• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2005년도 동계학술발표대회 논문집
• /
• pp.262-267
• /
• 2005

The evaporation heat transfer coefficient of $CO_2$ in a horizontal round tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section was made of a horizontal stainless steel tube with the inner diameter of 7.75 mm, and length of 5 m. The experiments were conducted at mass flux of 200 to 500 $kg/m^2s$, saturation temperature of $-5^{\circ}C$ to $5^{\circ}C$, and heat flux of 10 to 40 $kW/m^2$. The test results showed the evaporation heat transfer of $CO_2$ has great effect on more nucleate boiling than convective boiling. The evaporation heat transfer coefficients of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. In comparison with teat results and existing correlations, correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• 한국태양에너지학회 논문집
• /
• 제34권3호
• /
• pp.82-88
• /
• 2014

Using low outdoor temperature, free cooling system is used in a data center or industrial air-conditioning for energy saving. Because use of IT equipment has increased in some office building recently, there is a growing trend towards using free cooing system. Free cooling system performance is influenced by outdoor temperature. Therefore the performance is different with regions. In this study, performance characteristic of free cooling system is analysed and energy reduction is compared with some regions. Selected regions are 4 cities; including Ulsan analyzed in preceding research, Seoul, ChunCheon and Daejeon. The Aspentech software HYSYS 8.0v was used to conduct the analysis of free cooling system based on temperature per hour of 4 cities in 2013, respectively. The main result is following as. Free cooing system in this study has energy saving effect when outdoor temperature below $7^{\circ}C$. Becuase temperature of Chuncheon is relatively low, using free cooling system can conserve most air-conditioning energy. Energy reduction amount of Seoul is 11%, Chuncheon is 17.5%, Deajeon is 15%, Ulsan is 14%. In case of large scale of air-conditioning, it is reasonable to use free cooling system although the system is used in Seoul.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제13권4호
• /
• pp.167-174
• /
• 2005

The evaporation heat transfer coefficient of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator (test section). The test section consists of a smooth horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500kg/m^2s$, saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$, and heat flux of 10 to $40kW/m^2$. The test results showed the evaporation heat transfer of $CO_2$ has greater effect on nucleate boiling than convective boiling. The evaporation heat transfer coefficient of $CO_2$ is highly dependent on the vapor quality, heat flux and saturation temperature. The evaporation heat transfer coefficient of $CO_2$ is very larger than that of R-22 and R-134a. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Jung et al. But the existing correlations failed to predict the evaporation heat transfer coefficient of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• 융합신호처리학회논문지
• /
• 제21권4호
• /
• pp.177-182
• /
• 2020

친환경적이고 에너지 절약적인 난방 방법으로 히트펌프에 대한 관심이 높아지고 있다. 특히, 저온 지역에서 난방이 가능한 히트펌프를 개발하기 위해 실외기 표면에 서리가 발생하지 않도록 하는 연구가 많아지고 있다. 즉, 온도가 낮은 지역에서 히트펌프를 통해 난방을 할 경우 실외기 표면에 서리층이 형성되어 전열성능을 떨어뜨려 난방능력을 감소시키는 것이 일반적이다. 따라서 본 연구에서는 히트펌프의 실외기에 유입되는 습공기의 수증기를 흡착식 제습시스템을 부착하여 제거하고자 한다. 본 연구를 통해 저온지역에서 가장 효과적인 제습방법을 제시할 수 있을 것으로 판단된다. 그리고 히트펌프의 실외기 전면에 흡착식 제습시스템을 부착하여 에너지 효율이 높은 히트펌프를 개발할 수 있을 것으로 사료된다.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2008년도 동계학술발표대회 논문집
• /
• pp.186-191
• /
• 2008

In this study, a room temperature AMRR (Active magnetic regenerative refrigerator) was fabricated, and experimentally investigated. Gadolinium (Gd) was selected as a magnetic refrigerant with Curie temperature of 293 K. Permanent magnet was utilized to magnetize and demagnetize the AMR. To produce large magnetic field above 1 T in the magnetic refrigeration space, a special arrangement of permanent magnets, so called Halbach array, is employed. Sixteen segments of the permanent magnets magnetized different direction, constitute a hollow cylindrical shaped permanent magnet. The AMR is reciprocated along the bore of the magnet array and produces cooling power. Helium is selected as the working fluid and a helium compressor is utilized to supply helium flow to the regenerator. The fabricated AMRR has different structure and compared to a convectional AMRR since it has an additional volume after the regenerator. Therefore, the cooling ability is generated not only by magnetocaloric effect of magnetic refrigerant but also by the pulse tube effect. It is verified that the cooling ability of AMR is increased due to the magnetocalric effect by the fact that the temperature span becomes $16^{\circ}C$ while the temperature span is only $8^{\circ}C$ when the magnetic field is not applied to the regenerator.

