• Progress in Superconductivity and Cryogenics
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• v.11 no.1
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• pp.60-63
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• 2009

Most J-T (Joule-Thomson) refrigerators use a Giaque-Hampson type heat exchanger due to its excellent thermal performance and compactness. The cryoprobe (cryosurgical probe) treating prostate cancer usually has a dimension of 17 gauge (1.6 mm diameter), so it does not have enough space to bear a Giaque-Hampson type heat exchanger. In this paper, the triplet heat exchanger is adopted as the heat exchanger of cryoprobe, and the performance is investigated with an experimental test. The result shows that the triplet heat exchanger can be substituted for Giaque-Hampson type heat exchanger in the application of cryosurgery.

• Plant Journal
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• v.10 no.3
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• pp.45-51
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• 2014

This study performs several experiments on a newly developed temperature safety system that can be used for residential building heating systems, the heat source of which is derived from a conventional fuel cell. Prior to this, the hot water made from a fuel cell was not used in residential housing but just went to waste. The present safety system is installed in the current underfloor heating system. At first we used the CFD technique to develop a new heat exchanger. The fuel cell must satisfy the thermal conditions of the inlet temperature being $55^{\circ}C$ and the outlet temperature being $60^{\circ}C$. But variations in weather cause fluctuations in the heating water temperature. The experimental results show our new system capable of maintaining the temperature difference within a ${\pm}0.5^{\circ}C$ range. So we believe that our new PFMFC fuel cell stack array is a good candidate for being used in residential heating systems.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.14-14
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• 1999

비활성 가스제너레이터는 가스터빈 추진기관 및 기타 열기관을 이용하여 연소가 되지 않는 저온의 공기를 생산하는 기계장치를 말하며 이러한 저온의 비활성 기체를 화재 지역에 분사하는 경우 기존의 소방수를 이용한 화재 진압방식보다 매우 효율적으로 화재진압에 사용되어 질 수 있다. 일반적으로 민항기 등의 가스터빈 추진 기관에서 배기되는 기체내에는 터빈입구온도(TIT : Turbine Inlet Temperature)및 초과공기지수(Excess Air Coefficient)에 따라 다르게 나타나지만 TIT가 1500$^{\circ}$K인 경우 약 13-14%정도의 산소가 잔존하는 것으로 알려져 있다. 따라서 본 연구에서는 가스터빈 및 열교환 시스템 그리고 터빈 1단 등의 시스템 조합율을 통하여 대기 중의 기체의 온도를 영하 2$0^{\circ}C$ 및 산소함유량을 약 5%수준까지 낮춤으로서 이를 대형 화재 진압에 사용하기 위한 연구이다. 비활성 가스제너레이터에 사용하는 연료로는 Kerosene 및 CNG(Compressed Natural Gas)등이 사용될 수 있으며, 유량이 8.1kg/sec인 터보축 가스터빈 엔진을 사용하는 경우 18750㎥ 부피의 비활성기체를 생산하는데 Kerosene 연료가 약 1톤(200＄ 이하)이 필요한 것으로 계산되며 이에 소요되는 시간도 약 52분에 지나지 않는 것으로 계산되었다. 만일 50kg/sec의 보다 큰 가스터빈 엔진을 사용하는 경우 약 9분 정도가 필요한 것으로 계산되었다. 사용되는 가스터빈은 압축비가 15, 열교환기의 효율이 $\varepsilon$=0. 그리고 최종 터빈 1단의 팽창비가 1.25가 적합한 것으로 계산된다. 연구 분석 결과 기술적 문제점으로는 배기 가스온도가 낮은데 따른 출구 부분의 Bearing, Sealing이 문제가 될 수 있다고 판단되며 배기 가스 자체에 대기 공기중에 함유되어 있던 습기가 얼어붙는(Icing화) 문제가 발생하기 때문에 배기가스의 Icing을 방지하기 위하여 압축기 끝단에서 공기를 추출하여 배기부분에 송출할 필요성이 있는 것으로 판단되었다. 출구가스의 기체 유동속도가 매우 빠르므로 (100-l10m.sec) 이를 완화하기 위한 디퓨저의 설계가 요구된다고 판단된다. 또 연소기 후방에 물을 주입하는 경우 열교환기 및 기타 부분품에 발생할 수 있는 부식 및 열교환 효율 저하도 간과할 수 없는 문제로 파악되었다. 이러한 기술적 문제가 적절히 해결되는 경우 비활성 가스 제너레이터는 민수용으로는 대형 빌딩, 산림, 유조선 등의 화재에 매우 적절히 사용되어 질 수 있을 뿐 아니라 군사적으로도 군사작전 중 및 공군 기지의 화재 그리고 지하벙커에 설치되어 있는 고급 첨단 군사 장비 등의 화재 뿐 아니라 대간첩작전 등에 효과적으로 활용될 수 있을 것으로 판단된다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7736-7744
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• 2015

