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Performance Study of Refrigeration Units That Use the Refrigerant R-404A by Using Computer Simulation  [PDF]
Abed Alrzaq Sleman Alshqirate
Modern Mechanical Engineering (MME) , 2016, DOI: 10.4236/mme.2016.62008
Abstract: The performance parameters of vapor compression refrigeration units that used the refrigerant R-404A were studied by developing a computer simulation algorithm. The various performance parameters investigated per one kilowatt of refrigeration capacity, such as the mass flow rate, the compressor power consumption, the condenser heat rejection rate, the compressor exit temperature and the coefficient of performance. Two refrigeration cycles were tested under various evaporating and condensing temperatures: the standard cycle and the ideal cycle with superheating and sub-cooling. The results of the present work reveal that the compressor power variation over the evaporating temperature range from 10 to 15at Tc = 40 is decreased by 38.8% for standard cycle and by 43.8% for ideal cycle. The compressor power variation over the condensing temperature range from 30 to 50 at Te = 10 is increased by 122% for standard cycle and by 54.5% for ideal cycle. On the other hand, the COP for the ideal cycle with 5 superheating and sub-cooling is approximately 25% higher than that of the standard cycle at Te = 10 and Tc = 40 for the refrigerant R-404A.
Selection of the Capillary Tubes for Retrofitting in Refrigeration Appliances
A.S. Raut,U.S.Wankhede
International Journal of Engineering Science and Technology , 2011,
Abstract: Retrofitting the refrigeration appliances using the capillary tube is reviewed in this paper. If the refrigerant is changed in the existing system, the COP of the system will be affected. It is necessary to do some modifications in the existing system and retrofit it. Changes in compressor design are too complicated and expensive. Hence modification in capillary tube dimensions is preferred so as to compensate for theperformance of the system.
SIMULATION OF TEMPERATURE OF R744/ R290 REFRIGERANT AT EVAPORATOR OUTLET IN AUTOCASCADE REFRIGERATION SYSTEM
Rajinder Kumar Sidhu,,Jagdev Singh,,Simranpreet Singh Gill
International Journal of Engineering Science and Technology , 2011,
Abstract: The objective of present work is to predict the temperature of refrigerant mixture at evaporator outlet using fuzzy modeling in autocascade refrigeration system. The fuzzy model is presented in this paper for the prediction refrigerant mixture temperature at evaporator outlet. The autocascade refrigeration system provides the possibility of keeping the highest pressure within a limit by selecting the composition of the refrigerant mixture as compared to vapor compression system which uses pure carbon dioxide. The refrigeration system uses R744/R290 as refrigerant mixture. Pressure (kPa), temperature (°C) and concentration of CO2 are taken as input variable parameters for developing fuzzy model and the output istaken as the refrigerant mixture temperature at outlet of evaporator (°C). The model predictions are compared with a set of reliable experimental data available in the literature for the validation of fuzzy model and it is found that proposed fuzzy model gives the results which are well in agreement with experimental results.
Simulation technology for refrigeration and air conditioning appliances
Guoliang Ding
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-006-2072-6
Abstract: Simulation technology has been widely used for performance prediction and optimal design of refrigeration and air conditioning appliances. A brief history of simulation technology for refrigeration and air conditioning appliances is reviewed. The models for evaporator, condenser, compressor, capillary tube and thermal insulation layer are summarized, and a fast calculation method for thermodynamic properties of refrigerant is introduced in this paper. The model-based intelligent simulation technology and the simulation technology based on graph theory are also illustrated. Finally, an updated trend of simulation technology development for refrigeration and air conditioning appliances is discussed.
