Thermodynamic Analysis and Comparison on Low Temperature CO_2-NH_3 Cascade Refrigeration Cycle

Intheapplicationsofindustrialandcommercialrefrig erationsystem ,iftherequiredrefrigerationtemperatureisverylow ,theconventionalvaporcompressionsystemisdiffi culttomeettherequirementbecausewhenthedifferencebe tweentheevaporatingtemperatureandthecondensingtemper atureissohighthatitishardtofindarefrigeranttomeettheneedsasthecondensingpressureisnottoohighandtheevap oratingpressureisnottoolow .Whentherefrigeratingtemper atureisverylow ,thecascaderefrigerationcycleissuitabletobeused .Itcannotonlysat…     

基于循环模拟模型的二氧化碳循环效能分析

针对二氧化碳热泵性能改进问题,设计了一个基于循环模拟模型开展仿真模拟研究。通过改变该模型的输入参数和运行条件,研究模型的最佳工作条件及性能提高的途径。提出了采用中间冷却器的双级压缩机和带有膨胀箱的双级压缩机的工作模型,并对该模型进行仿真测试,结果表明最多可以比传统的工作系统提高跨临界二氧化碳循环20%的加热性能和28%的制冷性能。     

天然制冷剂CO2是21世纪汽车空调的首选

在汽车空调中，具有对环境友好性和优良的热物理特性的天然工质CO2与其他制冷剂相比有独特优势。近年来，美国、欧洲和日本等发达国家和地区的研究者们不断尝试将CO2应用于各种可能的制冷、空调和热泵系统，本文从制冷剂的替代、跨临界循环以及汽车空调特点上阐明无毒、不可燃的二氧化碳制冷剂将是下一代汽车空调的首选。     

二氧化碳低温制冷循环分析

对两种不同的二氧化碳双级压缩低温制冷循环进行了分析．得到在一定的蒸发温度和冷却器出口温度下．一次节流不完全中间冷却二氧化碳双级压缩循环COP较大、最优冷却压力较低、具有良好的发展前景。     

Experimental evaluation of the effect of an internal heat exchanger on a transcritical CO2 ejector system

This study presents experimental results focused on a performance comparison of a transcritical CO₂ ejector system without an internal heat exchanger (IHX) (EJE-S) to a transcritical CO₂ ejector system with an IHX (EJE-IHX-S). The comparison includes the effects of changes in operating conditions such as cooling water flow rate and inlet temperature. Experiments are conducted to assess the influence of the IHX on the heating coefficient of performance (COP_r), heating capacity, entrainment ratio, pressure lift, and other parameters. The primary flow rate of the EJE-IHX-S is higher than that of the EJE-S. The pressure lift and actual ejector work recovery are reduced when the IHX is added to the transcritical CO₂ ejector system. Using a more practical performance calculation, the compression ratio in the EJE-S is reduced by 10.0%–12.1%, while that of EJE-IHX-S is reduced only by 5.6%–6.7% compared to that of a conventional transcritical CO₂ system. Experimental results are used to validate the findings that the IHX weakens the contribution of the ejector to the system performance.     

Simulation of CO2 Brayton Cycle for Engine Exhaust Heat Recovery under Various Operating Loads

A bottoming cycle system based on CO2 Brayton cycle is proposed to recover the engine exhaust heat. Its performance is compared with the conventional air Brayton cycle under five typical engine conditions. The results show that CO2 Brayton cycle proves to be superior to the air Brayton cycle in terms of the system net output power, thermal efficiency and recovery efficiency. In most cases, the recovery efficiency of CO2 Brayton cycle can be higher than 9% and the system has a better performance at the engine’s high operating load. The thermal efficiency can be as large as 24.83% under 100% operating load, accordingly, the net output power of 14.86 kW is obtained.     

Thermodynamic Comparison Analysis on CO2 Transcritical Reverse Cycles with IHX or Expander

Attheendoftheyear2000,annualglobalfluo rocarbonrefrigerantemissionfrommobileandunitaryairconditioningequipmentsislikelytosurpass100000tons,correspondingtoaglobalwarmingim pactofmorethan150milliontonsofCO2.Evenlar gerindirectCO2emissionresultsfromthegeneration ofpowerconsumedtodrivethesystems[1].Within creasingfocusongreenhousegasemissionreductions,strictregulationsontheuseofsynthesizedrefrigerants suchasHCFCsandHFCsmaybeexpected,possiblyfollowedbyphase outtargetsanddates.Theinterna tionale…     

循环流化床烟气综合治理工程实例

介绍了20t/h流化床锅炉麻石脱硫除尘系统及其废水净化处理系统。用造纸黑液作为脱硫剂。采用自然蒸发法对除尘废水沉淀处理系统进行了局部地改进。结果表明，该处理工艺简单实用，运行成本低，效果良好。     

