Experimental investigation of startup characteristics of R290 rotary compressor under low ambient temperature heating condition

The cold and warm startup characteristics of an R290 heat pump system and its rotary compressor were experimentally investigated under a low ambient temperature heating condition. These startup characteristics included the temperatures in the compressor shell and system and the pressures in the cylinder and system. The results showed that the minimum suction gauge pressure (−48 kPa) during a cold startup was lower than that during a warm startup (155 kPa) under a low ambient temperature heating condition. In addition, the time required for the R290 heat pump system to reach a steady pressure was much longer than that of a system using R410A as the refrigerant. Compared with that of the cooling condition, smaller amounts of liquid were generated in the cylinder at the beginnings of both the cold and warm startup processes under the low ambient temperature heating condition.     

低温热泵用涡旋压缩机性能的试验研究

制定低温热泵用涡旋压缩机试验方案,对研制的原型机进行性能测试。试验结果表明：在冷凝温度不变的情况下,随着蒸发温度的降低,原型机的制热量有所减少,但减少的速度低于普通热泵系统用涡旋压缩机;压缩机的电功率有所增加,但增加的幅度不大,且压缩机的排气温度也有所降低,故在低温工况下采用准二级压缩热泵用涡旋压缩机比采用普通热泵用涡旋压缩机可以更有效地提高空气源热泵的低温制热性能,是寒冷地区用小型空气源热泵比较适宜采用的压缩机。     

Condensation heat transfer coefficients of R1234yf on plain, low fin, and Turbo-C tubes

In this study, external condensation heat transfer coefficients (HTCs) of HFC134a and R1234yf are measured on a plain, low fin, and Turbo-C tubes at the saturated vapor temperature of 39 °C with the wall subcooling of 3-8 °C. R1234yf is a new alternative refrigerant of low greenhouse warming potential for replacing HFC134a, one of the greenhouse gases in Kyoto protocol, used extensively in automobile air conditioners and other refrigeration systems. Test results show that the condensation HTCs of R1234yf are very similar to those of HFC134a for all three surfaces tested. For the development of heat transfer correlations, thorough property measurements are needed for R1234yf in the near future.     

低温条件下压缩机油位控制的实验研究

在低温条件下,为了保证直流变频多练空调的正常启动和运行,压缩机油池内的油位控制是非常重要的.压缩机启动控制对比实验研究结果表明,在启动阶段,延长回油平台时长以及增加回油循环和除霜循环有利于油位保持在安全油位之上.单台室内机开机启动时,相应的电子膨胀阀开度必须在350步以上,才能确保机组正常启动成功及油位安全.     

Characterization and simulation of an open piston compressor for application on automotive air-conditioning systems operating with R134a,R1234yf and R290

A semi-empirical characterization and simulation model for automotive air-conditioning open piston compressor is developed. The model is based on fundamental conservation principles and takes into account pressure drop and heat transfer in suction and discharge passages. Fundamental conservation principles equations, as well as volumetric and isentropic efficiencies, pressure drop, heat transfer and property equations are combined to form a system of non-linear algebraic equations. They are worked out so as to identify constants that are sole characteristics of the compressor and should not vary with different operating conditions or refrigerants. A numerical method determines such constants from existing experimental data, thus characterizing the compressor. Experimental data were obtained from tests carried out by Navarro et al. (2013) for an open piston compressor running with fluids R134a, R1234yf and R290. First, the experimental data were employed to determine the characterization parameters of the compressor. Then, the simulation model, with the R134a-based parameters, was applied to simulate the compressor operation with R1234yf and R290. Good agreement was obtained between predicted and experimental values, proving the suitability of the model for the study of new refrigerants.     

Evaluation of two-phase suction,liquid injection and two-phase injection for decreasing the discharge temperature of the R32 scroll compressor

R32 has been considered as an important alternative in the phase-out of hydrochlorofluorocarbons (HCFCs) due to its advantages such as relatively low global warming potential compared to R410A, favorable thermal properties. However, the increased discharge temperature of the R32 compressor, compared with R410A, is the main barrier affecting the wide and quick adoption. In this work, three promising methods to decrease the discharge temperature of R32 scroll compressor, namely, two-phase suction, liquid injection and two-phase injection, have been investigated. By considering the variations of motor efficiency and leakage rate, an improved distributed parameter model of the scroll compressor is rebuilt based on a previously developed one (Wang et al., 2008). By that model, the effectiveness of these three methods in decreasing discharge temperature and their influence on thermodynamic performance are researched. It is concluded that all the three methods show excellent potential in decreasing the discharge temperature of R32 scroll compressor. Besides, two-phase injection outperforms the other two methods in cooling capacity and COP by 11.8% and 4.8%, respectively.     

