水产品低温贮藏库的节能分析

通过利用线性拟合的方法对氨的物性进行模拟,在变冷凝温度和变冷间温度,以及在蒸发器和冷凝器压力降变化的条件下,分别对冷库中的氨双级蒸汽压缩系统进行能量分析,对系统各部件的炯损失和系统的炯效率进行计算分析,得出随着冷凝温度和冷间温度的改变,系统各设备的炯损失的排序变化的结果,以及随着压力降的变化系统的性能发生了变化,提出改进系统的性能可从减少冷凝传热温差和减少冷间传热温差,提高冷却水有效利用,改善蒸发器的压力降方面考虑。     

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．     

Experimental investigation on R134a vapour ejector refrigeration system

The experimental investigation of the performance of a vapour ejector refrigeration system is described. The system uses R134a as working fluid and has a rated cooling capacity of 0.5 kW. The influence of generator, evaporator and condenser temperatures on the system performance is studied. This kind of system can be operated with low grade thermal energy such as solar energy, waste heat, etc. The operating conditions are chosen accordingly as, generator temperature between 338 K and 363 K, condenser temperature between 299 K and 310.5 K, and evaporator temperature between 275 K and 285.5 K. Six configurations of ejectors of different geometrical dimensions are selected for the parametric study. The performance of the refrigeration system at different operating temperatures is presented.     

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.     

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.     

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).     

The substitution of R134a with R744: An exergetic analysis based on experimental data

This paper deals with the problem of R314a substitution with a natural refrigerant fluid. A comparison is performed between R134a and R744 (CO₂). R134a is a hydrofluorocarbon with a large direct warming impact (GWP), whereas the R744 contribution is negligible. A comparative exergetic analysis, carried out with experimental tests, has been presented. This paper compares a commercial R134a refrigeration plant and a prototype R744 system working in a trans-critical cycle. Based on the experimental data an exergetic analysis has been carried out on the overall plant and on each device. The overall exergetic performances of the classical vapour compression plant working with R134a are consistently better than that of R744 (from a minimum of 20 to a maximum of 44%). The performance of the individual components of the plant has been analyzed, in order to pinpoint those contributing most to the decrease in the exergetic performance of R744.     

Thermodynamic performance of air conditioners working with R417A and R424A as alternatives to R22

The energy and exergy parameters of R417A and R424A gases which can be used instead of R22 were experimentally investigated for a split-type air conditioner. Although GWP amounts of the available alternative refrigerants are higher compared to R22, their ODP values are zero. The experiments were accomplished for three different ambient temperature values of 25 °C, 30 °C and 35 °C. The covered test conditions were carried out for steady-state case while keeping the inside medium temperature at constant temperature of 22 °C. The cooling capacity, COP, exergy destruction of components in the unit (i.e., compressor, condenser, evaporator, and expansion device), exergetic efficiency and some other parameters of the system were determined. COP values for the refrigerants of R417A and R424A were noted to be smaller compared to R22. Similarly, both isentropic efficiency of the compressor and exergetic efficiency of the system were higher for R22. The use of R424A will be more suitable rather than R417A since COP values of R417A are lower about 5–16% compared to R424A. The COP value of R22 is greater than that of R417A and R424A by amounts of 17–23% and 4–18%, respectively. At the greater evaporation temperatures (0 °C to +5 °C as in the air-conditioners) it can be stated that R424A is more preferable than R417A as an alternative refrigerant to R22.     

微通道换热器两相分配特性对空调系统性能的影响

微通道换热器作为新一代换热器逐渐被使用在家电领域,其结霜、除尘、排水、分液等都是目前亟待解决的问题。通过R22家用空调系统的标准性能实验台,对三种流程数不同的微通道换热器用作冷凝器和蒸发器时,温度分布均匀性和其对系统性能的影响进行实验,研究发现,微通道换热器在用作冷凝器和蒸发器时,温度分布不均对系统性能的影响分别达到7.3%和3.5%,并且流程数对于温度分布均匀性的影响在作为冷凝器和蒸发器时是不同的。     

Performance evaluation of a heat pump cycle using NARMs by a simulation with equations of heat transfer and pressure drop

Simulation analyses for a vapour compression heat pump cycle using nonazeotropic refrigerant mixtures (NARMs) of R22 and R114 are conducted under the condition that the heat pump thermal output and the flow rate and inlet temperatures of the heat sink and source water are given. The heat transfer coefficients of the condensation and evaporation are calculated with empirical correlations proposed by the authors. The validity of the evaluation method and the correlations is demonstrated by comparison with experimental data. The relations between the coefficient of performance (COP) and composition are shown under two conditions: (1) the constant heat transfer length of the condenser and evaporator; and (2) the constant temperature of refrigerant at the heat exchanger inlet. The COP of the NARMs is higher than that of pure refrigerant when the heat transfer lengths of the condenser and evaporator are sufficiently long.     