Design and Construction of Refrigerant Charge Level Detecting Device in HVAC/R System with Microcontroller  [PDF]
Parvez Mahmud,Shahjadi Hisan Farjana
International Journal of Engineering and Advanced Technology , 2012,
Abstract: A charge level detecting device in residential and light commercial heating, ventilation, and air-conditioning (HVAC) systems and in refrigeration systems is used to detect the sufficiency of refrigerant or charge level whether it is proper or not. The most common problems affecting residential and commercial HVAC/R systems are slow refrigerant leaks, improper refrigerant charge and charging device. The usual methods for charge level detection are sight glass method and system high side and low side pressure measurement method. The limitation of sight glass method is it works only if a predictable amount of refrigerant remains in one part of system or constant flow of refrigerant is maintained throughout the system. Pressure of any HVAC/R system cannot be measured in a running system, and charge leaks occur in case of pressure method. Refrigerant charge level detecting device employs a method of determining if the refrigerant charge is within an acceptable range, including the steps of measuring the superheat and subcool temperatures at compressor inlet and condenser outlet. Actual superheat and actual subcooling values are calculated and these values are thus compared with target superheat and target subcool values in microcontroller device, thus obtained from manufacturers chart for particular type of refrigerant, which values depends on outdoor dry bulb temperature and indoor wet bulb temperature on system operating situation and shows the charge status result. The refrigerant charge indicator is based on the fact that when refrigerant starts to leak, the evaporator coil temperature starts to drop and the level of liquid sub cooling drops. An over charge in this system results in compressor flooding, damaging to the motor and mechanical components. Inadequate refrigerant charge can lead to increased power consumption, thus reducing system capacity and efficiency.
Application of adaptive control in a refrigeration system to improve performance
Bandarra Filho, Enio Pedone;Garcia, Francisco E. Moreno;Mendoza, Oscar S. Hernandez;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2011, DOI: 10.1590/S1678-58782011000200008
Abstract: this paper reports an experimental investigation using adaptive control in a refrigeration system. this system is composed basically of a semi-hermetic compressor, concentric tubes heat exchangers, the condenser and evaporator, and thermostatic expansion valve (txv). the refrigerant used in the refrigeration system was the hcfc-22 and also an ac frequency inverter was used to control the speed of the compressor. the temperatures were measured by pt-100 sensors and the pressures using piezoresistive pressure transducers. data acquisition was implemented using the labview software. an electronic card with analogical signal output was also used. these analogical signals were converted into digital through a programmable logic controller (plc) and then sent to the computer through a pc serial port. tests were performed with a variable speed compressor in the range from 30 to 70 hz and the experimental results showed that the highest performance (cop) was attained by working in the range of 50 hz, using adaptive fuzzy control.
Refrigerant Charge Reduction in a Small Commercial Refrigeration Systems  [PDF]
M.S. Tarawneh
Journal of Applied Sciences , 2004,
Abstract: In this paper different aspects of heat transfer and pressure drop in the heat exchanger as designed for the charge minimization are discussed. Focusing on the two-phase model prediction related to the charge in a small channel evaporator as a design choice for a significant charge reduction. Comparisons of the determined results between four evaporators with different channel diameters are presented in figures. Choice of void fraction correlations appears with greater effect on the refrigerant charge and three mass- flux void fraction correlations are recommended and compared. Concluding that the heat transfer mechanisms of these small diameters are different from those of larger diameters
全封闭R32滚动活塞压缩机的热分析
Thermal Analysis for Hermetic R32 Rolling Piston Compressor
 [PDF]

吴建华,胡杰浩,陈昂,梅佩佩,周杏标,陈振华
- , 2015, DOI: 10.7652/xjtuxb201503003
