• Journal of Energy Engineering
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• v.17 no.2
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• pp.116-123
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• 2008

In order to study the heat transfer, effectiveness and pressure drop of an internal heat exchanger (IHX) for $CO_2$, heat pump under heating condition, the experiment and numerical analysis were performed. Four kinds of IHXs were used. The section-by-section method and Hardy-Cross method were used for the numerical analysis. The effects of IHX on the flow rate of refrigerant, the IHX length, the operating condition of a gas-cooler and an evaporator and the type of IHXs were investigated. With increasing the flow rate, the heat transfer rate increased about 25%. The heat transfer of the micro-channel tube was larger about 100% than that of the coaxial tube. With increasing the IHX length, the heat transfer rate decreased. The low-side pressure drop was larger compared with that of the high-side. And the pressure drop of the microchannel tube was larger about 100% than that of the coaxial tube. With increasing the high-side temperature and decreasing the low-side temperature, the heat transfer rate increased about 3%. From this study, we can see that new correlation on $CO_2$ heat transfer characteristics and tube type is necessary.

• New & Renewable Energy
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• v.2 no.2 s.6
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• pp.86-93
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• 2006

유출지하수나 지표수를 열원으로 지열히트펌프의 지초자료로 활용하기 위하여 Pond Loop형 열교환기를 설계, 제작하여 유동이 없는 수조 내에서 수조의 온도가 변화함에 따라 일정한 열교환기 입구온도를 유지하면서 열전달량을 측정하였다. 그 결과 수조를 Heat Source로 사용하는 경우 $5,500{\sim}4,500kcal/h$의 열량이 전달되었고 수조를 Heat Sink로 사용할 경우 $5,200{\sim}3,500kcal/h$의 열량이 전달되었다. 또한 열교환기 관내 유속이 증가함에 따라 열전달량이 증가하는 경향성을 확인할 수 있었고 이는 동시에 열교환기 입출구의 차압을 증가시킴을 알 수 있었다. 열교환기의 설계단계에서 사용하였던 열전달관계식으로 구한 총괄열전달계수, U와 실험값을 통해 유추한 U값을 비교한 결과 실험에 의해 유추된 U값이 $24{\sim}27%$ 설계치보다 크게 나타났다. 본 연구를 통하여 유출지하수 뿐만 아니라 하수 및 하천수를 이용한 지열히트펌프의 기초자료를 확보할 수 있었다.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.15-19
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• 2006

유출지하수나 지표수를 열원으로 하는 지열히트펌프의 Pond Loop형 열교환기를 개발하기 위하여 미국에서 상용화된 Slim-Jim 열교환기와 본 연구에서 자체설계, 제작한 Pond-loop type의 열교환기를 유동이 없는 유출수조 내에서 수조온도가 변화함에 따라 일정한 열교환기 입구온도를 유지하면서 열전달량의 변화를 측정하였다. 그 결과 유출수를 Heat Source로 사용하는 경우 Slim-Jim에서는 $8,000{\sim}11,000 kcal/hr$의 열량이 전달되었고, 자체 제작한 열교환기에서는 $11,000{\sim}16,000kcal/hr$의 열량이 전달되었다. 유출수를 Heat Sink로 사용할 경우 Slim-Jim에서는 $2,500{\sim}7,000 kcal/h$의 열량이 전달되었고, 자체제작한 열교환기의 경우, $6,800{\sim}14,00 kcal/hr$의 열량이 전달되었다. 측정된 열전달량을 바탕으로 총괄열전달계수를 구한 결과 Slim-Jim 열교환기의 경우 $210{\sim}340 kcal/hr\;m^2{\circ}C$, 자체개발한 열교환기의 경우 $350{\sim}590 kcal/hr\;m^2{\circ}C$로 나타나 자체 개발한 열교환기의 열전달 성능이 비교적 우수함을 입증하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.445-450
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• 2006

유출지하수나 지표수를 열원으로 하는 지열히트펌프의 기초자료로 활용하기 위하여 Pond Loop형 열교환기를 설계, 제작하여 유동이 없는 수조 내에서 수조의 온도가 변화함에 따라 일정한 열교환기 입구온도를 유지하면서 열전달량을 측정하였다. 그 결과 수조를 Heat Source로 사용하는 경우 $5,500{\sim}4,500kcal/h$의 열량이 전달되었고, 수조를 Heat Sink로 사용할 경우 $5,200{\sim}3,500 kcal/h$의 열량이 전달되었다. 또한 열교환기 관내 유속이 증가함에 따라 열전달량이 증가하는 경향성을 확인할 수 있었고, 이는 동시에 열교환기 입출구의 차압을 증가시킴을 알 수 있었다. 열교환기의 설계단계에서 사용하였던 열전달관계식으로 구한총괄열전달계수, U와 실험값을 통해 유추한U값을 비교한 결과 실험에 의해 유추된 U값이 $24{\sim}27%$ 설계치보다 크게 나타났다. 본 연구를 통하여 유출지하수 뿐만 아니라 하수 및 하천수를 이용한 지열히트펌프의 기초자료를 확보할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.6
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• pp.1959-1970
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• 1996