Retrofit of lower GWP alternative R449A into an existing R404A indirect supermarket refrigeration system

R404A is going to be phased out from most of the commercial refrigeration systems due to its high GWP value of 3943. R449A (GWP of 1282) has been proposed to replace R404A with only minor system modifications in supermarkets. This paper presents the measurements of a light retrofit replacement of R404A using R449A in a medium temperature indirect refrigeration system (secondary fluid temperature at the evaporator outlet between −9 and −4 °C). It has been demonstrated that with a slight expansion device adjustment and 4% increase of refrigerant charge, R449A can be used in this refrigeration system designed for R404A because of its suitable thermodynamic properties and acceptable maximum discharge temperature. At a secondary fluid temperature at condenser inlet of 30 °C, the COP of R449A nearly matches that of R404A (both were between 1.9 and 2.2), despite having approximately 13% lower cooling capacity. As a conclusion, attending to the GWP reduction and similar energy performance, it was demonstrated using the TEWI methodology that the use of the recently developed refrigerant R449A in these applications can reduce the total CO₂ equivalent emissions of an indirect supermarket refrigeration system designed for R404A refrigerant.     

新型PVE油对R32分体式空调性能的影响

R32作为新一代替代制冷剂的应用范围很广,专用冷冻机油的开发和使用成为R32应用的关键问题之一。本文选取了一种新型PVE油搭配R32,通过实验对比R410A/POE油、R32/POE油以及R32/PVE油组合时2匹热泵分体式空调的制冷性能,研究了不同PVE油含油率下的空调蒸发器及冷凝器侧热阻的变化,PVE油量影响系统COP的原因。结果表明:PVE油的使用明显提升了R32空调的制冷性能,随着油量的增加,蒸发器侧热阻先增大后减小,冷凝器侧热阻逐渐增大,从而影响蒸发温度先升高后降低,冷凝温度持续上升,系统COP先增大后减小,在PVE充注油量270 m L附近达到最大值。     

Thermodynamic analysis of R 21-DMF vapour absorption refrigeration systems for solar energy applications

The concentration-enthalpy chart for R 21-DMF refrigerant-absorbent combination is presented for the temperature range of interest for solar-driven cooling applications. A thermodynamic analysis of the vapour absorption refrigeration system (VARS) working with R 21-DMF is made to study the theoretical performance characteristics. At evaporator temperatures lower than about 0°C, R 21-DMF has a distinct advantage over R 22-DMF systems in being able to operate at lower generator temperatures. Also R 21-DMF systems perform better than R 22-DMETEG systems.     

R290/R600a混合工质制冷系统泄漏点对系统性能的影响

混合工质在不同位置的泄漏所引起的系统中工质对组分比例发生变化会对制冷系统的性能产生很大影响。根据混合法则,从理论上研究R290/R600a工质对泄漏率在5%~40%范围内8种泄漏率条件下,系统工质对组分变化的规律。按照理论计算的要求建立制冷系统工质泄漏实验台,对实验台在4种泄漏率条件下的蒸发压力、冷凝压力、制冷量和COP进行研究。计算和实验结果表明,在蒸发器出口和冷凝器入口处的泄漏使低沸点组分R290在工质对中的比例增大,系统制冷量增加且COP下降;在蒸发器入口和冷凝器出口处的泄漏使高沸点组分R600a在工质对中的比例增大,系统制冷量下降且COP上升。     

Modeling evaluation of a direct-expansion solar-assisted heat pump water heater using R410A

A direct-expansion solar-assisted heat pump (DX-SAHP) system by using R410A as refrigerant is described, which can supply domestic hot water during the whole year. Based on the distributed parameter and homogeneous flow models of collector/evaporator and condenser, the lumped parameter models of compressor and electronic expansion valve, and the refrigerant charge model, a numerical model is developed to estimate the thermal performance of the system. Given the structure parameters, meteorological parameters, initial and final water temperatures, for a fixed superheat degree, the effects of the refrigerant charge quantity on the performance parameters of the system are analyzed, such as compressor power, heat gain of collector, heating time, collector efficiency and system COP. Furthermore, for a fixed refrigerant charge quantity, the effects of various parameters, including solar radiation, ambient temperature, compressor speed and initial water temperature, have been simulated and analyzed on the thermal performance of the system.     