Comparative performance analysis of the low GWP refrigerants HFO1234yf,HFO1234ze(E) and HC600a inside a roll-bond evaporator

This paper presents the comparative performance analysis of the low GWP refrigerants HFO1234yf, HFO1234ze(E) and HC600a inside a commercial roll-bond evaporator for household refrigerators. The vaporisation performances were evaluated at two evaporation temperatures, −15 and −20 °C, and different refrigerant mass flow rates and compared with those of the traditional refrigerant for domestic refrigeration HFC134a. The performance analysis was carried out using both thermocouples installed on the rear side of the roll-bond evaporator and an IR thermo-camera. Each of the low GWP refrigerants tested can be considered a good substitute for HFC134a, provided that the compressor displacement is adjusted to deliver the proper refrigerant mass flow rate. Only HFO1234yf exhibits performance similar to HFC134a at the same mass flow rate, therefore it can be considered a direct drop-in substitute for HFC134a.     

Experimental and theoretical study on a novel double evaporating temperature chiller applied in THICS using R32/R236fa

A novel chiller with double evaporating temperatures is proposed in this paper, which can be applied in temperature and humidity independent control system (THICS). A zeotropic mixture R32/R236fa is selected as the refrigerant, and chilled water with two different temperatures is produced. The experimental coefficient of performance (COP_exp), theoretical coefficient of performance (COP_th), and second law efficiency (η) of the chiller are studied. The performance of the chiller is studied by varying the mass fraction of R32 in the R32/R236fa (W(R32)), chilled water temperature, and the flow rates of the heat transfer media (chilled water and cooling water). The results show that the high temperature chilled water (T_H,out) can be at 15–18 °C, and the low temperature chilled water (T_L,out) can be at 6–8 °C. When T_H,out is 17 °C and T_L,out is 7 °C, the maximum COP_th and COP_exp are 4.73 and 3.97, respectively. Second law efficiency, η, increases to 31% as W(R32) increases from 0.3 to 0.6.     

Economic analysis of the application of expanders in medium scale air-conditioners with conventional refrigerants,R1234yf and CO2

Expanders have been shown to improve the energy efficiencies of refrigeration systems. The current technology is also adequate to manufacture and integrate expanders to practical air-conditioners. In this paper, an economic analysis of the installation of expanders on to existing vapor compression cooling systems, particularly medium scale air-conditioners, is presented. Various refrigerants, including the established and the newly proposed varieties, are considered. From the investigations, it was found that when the expander efficiency is 50%, the payback periods of most conventional systems are below 3 years in high temperature countries with high electricity tariffs and are above 5 years in other countries. Expanders are especially attractive for the transcritical CO₂ and the R404A systems. The payback periods are shorter for systems with highly efficient expanders, high cooling loads, high ambient temperatures and for low refrigerating temperature applications.     

Theoretical and experimental investigation on the performance of screw refrigeration compressor under part-load conditions

Slide valve is normally employed in screw refrigeration compressor to meet the cooling capacity demanded by the load variation. A mathematical model describing the working process of screw refrigeration compressor with a slide valve assembly under part-load conditions is established based on the calculation of the effective by-pass area and radial discharge area. Experimental investigation on a screw refrigeration compressor under part-load conditions with several evaporation and condensation temperatures is also carried out. Simulation results are in good agreement with the experimental ones. With the validated model, effects of key design parameters, i.e. the installation angles of the slide valve relative to the cylinder and the slide stop length, on the working process and performance of screw refrigeration compressor have been analyzed. These results can be useful for optimum design of the slide valve assembly to improve the energy efficiency of refrigeration system with screw compressor under part-load conditions.     

Experimental investigation on minichannel parallel flow condenser performance with R22, R410A and R407C

A performance evaluation of minichannel parallel flow (MCPF) condenser in residential/commercial refrigeration system has been carried out in calorimeter room with wind tunnel in this paper. The heat rejection and pressure drop characteristics for heat exchangers were compared using R22, R410A and R407C as working fluids. The experimental results showed that heat rejection of MCPF condenser with R410A was higher than that of R22 and R407C by 15.6~26.3% and 12.3~22.7% under full and partial load conditions, respectively. The refrigerant side pressure drop trend of R410A in MCPF condenser was smaller than that of R22 and R407C under the same mass flow rate.     

分离有机/有机混合物的PVA、CA系列膜及其渗透汽化性能研究(Ⅱ) 成膜条件对渗透汽化性能的影响

用溶剂完全蒸发法制备了PVA复合膜 .经对MTBE/MeOH混合物的分离实验得到了PVA复合膜的最佳成膜条件 ,即 :铸膜液中PVA、马来酸浓度分别为 7%、3% ,热处理温度130～ 15 0℃ .在 1%～ 2 %丙酮水溶液中浸泡处理 4～ 8h ,CTA中空纤维RO膜被改性成渗透汽化膜 .CTA中空纤维膜的分离性能优于其它醋酸纤维素系列膜 ,PVA/CA复合膜的性能优于PVA/PAN复合膜和CA/PAN复合膜     

Experimental investigation of the surface temperature and water retention effects on the frosting performance of a compact microchannel heat exchanger for heat pump systems

Frost formation on a louvered fin microchannel heat exchanger was experimentally investigated in this paper with the aim of determining the dominant factors affecting the time of frosting and frost growth rate. A novel methodology was developed to measure frost thickness and frost weight at intervals during the frosting period. Frost mass and thickness growth rates, corresponding coil heat transfer, capacity degradations and air pressure drop are measured and discussed. The experimental data showed that at a given air dry bulb temperature, the fin surface temperature and air humidity are the primary parameters that influence the frost growth rates. Water retention and air velocity had a secondary impact on the frosting performance. From digital images of the frost growth it was observed that frost does not nucleate from the water droplets retained in between fins but it developed from the leading edges of the fins.     

