• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.10
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• pp.930-937
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• 2005

The objective of this study is to investigate the heat transfer performance of flat plate finned-tube heat exchangers with large fin pitch. In this study, twenty-two heat exchangers were tested with a variation of fin pitch, number of tube row, and tube alignment. The heat transfer coefficient decreased with a reduction of the fin pitch and an increase of the number of tube row. The staggered tube alignment improved heat transfer performance more than $10\%$ compared to the inline tube alignment. A heat transfer correlation was developed from the measured data for flat plate finned-tubes with large fin pitch. The correlation yielded good predictions of the measured data with mean deviations of $3.6\%\;and\;6.4\%$ for the inline and staggered tube alignment, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.1
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• pp.48-56
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• 1992

The purpose of this study was to investigate the enhancement of heat transfer without additional external power in the case of rectangular air jet impinging vertically on the flat heating surface. In an attempt to enhance the heat transfer rate in two-dimensional impinging jet, the technique used in the present study was placement of square rod bundles as a turbluence promoter in front of the heat transfer surface. The effects of the clearance between the flat plate and square rod, and the nozzle exit velocity on the heat transfer characteristics have been investigated experimentally. The results obtained through this study were summerized as follows. High heat transfer enhancement was achived by means of flow acceleration and thinning of boundary layer by inserting rods in front of the heating flat plate. The smaller the clearance between rod and heating plate was, the larger heat transfer effect became. Average Nusselt number reached maximum at $Re=5.76{\times}10^4$ and C＝1㎜ and the enhancement rate of heat transfer became maxium at this condition with the enhancement ratio as high as about 1.427 when normalized by the flat plate value. The correlating equation of average Nusselt number and Reynolds number was obtained, which is $\bar{N}uo=1.324{\cdot}Re^{0.459}{\cdot}(C/A)^{-0.034}$.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.4
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• pp.147-152
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• 2017

In the present study, we used a loop thermosyphon heat exchanger consisting of condensers with internal fins and external plate fins which are 480 mm wide, 68 mm long, and 1,000 mm high. The heat transfer pipes in the heat exchanger were 15 mm in diameter and 1,000 mm in length, and 98 heat transfer pipes were installed in the heat exchanger. According to the experimental results, as the spaces between the internal discontinuous pins decreased, the frequency of pressure drops increased and changes in temperature at the outlet of the condenser were shown to be a little smaller. Therefore, we can see that as the spaces between internal discontinuous pins decreased, the heat transfer performance increased. For the loop heat pipe heat exchanger consisting of a condenser with internal and plate fins, as the temperature of the air flowing into the condenser increased, the condensation heat transfer rate also increased, and as the condenser refrigerant inflow temperature increased, the condensation heat transfer rate increased as well.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.29-36
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• 2014

Recently, in order to enhance the function and usefulness of products, cladding of dissimilar materials that maximizes the performance of the material is being widely used in all areas of industry as an important process. Clad steel plate, produced by cladding stainless steel plate, an anticorrosive material, on carbon steel plate, is being used to produce pressure vessels. Stainless steel plate has good corrosion resistance, and carbon steel plate has good rigidity and strength; clad steel can satisfy all of these qualities at once. This study aims to find the ${\delta}$-ferrite behavior, mechanical properties, structure change, integrity and reliability of clad steel weld on hot rolled steel plates. For this purpose, multi-layer welding, repair welding and post weld heat treatment were implemented according to welding procedure specifications (WPS). In order to observe the mechanical properties and toughness of clad steel weld zone, post weld heat treatment was carried out according to ASME Sec. VIII Div.1 UW-40 procedure for post weld heat treatment. With heat treatment at $625^{\circ}C$, the hold time was used as the process variable, increased by intervals that were doubled each time, from 80 to 1,280 min. The structure of weld part was typical cast structure; localized primary austenite areas appeared near central vermicular ferrite and fusion line. The heat affected zone showed rough austenite structure created by the weld heat input. Due to annealing effects of heat treatment, the mechanical properties (tensile strength, hardness, impact value) of the heat affected area tended to decrease. From the results of this study, it is possible to conclude the integrity of clad steel welds is not affected much in field welding, repair welding, multi-layer welding, post weld heat treatment, etc.

