• 동력기계공학회지
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• 제13권6호
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• pp.70-75
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• 2009

In this paper, cycle performance analysis of R744($CO_2$) two-stage compression and one-stage expansion refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include superheating degree, compressor efficiency, gas cooling pressure, mass flowrate ratio, outlet temperature of gas cooler and evaporating temperature in the carbon dioxide two-stage refrigeration cycle. The main results were summarized as follows : The cooling capacity of two-stage compression and one-stage expansion refrigeration system increases with the increasing superheating degree, compressor efficiency and gas cooling pressure, but decreases with the increasing mass flowrate ratio and evaporating temperature. The compression work of two-stage compression and one-stage expansion refrigeration system increases with the increasing superheating degree, outlet temperature of gas cooler, gas cooling pressure and evaporating temperature, but decreases with the increasing compressor efficiency and mass flowrate ratio. The COP of two-stage compression and one-stage expansion refrigeration system increases with the increasing compressor efficiency, but decreases with the increasing superheating degree, gas cooling pressure, mass flowrate ratio and evaporating temperature. Therefore, superheating degree, compressor efficiency, gas cooling pressure, mass flowrate ratio, outlet temperature of gas cooler and evaporating temperature of R744($CO_2$) two-stage compression and one-stage expansion refrigeration system have an effect on the cooling capacity, compressor work and COP of this system.

• 대한기계학회논문집B
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• 제25권8호
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• pp.1131-1139
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• 2001

Experimental results are presented, which describe the effect of blowing ratio on film cooling from two rows of holes with opposite orientation angles. The inclination angle is fixed at 35°, and the orientation angles are set to be 45°for the downstream row, and -45°for the upstream row. The studied blowing ratios are 0.5, 1.0 and 2.0. The boundary layer temperature distributions are measured using thermocouple at two downstream locations. Detailed adiabatic film cooling effectiveness and heat transfer coefficient distributions are measured with TLC(Thermochromic Liquid Crystal). The adiabatic film cooling effectiveness and heat transfer coefficient distributions are discussed in connection with the injectant behaviors inferred from the boundary layer temperature distributions. Film cooling performance, represented by heat flux is evaluated from the adiabatic film cooling effectiveness and heat transfer coefficient data. The results show that the investigated geometry provides improved film cooling performance at the high blowing ratios of 1.0 and 2.0.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.113-118
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• 2000

Experimental results describing the effects of blowing ratio on film cooling from two rows of holes with opposite orientation angles are presented. The inclination angle was fixed at $35^{\circ}$ and the orientation angles were set to be $45^{\circ}$ for downstream row. and $-45^{\circ}$ for upsream row. The studied blowing ratios were 0.5, 1.0 and 2.0. The boundary layer temperature distributions were measured using thermocouple at two downstream loundary layer temperature distributions were measured using thermocouple at two downstream locations. Detailed adiabatic film cooling effectiveness and heat transfer coefficient distributions were measured with TLC(Thermochromic Liquid Crystal). The adiabatic film cooling effectiveness and heat transfer coefficient distributions are discussed in connection with the injectant behaviors inferred from the boundary layer temperature distributions. Film cooling performance, represented by heat flux was calculated with the adiabatic film cooling effectiveness and heat transfer coefficient data.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.43-48
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• 2011

Cooling system's operation ratio shall be controlled automatically by the internal external temperature sensors in rolling stock. The Cooling System shall be the automatic operation ratio control system which automatically controlling the rotation speed of condenser, evaporator etc. using temperature detection from outside and inside of cabin. This paper will examine the cooling system that can be provide comfortable cooling service for passenger in summer.

• 오토저널
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• 제5권1호
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• pp.89-93
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• 1983

This paper describes on experimental investigation into the heat dissipation of Diesel engine, placing emphasis on the variations of compression ratio and cooling water temperature. The engine used for this test was a vertical single-cylinder four-cycle type, having a direct injection. Engine performance and heat transfer rates was tested under the compression ratio 14.3 and 17.4. In this study, the results showed that output and transfer rates of engine decrease in accordance with the decrease of compression ratio. The effect of cooling water temperature and injection delay of fuel on the heat dissipation brings about the decrease of heat transfer rates from cylinder to cooling water.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.194.2-194.2
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• 2011

