• Proceedings of the KSME Conference
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• 2001.06d
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• pp.534-539
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• 2001

An experimental investigation of heat transfer characteristics on confined jet impinging plate using multiple slot jets has been performed. The effects of jet Reynolds numbers(Re=2000, 3950, 5900, 7900), dimensionlesss slot-to-plate distances(H/B=2, 4, 6, 8) and jet-to-jet distances(S=16B, 20B, 24B, 30B) on the local and average heat transfer coefficients have been examined. To clarify local heat transfer characteristics, naphthalene sublimation technique were used. From the experimental results, it was found that the local and average heat transfer rates increase with increasing jet Reynolds number. Measurements of local heat transfer coefficients produced by multiple of slot jets have given an indication of the nature of the interaction between jets and of the uniformity of heat transfer obtainable with various arrangements. At S/B=20, Re=7900 and H/B=6, maximum average Nusselt number is obtained.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.373-380
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• 1988

The effect of sound on the heat transfer from an isothermal cylinder in cross flow is investigated by numerical analysis. The modeling is made for the laminar incompressible flow fluctuating in the range of the Reynolds number, 5.leq.Re.leq.35, by the sinusoidal acoustic field. The instantaneous response of the flow and heat transfer is simulated for various frequencies. It is shown that the heat transfer amplitude decreases and the phase lags behind the flow velocity with increase in the frequency. The time-mean effects of the acoustic field on the flow field and heat transfer, known as the acoustic and thermoacoustic streaming, are analyzed. The time-mean heat transfer coefficients are decreased around the forward stagnation point but increased in the wake region. Such a local difference in heat transfer coefficients is a function of the frequency and becomes greatest at some frequency. However, with balance between the local increase and decrease, the overall heat transfer coefficient is almost unaffected by sound.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.274-279
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• 2001

An experimental investigation of heat transfer characteristics at the surface of two-dimensional protruding heated blocks using confined impinging multiple slot jets has been performed. The effects of jet-to-jet distances(S=16B, 24B), dimensionless nozzle-to-block distances(H/B=2, 6) and jet Reynolds numbers(Re=2000, 3900, 5800, 7800) on the local and average heat transfer coefficients have been examined with five isothermally heated blocks at streamwise block spacing(p/w=1). To clarify local heat transfer characteristics, naphthalene sublimation technique was used. From the results, it was found that the local and average heat transfer of heated blocks increases with decreasing jet-to-jet distance and increasing jet Reynolds number. Measurements of local heat transfer coefficients have given an indication of the nature of the interaction between jets and of the uniformity of heat transfer obtainable with various arrangements. In the case of S/B=16, H/B=6 and Re=7800, maximum average Nusselt number of overall blocks was obtained.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.4
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• pp.570-577
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• 2000

Local heat transfer characteristics inside a hard disk driver(HDD) are investigated in this study. The investigation is considered between disks co-rotating in a cylindrical enclosure. The gap spacing, rotating speed and head-arm positions are mainly considered to understand the flow and heat transfer in the co-rotating disks. The naphthalene sublimation technique is used to determine local heat/mass transfer coefficients on the rotating disk. Flow patterns inside the co-rotating disks are investigated using a Laser Doppler Anemometer (LDA) and also analyzed numerically. The results show that the heat transfer coefficients on the disk changed little with the gap spacing between disks. Heat transfer rates in the outer region increases with increasing rotating Renolds number, but the values normalized by that on a free rotating disk give a similar pattern for the tested cases. The head-arm inserted between the rotating disks destroys the inner region resulting in enhancement of heat transfer in that region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.10
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• pp.3293-3303
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• 1996

Numerical analyses have been performed to estimate the absorption heat and mass transfer coefficients in absorption process of the LiBr aqueous solution and the total heat and mass transfer rates in a vertical tube absorber which is coolING ed by air. Axisymmetric cylindrical coordinate system was adopted to model the circular tube and the transport equations were solved by the finite volume method. Absorption behaviors of heat and mass transfer were analyzed through falling film of the LiBr aqueous solution contacted by water vapor in tube. Effects of film Reynolds number on heat and mass transfer coefficients have been also investigated. Especially, effects of tube diameter have been considered to observe the total heat and mass transfer rates through falling film along the tube. Based on the analysis it has been found that the total mass transfer rate increases rapidly in a region with low film Reynolds number(10 ~ 40) as the film Reynolds number increases, while decreases beyond that region. The total heat and mass transfer rates increase with increasing the tube diameter.

