• 한국초전도ㆍ저온공학회논문지
• /
• 제24권3호
• /
• pp.62-67
• /
• 2022

Liquid hydrogen (LH₂) has a higher density than gaseous hydrogen, so it has high transport efficiency and can be stored at relatively low pressure. In order to use efficient bulk hydrogen in the industry, research for the LH₂ supply system is needed. In the high-pressure hydrogen station based on LH₂ currently being developed in Korea, a heat exchanger is used to heat up supercritical hydrogen at 700 bar and 60 K, which is pressurized by a cryogenic high-pressure pump, to gas hydrogen at 700 bar and 300 K. Accordingly, the heat exchanger used in the hydrogen station should consider the design of high-pressure tubes, miniaturization, and freezing prevention. A helical heat exchanger generates secondary flow due to the curvature characteristics of a curved tube and can be miniaturized compared to a straight one on the same heat transfer length. This paper evaluates the heat transfer performance through parametric study on the distance between coils, guide effect, and anti-icing design of helical heat exchanger. The helical heat exchanger has better heat transfer performance than the straight tube exchanger due to the influence of the secondary flow. When the distance between the coils is uniform, the heat transfer is enhanced. The guide between coils increases the heat transfer performance by increasing the heat transfer length of the shell side fluid. The freezing is observed around the inlet of distribution tube wall, and to solve this problem, an anti-icing structure and a modified operating condition are suggested.

• Journal of Mechanical Science and Technology
• /
• 제15권11호
• /
• pp.1555-1562
• /
• 2001

In a conventional shell-and-tube heat exchanger, fluid contacts with tubes flowing up and down in a shell, therefore there is a defect in the heat transfer with tubes due to the stagnation portions . Fins are attached to the tubes in order to increase heat transfer efficiency, but there exists a limit. Therefore, it is necessary to improve heat exchanger performance by changing the fluid flow in the shell. In this study, a highly efficient shell-and-tube heat exchanger with spiral baffle plates is simulated three-dimensionally using a commercial thermal-fluid analysis code, CFX4.2. In this type of heat exchanger, fluid contacts with tubes flowing rotationally in the shell. It could improve heat exchanger performance considerably because stagnation portions in the shell could be removed. It is proved that the shell-and-tube heat exchanger with spiral baffle plates is superior to the conventional heat exchanger in terms of heat transfer.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2006년도 하계학술발표대회 논문집
• /
• pp.357-362
• /
• 2006

This research focused on the multi-pass heat exchanger using the minichannel possessing the spring fin. An air-water was used as working fluid. The characteristics of liquid single phase heat transfer were verified. The compact heat exchanger (heat transfer area density : ${\beta}=2,146 m^2/m^3$), based on the shape of header(Top combining header), 63 minichannels ($D_i$ : 1.4 mm, L : 0.25 m) and the air side adopting the copper wire spring fin, was fabricated. The heat transfer area density of the air side was improved up to 161% when compared with the conventional fin-tube heat exchanger that adopts the heat transfer tube with the inner diameter of 5 mm. With regard to heat transfer performance, heat transfer rate per unit volume increased up to 142% when compared with the fin-tube heat exchanger adopting the heat transfer tube with the inner diameter of 5 mm.

• 한국산학기술학회논문지
• /
• 제8권6호
• /
• pp.1337-1342
• /
• 2007

본 연구에서는 동시 냉난방 히트펌프용 열교환기의 성능평가 및 설계해석 기술의 확보를 위해 난방운전 온도조건에서 6종의 루버핀-관 열교환기의 공기측 열전달특성 및 마찰특성을 실험을 통하여 조사하였다. 실험을 위해 공기엔탈피방식의 칼로리미터와 항온수조를 이용하였다. 전열량의 증가는 핀피치보다 열수에 의해 더 크게 나타났고, 핀피치가 작을수록 열전달계수는 더 높았다. 또한 핀피치가 작을수록 열수증가에 의한 열전달계수의 증가폭이 커졌다. 핀피치와 열수변화에 대한 j-계수와 f-계수는 레이놀즈 수가 증가할수록 감소하였고, 레이놀즈 수 400부근의 영역에서 역전현상이 존재하였다.

• 수산해양교육연구
• /
• 제26권6호
• /
• pp.1352-1357
• /
• 2014

In the present study, the heat transfer performance on the heat recovery ventilator with rotary disk were experimentally investigated. The temperature of entrance and exit of the heat recovery ventilator, air flow distribution of high temperature air and low temperature air, heat flux and the overall heat transfer coefficients are estimated from the experimental results. As the number of revolution of rotary disk, the air flow distribution increase, heat flux and overall heat transfer coefficients increase.

