• Journal of Energy Engineering
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• v.10 no.4
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• pp.349-356
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• 2001

Phenomenon of direct contact condensation (DCC) heat transfer between steam and water is characterized by the transport of heat and mass through a moving steam/water interface. Since the DCC heat transfer provides some advantageous features in the viewpoint of enhanced heat transfer, it is widely applied to the diversified industries. This study proposes a simple condensation model on the stable steam jets discharging into a quenching tank with subcooled water from a single horizontal pipe for the prediction of the steam jet shapes. The model was derived from the mass, momentum and energy equations as well as thermal balance equation with condensing characteristics at the steam/water interface for the axi-symmetric coordinates. The extremely large heat transfer rate at the steam/water interface was reflected in the effective thermal conductivity estimated from the previous experimental results. The results were compared with the experimental ones. The predicted steam jet shape(i. e. radius and length) by the model was increasing as the steam mass flux and the pool temperature were increasing, which was similar to the trend observed in the experiment.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.3
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• pp.91-100
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• 1996

Experimental results for forced convection condensation of non-azeotropic refrigerant mixtures inside a horizontal smooth tube are presented. The mixtures of R-22+R-134a and pure refrigerants R-22 and R-134a are used as the test fluids and a double pipe heat exchanger of 7.5mm ID and 4800mm long inside tube is used. The range of parameters are 100-300kg/h of mass flow rate, 0-1.0 of quality, and 0, 33, 50, 67, and 100 weight percent of R-22 mass fraction in the mixtures. The heat flux, vapor pressure, vapor temperature and tube wall temperature were measured. Using the data, the local and average heat transfer coefficients for the condensation have been obtained. In the same given experimental conditions, the liquid heat transfer coefficients for NARMs were considerally lower than that of the pure refrigerant of R-22 and R-134a. Local heat transfer characteristics for NARMs were different from pure refrigerant R-22 and R-134a. In some regions, local heat transfer coefficients for NARMs were increased in the following order ; Bottom$\rightarrow$Top$\rightarrow$Side. The condensation heat transfer coefficients for NARMs increased with mass velocity, heat flux, and quality, but were considerably lower than that of pure refigerant R-22 and R-134a.

• Journal of the KSME
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• v.18 no.3
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• pp.18-24
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• 1978

열고환기에는 boiler와 같이 다량의 열 energy를 취급하는 것을 비롯하여 가정용 냉장고, 냉방기 기와 같이 비교적 적은 양의 열 energy를 취급하는것, 가종 고온 gas-gas 열교환기, 초전도송전 등의 초저온기기에 부속되는 저온열교환기 혹은 배열회수, 태양열이용을 위한 장치에 포함되는 열교환기등이 있으며, 그 종류와 내용에 있어서 다양하다. 따라서 새 형식의 열교환기 혹은 우수 한 전열특성을 갖는 표면, 형상을 갖는 전열관의 연구, 개발은 한층더 절실하게 요망된다. 최근주 목을 받고 있는 열교환기용전열관중에는 관축방향을 따라 표면을 파상으로 가공한 것(corrugate 식)과 축과 평형이 되게 만든 좁은 흠을 갖는 관(fluted tube)등이 있는데 이들에 있어서는 다같 이 표면의 요철에 의한 면부근의 난동을 촉진시켜서 우수한 대류열전달의 특성을 갖도록 하고 있다. 한편 응축과 비등등의 상변화를 동반하는 열전달에 대해서는 세구, 기공질금속층, 세공등을 갖는 면에 관해서 새로운 관심이 집중되고 있다. 이 후자의 전열면은 유축열전달에서는 평활면보 다 약10배의 높은 열전달율을 가지며 불등열전달에서는 벽면과 액의 온도차는 평활면의 경우보다 약1/5의 값을 갖는다. 동시에 한계열유속은 5활이상으로 증가시킬 수 있음이 알려져 있다. 따라서 본론에서는 후자의 전열면중에서 최근에 알려진 비약적으로 높은 전열성능을 갖는 전열면에 관해 서 소개하기로 한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.4802-4808
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• 2014

A plate-fin tube type heat exchanger has a lighter weight, approximately 30%, than the conventional circular-fin type condenser of household refrigerator. Because the low weight means low cost, it can have significant effects on the growth of related businesses if similar performance can be guaranteed. To check the possibility of the use of such a plate fin-tube condenser, experimental evaluations were performed in this study. Four different condensers including a conventional circular fin-tube condenser were used for the test. A well designed refrigerant supply system was used to supply similar conditions with a refrigerator, and the heat transfer rate and pressure drops of air side were measured precisely. As a result, the plate fin-tube type condensers showed a lower heat transfer rate of more than 13% than the conventional circular fin-tube type condenser, but the air side pressure drop was reduced and the heat transfer per unit weight was increased. Therefore, it shows the possibility of the use of a plate fin-tube type condenser after optimizing the air flow path and increasing the air flow to make a similar heat transfer rate.