Experimental and numerical research on high‐temperature thermal insulation performance of lightweight porous ceramic/nanomaterial composite structure

The thermal protection structure of hypersonic vehicles must meet the design requirements of high efficiency and light weight, and its heating surface must also be able to withstand thermal erosion by high‐speed and high‐temperature airflow. In this paper, a light‐weight porous ceramic material and a lightweight nanoscale thermal insulation material with excellent thermal insulation performance are combined to form an integrated thermal protection structure. Experimental study and numerical simulation of the structure's high‐temperature thermal insulation performance are carried out. The experimental results show that a composite sheet made from a 20 mm‐thick lightweight porous ceramic material and a 10 mm‐thick nanomaterial exhibit a temperature drop of 85 % between its back surface and front surface in four thermal environments (1200, 1000, 800 and 600 °C) at 1800 s. This indicates excellent thermal insulation performance of the composite sheet. In addition, the operating temperature limit (<1000 °C) is obtained through high‐temperature thermal performance tests on single‐layer nanomaterial sheets and scanning electron microscopy results. This provides an important basis for determining and optimizing the thickness ratio of the two materials in composite structure.     

An experimental investigation on the performance,combustion and emission characteristics of a variable compression ratio diesel engine using diesel and palm stearin methyl ester

An attempt has been made to use biodiesel prepared from non-edible portion of palm oil as fuel of a conventional mono-cylinder compression ignition engine. The present experimental investigation takes into account the combined effect of using blends of diesel–palm stearin biodiesel as fuels and the compression ratio on different performance, combustion and emission characteristics of the said engine. The experiments have been carried out on a single-cylinder, direct injection diesel engine at varying compression ratio of 16:1–18:1 in four steps. It is observed that the brake thermal efficiency reduces by 7.9% when neat biodiesel is used instead of diesel. But, it increases with the increase in compression ratio for all the blends. Brake specific fuel consumption and exhaust gas temperature increase with the addition of biodiesel to diesel and also with the increase in compression ratio. Heat release rate decreases with biodiesel, and it is minimum at the rated compression ratio of 17.5:1 for all the fuels considered here. On the other hand, ignition delay is found to be more with neat diesel, and it increases with the decrease in compression ratio. Significant reductions in emissions of carbon monoxide (CO), hydrocarbon (HC) and smoke are observed with biodiesel, while the emissions of oxides of nitrogen (NO_x) and carbon dioxide (CO₂) increase. The decrease in compression ratio increases the emissions of CO, HC and smoke, but the emissions of NO_x and CO₂ decrease with the decrease in compression ratio.     

Complement activation by cellulose: investigation of the effects of time, area, flow rate, shear rate and temperature on C3a generation in vitro, using a parallel plate flow cell

The development and utilization of a parallel plate flow system to study the blood response to flat sheet biomaterials, is described. Unlike most other parallel plate flow systems, which have been used to study cellular interactions with biomaterials, the controlled flow test cell described below employs the test materials on both sides of the channel through which the blood flows. The flow cell is used to conduct an investigation into the in vitro generation of C3a by a regenerated cellulose membrane, Cuprophan. The effects of experimental variables such as temperature, blood flow rate, contact area and wall shear rate on C3a generation by Cuprophan were studied. The results show that C3a generation by Cuprophan is lower at 12 °C than at 22 °C, which is in turn lower than C3a generation at 37 °C. Furthermore, a decrease in contact area, and increase in wall shear rate and blood flow rate, can produce a decrease in C3a concentration.     

Effects of temperature and clay content on water absorption characteristics of modified MMT clay/cyclic olefin copolymer nanocomposite films: Permeability,dynamic mechanical properties and the encapsulated organic device performance

In the present study, amino-silane modified layered organosilicates were used to reinforce cyclic olefin copolymer to enhance the thermal, mechanical and moisture impermeable barrier properties. The optimum clay loading (4%) in the nanocomposite increases the thermal stability of the film while further loading decreases film stability. Water absorption behavior at 62 °C was carried out and compared with the behavior at room temperature and 48 °C. The stiffness of the matrix increases with clay content and the recorded strain to failure for the composite films was lower than the neat film. Dynamic mechanical analysis show higher storage modulus and low loss modulus for 2.5–4 wt% clay loading. Calcium degradation test and device encapsulation also show the evidence of optimum clay loading of 4 wt% for improved low water vapor transmission rates compared to other nanocomposite films.