• 한국태양에너지학회 논문집
• /
• 제22권2호
• /
• pp.19-26
• /
• 2002

This study aims at numerically analyzing on heat transfer the characteristics and pressure drop of plate heat exchanger(PHE) using the Phoenics 3.1 VR Editor for the standard k-$\varepsilon$ model. Computations have been carried out for a range of chevron angle from $30^{\circ}$ to $60^{\circ}$, inlet velocity from 0.03m/s to 0.63m/s and the height of corrugation from 0.0045m to 0.0060m. The results show that both of heat transfer performance and pressure drop increase as chevron angle increases. This is because higher troughs produce higher turbulence and a higher heat transfer coefficient in the liquids flowing between the plates. As inlet velocity from 0.03m/s to 0.63m/s increases, heat transfer performance and pressure drop increase parabolically. As the height of corrugation increases, both of heat transfer performance and pressure drop decrease with the decrease of velocity. And the pressure drop decreases and the friction factor increases as the height of corrugation increases.

• 한국추진공학회지
• /
• 제23권2호
• /
• pp.27-37
• /
• 2019

쉘-튜브 열교환기가 나로우주센터 추진기관종합시험장(PSTC)에 설치되었으며, 이 열교환기는 극저온의 헬륨을 고온의 열매유와 열교환하여 약 500 K 까지 가열시키는 역할을 한다. 열교환기에서 토출되는 헬륨의 온도가 설계보다 100 K 낮게 나옴에 따라, 성능저하의 원인으로 열매유의 격막효과가 지목되었다. CFD 해석을 통해 격막효과의 유무를 확인하였으며, 격막효과에 의한 열교환기 성능저하는 미미한 것으로 판단되었다. 추가적으로 열교환기의 성능을 증가시키기 위하여 열매유 교체에 따른 열교환기 성능 변화를 알아보았다. 열매유를 사용하는 열교환기의 성능향상을 위해서는 500 K 부근에서 점성이 낮아야 하고, 열전도도가 높아야 한다는 것을 확인할 수 있었다. 추진기관종합시험장에서 운용된 극저온 헬륨과 고온 열매유의 열교환 시스템의 시험 결과를 본 논문에서 확인할 수 있다.

• Journal of Mechanical Science and Technology
• /
• 제17권11호
• /
• pp.1801-1811
• /
• 2003

An experimental study was conducted to investigate the effects of air-side fouling and cleaning on the performances of various condenser coils used in unitary air-conditioning systems. A total of six condenser coils with different fin geometry and row number were tested. Performance tests were performed at three different conditions: clean-as-received, after fouling, and after cleaning. In all cases, it was observed that the fouling was mostly confined to the frontal face of the heat exchanger as reported in the previous investigations. The amount of deposited dust was more dependent on fin geometry for the single-row heat exchangers than for the double-row heat exchangers. The predominant effect of fouling was to cause a more significant increase in air-side pressure drop than a degradation in heat transfer performance. For the single-row heat exchangers, the pressure drop increased by 28 to 31%, while the heat transfer performance decreased by 7 to 12% at the standard air face velocity of 1.53 m/s depending on fin shape. For the double-row heat exchangers, the pressure drop increased by 22 to 37%, and heat transfer performance decreased by only 4-5% at the same air face velocity. Once the contaminated coils were cleaned according to the given cleaning procedure the original performance of the heat exchangers could almost be recovered completely. The pressure drop could be restored within 1 to 7% and the heat transfer performance could be recovered to within 1 to 5% of the originally clean heat exchangers. Therefore, it is concluded that a periodic application of the specified cleaning technique will be effective in maintaining the thermal performance of the condenser coils.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2009년도 하계학술발표대회 논문집
• /
• pp.266-271
• /
• 2009

The present study numerically investigated the effect of the geometry of the flattened tube on the thermal performance of a high temperature generator (HTG) of a double effect LiBr-water absorption system. The heat transfer tubes of the HTG were arranged behind a metal fiber burner. The heat transfer of the tubes of HTG were consisted with a set of circular and flattened tubes in series. FLUENT, as a commercial code, was applied for estimating the thermal performance of the HTG. Key parameters were the tube arrangement in the HTG. Temperature and velocity profiles in the HTG were calculated to estimate the thermal performance of the HTG. The heat transfer rate of a HTG tube was increased, and the gas temperature around the flattened tube was decreased as the pitch ratio was increased. The heat transfer rate for the circular tube bundle with the pitch ratio of 2.48 were larger by 10% respectively than that of 2.10 and the heat transfer rate for the flattened tube bundle with the pitch ratio of 1.88 were larger by 36% respectively than that of 1.63.

• 한국전산유체공학회지
• /
• 제12권3호
• /
• pp.47-54
• /
• 2007

A periodic CFD approach for the performance analysis of compact high temperature heat exchangers is introduced and applied to selected benchmark problems, which are a fully developed 2D laminar heat transfer, a conjugate heat transfer between parallel plates which have exact solutions, and a heat transfer in a real high temperature heat exchanger module. The results for the 2D laminar heat transfer and the 2D conjugate heat transfer showed a very good agreement with the exact solutions. For the high temperature heat exchanger module, the pressure drops were predicted well but some difference was observed in the temperature parameters when compared to the full channel CFD analysis due to assumptions introduced into the periodic approach. Considering its assumptions and simplicities, however, the results showed that the periodic approach provides physically reasonable results and it is sufficient to predict the performance of a heat exchanger within an engineering margin and with much less CPU time than the case of a full channel analysis.