• 한국자동차공학회논문집
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• 제16권1호
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• pp.121-126
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• 2008

The cooling heat transfer coefficient of $CO_2$ (R-744) in a horizontal and helically coiled tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater, evaporator and gas cooler (test section). The test section consists of a horizontal stainless steel tube and hellically coiled copper tube of 4.57 and 7.75 mm. The experiments were conducted at saturation temperature of 100 to $20^{\circ}C$, and mass flux of 200 to $500kg/m^2s$. The test results showed the variation of the heat transfer coefficient tended to decrease as cooling pressure of $CO_2$ increased. The heat transfer coefficient with respect to mass flux increased as mass flux increased. The experimental results were also compared with the existing correlations for the supercritical heat transfer coefficient, which generally underpredicted the measured data. However, the experimental data showed a relatively good agreement with the correlations of Pitla et al. except for the pseudo critical temperature.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.190-190
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• 2011

In South Korea the gross generation and heated effluent of power generation plant was 259 TWh and 4.73 billion tons in 2008. And then the waste heat from power generation was 388 TWh. It shows that the efficiency of thermal power generation plant is about 40%. Therefore to reduce $CO_2$ emission from thermal power generation plant, the energy of this heated effluent must be reused to heat buildings or farm facilities. In South Korea horticultural facilities of about 25% are heated in winter season. Total area of greenhouses which are heated is about 13,000 ha. Total heat amount needed to warm greenhouse of 13,000 ha in winter season is only 3.4% of total waste heat from power generation plant. In this study a heat pump system was designed to reuse the waste heat from power generation. Especially new heat exchanger was developed to recover the thermal energy from waste water and this model considered anti-corrosion against sea water and low cost for economic feasibility. This heat recovery system was installed in mango growing greenhouse around thermal power generation plant in Seogwipo-city, Jeju Special Self-Governing Province. The result of preliminary test shows that the heating cost of about 90% is saved as compared to boiler using tax free light oil as a fuel.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.587-589
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• 2009

The districts of underground geologic structure in Jeju island where underground air is distributed are lava cave, pyroclastic, open joint, and crushing zone. Such districts are identified to secure an enough airflow when air ventilation layer is to secure 25-35m in depth. In Jeju, Ground air is used for heating greenhouse and fertilizing natural $CO_2$ gas by suppling directly into greenhouse. But the heating method by suppling ground air into greenhouse directly bring about several problem. The occurrence of disease of the crops by high humidity is worried because the underground air which becomes discharge from underground air layer has over 90% relative humidity. The underground air is inadequate in heating for crops which need high temperature heating such as mangos, Hallbong and mandarin orange because the temperature of it is $15{\sim}18^{\circ}C$. Also There is worry where the ventilation loss becomes larger because the air pressure inside greenhouse is high by supplying underground air directly. In this study the heat pump system using underground air as heat source was developed and heating performance of the system was analysed. Heating COP of the system was 2.5~5.0 and rejecting heat into greenhouse and extracting heat from underground air were 40,000~27,000 kcal/h, 30,000~18,000 kcal/h respectively.

• Journal of Advanced Marine Engineering and Technology
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• 제31권3호
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• pp.263-271
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• 2007

The heat transfer coefficient and pressure drop during 9as cooling process of $CO_2$ (R744) in a helically coiled copper tube with the inner diameter of 4.55 mm and outer diameter of 6.35 mm were investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump. a mass flow meter a pre-heater and a helically coiled type gas cooler (test section). The refrigerant mass fluxes are varied from 200 to $800kg/m^2s$ and the inlet pressures of gas cooler are 7.5 to 10.0 MPa. The heat transfer coefficients of $CO_2$ in a helically coiled tube are higher than those in a horizontal tube. The Pressure drop of $CO_2$ in the gas cooler shows a relatively good agreement with those predicted by Ito's correlation developed for single-phase in a helically coiled tube. The local heat transfer coefficient of $CO_2$ agrees well with the correlation by Pitla et al. However. at the region near pseudo-critical temperature. the experiments indicate higher values than the Pitla et al correlation. Therefore, various experiments in helically coiled tubes have to be conducted and it is necessary to develop the reliable and accurate prediction determining the heat transfer and pressure drop of $CO_2$ in a helically coiled tube.

• 설비공학논문집
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• 제16권2호
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• pp.158-166
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• 2004

The performance of a heat pump using $CO_2$ is predicted and analyzed by using a cycle simulation model developed in this study. Cycle simulations are conducted by varying design parameters and operating conditions with the applications of advanced techniques to improve system performance. The applied systems in the simulations are internal heat exchanger, expander, and 2-stage compression with intercooling. As a result, the applications of advanced techniques improve the heating and cooling performances of the transcritical $CO_2$ cycle by 8∼26％ and 20∼30％, respectively, over the basic cycle.