Refrigerants for vapour compression refrigeration systems

With the mandate of Montreal Protocol banning ozone depleting substances, and Kyoto Protocol later on curtailing the use of substances which contribute to global warming, conventional refrigerants are to be replaced by environment-friendly working fluids. Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are being substituted by hydrofluorocarbons (HFCs), hydrofluorooelifins (HFOs), and a variety of mixtures. In view of the global warming potential of these newly synthesized refrigerants, the recent trend is to go back to the originally used natural fluids such as ammonia, carbon dioxide, hydrocarbons, water vapour, etc. In this article, various issues related to this changeover of refrigerants being used in vapour compression refrigeration systems are discussed.     

Configuration Consideration for Expander in Transcritical Carbon Dioxide Two-Stage Compression Cycle

To investigate the configuration consideration of expander in transcritical carbon dioxide two-stage compression cycle, the best place in the cycle should be searched for to reinvest the recovery work so as to improve the system efficiency. The expander and the compressor are connected to the same shaft and integrated into one unit, with the latter being driven by the former,thus the transfer loss and leakage loss can be decreased greatly. In these systems, the expander can be either connected with the first stage compressor ( shortened as DCDL cycle) or the second stage compressor ( shortened as DCDH cycle), but the two configuration ways can get different performances. By setting up theoretical model for two kinds of expander configuration ways in the transcritical carbon dioxide two-stage compression cycle, the first and the second laws of thermodynamics are used to analyze the coefficient of performance, exergy efficiency, inter-stage pressure,discharge temperature and exergy losses of each component for the two cycles. From the model results, the performance of DCDH cycle is better than that of DCDL cycle. The analysis results are indispensable to providing a theoretical basis for practical design and operating.     

Performance of a single-stage auto-cascade refrigerator operating with a rectifying column at the temperature level of-60 ℃

This paper proposes a new approach to the performance optimization of an auto-cascade refrigerator (ACR) operating with a rectifying column and six types of binary refrigerants (R23/R134a, R23/R227ea, R23/R236fa, R170/R290, R170/R600a, and R170/R600) at a temperature level of −60 °C. Half of the six binary refrigerants are nonflammable, of which the 0.5 and the 0.6 mole fractions of R23 for the R23/R236fa possess the most prospective composition for the medium and low suction pressure compressors, respectively. The remaining three binary refrigerants are flammable but with low global warming potentials, of which the 0.6 mole fraction of R170 for the R170/R600 is the most prospective one. The results show that the overall matching as well as local matching of heat capacity rates of hot and cold refrigerants in the recuperators are important for the improvement of coefficient of performance of the cycle, which can be adjusted through the simultaneous optimization of the pressure level and composition. The new approach proposed also offers a wider range of applications to the optimization in performance of the cycle using multi-component refrigerants.     

氨水吸收/压缩复合制冷循环性能分析(英文)

针对氨水吸收/压缩复合制冷循环的方式不同,结合Schulz氨水溶液状态方程,分别对压缩机处于系统高压区和低压区2种不同的组合方式进行了理论分析计算.分析了在给定中间压力下,蒸发温度Te、热源温度Th和冷却水温度Tw对2种组合方式下压缩机当量热耗量qCW、热源耗热量qG和循环性能系数COP的影响.结果表明:压缩机当量热耗量对循环性能系数的影响要低于热源耗热量的影响;压缩机处于系统高压区时循环的一次用能量要明显高于压缩机处于系统的低压区;压缩机处于系统低压区时循环性能要优于压缩机处于系统的高压区.当中间压力给定时,存在一个最佳热源温度,使得氨水吸收/压缩复合制冷循环的性能系数取得最大值.     

Experimental investigation of an adjustable ejector for CO2 heat pump water heaters

An adjustable ejector expansion device for a CO2 heat pump water heater （HPWP） is proposed to improve the system performance. It has been designed to investigate experimentally the effects of the motive nozzle throat area of the ejector, entrained flow pressure, back pressure and primary flow pressure on the entrainment ratio. Experiments based on different motive nozzle throat areas were conducted and the results of the prototype ejector using CO2 as working fluid are presented. The results show that an adjustable ejector can achieve high performance and work well in a wide range of working conditions.     

