

回收低温余热的有机朗肯循环性能分析及优化

选取R113、R114、R141b、R123、R245fa、R245ca、R600、R600a作为回收120~200℃低温余热的有机朗肯循环工质,从净功量、热效率、不可逆损失等方面对有机朗肯循环系统性能进行分析和优化,得出系统最佳运行工况。     

针对不同工业余热温度的有机朗肯循环工质优选

基于工业余热回收领域的有机朗肯循环低温余热发电系统,利用MATLAB软件编程,针对不同余热温度,考虑外部冷热源对系统经济性影响,研究不同有机工质在单位净输出功率造价、热回收效率、输出功率、膨胀比和蒸发压力等方面的表现。结果表明:R134a、R245fa和R601a分别在余热温度100～124℃、124～130℃和130～240℃条件下,单位净输出功率造价最优;R134a、R152a、R142b和R141b分别在余热温度100～124℃、124～130℃、130～160℃和160～200℃条件下,输出功率和热回收效率均为最优;余热温度160℃以下时,采用11种工质的有机朗肯循环系统的膨胀比均在10以下,而余热温度160℃以上时,膨胀比迅速增大;在蒸发压力限定不大于2.5 MPa条件下,R134a适用的余热温度范围最小,为100～118℃,R113适用的余热温度范围最大,为100～240℃。     

新型中高温热泵工质的理论研究

在70～90℃冷凝温度范围内,对19种环境友好、压力温度水平适宜的流体进行了中高温热泵理论循环计算对比分析,结果表明R124,R600a,R142b和R236ea等工质的性能较优.并从中筛选出6种混合工质N1-M6,通过计算比较其性能,再选出最优工质.     

低温有机朗肯循环的工质选择及系统性能分析

选取R123,R141b,R245ca,R245fa,R601,R601a作为有机朗肯循环的工质,在不同蒸发温度条件下,对其热力循环特性进行了计算分析,以热力学第一定律和第二定律为基础进行了比较.结果表明,R141b是适合本循环系统的最佳工质.同时还研究了汽轮机进口温度和进口压力对该系统的净功量、吸热量及热效率的影响.     

应用热力学分析方法与AHP_熵值法对ORC的工质比较及优化

选取4种有机工质R245fa、R123、R600和R141b做为循环工质,采用火用分析方法在烟气入口温度为150℃、出口温度为75℃的条件下,在蒸发温度为80-140℃范围内对4种有机工质的亚临界有机朗肯循环进行分析,发现系统各设备的火用效率、系统总的火用效率、热效率、净输出功随蒸发温度的升高而升高,火用损失随蒸发温度的升高而降低。当蒸发温度达到140℃时,系统各设备的火用效率、系统总的火用效率、热效率、净输出功均达到最大值,而火用损失达到最小值。因此,4种有机工质蒸发温度在80-140℃范围内的最佳蒸发温度都为140℃,且4种工质中R141b的有机朗肯循环系统各设备的火用效率、系统总的火用效率、热效率、净输出功最大,火用损失最少,所以R141b为该系统的最适合工质,R123、R600和R245fa依次次之。以系统总火用损失、热效率、火用效率和净输出功为评价指标,采用层次分析法(The Analytic Hierarchy Process,AHP),通过熵值法确定权重因子,得到R600和R245fa的综合评价指标ξ,发现R600比R245fa更优。     

喷射器性能及太阳能喷射制冷系统工质的优化

考虑实际流体热力学性质、混合效率和激波等因素,建立了喷射器热力学模型,计算结果与文献中实验数据吻合很好。文中计算了采用环境友好工质R134a、R152a、R717、R290、R600a时喷射系数及喷射制冷系统性能系数。结果表明,对于确定几何参数的喷射器,喷射系数和喷射制冷系统性能系数主要取决于膨胀比与压缩比,两者分别随膨胀比的增加而增大,压缩比的增加而减小。太阳能驱动喷射制冷系统时(发生温度在80℃左右),采用R134a可以使喷射系数和喷射制冷系统能效比最大,明显优于其他工质。     

低温地热有机朗肯循环(ORC)工质选择

对低温(60～150℃)地热有机朗肯循环(ORC)系统,以净输出电功和系统能量损失作为评价指标,分析不同地热流体温度下有机工质R290,R134a,R600a,R600,R601a的做功能力,确定最佳循环工质.分析结果表明:对于湿流体工质,由于临界温度较低,当地热流体温度高于其临界温度20℃时,不存在最佳蒸发温度:对于60～80℃的地热流体,工质R601a的最大净输出电功最大;对于90～120℃的地热流体,工质R134a的最大净输出电功最大;对于125～150℃的地热流体,工质R290的净输出电功最大.这些结果为中低温地热利用提供设计依据.     