• Transactions of the Korean hydrogen and new energy society
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• v.12 no.4
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• pp.267-275
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• 2001

To clear the differences of heat transfer coefficient of in-cylinder gas with fuel properties, the transient heat transfer coefficient of hydrogen gas is investigated by using the hydrogen fueled engine. The measured results were also compared with those of gasoline engine and several empirical equations. Transient heat transfer coefficients were determined by measurements of unsteady heat flux and instantaneous wall temperature in the cylinder head. As the main results, it is shown that transient heat transfer coefficients have remarkable differences according to fuel properties, and it's value for hydrogen engine is twice higher than that of gasoline engine. It means that equation of heat transfer coefficient that the effect of fuel properties is considered sufficiently, is needed to analyze or simulate the gas engine performance.

• Journal of the Korean Solar Energy Society
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• v.26 no.4
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• pp.93-100
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• 2006

An experimental study of a counterflow heat exchanger was performed. The heat exchanger had an effective heat transfer length of 1000mm and was operated in a counterflow arrangement with hot water($30{\pm}0.5^{\circ}C$, $Re_i=3500{\sim}20000$) in the inner tube(copper tube, $d_0=9.52mm$) and cold water($15{\pm}0.5^{\circ}C$, $Re_{DH}=10700{\sim}39000$) in the annulus(copper tube, $D_0=19.05mm$). Overall heat transfer coefficients were calculated and heat transfer coefficients in the inner tube and the annulus were determined using Wilson plots. The inner Nusselt number was compared with that of Gnielinski's correlation and they agreed within ${\pm}10%$ error. The trends were typical for a fluid-to-fluid heat exchanger with the overall heat transfer coefficient increasing with both inner and annulus flow rates. In the range of this experiment, Nusselt numbers for the inner tube flow were almost identical with those of the annulus flow at the same Reynolds number.

• International Journal of Air-Conditioning and Refrigeration
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• v.14 no.2
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• pp.49-56
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• 2006

Heat transfer performances of individual row of two-row fin and tube heat exchangers are experimentally investigated. Tested are four heat exchangers which are geometrically identical with the exception of fin shape, slit or louver, and that the fins between the first row and the second row are connected or separated. The tube diameter and fin spacing of the heat exchangers examined are 7mm and 1.4mm, respectively. All thermal fluid measurements are made using a psychrometric calorimeter. In order to evaluate air-side heat transfer coefficients of individual rows, tube-side water flow rates of individual rows are independently controlled such that the water-side temperature drops in each row remain at $5^{\circ}C$. Frontal air velocity varies in the range from 0.7m/s to 2.5m/s. Heat transfer coefficients are presented in terms of Colburn ${\jmath}-factor$. The results show that the heat transfer coefficient of the upstream row is larger than that for the downstream row at low Reynolds numbers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1466-1474
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• 1997

In order to design and develop a spark ignition engine, many studies must be preceded about the characteristics of thermal flow. For measurement of transient wall temperature thin film thermocouples of Bendersky type were manufactured and these probes were fixed into the wall of combustion chamber. Surface wall temperatures were measured in experiments of various engine speeds. Transient heat fluxes were calculated from the wall temperature measurements. Pressure was measured from combustion chamber using pressure transducer and gas temperatures were calculated using the state equation of ideal gas. And instantaneous heat transfer coefficients were obtained. It will be the basic data for the formulae of instantaneous heat transfer coefficients.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.911-918
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• 2002

Evaporation heat transfer coefficients of carbon dioxide($CO_2$), R-22, and R-134a in a horizontal smooth tube were measured and analyzed as a function of heat flux, mass flux, and evaporating temperature. The experiments were carried out by varying heat flux from 10 to 20 $kW/m^2$, mass flux from 170 to 340 $kg/m^2s$, and saturation temperatures of 5 and $10^{\circ}C$. It was found that the heat transfer coefficient of $CO_2$ decreased with a rise of quality due to an earlier liquid-film dryout as compared to R-22 and R-134a. Averaged heat transfer coefficients of $CO_2$ were 22-63% higher than those of R-22 and R-134a at all test conditions. The effects of mass flux and heat flux on averaged heat transfer coefficients were much greater in $CO_2$ than in R-22 and R-134a. When comparing $CO_2$ test results with the correlations in the literature, the existing models yielded large deviations at medium and high qualities. Therefore, a generalized correlation for $CO_2$evaporation heat transfer needs to be developed by including the effects of dryout phenomenon.