基于低品位余热驱动的正逆耦合空调系统性能分析

针对低品位余热的利用,将有机朗肯系统与复叠式制冷系统耦合,建立了热力学模型;采用R141b作为朗肯循环系统制冷工质,分别采用R22/R23、R404A/R23、R290/R744、R717/R744四种工质对作为复叠式制冷系统高低温级循环的制冷工质;基于EES软件编写了循环性能计算程序,研究了低温级冷凝温度T_(10)、低温级蒸发温度T_e、蒸发冷凝传热温差ΔT对系统性能COPs以及高低温级质量流量比G的影响,并以COPs与G为评价指标选出最佳工质。结果表明系统的COPs会随着低温级冷凝温度的升高而先增大后减小,并存在一个最佳值;系统COPs随着低温级蒸发温度的升高而增大,随着蒸发冷凝传热温差的增大而减小;高低温级质量流量比随着低温级冷凝温度的增大而减小;R717/R744最适合作为有机朗肯-复叠制冷系统复叠制冷部分工质。     

中温地热能驱动的有机朗肯-复叠式制冷系统性能分析

针对中温地热能的利用,建立了有机朗肯-复叠式制冷系统的热力学模型,其中高温部分分别采用R245fa,R600a,R141b做工质,低温部分利用R744做工质。通过热力学模拟计算,分析了该系统性能系数COPs在低温级冷凝温度、高温级冷凝温度、低温级蒸发温度改变时的变化规律,并以系统性能系数COPs及高低温级质量流量比G作为评价指标,优选出最佳工质。分析表明:系统存在一个最佳低温级冷凝温度,使系统性能系数COPs最大;在一定运行工况下,系统的COPs随着蒸发冷凝器传热温差的加大而逐渐减小,随着高温级冷凝温度的升高而降低,随着低温级蒸发温度的升高而增高;高低温级质量流量比G随着低温级蒸发温度的升高而逐渐降低。为提高系统性能和保证系统的安全运行,应尽可能提高低温级蒸发温度、降低高温级冷凝温度和减小蒸发冷凝器传热温差。综合比较,以R141b/R744为工质的有机朗肯-复叠式制冷循环具有很好的发展前景。     

CO2为低温循环工质的复叠式制冷系统的分析比较

通过对NH3/CO2、R290/CO2和R404A/CO2三种复叠式制冷系统的COP、最优低温循环冷凝温度和最佳质量流量比等进行理论分析及性能比较,得出在一定的蒸发温度、冷凝温度和冷凝蒸发器传热温差下,三种复叠式制冷系统的COP都随着低温循环冷凝温度的升高呈现出先增大后减少的趋势,其中NH3/CO2复叠式制冷系统的COP最大;三种复叠式制冷系统的最佳低温循环冷凝温度和最佳质量流量比都随着蒸发温度的升高而升高,其中R404A/CO2复叠式制冷系统的最佳低温循环冷凝温度最高,NH3/CO2复叠式制冷系统的最佳质量流量比最大。     

自然工质复叠式制冷热泵系统的性能分析

介绍了以自然工质CO2为高温循环工质,R290为低温循环工质,同时制冷和供热的CO2/R290复叠式制冷热泵系统,通过对CO2/R290复叠式制冷热泵系统的性能分析,得到了气体冷却器的入口压力和出口温度,复叠式循环的蒸发温度,低温循环的冷凝温度对复叠式制冷热泵系统性能的影响,为今后的CO2/R290复叠式制冷热泵系统的优化设计和开发应用打下了一定的基础。     

微型压缩机驱动的单级与自复叠耦合系统的实验研究

搭建了微型压缩机驱动的单级与自复叠耦合系统的实验台,以单级制冷系统对自复叠系统进行预冷的方式获得更低的蒸发温度。高温级工质选用R404A,低温级工质选用R290/R170/R14组成的混合工质(充注质量比为0.33/0.17/0.50),在25℃环境温度,获得了系统的运行特性以及环境温度和高温级预冷温度对系统性能的影响。研究表明:在157 min的降温时间内,蒸发器进口温度达到-112℃,出口温度达到-111℃并保持稳定;环境温度从15℃升高到32℃,系统所能达到的最低温度由-116.68℃升高到-95.31℃;高温级预冷温度从-27℃降低到-37℃,系统蒸发器进口温度由-91.18℃降低到-112.7℃。     

微型压缩机驱动的单级与自复耦合系统的实验研究

搭建了微型压缩机驱动的单级与自复叠耦合系统的实验台，以单级制冷系统对自复叠系统进行预冷的方式获得更低的蒸发温度。高温级工质选用R404A，低温级工质选用R290/R170/R14组成的混合工质(充注质量比为0.33/0.17/0.50),在25 ℃环境温度，获得了系统的运行特性以及环境温度和高温级预冷温度对系统性能的影响。研究表明:在157 min的降温时间内，蒸发器进口温度达到-112 ℃，出口温度达到-111 ℃并保持稳定；环境温度从15 ℃升高到32 ℃，系统所能达到的最低温度由-116.68 ℃升高到-95.31 ℃；高温级预冷温度从-27 ℃降低到-37 ℃，系统蒸发器进口温度由-91.18 ℃降低到-112.7 ℃。     