太阳能超临界有机朗肯循环的工质选择和性能分析

选取R123、R134a、R152a、R22和R245fa 5种有机工质作为候选工质进行太阳能超临界有机朗肯循环的计算和分析。结果表明:当膨胀机出口工质过热度一定时,太阳能超临界有机朗肯循环的热效率高于亚临界工况,且R123在系统热效率方面表现出比其他工质更加明显的优势,是一种较理想的有机工质。以R123为例,蒸发器出口温度一定时,随着蒸发压力的升高,有机朗肯循环的工质流量不断增大。蒸发压力一定时,随着蒸发器出口温度的升高,工质流量不断减小,循环热效率先增后减,存在一个最佳的蒸发器出口温度,此时循环热效率最大。     

R1234yf/R152a用作汽车空调制冷剂的配比范围研究

使用PR方程结合vdW法则建立了R1234yf/R152a的热物性模型,在此基础上结合余函数法编制了R1234yf/R152a的热力性质和制冷系统循环性能计算程序。在汽车空调制冷工况下,获得了R1234yf/R152a在不同摩尔组分比下的压力比、排气温度、COP、单位质量制冷量、单位体积制冷量和压缩机吸气口比容,并与R134a和R1234yf/R134a(0.89/0.11)进行了比较。之后,结合燃烧速度、GWP与循环性能获得了适宜的摩尔组分比范围。当R1234yf的液相摩尔分数在0.65～0.67时,R1234yf/R152a为近共沸混合物,具有较高的安全性,且制冷循环性能与R134a较为接近。     

Comparative assessment of environment-friendly alternatives to R134a in domestic refrigerators

In the present work, the possibility of using R152a and hydrocarbon refrigerants (such as R290, R1270, R600a, and R600) as alternatives to R134a in domestic refrigerators has been assessed theoretically. The refrigerants are assessed over wider range condensing and evaporator temperatures. The assessment was done with standard parameters such as pressure ratio, volumetric cooling capacity (VCC), coefficient of performance (COP), compressor input power, compressor discharge temperature, and total equivalent warming impact (TEWI). The results obtained showed that pure hydrocarbon refrigerants are not suitable to be used as alternatives to R134a due to its mismatch in VCC. R152a has approximately the same VCC with about 9% higher COP and lower values of operating pressure and compressor input power. The discharge temperature of R152a was higher than that of R134a by about 14–26 K. TEWI of R152a was about 7% lower than that of R134a. The reported results proved that R152a is an energy-efficient and environment-friendly alternative to phase out R134a in domestic refrigerators.     

Estimation of viscosity and thermal conductivity of R142b and R152a

In this paper the viscosity and thermal conductivity of both the liquid and vapour for the refrigerants R152a and R142b have been estimated and presented. Available properties of liquid thermal conductivity of R142b and R152a and the liquid viscosity of R152a are compared with the estimated values. It is found that the agreement is good. Transport properties of R142b, which is a potential replacement for R114 in medium temperature heat pump applications, is compared with that of R114. Also, the properties of R152a, which is considered as a possible replacement of R12 in refrigeration and low-temperature heat pump applications, is compared with the properties of the other possible replacement of R134a.     

A performance comparison of vapour-compression refrigeration system using various alternative refrigerants

A theoretical performance study on a traditional vapour-compression refrigeration system with refrigerant mixtures based on HFC134a, HFC152a, HFC32, HC290, HC1270, HC600, and HC600a was done for various ratios and their results are compared with CFC12, CFC22, and HFC134a as possible alternative replacements. In spite of the HC refrigerants' highly flammable characteristics, they are used in many applications, with attention being paid to the safety of the leakage from the system, as other refrigerants in recent years are not related with any effect on the depletion of the ozone layer and increase in global warming. Theoretical results showed that all of the alternative refrigerants investigated in the analysis have a slightly lower performance coefficient (COP) than CFC12, CFC22, and HFC134a for the condensation temperature of 50 °C and evaporating temperatures ranging between − 30 °C and 10 °C. Refrigerant blends of HC290/HC600a (40/60 by wt.%) instead of CFC12 and HC290/HC1270 (20/80 by wt.%) instead of CFC22 are found to be replacement refrigerants among other alternatives in this paper as a result of the analysis. The effects of the main parameters of performance analysis such as refrigerant type, degree of subcooling, and superheating on the refrigerating effect, coefficient of performance and volumetric refrigeration capacity are also investigated for various evaporating temperatures.     

A comparative study of water as a refrigerant with some current refrigerants

Water as a refrigerant (R718) is compared with some current natural (R717 and R290) and synthetic refrigerants (R134a, R12, R22, and R152a) regarding environmental issues including ozone depletion potential (ODP) and global warming potential (GWP), safety (toxicity and flammability), operating cost, refrigeration capacity and coefficient of performance (COP). A computer code simulating a simple vapour compression cycle was developed to calculate COPs, pressure ratios, outlet temperatures of the refrigerants from the compressor, and evaporator temperatures above which water theoretically yields better COPs than the other refrigerants investigated. The main difference of this study from other similar studies is that both evaporator temperature and condenser temperature are changed as changing parameters, but the temperature lift, which is the temperature difference between condenser and evaporator, are held constant and the irreversibility during the compression process is also taken into consideration by taking the isentropic efficiency different from 100%. It is found that for evaporator temperatures above 20°C and small temperature lift (5 K), R718 gives the highest COP assuming exactly the same cycle parameters. For medium temperature lifts (20–25 K), this evaporator temperature is above 35°C, whereas for even greater temperature lifts it decreases again. Furthermore, with increased values of polytropic efficiency, R718 can maintain higher COPs over other refrigerants, at lower evaporator temperatures. Copyright © 2005 John Wiley & Sons, Ltd.     

