This paper presents a comprehensive review of two-phase ejector as an expansion device in vapor compression refrigeration cycle over the past two decades. It also covers research opportunities that ...are still open in the field of two-phase ejectors as an expansion valve. The studies of the application of ejector as an expansion device are relatively scarce compared to the application of ejector as heat-driven refrigeration system. A better understanding of two-phase flow in the ejector is necessary to optimize energy saving of the system. This paper also presents effects of geometric parameters of the ejector as an expansion valve on the performance of vapor compression refrigeration cycle. In addition, the effect of working fluid on the two-phase expansion refrigeration system is covered. The authors predict that the challenge of future research on design of two-phase ejector is how to generate a pressure rise in diffuser for minimum compressor work and optimum COP improvement.
In industrial application,unintentional manufacturing line troubles often consequence in heating raw materials excessively,in terms of either time or temperature.One of the effects of such occurrence ...is a product with a variation of prior austenite grain size,even if after the heat treatment the end result is the same,martensite.The variation of the prior austenite grain size is believed to vary the end results of the martensite.This undesirable variation includes the variation of fatigue resistance,impact strength,yield strength,hardness,etc.This research studies the effect of the prior austenite grain size on the morphology of the martensite microstructure.The results show that within the typical industrial application of temperature and holding time set up,as holding time or the temperature increases,the prior austenite average diameter increases.The block and packet sizes in the martensite also increase.The variation of mechanical property dependence on the grain size is indeed due to the different characteristics reflected in the martensite morphology.With respect to the same area,smaller grain has more blocks and packets,which agrees with higher dislocation density verified with transmission electron microscopic evaluation.
In residential sector, air conditioning (A/C) system contributes the largest power consumption. As a result, several methods have been developed to improve the system performance. Subcooling is a ...method to improve the performance of A/C by increasing the cooling capacity. Because R32 has much lower global warming potential (GWP) than that of R22 and R410A, this refrigerant is projected as a substitute of R22 and R410A. This study investigates the performance improvement of residential (A/C) using condensate water as a compressor discharge cooler to generate subcooling. In present study, the experiment was carried out on a split-type A/C using R32 as working fluid. During the experiment, the indoor and outdoor temperatures were controlled at 20°C and 33°C, respectively. The experimental results showed that the average decrease in refrigerant temperature at the condenser outlet was 4.5°C. The decrease in temperature at the condenser outlet indicated that the subcooling occurred on the system. The subcooling on the condenser outlet resulted in increase in cooling capacity by 12.1%. In addition, the use of condensate water as a compressor discharge cooler increased the COP by 21.7%.
This paper presents a numerical approach in the investigation on the effect of engine speed on the performances of automotive air conditioning system using R134a and R152a as refrigerants. In the ...near future, R152a refrigerant is projected to replace R134a as working fluid in vehicle air conditioning systems. In this study, four engine rotations, i.e., 1000, 2000, 3000 and 4000 rpm that represent: idle, city, medium speed and high speed conditions, respectively, were investigated. In the modeling, the evaporating and condensing temperatures were assumed constant at 5°C and 45°C, respectively. The results showed that coefficient of performances (COPs) of the automotive air conditioning using R152a were higher than that of R134a for all engine speeds. The COP improvement of R152a increased with the increase in engine speed. At engine rotation of 4000 rpm, the COP improvement was by as much as 6.4%. The disadvantage of R152a compared to R134a was in its high discharge temperature. This condition is anticipated to affect the reliability of the compressor in the long run.
Reducing energy consumption and ensuring thermal comfort are two important considerations in designing an air conditioning (AC) system. An AC system, originally operated on an on/off control ...mechanism, was retrofitted to enable the application of the new controllers. This paper deals with independent control methods for the AC system based on the thermostat on/off control, digital on/off control, digital on/off control with a personal computer (DPC) and fuzzy logic control (FLC). Measurements were made at a time interval of one minute for set point temperatures of 22, 23 and 24oC. The room air temperature, energy consumption and energy saving were analyzed for all control methods. The main objective is to determine the amount of energy savings when digital on/off control, DPC and FLC are applied to the AC system. The experimental results showed that these controls saved energy consumption and improved indoor comfort significantly for a building AC system compared to a thermostat on/off control method.