Thermodynamic analysis of R 21-DMF vapour absorption refrigeration systems for solar energy applicationsAnalyse thermodynamique des systèmes frigorifiques à absorption de R 21-DMF (diméthylformamide) pour les applications à l'énergie solaire

The concentration-enthalpy chart for R 21-DMF refrigerant-absorbent combination is presented for the temperature range of interest for solar-driven cooling applications. A thermodynamic analysis of the vapour absorption refrigeration system (VARS) working with R 21-DMF is made to study the theoretical performance characteristics. At evaporator temperatures lower than about 0°C, R 21-DMF has a distinct advantage over R 22-DMF systems in being able to operate at lower generator temperatures. Also R 21-DMF systems perform better than R 22-DMETEG systems.     

Experimental investigation on the drop-in performance of R407C as a substitute for R22 in a screw chiller with shell-and-tube heat exchangers

A drop-in test of a mixed refrigerant R407C is performed in a commercial screw chiller with shell-and-tube heat exchangers originally designed for R22. The test results show a severe performance reduction when substituting the refrigerant from R22 to R407C. The reason for the performance reduction is analyzed comprehensively, and the influence of thermodynamic properties, compressor efficiency, and heat transfer is evaluated quantitatively. The major factor causing the performance reduction is assessed as the degradation of the heat transfer in using the mixed refrigerant, R407C. The heat transfer degradation in the evaporator is found to be larger and influences more on the chiller performance reduction. The performance reduction caused by the evaporator is approximately two times compared with that of the condenser.     

Energy and exergy analysis of single effect and series flow double effect water–lithium bromide absorption refrigeration systems

In this paper, the energy and exergy analysis of single effect and series flow double effect water–lithium bromide absorption systems is presented. A computational model has been developed for the parametric investigation of these systems. Newly developed computationally efficient property equations of water–lithium bromide solution have been used in the computer code. The analysis involves the determination of effects of generator, absorber and evaporator temperatures on the energetic and exergetic performance of these systems. The effects of pressure drop between evaporator and absorber, and effectiveness of heat exchangers are also investigated. The performance parameters computed are coefficient of performance, exergy destruction, efficiency defects and exergetic efficiency. The results indicate that coefficient of performance of the single effect system lies in range of 0.6–0.75 and the corresponding value of coefficient of performance for the series flow double effect system lies in the range of 1–1.28. The effect of parameters such as temperature difference between heat source and generator and evaporator and cold room have also been investigated. Irreversibility is highest in the absorber in both systems when compared to other system components.     

A study of working fluids for heat driven ejector refrigeration using lumped parameter models

This paper studies the influence of working fluids over the performance of heat driven ejector refrigeration systems performance by using a lumped parameter model. The model used has been selected after a comparison of different models with a set of experimental data available in the literature. The effect of generator, evaporator and condenser temperature over the entrainment ratio and the COP has been investigated for different working fluids in the typical operating conditions of low grade energy sources. The results show a growth in performance (the entrainment ratio and the COP) with a rise in the generator and evaporator temperature and a decrease in the condenser temperature. The working fluids have a great impact on the ejector performance and each refrigerant has its own range of operating conditions. R134a is found to be suitable for low generator temperature (70–100 °C), whereas the hydrocarbons R600 is suitable for medium generator temperatures (100–130 °C) and R601 for high generator temperatures (130–180 °C).     

R1234yf and R1234ze(E) as low-GWP refrigerants for residential heat pump water heaters

Owing to the growing concerns about the relatively high global warming potential (GWP) of current refrigerants, a serious effort is in progress to find lower-GWP substitutes. The hydrofluoroolefin (HFO)-based refrigerants R1234yf and R1234ze(E) are being considered for use in multiple heating, ventilation, air conditioning, and refrigeration applications because of their very low GWP. A study was conducted to model a residential heat pump water heater using these HFOs. A system model was calibrated using experimental data and the calibrated model was used to evaluate the potential of HFOs to replace R134a. A series of parametric analyses were used to investigate the impacts of condenser wrap pattern, condenser tube size, evaporator size, and heat loss factor from the storage tank. It has been shown that both R1234yf and R1234ze(E) can be substituted for R134a with comparable performance and no substantial modifications to the original system. This study presents a detailed feasibility analysis for successful replacement of high-GWP refrigerants with low-GWP refrigerants with acceptable performance.