气液两相流动及沸腾传热流体模化分析

基于制冷剂类物质热物性表与水和水蒸气热力性质图表,计算并比较了R12、R22、R123、R134a在相同气液密度比条件下模化水热力过程的能力;应用相似原理与量纲理论分析了流体模化方法在研究气液两相流动特性、高温高压传热过程、临界热流密度现象以及近临界和超临界传热方面的优势与方法.结果表明:制冷剂类物质具有良好的热力性质,其中R134a在相同气液密度比条件下的压力值仅约为水的1/5,而且其臭氧消耗潜能值为0,是环境友好的理想模化流体.提出并探讨了从本质上革新准则数以及基于模型探索新的模化条件和发展新的准则关系式的流体模化技术发展思路.     

基于模糊层次分析法的制冷剂选择

制冷剂选择是复叠式热泵研究的一个重要方向。在分析模糊、灰色关联在制冷空调领域应用及复叠式热泵制冷剂选择研究现状基础上,采用模糊层次分析法构建了包括安全性、热力性能、环保性能、成本和热物性5个方面共27个指标组成的制冷剂评价指标体系,建立制冷剂性能综合评价模型,利用该模型在47种纯工质范围内为复叠式热泵选择合适的工质。结果表明,综合性能较好的制冷剂组合为R134a/R601a、R134a/R601、R1234yf/R236ea等。     

Effect of saturation‐temperature on the performance of a vapour‐compression refrigeration‐cycle working on different refrigerants using exergy method

In this study, the behaviour of a vapour‐compression refrigeration cycle, for different refrigerants such as NH₃, R‐12, R‐22 and HFC‐134a was investigated using the exergy method. The cooling load of the plant and the saturation‐temperature of the cold chamber were held constant, whereas the saturation‐temperatures of the evaporator and the condenser were varied from 303 to 313 K and 258 to 248 K, respectively. The irreversibility rates (or exergy destruction rates) of sub‐regions for the whole cycle, using energy and exergy analysis, were determined for each refrigerant. The effects of changes in the saturation‐temperature in the condenser and evaporator on the irreversibility rate of the cycle were obtained for each refrigerant. The relations between the total irreversibility rate of the plant and the irreversibility rate of the condenser and the evaporator were determined for different values of saturation temperatures of the condenser and the evaporator. The COP of the cycle and the rational efficiency were determined for each of the refrigerants and compared with each other. Among the refrigerants used, R‐12 was found to be the most economical refrigerant as compared with the others. Copyright © 2005 John Wiley & Sons, Ltd.     

Investigation of refrigerating system with R12 refrigerant replacements

This paper deals with the influence of R12 working fluid replacements on energy efficiency and global warming expressed by values of Coefficient of Performance (COP) and Total Equivalent Warming Impact (TEWI). Experimental investigations are presented which relate the use of refrigerants R134a, R401A, R409A, R22 and the mixture of R134a with R12 to the values of COP and TEWI of refrigerating system in comparison with R12 application. It is shown that the use of R134a, R401A and R409A refrigerants enables the increase of COP coefficient and significantly reduces the value of TEWI in comparison with R12 application.     

过冷度对蒸气压缩式制冷循环性能的影响分析

在蒸气压缩式制冷循环中,存在高压液体的过冷现象。过冷液体温度与其饱和温度之间的差值称为过冷度。液体过冷可明显提高一些制冷剂的单位质量制冷量和性能系数。本文运用热力学定律,对多种常用工质的蒸气压缩式制冷循环进行了理论分析,并计算了在不同的过冷度下,循环的制冷量、性能系数等参数与蒸发温度、冷凝器出口温度的关系,得出了不同工质在不同过冷度下的表现等规律和结论,为制冷设备循环方式和制冷工质的选择提供一些参考。     

Experimental study of R152a and R32 to replace R134a in a domestic refrigerator

This paper presents an experimental study of R152a and R32, environment-friendly refrigerants with zero ozone depletion potential (ODP) and low global warming potential (GWP), to replace R134a in domestic refrigerator. A refrigerator designed and developed to work with R134a was tested, and its performance using R152a and R32 was evaluated and compared with its performance when R134a was used. The results obtained showed that the design temperature and pull-down time set by International Standard Organisation (ISO) for small refrigerator were achieved earlier using refrigerant R152a and R134a than using R32. The average coefficient of performance (COP) obtained using R152a is 4.7% higher than that of R134a while average COP of R32 is 8.5% lower than that of R134a. The system consumed less energy when R152a was used. The performance of R152a in the domestic refrigerator was constantly better than those of R134a and R32 throughout all the operating conditions, which shows that R152a can be used as replacement for R134a in domestic refrigerator.