Effects of oscillatory flow upon heat transfer characteristics have been studied experimentally for oscillating flow in a circular tube. The experimental apparatus was designed to simulate the heat exchangers of the Stirling or Vuilleumier cycle machines and the test section consists of heater and cooler. Measurements were presented of heat flux, axial wall temperature distribution, and radial temperature profile of the working fluid for several cases of oscillation frequency and swept distance ratio. The influences of two main parameters, frequency and tidal displacement of the oscillation were investigated. Then the heat transfer coefficient at the heater is obtained. The carried by the authors with a assumption of oscillatory laminar slug flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.5
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• pp.515-522
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• 2010

The objective of this study is to investigate the air-side heat transfer characteristics of a spirally-coiled circular fin-tube heat exchanger for various geometric parameters under non-frosting conditions. The heat transfer characteristics of the heat exchanger were analyzed with respect to heat exchanger geometries, and then, the characteristics were compared with those of rectangular-plate fin-tube heat exchangers with discrete fins. The heat transfer coefficient increased with a decrease in the number of tube rows and an increase in the fin pitch. The optimum length of the L-foot was 2.7 mm. In addition, the heat transfer rate increased with a decrease in the tube pitch and the tube thickness. The heat transfer coefficient of the spirally-coiled circular fin-tube heat exchanger was 24.3% higher than that of the rectangular-plate fin-tube heat exchanger.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.105-112
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• 2011

The objective of this study is to predict the heat-transfer performance of a spirally coiled circular fin-tube evaporator in which either R134a or R600a was used; this heat-transfer performance was predicted by varying the mass flow rate, inlet air temperature, air flow rate, and tube thickness. Mean deviation for the analytical model from the measured data was ${\pm}8.3%$. Simulation results revealed that at a given mass flow rate, the heat-transfer rate of the evaporator using R600a was higher than that usingR134a because the enthalpy of the former is higher than that of the latter at the given conditions. The heat-transfer rate of both refrigerants increased with an increase in the air flow rate and inlet air temperature but decreased with an increase in the tube thickness.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1584-1595
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• 1993

Many researches were carried out to estimate heat transfer rate on a circular cylinder in a uniform flow. Various empirical correlations were suggested in the past through expermental studies, however there are considerable discrepancies in the estimated values of heat transfer coefficient. Effects of variable properties of fluid on the heat transfer between a circular cylinder and the external uniform flow were numerically investigated in the present study. The flow and temperature fields were solved using a finite volume method for the uniform flow temperature of 200-900K and the wall temperature of 300-900K. The cold as well as the hot cylinders in the uniform flow of constant temperature were investigated. A unified correlation was obtained for the both cases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.8
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• pp.553-561
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• 2017

The main motivation for this study was to establish a CFD-based procedure for the analysis of heating characteristics, particularly in industrial furnaces. As certain open-source software packages have gained popularity in dealing with complex industrial problems, the OpenFOAM framework was selected for further development of advanced physical models to meet industrial requirements. In this study, the newly developed comprehensive model was applied to simulate physical processes in the full-scale horizontal furnace of a continuous galvanizing line (CGL). The numerical results obtained indicate that the current approach predicts heating characteristics reasonably well. It was also found that radiative heat transfer plays a dominant role in heating the moving strip. To improve the predictability of our method, further work is required to model the turbulence-chemistry interaction realistically, as well as to impose a physically correct thermal wall boundary condition.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.399-402
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• 2006

The purpose of this study is to propose a method for protecting injector face for prolonged combustion time and heat flux measurement technique at the injector face. To obtain basic design data and verify the performance of the proposed method, a regenerative cooling injector face was designed and manufactured for the hot firing test. Due to the safety reason, hot fire test were performed 3, 10, 30, 60 and 120 seconds time step. The discrepancy between analytical results adapting to combustion and nozzle and experimental results is believed due to the over estimation of the convection heat transfer calculation. for the injector face, flow velocity is almost negligible, therefore radiation is more important than convection. Consecutive hot firing test during 10, 30, 60 and 120 seconds combustion time shows good repeatability.