三级复叠式制冷系统低温级制冷剂的应用分析

为研究三级复叠制冷系统中低温循环制冷剂替代的可行性方案,采用R1150/R170/R717、R50/R170/R717和R14/R170/R717三种工质组合,对三级复叠式制冷系统的高低温循环压缩机的排气温度、压缩机输入功率、COP、热力学完善度、系统的■效率、■损失以及系统中各个部件■损失所占比例随蒸发温度的变化进行热力学分析。研究结果表明:不同蒸发温度下均存在最佳中间循环冷凝温度,使COP值最大。蒸发温度由-100.0℃升高到-80.0℃时,R1150/R170/R717的■损失最小,COP、热力学完善度和■效率最大。R1150/R170/R717的COP由0.60增大到0.82。R1150/R170/R717的COP比R14/R170/R717的COP高3.47%～4.49%。主要的■损失部件是冷凝器,冷凝器的■损失所占比例随蒸发温度的升高而升高。推荐在三级复叠式制冷系统中采用R1150/R170/R717制冷剂组合方案,研究结果为三级复叠式制冷系统工质组的选择提供理论依据。     

海洋温差发电系统热力学及热经济性分析

以热力学基本原理为基础,建立了海洋温差发电系统仿真模型,对比分析了亚临界状态下R717、R134a和R600三种工质系统在约束蒸发器窄点温差条件下优化目标函数随蒸发温度的变化规律。结果表明:蒸发温度越高,不同系统换热器的热负荷以及冷、热海水泵功率越小,最佳蒸发压力和工质泵功率越大;不同系统的热效率和单位换热面积输出电量与蒸发温度的相关性较大,随蒸发温度的增加近似线性递增。蒸发器的换热面积与循环工质种类的相关性较小,但冷凝器的换热面积与循环工质种类的相关性较大。R717循环更接近于卡诺循环,R717的系统热效率最大,热负荷及泵功率最小,且其热经济性目标函数值在合适的范围内,是海洋温差发电系统较为理想的循环工质。研究结果可为海洋温差发电系统的设计、试验及设备选型提供理论参考。     

R404A在低温空气源热泵中替代传统工质的性能研究

基于制冷剂物性软件Cool Pack,通过计算对R404A、R22、R407C、R410A在螺杆式单级压缩热泵系统理论循环中的制热量、排气温度、压缩比、压缩机功耗、COP、质量流量进行了对比分析,系统工况设定为冷凝温度50℃,蒸发温度在-40~10℃范围内变化。计算结果表明:R404A作为低温空气源热泵系统的工质具有稳定的低温适应性。     

非共沸混合工质应用于复叠式高温热泵系统低温回路的试验研究

为研究不同滑移温度的混合工质应用于复叠式热泵系统低温回路对热泵机组性能的影响,搭建复叠式高温热泵实验台,选用R245fa与R134a/R245fa(质量比分别为9:1、8:2、7:3、6:4)作为高温、低温级循环工质,蒸发器进水温度在20～40℃,冷凝器出水温度在110～130℃的情况下进行试验,并对机组的COP、制热...     

Cycle performance study on R32/R125/R161 as an alternative refrigerant to R407C

This paper presents the new ternary non-azeotropic mixture of R32/R125/R161 as an alternative refrigerant to R407C. The physical properties of the ternary mixture are similar to those of R407C, and it is environmental friendly, that is, it has zero ozone-depletion potentials (ODP) and lower global warming potentials (GWP) than R407C. Theoretical cycle performances of R32/R125/R161 and R407C are calculated and analyzed firstly. Based on the theoretical study, experimental tests are performed on a vapor-compression refrigeration system with a rotor compressor which was originally designed for R407C (without any modifications to system components for R407C). Experimental results under different working conditions indicate that the pressure ratio and power consumption of the new refrigerant are lower than those of R407C, and its refrigerating capacity and coefficient of performance (COP) are superior to those of R407C, respectively, and its discharge temperature is slightly higher than that of R407C. Therefore, the new refrigerant R32/R125/R161 could be considered as a promising refrigerant to R407C.     

On blends R32/R134a and R32/R125: Thermodynamic and heat transfer aspects

In this paper the author develops an algorithm on the basis of heat and thermodynamics theory, to predict data for film condensation on horizontal integral—fin tubes for R32/R134a and R32/R125 mixtures in 25/75, 50/50 per cent compositions by mass correspondingly. Emphasis is focused on the presentation of thermophysical properties of the blends involved in the process considered, i.e. liquid density, viscosity, surface tension, thermal conductivity and latent heat of vaporization. The main point of this work is to define with computational techniques the blend with the most favourable composition, as an environmentally acceptable solution for R22 replacement in some shell‐side condensers. Copyright © 2001 John Wiley & Sons, Ltd.     