图的直接和的Hamilton圈研究

本文定义了图的直接和的概念,讨论了图的直接和中Hamilton圈的存在性。当图本身存在Hamilton圈时,它的直接和中的Hamilton圈也存在;设图G是n阶图,如果它的极大Hamilton子圈与Cn-1同构,那么它的直接和存在Hamilton圈;本文还研究了极大Hamilton子圈同构于Cn-2的n阶图并得到了三个充分条件。本文最后用超立方体Q4为例展示了这些命题的应用。     

Performance of a single-stage Linde-Hampson refrigerator operating with binary refrigerants at the temperature level of-60 ℃＊

The optimization of the performance of a single-stage Linde-Hampson refrigerator （LHR） operating with six different binary refrigerants （R23/R134a, R23/R227ea, R23/R236ea, R170/R290, R170/R600a and R170/R600） with ozone depletion potentials （ODPs） of zero was conducted using a new approach at the temperature level of-60℃. Among these binary refrig- erants, the 0.55 and the 0.6 mole fractions of R23 for R23/R236ea are the most prospective nonflammable ones for the medium and low suction pressure compressors, respectively. For these two kinds of compressors, the 0.6 and the 0.65 mole fractions of R170 for R 170/R600, respectively, are the most prospective binary refrigerants with low global warming potentials （GWPs）. The results of optimization of pressure levels indicate that the optimum low pressure value for coefficients of performance （COP） is achieved when the minimum temperature differences occur at both the hot and the cold ends of the recuperator at a specified composition and pressure ratio. Two useful new parameters, the entropy production per unit heat recuperated and the ratio of heat recuperating capacity to the power consumption of the compression, were introduced to analyze the exergy loss ratio in the recuperator. The new approach employed in this paper also suggests a promising application even to the optimization of the performance with multi-component refrigerants.     

Numerical study of PV/T-SAHP system

In order to utilize solar energy effectively and to achieve a higher electrical efficiency by limiting the operating temperature of the photovoltaic （PV） panel, a novel photovoltaic/thermal solar-assisted heat pump （PV/T-SAHP） system was proposed and constructed. The hybrid solar system generates electricity and thermal energy simultaneously. A distributed parameters model of the PWT-SAHP system was developed and applied to analyze the system dynamic performance in terms of PV action, photothermal action and Rankine cycle processes. The simulation results indicated that the coefficient of performance （COP） of the proposed PV/T-SAHP can be much better than that of the conventional heat pump. Both PV-efficiency and photothermic efficiency have been improved considerably. The results also showed that the performance of this PV/T-SAHP system was strongly influenced by the evaporator area, tube pitch and tilt angle of the PV/T evaporator, which are the key factors in PV/T-SAHP system optimization and PV/T evaporator design.     

双元非共沸制冷剂在喷射制冷中应用的可能性(英文)

分析了双元非共沸制冷剂在喷射制冷中应用的可能性．使用相平衡关联式和ＰＲ状态方程完成了两种混合工质对（Ｒ３０／Ｒ１４２ｂ,Ｒ３０／Ｒ１２４）的热力循环性能计算,对计算结果进行了分析讨论．理论计算表明,实施双元工质在低温域的蒸发可提高制冷品质,而喷射器可压缩双相流介质的特点保证了这种循环的正常运行．     

蒸发制冷系统的冷凝和蒸发过程性能分析

双级复叠蒸汽压缩制冷系统在不同条件下工作性能相差较大,为了提高蒸发制冷系统的制冷效率,在对蒸发制冷系统的冷凝和蒸发过程性能进行详细分析的基础上,研究了双级复叠蒸汽压缩制冷系统的热力理论关系式,并结合制冷系统的工作过程,给出了主要参数的计算关系式。然后再对双级复叠蒸汽压缩制冷系统进行了实验测试与分析,得到了主要制冷参数之间的相互关系式。     

Needs of thermodynamic properties measurements and modeling in the frame of new regulations on refrigerants

In 1987, the Montreal Protocol prohibited the worldwide use and production of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) and hydro fluorocarbons (HFCs) were proposed as alternative refrigerants. Unfortunately, HFCs have non negligible global warning potential and therefore new refrigerants must be proposed or old refrigerants must be used associated with HFC. Accurate experimental thermodynamic data and predictive techniques are required for better under-standing of the performance of the newly proposed refrigerants. In this communication, experimental techniques based on either analytic or synthetic methods are first described. Data are reported. Then two newly developed predictive models based on thermodynamic approach with the isofugacity criterion and artificial neural network method are presented. The results can provide better evaluation of refrigerants, especially with the aim of studying global warning effects.     

基于废热的制冷循环系统研究与设计

针对废弃热量利用率低的问题,深入研究喷射制冷循环系统的工作原理和主要的内部结构,对喷射制冷循环系统的工作过程进行建模分析,得出系统中主要工作参数之间的数学关系。然后引入蒸汽压缩制冷原理,设计一个增压喷射制冷循环系统,对系统的性能特点进行详细分析,并给出在不同现实需求下的改进优化策略。测试结果表明设计的增压喷射制冷循环系统可以提高低品味的热量的利用率。