Abstract: 利用计算流体动力学软件对全封闭R32滚动活塞压缩机壳体、泵体零件、电机、制冷剂及润滑油的导热与对流换热进行了数值模拟。采用流固耦合传热分析法,将相接触的流体域和固体域进行整体计算,并在房间空调器压缩机高效工况以及ARI和ASHRAE/T1工况下测量了压缩机内部气缸、油池、电机及气体的温度。结果表明:计算与实验结果吻合较好;在气缸侧面润滑油温降较大,在气缸下部润滑油温度场较为均匀;气缸内表面温度沿周向从吸气孔到排气侧逐渐升高;电机绕组温度高于铁心温度,3种工况下定子绕组顶部温度均最高,分别为94??0、119??2、136??9℃;ASHRAE/T1工况下定子绕组温度已超过电机常用B级绝缘所要求的130℃,此时应采取措施降低压缩机的排气温度。该结果可为R32压缩机及其系统的研制提供参考。
The heat conduction and convection between components, refrigerant and lubricant oil in R32 rolling piston compressor are numerically simulated. The interactive fluid area and solid parts are totally evaluated by fluid??solid coupled heat transfer analysis. And the temperatures of cylinder, oil, motor and refrigerant vapor inside the compressor are measured experimentally under GX, ARI and ASHRAE/T1 conditions for a compressor used for room air conditioner. The theoretical predictions well coincide with the experimental data. The oil temperature on side of pump drops quickly and the temperature distribution in the bottom of pump is relatively uniform; the temperature on inner cylinder surface increases gradually from the suction port to exhaust side, and the winding temperature of motor is higher than core temperature; the temperatures at the top of stator winding are 94??0℃, 119??2℃, 136??9℃, respectively, under the above three conditions; the stator winding temperature under ASHRAE/T1 condition is more than 130℃ beyond common B insulation level, thus it is necessary to reduce discharge temperature of compressor
Oil Concentration Measurement In Saturated Liquid Refrigerant Flowing Inside A Refrigeration Machine  [cached]
Jean-Marc Lebreton,Louis Vuillame,Evelyne Morvan,Olivier Lottin
International Journal of Thermodynamics , 2001, DOI: 10.5541/ijot.61
Abstract: An ultrasonic device was calibrated to measure in situ and in real time the polyol ester oil (POE) concentration of the refrigerant liquid R 410A. The first part of this paper is devoted to the properties of the mixture, to the effects of the presence of oil on the speed of sound in the liquid phase and to the calibration and validation procedures carried out with a saturated liquid refrigerant. In order to have a number of calibration points that is not too large, it is necessary to maintain the mixture as close as possible to saturation conditions, which constrains the choice of the location of the sensor on the installation investigated. In the second part, the first results obtained on this installation are presented. It appears that the speed of sound in the POE / R 410A mixture is a strong function of the temperature and oil concentration, as was expected, but it also significantly depends on the pressure. Consequently, if the use of a sensor in a sub-cooled area is considered, additional calibration and validation procedures are necessary. This paper was presented at the ECOS'00 Conference in Enschede, July 5-7, 2000
间隙对双螺杆制冷压缩机性能的影响
Clearance Effects on Performance of Twin Screw Refrigeration Compressor
 [PDF]

吴华根,唐昊,王养浩,邢子文
- , 2015, DOI: 10.7652/xjtuxb201502022
Abstract: 为清楚解析间隙对螺杆制冷压缩机性能的影响及提高压缩机性能,针对双螺杆制冷压缩机中的啮合间隙和排气端面间隙对压缩机性能的影响程度进行了理论计算和实验研究,结果表明:在相同间隙值下,啮合间隙对螺杆制冷压缩机的容积效率和绝热效率等的影响数倍于排气端面间隙的影响,每增加0.01 mm的啮合间隙,会减少0.4%左右的容积效率,而每增加0.01 mm的排气端面间隙,会减少0.13%左右的容积效率;在较大啮合间隙工况下,排气端面间隙的改变基本不影响压缩机的容积效率、绝热效率以及系统性能系数(COP)等,但是同时增加啮合间隙和排气端面间隙,会引起压缩机性能参数、制冷量及系统性能系数的下降。因此,在螺杆制冷压缩机的设计中更应注重啮合间隙分布设计,从而有效提高双螺杆制冷压缩机的性能。
The effects of meshing clearance and discharge end clearance on the performance of twin screw refrigeration compressor are investigated theoretically and experimentally. The theoretical analysis shows that the influence of the meshing clearance on the volumetric efficiency and the adiabatic efficiency of compressor is several??fold greater than the discharge end clearance under the same gap value which is verified by the experimental measure data. The volumetric efficiency of compressor decreases by 0.4% for every 0.01 mm of increasing meshing clearance and drops 0.13% for 0.01 mm of increasing discharge end clearance. The experiments indicate that the change of the discharge end clearance value slightly affects the compressor performance, such as the volumetric efficiency, adiabatic efficiency and COP, when the meshing clearance increases greatly. Moreover, if the gap is enlarged, the volumetric efficiency, adiabatic efficiency, refrigeration capacity and COP all drop. Thus the meshing clearance ought to be paid more attention than the discharged end clearance in the design of twin screw refrigeration compressor
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