Heating and cooling performance has been analyzed for the water-source heat pump system using raw water from Daechung reservoir. During heating operation from March to May, water temperature is not good condition for a heat source due to the higher atmospheric temperature. Avearged heating load ratio is only 14.3%, and the averaged unit COP and system COP are estimated to be 2.46 and 2.15 respectively. The COP is affected considerably by the water temperature, and the unit COP is increased from 2.16 at $5^{\circ}C$ to 2.95 at $11^{\circ}C$. Cooling performance is analyzed with the measured data from June to August. During cooling operation, raw water has lower temperature by 4. $5^{\circ}C{\sim}4.7^{\circ}C$ than the atmosphere. The load ratio is 39.2%, and the averaged unit COP and system COP are estimated to be 7.25 and 6.13 respectively. The heating COP is affected by the load ratio rather than water temperature. The COP is increased for 20%~40% load ratio, while is decreased for 40%~60% load ratio. It is estimated that the compressor operation combination for 3 (two constant speed and one inverter) compressors is changed for the load ratio.

• International Journal of Advanced Culture Technology
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• 제4권2호
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• pp.47-56
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• 2016

In transformer cooling systems, oil temperature is controlled through the use of a blower and oil pump. For this paper, set-point algorithms, a reset algorithm and control algorithms of the cooling system were developed by neural networks and fuzzy logics. The oil inlet temperature was set by a $2{\times}2{\times}1$ neural network, and the oil temperature difference was set by a $2{\times}3{\times}1$ neural network. Inputs used for these neural networks were the transformer operating ratio and the air inlet temperature. The inlet set temperature was reset by a fuzzy logic based on the transformer operating ratio and the oil outlet temperature. A blower was used to control the inlet oil temperature while the oil pump was used to control the oil temperature difference by fuzzy logics. In order to analysis the performance of these algorithms, the initial start-up test and the step change test were performed by using the dynamic model of a transformer cooling system. Test results showed that algorithms developed for this study were effective in controlling the oil temperature of a transformer cooling system.

• 대한기계학회논문집
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• 제17권10호
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• pp.2590-2600
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• 1993

The present paper describes numerical predictions for the film cooling effectiveness from a row of hole at various injection ratios and injection alngles.Numerical calculations were performed to investigate film cooling effectiveness and the characteristics of flow and temperature distributions in the region near the downstream of injection hole including the region of adverse pressure gradient. The elliptic 3-dimensional governing equations with variable thermal properties were solved by SIMPLE algorithm. The results showed that the presence of adverse pressure gradient in the region near the downstream of injection hole induces large temperature gradient. At injection angle of $35^{\circ}$ the average film cooling effectiveness was increased as increased of injection ratio up to 1.0. At injection angle of $90^{\circ}$ however, the average film cooling effectiveness was decreased from injection ratio larger than 0.4.

• 대한기계학회논문집B
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• 제25권8호
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• pp.1122-1130
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• 2001

Film cooling performance from two rows of holes with opposite orientation angles is evaluated in terms of heat flux ratio. The film cooling hole has a fixed inclination angle of 35°and orientation angle of 45°for the downstream row and -45°for the upstream row. Four film cooling hole arrangements including inline and staggered configurations are investigated. The blowing ratio studied was 1.0. Boundary layer temperature distributions are measured to investigate injectant behaviors and mixing characteristics. Detailed distributions of the adiabatic film cooling effectiveness and the heat transfer coefficient are measured using TLC(Thermochromic Liquid Crystal). For the inline configuration, there forms a downwash flow at the downstream hole exit to make the injectant well attach to the wall, which gives high adiabatic film cooling effectiveness and heat transfer coefficient. The evaluation of heat flux ratio shows that the inline configuration gives better film cooling performance with the help of the downwash flow at the downstream hole exits.

• 한국식품저장유통학회지
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• 제4권3호
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• pp.237-243
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• 1997

Numerous variables affect product cooling rate of pressure cooling system for fruits and vegetables. These include carton vent area, initial and desired final product temperature, flow rate and temperature of the cooling air, product size, shape and thermal properties and product configuration(whether in bulk or packed in shipping cartons). This study was carried out to determine the influence of each of these variables as they affect cooling time. The opening ratio and number of the vent hole were recomended as 4∼10% and 2∼4ea., respectively, for a minimum alt flow resistance and for a uniform air flow pattern. In the cooling experiment for tomatoes and mandarins, optimum air flow rate was 0.04 m3/min.kg in terms of energy saving. The cooling air temperature should be about 2$^{\circ}C$ less than the desired final product temperature for reducing cooling time.