Chasik Park

Performance Characteristics of a Drop-in System for a Mobile Air Conditioner Using Refrigerant R1234yf

In this study, the performance of mobile air conditioner(MAC) systems to which the refrigerants R134a and R1234yf were used was evaluated to compare the characteristic of automotive refrigeration cycles with refrigerant. The experimental setup of a MAC consists of an belt driven compressor, a condenser, an evaporator and a block type thermal expansion valve. The drop-in test on MAC were carried out under variable compressor speed from 800 to 2500 rpm. Performance test by using R1234yf and R134a in the same system revealed low the charge amount and mass flow rates for using R1234yf, that is, up to 10% and 17%, respectively. The compressor discharge temperature of R1234yf is 8℃ lower than that of R134a. The cooling capacity with R1234yf system decreased by 4~7% compared with R134a system. In addition, The COP of R1234yf system is lower 3~4% than that of R134a system.

Study on the Performance Improvement for an Automobile Air Conditioning System Using Alternative Refrigerant R1234yf

The performance of automobile air conditioning systems of R1234yf was evaluated and compared with that of R134a. In particular, the performance evaluation was carried out by installing an internal heat exchanger in order to improve the performance of the system used in R1234yf. A performance comparison between the R1234yf and R134a for automotive air conditioning revealed that the cooling capacity and COP of the 1234yf system without the IHX decreased by up to 7% and 4.5%, respectively, but those with the IHX decreased by up to 1.8% and 2.9%, respectively.

A Numerical Study on the Performance of a Vapor Compression Cycle Equipped with an Ejector Using Refrigerants R1234yf and R134a

Abstract This paper presents a numerical study on the performance of a vapor compression cycle equipped with an ejectoras an expansion device to improve the COP by reducing the expansion loss and compressor work. The simulation is carriedout using a model based on the conservation of mass, energy and momentum in the ejector. From the results of the simulation,the vapor compression cycle equipped with an ejector showed a maximum COP improvement of 14.0% when using R134a refrigerant and 16.8% when using R1234yf. In addition, the performance of the system with an ejector represents the increasedperformance as the temperature difference between condensing and evaporating increased. Key words Ejector(이젝터), Entrainment ratio(유입비), Area ratio(면적비), R1234yf(R1234yf), GWP(지구온난화지수), COP(성능계수)†Corresponding author, E-mail: cspark@hoseo.edu 기호설명 A ： 단면적 [m 2 ] COP ： 성적계수 h ： 엔탈피 [kJ/kg]  ： 질량유량 [kg/s] P ： 압력 [kPa] Q ： 냉방용량 [kW] S ： 엔트로피 [kJ/kg ℃ ] V ： 속도 [m/s] W ： 압축기 소요동력 [kW] x ： 건도그리스 문자  ：

An Experimental Study of the Bioelectrical Signals and Subjective Response in Changing from Unpleasant to Pleasant Temperatures in a Learning Environment

Abstract In this study, experiments using bioelectronic signals and questionnaire surveys were carried out in learning conditionswhen temperatures changed from low- and high-uncomfortable to comfortable. As a result, the stress factor Photoplethysmo-graphy (PPG) decreased, while the Root Mean Square of Standard Deviation (RMSSD) of PPG increased when the indoortemperature was changed from low- or high-uncomfortable to comfortable. Additionally, the absolute power of the α-wave in the brain increased. According to the analysis of the association between the questionnaire and bioelectronic signals, thestandard deviation of the stress factor as measured by pulse was closely related to the result of the thermal sensation questionnaire. In addition, it was found that the concentration on studying improved under comfortable temperatures when compared to uncomfortable temperatures. Key words Biological electricity(생체전기신호), Electroencephalogram(뇌파), Photoplethysmography(광용적맥파), Comfort sensation vote(쾌적감설문), Thermal sensation vote(온열감설문)†Corresponding author, E-mail:

Performance Evaluation of a Two-Stage Compression Heat Pump System for District Heating

ABSTRACT:The objective of this study is to investigate the performance of a two-stage com-pression heat pump system for district heating. The experimental setup of heat pump consists of compressor, condenser, evaporator, expansion device, intercooler, flash tank, oil separator and accumulator. The experimental evaluations on the two-stage compression cycle were carried out under various operating conditions which were heat source temperature, the degree of compressor inlet superheat, and intermediate pressure. The temperature ranges of unutilized energy as the heat source were used in the test conditions. As the heat source temperature increased from 10℃ to 30℃, the COP and heating capacity of the heat pump system increased by 22.6% and 45.8%, respectively. The performance of the two-stage heat pump system increased by 5.2% with the variation of the intermediate pressure in the same heat source temperature conditions.Keywords:District heating(지역난방), Intermediate pressure(중간압), Two-stage compression heat pump(2단 압축 히트펌프), Unutilized energy(미활용에너지)

Performance Evaluation of an YBCO Insert and a BSCCO Outsert Magnet Manufactured With Double Pancake Windings

When there is an air gap between the pancake windings in an HTS superconducting magnet, the central magnetic field is increased. To prove the effectiveness of the air gap for increasing the central magnetic field, an HTS magnet with an outsert and an insert magnet was manufactured and tested. The test results proved that the air gap between the pancake windings of the outsert magnet increased the central magnetic field by 11.0%. The critical current of the outsert magnet with the air gap increased by 73.9%. The uniformity of the magnetic field near the center of the magnet also increased. The measured values were compared with the calculated values.