Prediction of the condensation and boiling characteristics of R12 substitutes R22/r152a/R114 and R22/R152a/R124 inside enhanced-surface tubing

In this paper, the heat-transfer behaviour of two ternary refrigerant blends proposed as an R12 substitute, has been studied during condensation and boiling inside horizontal enhanced surface tubing. Correlations are proposed to predict the average heat transfer coefficients as well as pressure drops of newly proposed ternary refrigerant blends flow, inside enhanced surface tubing.     

Ozone friendly binary blends R 32/R 134a and the ternary R 407b

The objective of this paper is to present thermodynamic properties and characteristics of the binary refrigerant mixtures R 32/R 134a in compositions 20/80%, 30/70%, 40/60% by mass and of the ternary mixture R 407b: 10 wt% R 32+70 wt% R 125+20 wt% R 134a. A computer code has been developed and by use of a Peng–Robinson type equation of state, PVT data for all working fluids are determined. Based on the thermodynamics theory, analytical relationships for the enthalpy, entropy, constant pressure and constant volume specific heats as well as for k-type isentropic change exponents are given. Furthermore, comparisons are provided by means of diagrams illustrating the influence of state conditions on the k-type exponents k_p,V, k_T,V, k_p,T, and classical k (k=c_P/c_V). A systematic study has also been carried out and the data obtained are plotted for a better physical feeling related to the sound velocity of real gas for the R 32/R 134a blend in composition 20/80%. The results are compared with corresponding ones of the ternary R 407b.     

R6 and R5 procedures: The way forward

This paper first briefly summarises the existing methods in the low-temperature fracture assessment procedure, R6, and the high-temperature procedure, R5, for treating the effects of secondary stresses on structural integrity. Recently, there have been a number of developments, which identify the way forward for these procedures. A modified J-integral definition has been derived, which is path independent for cases of proportional and non-proportional loading and is ideal for evaluating the crack driving force for defects in secondary and residual stress fields. Results of finite element analysis are presented that show that the use of the modified J-integral can lead to a lower crack driving force for secondary stresses than current simplified R6 methods. More detailed calculations have assessed the effects on fracture of a slowly growing crack and constraint effects associated with secondary stresses. Preliminary results are presented, showing the long-term potential of more advanced methods in providing significant benefits in structural integrity assessments. For high-temperature applications, the paper presents methods for calculating the relaxation of secondary stresses due to both creep strain and creep crack growth, extending current methods in R5 that only allow for relaxation due to creep strain. Related work addressing the combined effects of plasticity and creep on relaxation of the crack tip fields is also presented and the results are illustrated for a typical geometry and loading.     

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.     

混合工质R134a/R23替代R22的可行性研究

叙述了基于新型环保型混合制冷剂R134a/R23替代制冷剂R22的问题,以及通过REFPROP7.5,对混合工质R134a/R23从物性和热力学特性进行的理论计算分析,指出,由质量分数为70%的R134a和质量分数为30%的R23组成的混合制冷剂与R22性能最为接近,在变工况运行条件下,其COP值比R22高8%左右,其冷凝压力比同条件下用R22作为循环工质低21%～36%,理论上完全具有替代R22的可能性。     

含R227ea的混合制冷剂替代R22研究

由于R410，R407系列混合制冷剂在替代R22方面的不足，更多新型的制冷剂列入了研究。R227ea具有良好的环境性能，最典型的特点是具有很好的阻燃性。文章对含R227ea各种混合物进行了理论计算和比较，并对其安全性进行了分析。计算结果表明，混合物R32／R134a／R227ea及R32／R125／R227ea不论是COP还是Qv值，都能和R22相匹配，而且优于R410A的最大特点是其冷凝压力大大降低，甚至低于R22，非常有利于原装置替代。     

The performance of a triple pressure level absorption cycle (TPLAC) with working fluids based on the absorbent DMEU and the refrigerants R22, R32, R124, R125, R134a and R152a

This paper compares the performance of a single-stage triple pressure level (TPL) absorption cycle with different refrigerant–absorbent pairs. Four HFC refrigerants namely: R32, R125, R134a and R152a which are alternative to HCFC, such as R22 and R124, in combination with the absorbent dimethylethylenurea (DMEU) were considered. The highest coefficient of performance (COP) and the lowest circulation ratio (f), were found as a function of the generator temperature for a given evaporating and cooling water temperatures. The sensitivity of the COP and f for evaporator and cooling water temperatures changes at the maximum COP for the best three working fluids were also examined. It was obtained that the preferable pair is R124–DMEU and among working fluids based on HFC the preferable pair is the R125–DMEU.