• 설비공학논문집
• /
• 제8권2호
• /
• pp.254-266
• /
• 1996

Boiling heat transfer coefficients of pure refrigerants(R22, R32, R125, R134a, R290, and R600a) and refrigerant mixtures(R32/R134a and R290/R600a) are measured experimentally and compared with several correlations. Convective boiling term of Chen's correlation predicts experimental data for pure refrigerants fairly well(root-mean-square error of 12.1% for the quality range over 0.2). An analysis of convective boiling heat transfer of refrigerant mixtures is performed for an annular flow to study degradation of heat transfer. Annular flow is the subject of this analysis because a great portion of the evaporator in refrigeration or air conditioning system is known to be in the annular flow regime. Mass transfer effect due to composition difference between liquid and vapor phases, which is considered as a driving force for mass transfer at interface, is included in this analysis. Correction factor $C_F$ is introduced to the correlation for the pure substances through annular flow analysis to apply the correlation to the mixtures. The flow boiling heat transfer coefficients are calculated using the correlation considering nucleate boilling effect in the low quality region and mass transfer effect for nonzazeotropic refrigerant mixtures.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제10권3호
• /
• pp.129-137
• /
• 2002

In this study, evaporation pressure drop experiments were conducted with two types of plate and shell heat exchangers (P&SHE) using R-22. An experimental refrigerant loop has been established to measure the evaporation pressure drop of R-22 in a vertical P&SHE. The flow channels were formed by stacking three plates having a corrugated channel of a chevron angle of 45 dog. The R-22 flows down in one channel exchanging heat with the hot water flowing up in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality were explored in detail. During the experiment, the quality change between the inlet and outlet of the refrigerant channel ranges from 0.03 to 0.15. The present data showed that two types of P&SHE have similar trends. The pressure drop in-creases with the vapor quality for both types of P&SHE. At a higher mass flux, the Pressure drop is higher for the entire range of the vapor quality. Also, the increase in the average heat flux increases the pressure drop. Finally, at a higher system pressure, the pressure drop is found to be slightly lower compared to the lower system pressure.

• 한국가금학회:학술대회논문집
• /
• 한국가금학회 2006년도 제23차 정기총회 및 학술발표회
• /
• pp.60-61
• /
• 2006

Effect of dietary salmonella lysate in broiler chicks inoculated with Salmonella typhimurium on the antioxidant system(freshness) of broiler meats during 4$^{\circ}$C refrigeration was investigated. In Pectoral and leg muscle, regardless experimental diets, as the refrigeration day passed, CuZnSOD activity decreased gradually, while at 7d MnSOD activity and peroxide level raised and then lowered at 14d. MnSOD and peroxidase activity, however, had differed according to experimental diets. The results indicated that antioxidant system of broiler meats will be changed according to experimental diets(nutrients). As the CuZnSOD, MnSOD and peroxidase activity are responsible for proteolysis of muscle protein, it was concluded that change of antioxidant system during 4$^{\circ}$C storage explain the biological activity(freshness) of broiler meats.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2009년도 하계학술발표대회 논문집
• /
• pp.893-898
• /
• 2009

The quantity of discharged oil from a compressor is one of the most important issues for proper operation of refrigeration system. If the oil is increased in the system not only pressure drop is increased in other components, such as evaporator and gas cooler but also heat transfer coefficient in the heat exchangers is decreased. In addition, the lack of oil in the compressor may cause a critical of the system failure. In this study, one stage single rotary compressor is used for measuring oil circulation ratio(OCR). Carbon dioxide and PAG oil are used as refrigerant and lubricant. Using a U-tube densimeter, mixture density is measured. Characteristics of oil circulation ratio have been investigated for $CO_2$ rotary compressor in the range of operation frequency 45 Hz to 63 Hz and the suction temperature range of $0^{\circ}C$ to $15^{\circ}C$. The results obtained indicate that the oil circulation ratio is increased as the suction temperature or compressor operating frequency is increased.

• Journal of Advanced Marine Engineering and Technology
• /
• 제18권2호
• /
• pp.25-32
• /
• 1994

The characteristics of the R-22 two-stage compression refrigeration systems were investigated. The apparatus consisted of 0.5HP and 1HP hermetic reciprocating compressors for the high and low stage sides respectively, a condenser, an evaporator, a heat exchanger, four expansion valves, and two intercoolers. The experiments covered a range of refrigerant flow rates from 24 to 84kg/h, and the inlet temperature of cooling water in the condenser and heat source water in the evaporator ranged from 20 to 30$^.\circ}C$The results Showed that the refrigerant flow rate had greater effect on the refrigerating capacities, the compression efficiency and the coefficient of performance of two-stage compression systems than the inlet temperature of heat source water. And all these values were decreased with increasing inlet temperatures of the cooling water. The pressure drops in the evaporator of two-stage compression systems were decreased in proportion to the increase in the inlet temperature of the heat source and cooling water, but it was increased by the refrigerant flow rate.