• Journal of the Korean Solar Energy Society
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• v.27 no.3
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• pp.149-154
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• 2007

It is essential to know the heat transfer characteristics at the absorber plate of Flat-plate solar collector for optimum design. For flat-plate solar collector, it is difficult to experimentally study the effect for the Reynolds number of riser considering low mass flow rate being applied into the collector with one riser tube. So, this study were performed to show the heat transfer characteristics of flat-plate solar collector with single absorber plate and riser for various Reynolds number at riser using commercial code FLUENT 6.0. The base collector size is chosen with $0.4m^2$ as 0.2m by 2m with single riser in this study, Reynolds number at riser is from 200 to 1200 including about 530 at typical flat-plate collector with 10 risers considering the mass flow rate of 0.02kg/s per collector area for the certificate test Through the simulation, the results were presented as the temperature distribution at the absorber plate for various flow rate and solar irradiance conditions, then showed the effective length scale of the absorber plate The real solar irradiation condition is assumed as the constant heat flux condition of $500w/m^2$ considering the annual average solar irradiance in Korea.

• Journal of Power System Engineering
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• v.13 no.2
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• pp.49-55
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• 2009

Recently, a study on condensers for refrigerators has focused on new model which will cost less and will be more efficient. Some widely used condensers for domestic refrigerators are wire-and-tube type condenser, hot-wall type condenser, and spiral type condenser. Some companies which use the spiral type condenser at the moment try to develop a new tube-and-plate type condenser which will cost less and will be as efficient as the spiral type. As a standard condenser type, tube-and-plate type condenser is used in this study. A two-dimensional numerical model for the tube-and-plate type condenser is proposed, and the flow and heat transfer characteristics for several types of condensers are investigated.

• Journal of Welding and Joining
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• v.13 no.1
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• pp.138-144
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• 1995

Recently, as the industrial structure tends to become large, the thickness of structural plate becomes thicker. Therefore, the thicker the plate of welded structure is, the larger the shape of welded joint. The effect of large heat input makes large heat affected zone(HAZ). These bring to complict welding residual stress and to weaken material, which may cause extremely harm to the safety of structures. Nevertheless, welding is design is regulated by the KS, JIS or standard in the resister of shipping such as KR, ABS or LR. However, these rules are based on rather experimental than theoretical. In this study, the computer program of heat conduction, considering un-steady state and quasi-steady state, is developed for optimizing(minimizing) a shape of welded joint. The characteristics of heat on the welded joints with various shapes are clarified by the results of the analyses.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1306-1311
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• 2004

The performance test apparatus of liquid-phase plate heat exchanger was installed and the computer program for design was developed in this study. The detail temperature distribution of hot and cold fluids in each path of heat exchanger was calculated by numerical method and the correlation for the heat transfer coefficient was defined. The heat transfer coefficients were measured using the working fluids of water and glycerine to investigate the effect of fluid viscosity. The measured heat transfer coefficients were compared with the calculated values obtained from the computer program and it was shown that error of the calculated values was generally less than 5%.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.4
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• pp.593-602
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• 2004

This paper is a study on the model of simultaneous heat and mass transfer process in the absorption of refrigerant vapor into a lithium bromide solution of water-cooled vertical plate absorber. The model can predict temperature and concentration profiles as well as the effect of Reynolds number on them. Also. the variations of the absorption heat and mass fluxes. and the heat and mass transfer coefficients have been investigated. The numerical result shows that the interface temperature and concentration decrease as film Reynolds number does. The absorption heat and mass fluxes, and the heat and mass transfer coefficients get their maximum values adjacent to the inlet solution. Analyses on a constant wall temperature condition have been also carried out to exam the reliability of the present numerical method by comparing to previous investigations.

• Solar Energy
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• v.20 no.3
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• pp.31-38
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• 2000

In order to study on influence of fin pitch and shape of heat exchanger on the elevation of heat transfer efficiency, we make models of louvered fin type heat exchanger which was given a transformation of fin pitch in louvered fin type heat exchanger which are of en used now. And the influence of fin pitch on pressure drop and characteristics of heat transfer was experimented and analysed when air velocity and fin pitch was a variable. The results of experiment shows below. Pressure drop shows larger in louvered fin type heat exchanger than in plate fin type heat exchanger, size of pressure drop shows like this order that fin space is 4mm, 5mm, 6mm. Mean heat transfer coefficient shows higher in louvered fin type heat exchanger than in plate fin type heat exchanger, size of mean heat transfer coefficient by fin space shows same in both case in louvered fin type heat exchanger and plate fin type like this order that fin space is 4mm, 5mm, 6mm.