• 설비공학논문집
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• 제26권11호
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• pp.504-511
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• 2014

The objective of this study is to theoretically analyze the performance of an open wet air-cycle refrigeration system, which nowadays is increasingly generating environmental concern. The temperature and relative humidity of the outside air are selected as the most important parameters. As the temperature and relative humidity of the outside air increase, the pressure ratio of the ACM compressor is determined to be nearly constant, the air temperature at the exit of the system increases, and the amount of condensed water, the cooling capacity, the COP, and the total entropy production rate increase overall. The effects of the effectiveness of the heat exchanger and the efficiency of the turbine on the performance are greater than that of the efficiency of the ACM compressor. Also, the performance of the wet air-cycle refrigeration system with two heat exchangers is enhanced, with a high COP and low total entropy production rate, compared to the system with a single heat exchanger.

• 설비공학논문집
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• 제17권10호
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• pp.891-897
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• 2005

The characteristics of energy Performance for total heat exchanger have been investigated under various conditions. In cooling operation the latent and enthalpy efficiency are affected by the difference of absolute humidity ratio between indoor and outdoor air. In addition to this the characteristics of absorbing material in the element affects the energy performance. Low dry bulb temperature of indoor air or high absolute humidity ratio in outdoor air give high latent and enthalpy efficiency even with the same temperature difference of dry bulb temperate between indoor and outdoor air.

• 한국세라믹학회지
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• 제28권10호
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• pp.819-823
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• 1991

Pure zirconia ceramic fiber experiences severe volume changes through thermal cyclings of heating and cooling. Zirconia fiber was doped with CaO to stabilize the phase and its effect of CaO was studied on volumetric ratio of each phases, phase transition temperature and microstructure. Tetragonal phase was increased as CaO increases up to 10 mol% and cubic phase was stabilized when CaO was added more than 10 mol%. The average grain size of zirconia fiber was increased as CaO increased and transition temperature was shifted to lower temperature.

• Journal of Advanced Marine Engineering and Technology
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• 제25권6호
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• pp.1324-1329
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• 2001

The depression of the external situation like the departure of WTO system and the plan of EEZ proclaim is forcing fishery into improving their fishing condition. By this international and domestic circumstance, development of the sea water cooling apparatus for fish hold storage is demanded sincerely. This study represents the thermal characteristics of the fish hold storage during transportation. The numerical analysis in this study is the finite volume method with the SIMPLE computational algorithm to study the seawater flow behavior in the fish hold storage. The computation were carried out with the variations of the circulating flow velocity and depth of fish hold storage. As the result of the three dimensional simulations, the mean temperature doesn't almost change by the circulating flow rate. find the mean temperature is suddenly changed by the ratio of depth of fish hold storage.

• 태양에너지
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• 제4권2호
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• pp.43-49
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• 1984

Experiments were performed to study freezing on a finned vertical tube when either conduction in the solid or natural convection in a liquid controls the heat transfer. Conduction is the controlling mode when the liquid is at its fusion temperature, whereas natural convection controls when the liquid temperature is above the fusion value. The liquid was housed in a cylinderical containment vessel whose surface was maintained at a uniform, time-invariment temperature during a data run, and the freezing occurred on a finned vertical tube positioned along the axis of the vessel. The phase change medium was n-octacosan, a paraffin which freezes at about $61^{\circ}C$. For conduction-controlled freezing, the enhancement of the frozen mass due to finning is greatest when the frozen layer is thin and decrease as the layer grows thicker. The degree of enhancement is generally less than the surface area ratio of the finned and unfinned tube.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.265-268
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• 1999

In this study, we manufactured the ultra-high strength concrete using mineral admixture which is easily workable. From the test results of compressive strength, It is concluded that the proper replacement ratio of silica fume should not exceed to 10% and the replacement of slag is more effective that the replacement of fly ash to gain very high compressive strength. Thermal stress analysis is conducted to find the way of controlling the thermal crack of ultra-high strength concrete. As results of thermal stress analysis, it was found that reducing placing temperature of concrete(pre-cooling) is effective to reduce thermal crack and placing concrete in high air temperature is more effective than placing concrete in low air temperature.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.696-702
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• 2002

In the present paper, the effects of inlet pressure on the heat and mass transfer rates of an air cooler are numerically predicted by a local analysis method. The pressures of the moist air vary from 2 to 4 bars. The psychrometric properties such as dew point temperature, relative humidity and humidity ratio are employed to treat the condensing water vapor in the moist air when the surface temperatures are dropped below the dew point. The effects of the inlet pressures on the heat transfer rate, the dew point temperature, the rate of condensed water, the outlet temperature of air and cooling water are calculated. The condensation process of water vapor is discussed in detail. The results of present calculations are compared with the test data and shows good agreements.

• 신재생에너지
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• 제4권4호
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• pp.17-22
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• 2008

A low concentrating (< 5X) photovoltaic module with aluminum reflectors is fabricated and evaluated which is designed to reduce the affection of the high temperature to the solar cell modules preventing the efficiency lowering. As results, the output power is increased of 1.97X from the concentrating photovoltaic module which is designed with the concentrating ratio of 2.25X and to control the module temperature cooling the module by air circulation. Also, the effect of the concentrating module with aluminum reflectors on the conventional PV module is investigated at the field. The result shows the increase of the output power more than about 20% and the improvement of the module efficiency of 1.4X in spite of the increase of average module temperature.

• Macromolecular Research
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• 제10권6호
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• pp.365-368
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• 2002

Thermoplastic polyurethanes (TPUs) with different hard segment length has been prepared from a fixed molar ratio of poly(tetramethylene ether glycol), 4,4'-diphenylmethane diisocyanate, and 1,4-butanediol by different polymerization procedures. Results reveal that the on-set temperature of endotherms ( $T_{cc}$ ) due to the crystallization of hard segments by cooling the TPUs from melt and the peak temperature of endotherms due to the melting of hard segments ( $T_{mh}$ ) by heating the TPUs increased and levelled off with increasing the hard segment length of TPUs. It has also been observed that soft segment glass transition temperature ( $T_{gs}$ ) of TPU decreased slightly with increasing the hard segment length, which explains less mixing of soft segments and hard segments. In tensile measurement of TPUs, strain hardening is observed with increasing the hard segment length, which is attributed to the strain induced crystallization of soft segments.

• 대한기계학회논문집B
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• 제40권4호
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• pp.213-220
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• 2016

본 연구의 목적은 열대 지방에서 사용되는 특수목적 자동차용 에어컨 시스템의 냉방성능 특성을 고찰하는 것이다. 이를 위하여 R-134a를 사용하는 듀얼 냉동사이클을 구성하였고 냉매량 및 실내온도를 변화시켜가면서 냉방성능을 비교하였다. 외기온도 $40.0^{\circ}C$에서 듀얼 냉동사이클의 실내 냉각속도 및 압축비(토출압력) 등을 고려하여 최적 냉매량을 1.5kg으로 선정하였다. 실내온도가 증가할수록 냉방부하가 증가하여 $25.0^{\circ}C$에서 $32.5^{\circ}C$로 실내온도를 높일 경우 $15.0^{\circ}C$에 도달하는데 걸리는 시간은 86.5% 증가하였고, $32.5^{\circ}C$에서 $40.0^{\circ}C$로 증가할 경우 38.1% 증가하였다. 또한, 실내온도가 $25.0^{\circ}C$에서 $40.0^{\circ}C$로 증가할수록 냉방용량은 19.1 kW에서 20.5 kW로 7.3% 증가했으나 냉방성능(COP)는 4.67에서 5.1로 7.0%감소하였다.