Considering the significant waste of industrial energy, effective use of low temperature waste heat is extremely important. In this study, a heat pump cycle with double effect and double stage was realized, which escalates the hot water temperature from $50^{\circ}C$ to $70^{\circ}C$ using $160^{\circ}C$ high temperature heat source and $17^{\circ}C$ low temperature heat source. The steam generated in the first generator condenses in the first condenser generating steam in the second generator. The steam condenses in the second condenser and is provided to the second evaporator. Part of the water out of the second evaporator is supplied to the first evaporator, which evaporates using low temperature waste heat. The evaporated steam enters the first absorber and the second evaporator. The steam out of the second evaporator is absorbed into the solution at the second absorber. The hot water temperature is raised in the second condenser and in the second absorber. Proper flow rates and UA values, which satisfied temperature lift $20^{\circ}C$ and COP 1.6, were deduced through trior and error. The COP increases as the temperature of the high temperature water increases, hot water temperature decreases and flow rate increases, waste water temperature and flow rate increases, solution circulation rate decreases. On the other hand, the temperature rise of the hot water increases as the temperature of the high temperature water increases, hot water temperature increases and flow rate decreases, waste water temperature and flow rate increases, solution circulation rate increases. In addition, the COP and hot water temperature rise increase as UAs of the heat exchangers increase.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.11
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• pp.699-707
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• 2017

This study presents a comparative thermodynamic analysis of subcritical and transcritical organic Rankine cycles for the recovery of low-temperature heat sources considering nine substances as the working fluids. The effects of the turbine inlet pressure, source temperature, and working fluid on system performance were all investigated with respect to metrics such as the temperature distribution of the fluids and pinch point in the heat exchanger, mass flow rate, and net power production, as well as the thermal efficiency. Results show that as the turbine inlet pressure increases from the subcritical to the supercritical range, the mismatch between hot and cold streams in the heat exchanger decreases, and the net power production and thermal efficiency increase; however, the turbine size per unit power production decreases.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.5
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• pp.368-376
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• 2001

Performance of heat exchanger was evaluated to heat exchanger using oscillating heat pipe for waste heat recovery of low temperature. Oscillating heat pipe used in this study was formed to the closed loop of serpentine shapes using copper tubes. Heat exchanger was formed to shell and tube type and composed of low finned tube. R-22 and R-141b were used to the working fluids of tube side and their charging ratio was 40%. And, water was used to the working fluid of shell side. As the experimental parameters, the inlet temperature difference of heating and cooling part of secondary fluid and the mass velocity of secondary fluid were used. The mass velocity of secondary fluid was changed from 90 kg/$m^2s\; to\;190 kg/m^2$s from the experimental results, heat recovery rate was linearly increased to the increment of the mass velocity of secondary fluid and the inlet temperature difference of secondary fluid. Finally, the performance of heat exchanger was evaluated by using $\varepsilon$-NTU method. It was found that NTU was about 1.5 when effectiveness was decided to 80%.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.37-46
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• 2018

A design study on the cooling channel configuration in a regeneratively cooled supersonic combustor was performed. The flow parameters on the hot- and cold-side channels were calculated using a quasi-one-dimensional model. The heat transfer between these two sides was estimated as a part of the flow calculation. For the reference configuration, the total amount of heat exchanged was 10.7 kW, the heat flux was $566kW/m^2$, and the fuel temperature increase between the inlet and outlet was 153 K. Seven designs of the heat exchanger channel were compared for their heat transfer performance.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.176-181
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• 2017

This study attempted to examine a method of anti-freezing on a plate-type heat exchanger in a low-temperature environment. Freezing condition was observed after ultrasonic waves were generated. Data were recorded to determine the optimal conditions for freezing. Ethylene glycol, which is commonly used in antifreeze formulations, was used as the brine, and the temperature was varied between -8 and $-16^{\circ}C$. The water for freezing provided by the thickness of 1-3 mm. In addition, experiments were conducted by adjusting the output to identify the changes that occurred due to the incidence of ultrasonic energy. The results of the anti-freezing effect were brine temperature, freezing thickness, and frequency band of ultrasonic waves.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.4
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• pp.296-301
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• 2017

In various industrial places such as power generation plants, petrochemical and unit factories, the demands of systems that produce hot water by utilizing wasted or surplus steam have been increased. Compact steam unit(CSU) is a system that can meet these demands and produce hot water by using surplus or wasted steam, and it is also one of the good solutions in view of energy reuse. The new CSU with a capacity of 1,600 kW was developed with a hybrid plate heat exchanger of which thermal performances are better than a conventional plate heat exchanger, an improved temperature control valve, a user-friendly control system, and other components in this study. The purpose of this study was to obtain performance data of the new CSU through various experiments and utilize them for the CSU commercialization. The experimental results show that heat balances between the hot side(steam) and the cold side(cold water) were within ${\pm}0.77%$, and the fluctuations of outlet temperature of the secondary side which are one of the most important evaluation factors in the CSU were $(0{\sim}0.3)^{\circ}C$.

• 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.