• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.451-456
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• 2004

This present experimental study has dealt with the heat transfer characteristics of plastic particle slurry which flows in a circular tube. This type of slurry is suggested for heat transfer enhancement effect cause by random and vortex effect of plastic particle dispersed in water. As a result, the thermal boundary layer becomes thin so the heat transfer coefficient on the tube wall more increase compare to pure water flow. This experimental test section was composed with stainless pipe which has the length of 2000mm, inner pipe diameter of 14mm and outer pipe diameter of 60mm. The most effective and important parameter of this experiment is plastic packing factor(PPF). The focuses of these results are pressure drop and heat transfer coefficient. As results, the friction factor of plastic particle slurry becomes higher at laminar flow region than pure water because of buoyancy effect of plastic particle but the local heat transfer coefficient becomes higher.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.2
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• pp.10-19
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• 1995

Heat trnasfer for absorbing and emitting media in laminar layer along the cylinders has been analyzed. Governing equation are transformed to local nonsimilarity equations by the dimensional analysis. The effects of the Stark number, Prandtl number, Optical radius and wall emissivity are mainly investigated. For the formal solution a numerical integration is performed and the results are compared with those obtained by P-1 and P-3 approximation. The results show that boundary layers consist of conduction-convection-radiation layer near the wall and convection-radiation layer far from the wall. As the Stark number of wall emissivity increases the local radiative heat flux is increased. The Pradtl number or curvature variations do not affect the radiative heat flux from the wall, but The Prandtl number or wall emissivity variations affect the conduction heat flux. Consequently the total heat flux from the wall are affected by the Prandtl number or wall emissivity variation.

• Journal of Mechanical Science and Technology
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• v.14 no.5
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• pp.537-546
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• 2000

The heat transfer characteristics of refrigerant-oil mixture for horizontal in-tube evaporator have been investigated experimentally. A smooth copper tube and a micro-fin tube with nominal 9.5 mm outer diameter and 1500 mm length were tested. For the pure refrigerant flow, the dependence of the axial heat transfer coefficient on quality was weak in the smooth tube, but in the micro-fin tube, the coefficients were 3 to 10 times greater as quality increases. Oil addition to pure refrigerant in the smooth tube altered the flow pattern dramatically at low mass fluxes, with a resultant enhancement of the wetting area by vigorous foaming. The heat transfer coefficients of the mixture for low and medium qualities were increased at low mass fluxes. In the micro-fin tube, however, the addition of oil deteriorates the local heat transfer performance for most of the quality range, except for low quality. The micro-fin tube consequently loses its advantage of high heat transfer performance for an oil fraction of 5%. Results are presented as plots of local heat transfer coefficient versus quality.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.468-476
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• 2002

This paper deals with heat and mass transfer characteristics and performance evaluation of a counter flow double-tube condenser for a multi-component refrigerant mixture. The local heat and mass transfer characteristics of ternary zeotropic refrigerant mixtures composed of HFC32/HFC125/HFC134a are evaluated for a counter flow double-tube condenser cooled by water. Then, the local values of vapor quality, thermodynamic states at bulk vapor, vapor-liquid interface and bulk liquid, heat flux and condensation mass flux are obtained. The heat exchange performance for ternary zeotropic refrigerant mixtures composed of HFC32/HFC125/HFC134a on the total pressure drop and the heat transfer characteristics are also compared with those for R404A, R410A, R502, R22, R32, Rl23 and R134a.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.12
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• pp.837-845
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• 2012

The purpose of this research is to investigate the heat transfer enhancement by the multiple tripping wires installed on a flat plate. Naphthalene sublimation technique is used to measure the local mass transfer coefficients, and then heat transfer coefficients are calculated using heat/mass transfer analogy. Experiments are performed for the developed and developing flow conditions. Local and average heat transfer coefficients from the flat plate with three tripping wires are compared with those of no and one tripping wire. Remarkable heat transfer enhancements are found resulting from the boundary layer separation by the tripping wires, especially in the laminar boundary layer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.5
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• pp.615-623
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• 1999

The objective of present study is to analyze a hot steel-tube cooling system as a kind of concentric triple-passage heat exchanger, whose inner tube is moving with a constant speed. Velocities and temperatures of an antioxidant gas flowing between inner and outer tubes are calculated theoretically for both laminar and turbulent flow regimes and used to give Nusselt numbers and friction factors with respect to various radius ratios and velocity ratios. In addition, it is shown that heat transfer coefficients based on ratios of average heat fluxes from inner and outer tubes might result in great errors for the temperature distributions of the flows, since the local heat transfer coefficients are dependent on the local heat flux ratios.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1395-1405
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• 1996

The purpose of this experimental research is to investigate the local heat transfer characteristics in the upward free water jet impinged on a downward flat plate of uniform heat flux. The inner shape of rectangular nozzle used was sine curve type and its contraction ratio of inlet to outlet area was five. Experimental parameters considered were Reynolds number, nozzle exit-flat plate distance, and level of supplementary water. Local Nusselt number was influenced by Reynolds number, Prandtl number, supplementary water level, and distance between the nozzle exit and flat plate. Within the impingement region, the Nusselt number has a maximum value on the nozzle center axis and decreases monotonically outward from center. Outside of the impingement region, on the other hand, the Nusselt number has a secondary peak near the position where the distance from nozzle center reaches four times the nozzle width. However if nozzle exit velocity exceeds 6.2 m/s, the secondary peak appears also in the impingement region. The empirical equation for the stagnation heat transfer is a function of Prandtl, Reynolds, and axial distance from the nozzle exit. The optimum level of supplementary water to augment the heat transfer rate at stagnation point was found to be twice the nozzle width.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2381-2384
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• 2008

The heat exchange between the Borehole Heat Exchanger(BHE) and the surrounding ground depends directly on ground thermal conductivity k at the certain site. The k is thus a key parameter in designing BHE and coupled geothermal heat pump systems. Currently, although a thermal hydraulic Response Test(TRT) is mostly used in practice, the thermal hydraulic TRT needs additional power and is generally time-consuming. A new, simple wireless probe for hi-speed k determination was introduced in this paper. This technique using a wireless probe is less time-consuming and requires no external source of energy for measurement and predicts local thermal properties by measuring soil temperatures along the depth. Measured temperature data along the depth was analyzed. As a result, the electronic wireless probe can replace the conventional hydraulic TRT method after carrying out the additional research on a lot of local heat flow, etc.

• Journal of the Korean Solar Energy Society
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• v.39 no.1
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• pp.67-76
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• 2019

A ground source heat pump (GSHP) system can stable system operation by using underground heat source and has high reliability for energy production. However, wide-spread of the GSHP system is delayed to high initial investment costs. In previous studies, horizontal and unit-type ground heat exchanger (GHX) have developed to overcome disadvantages such as high initial cost. However, these performances of GHXs are greatly influenced by climate and weather conditions. It is necessary to analyze the performance of GHX according to the ground temperature change in the installation site. In this study, the ground temperature of each installation site confirmed and performance of unit-type GHX quantitatively analyzed by numerical analysis. As the result, the performance of the unit type GHX was 33.9 W/m in Seoul, 34.2 W/m in Daejeon, and 37.2 W/m in Busan.The result showed the difference performance of GHX according to local climate was maximum of 9.7%.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.1117-1118
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• 2012