Through an investigation of the field failure analysis and laboratory experiment, a study on (stress corrosion cracking) SCC behavior of steel and aluminum was performed. All samples were extracted ...from known operating conditions from the field failures. Similar but accelerated laboratory test was subsequently conducted in such a way as to mimic the field failures. The crack depth and behavior of the SCC were then analyzed after the laboratory test and the mechanism of stress corrosion cracking was studied. The results show that for the same given stress relative to ultimate tensile strength, the susceptibility to SCC is greatly influenced by heat treatment. Furthermore, it was also concluded that when expressed relative to the (ultimate tensile strength) UTS, aluminum has similar level of SCC susceptibility to that of steel, although with respect to the same absolute value of applied stress, aluminum is more susceptible to SCC in sodium hydroxide environment than steel.
This paper presents a numerical approach to determine the exergy loss in an air conditioner using (A/C) R22 and R290 as working fluid. The exergy loss should be minimized in order to increase the ...performance of the air conditioner. The present study investigates the A/C with cooling capacity of 2.4 kW. The results show that the total exergy loss of R290 is lower than that of R222, viz. 0.667 and 0.857 kW, respectively. This indicates that the use of R290 in the air conditioner using ejector as expansion device will generate a better COP improvement than that of R22. In addition, energy analysis shows that the COP improvements using R290 is higher than that of R22, for instance, 12.24 and 8.15% for R290 and R22, respectively, at the ambient temperature of 35degreesC.
The present study describes thermodynamic modeling of a novel cycle of ejector as an expansion device - called modified ejector cycle (MEC) - on residential air conditioner (A/C) to further enhance ...the COP improvement on standard ejector cycle (SEC). The difference between the SEC and MEC is the separator, namely the SEC uses a separator that has an inlet and two outlets, whereas in modified ejector cycle (MEC), the separator has only an inlet and an outlet in the system. Due to its environmental friendliness of R290 (propane), it is used to replace R22 as a working fluid in the numerical. The modeling results on the residential air conditioner with cooling capacity of 2.5 kW using R290 as working fluid showed that the COP improvement of the MEC was 42.86% at the condenser temperature of 45°C.
The present study describes a numerical analysis of the effect of subcooling using liquid-suction heat exchanger (LSHX) on the performance of automotive air conditioner. Besides increasing the ...cooling capacity, subcooling using LSHX also generates superheating in the suction of the compressor, where the superheating ensures only vapor phase of refrigerant entering the compressor suction and reduces the risk of damage to the compressor. The results show that the refrigeration capacity improvements and COP improvements up to 11.86% and 5.64%, respectively, for the subcooling of 1 K to 10 K and the condenser temperature of 40°C to 50°C.
Working fluid of R134a is widely used as a refrigerant in automotive air conditioner. This refrigerant has a good performance on the automotive air conditioner. However, because R134a still has a ...high global warming potential, this refrigerant must be reduced and replaced by environmentally friendly refrigerants. Hydrocarbons of R600a, R290 and their mixtures are widely used as substitute refrigerant. These refrigerants are natural fluids, no effect on the climate, inexpensive and readily available. There are three performances will be discussed in the present study, namely COP, mass flow rate and compression ratio. The present study investigates the effect of three refrigerants, i.e. R134a, R600a and R290 on the performance of automotive air conditioner. The results show that the COP of R600a is higher than those R134a and R290. For the same cooling capacity, the mass flow rate of R600a is approximately 50% of R134a for all ambient temperatures. In addition, the compression ratio of R600a is lower than that of R134a.
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