• 생물환경조절학회지
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• 제22권4호
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• pp.328-334
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• 2013

본 연구에서는 온실 내부의 태양 잉여열과 외부의 공기열을 선택적으로 열원으로 이용함으로써 히트펌프의 성능을 향상시키고, 온실의 환기 지연을 통해 이산화탄소 시용비용을 절감할 수 있는 온실 공조시스템을 개발하고자 하였다. 본 시스템의 축열 과정은 태양 잉여열을 이용하는 내부순환모드와 외기열을 이용하는 외부순환모드가 온실 내부온도에 따라 자동으로 절환되도록 구성하였으며, 히트펌프 가동, 축열모드 절환, 난방 가동을 위한 6개의 온도값을 입력함으로써 축열과 난방이 자동으로 수행되도록 설계하였다. 단동온실을 대상으로 무환기 조건에서 기초시험을 수행한 결과, 태양 잉여열을 이용한 축열은 약 11시부터 시작되어 평균 3시간 30분 정도 유지되었으며, 주간의 온실 내부온도는 환기를 수행하지 않음에도 대부분 약 $20{\sim}28^{\circ}C$ 범위를 유지하였다. 주간 내부순환모드에서 시스템의 난방성능계수는 약 3.35로 야간 외부순환모드의 2.46 및 주간 외부순환모드의 2.67에 비해 각각 36% 및 25% 향상됨을 확인하였다. 본 시스템의 개선사항으로 태양 잉여열의 효율적 이용을 위해 축열조 관리온도를 상승시킬 수 있는 고효율 히트펌프의 적용이 필요하며, 온실의 무환기 운용에 따른 과습환경의 조성을 방지하고 태양 잉여열 수준이 높은 시기에 온실의 온도상승을 방지하기 위해 강제환기를 운전모드에 추가할 필요가 있는 것으로 판단되었다.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.216-221
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• 2005

The heat transfer coefficient and pressure drop during gas cooling process of carbon dioxide in a helically coiled tube were investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a double pipe type heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. It was made of a copper tube with the inner diameter of 4.85 [mm], the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were 200${\sim}$600 [kg/$m^2$s] and the average pressure varied from 7.5 [MPa] to 10.0 [MPa]. The main results were summarized as follows: The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

• 대한기계학회논문집B
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• 제25권1호
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• pp.54-61
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• 2001

Condensing heat transfer coefficients of R-22 and R-134a were measured in smooth, horizontal copper tubes with inner diameters of 1.77mm, 3.36mm, and 5.35mm, respectively. The experiments were conducted in the closed loop, which was driven by a magnetic gear pump. Data are presented for the following range of variables : mass velocity from 200 to 500kg/$m^2$.s and quality from 0 to 1.0. The heat transfer coefficients in the small diameter tubes (ID < 7mm) were observed to be strongly affected by various diameters and the heat transfer characteristics in the small diameter tubes differed from those in the large diameter tubes. Heat transfer coefficients in the small diameter tubes are higher than those in the large diameter tubes at the same experimental condition. It was found that some well-known previous correlations(Shahs correlation and Cavallini-Zecchins correlation) were not suitable for small diameter tubes.

• 한국가스학회지
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• 제11권3호
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• pp.1-6
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• 2007

본 연구에서는 경사진 헬리컬 코일형 동관내 이산화탄소의 증발 열전달 계수와 압력강하를 실험적으로 조사하였다. 냉매 순환루프의 주요구성품은 수액기, 변속펌프, 질량유량계, 예열기, 경사진 헬리컬 코일형 가스냉각기(시험부)로 구성된다. 시험부는 내경 4.55 mm의 평활 동관으로 이루어져 있다. 냉매질량 유속은 $200kg/m^2s$에서 $600kg/m^2s$까지 변화시켰고, 가스냉각기의 입구압력은 7.5 MPa에서 10.0 MPa까지이다. 경사진 헬리컬 코일관내 이산화탄소의 열전달 계수는 질량유속과 냉각압력의 증가와 함께 따라 증가하였다. 이산화탄소의 압력강하는 헬리컬 코일관내 단상 상관식인 Ito식과 좋은 일치를 보였고, 이산화탄소의 국소 열전달 계수는 Pilta 등이 제안한 상관식과 좋은 일치를 보였다. 하지만, 유사임계 온도 영역부근에서는 실험데이터가 더 높게 나타났다.

• 설비공학논문집
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• 제17권2호
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• pp.173-182
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• 2005

The Performance of U-tube ground heat exchanger for geothermal heat Pump systems depends on the thermal properties of the soil, as well as grout or backfill materials in the borehole. In-situ tests provide a means of estimating some of these properties. In this study, in-situ thermal response tests were completed on two vertical boreholes, 130 m deep with 62 mm diameter high density polyethylene U-tubes. The tests were conducted by adding a monitored amount of heat to water over a $17\~18$ hour period for each vertical boreholes. By monitoring the water temperatures entering and exiting the loop and heat load, overall thermal conductivity values of grout/soil formation were determined. Two parameter estimation models for evaluation of thermal response test data were compared when applied on the same temperature response data. One model is based on line-source theory and the other is a numerical one-dimensional finite difference model. The average thermal conductivity deviation between measured data and these models is of the magnitude $1\%$ to $5\%$.