• 설비공학논문집
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• 제28권5호
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• pp.195-201
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• 2016

Enhanced tubes are widely used in air-conditioning and process industries. Structural tubes having three-dimensional roughness are well known to be able to significantly enhance pool boiling heat transfer of refrigerants. In this study, five structural enhanced tubes having different fin density, fin height, and fin gap width were tested using R-134a. Results showed that the heat transfer coefficient was increased with increased fin density. Within test range, the effect of fin height on pool boiling heat transfer coefficient was insignificant. The heat transfer coefficients of the optimum configuration (2047 fpm, 0.21 mm gap width) tube were lower than those of other commercial enhanced tubes. This might be due to the larger fin gap width of the present enhanced tube.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1351-1359
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• 2003

This study presents a numerical procedure to optimize shape of streamwise periodic ribs mounted on both of the principal walls to enhance turbulent heat transfer in a rectangular channel flow. The response surface method is used as an optimization technique. The optimization is based on Navier-Stokes analysis of flow and heat transfer with $k-{\varepsilon}$ turbulence model. The width-to-height ratio of a rib, rib height-to-channel height ratio and rib pitch to rib height ratio are chosen as design variables. The object function is defined as a function of heat transfer coefficient and friction drag coefficient with weighting factor. Optimum shapes of the rib have been obtained for the range of 0.02 to 0.1 of weighting factor.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.328-334
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• 2000

This research was concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different horizontal tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare tube, floral tube, hydrophilic tube. The additive concentration was about $0.05{\sim}5.5mass%$. The heat transfer coefficient was measured as a function of solution flow rate in the range of $0.01{\sim}0.034 kg/ms$. The experimental result were compared with cases without surfactant. The enhancement of heat transfer by Marangoni convection effect which was generated by addition of the surfactant is observed in each test tube.

• 한국분무공학회지
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• 제22권1호
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• pp.36-41
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• 2017

The present study investigates the evaporation heat transfer characteristics of nanofluid droplet for different nanoparticle sizes. Also, the heat transfer coefficient was measured at different nanoparticle concentrations during evaporation. From the experimental results, it is found that the evaporation behavior of sessile droplet can be considered as constant radius mode due to pinning effect. The total evaporation time of sessile droplet decreases with nanoparticle size up to 7.9% for 0.10 vol% nanofluid droplet. As nanoparticle concentration increases, the clear difference in heat transfer coefficient is observed, showing that the size effect should be examined. This result would be helpful in designing the correlation between the nanoparticle size and the heat transfer characteristics for various applications.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.245-251
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• 1999

The structural analysis of a reactor coolant pump(RCP) of a nuclear power plant is very important for the safety assessment of the plant. Accurate boundary conditions for the heat transfer coefficient are required for reliable thermal stress analysis of the pump casing, especially in transient operations of the pump since the coolant properties are largely dependent on operational conditions. In the present study, a 3D mixed flow type coolant pump was modeled from the RCP drawings and analyzed in the steady state and number of transient flow conditions by using a commercial code STAR-CD. From the result of the computation, it is seem that the average heat transfer coefficients for the cases considered are found to be the suggested values of the manufacturer, Westinghouse Energy System. The unevenness in local heat transfer coefficients, however, is found to be considerable so that the use of average heat transfer coefficients in all boundaries might not give reliable thermal stresses.

• Journal of Advanced Marine Engineering and Technology
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• 제25권3호
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• pp.581-587
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• 2001

Plate heat exchange(PHE) will be applied to the refrigeration and air conditioning systems as evaporators or condensers for their high efficiency and compactness. The purpose of this study is the analyze the characteristics of heat transfer and pressure drop of plate heat exchanger. Numerical work was conducted using the FLUENT code k-$\varepsilon$model. Also the dependence of heat transfer coefficient and friction factor on Reynolds number was investigated. As the Reynolds number increases, it is found that heat transfer coefficient also increases, but friction factor decreases. The study examines the internal flow, thermal distribution and the pressure distribution in the channel of plate heat exchanger. The results of CFD analysis compared with experimental data, and the difference of friction factor and Nusselt number in plate heat exchanger are 10% and 20%, respectively, Therefore the CFD analysis model is effective for the performance prediction of plate heat exchanger.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권4호
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• pp.184-191
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• 2002

This study concerns the performance of the condensing heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having 50, 60, 70, 80, 90 internal micro grooves. Distilled water, methanol, ethanol have been used as the working fluid. The numbers of grooves and operating temperature have been investigated as the experimental parameters. Condensing heat transfer coefficients and heat flux are obtained from experimental data for each case of specific parameter. The experimental results are assessed and compared with existing correlations. The results show that working fluids, numbers of grooves are very important factors for the operation of thermosyphons. The working fluid with high latent heat such as water has a good heat transfer rate compared to methanol and ethanol. The relatively high rate of heat transfer is achieved when the thermosyphon with internal micro grooves is used compared to that with plain tube. Condensing heat transfer coefficient of grooved thermosyphon is 1.5∼2 times higher in methanol and 1.3∼l.5 times higher in ethanol compared to plain tube. The best condensation heat transfer performance is obtained for 60 grooves, and the maximum value of this case is 2.5 times higher than that of the plain tube.

• 설비공학논문집
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• 제9권2호
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• pp.153-162
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• 1997

In this study, the wet surface heat transfer coefficients and friction factors of the heat exchanger with slit-wavy fin were measured. Four sample cores of two or three row with fins of 12 fpi or 16 fpi were tested. Tests were conducted in a closed loop wind tunnel, where the heat exchanger was mounted at 45 degree inclination angle. The wet surface heat transfer coefficient was reduced following the procedure given in ARI 420-81. During the course, new definitions of the $\varepsilon$-NTU applicable to enthalpy driving system were introduced. The wet surface heat transfer coefficients were approximately equal to the dry surface values. However, the friction factors were approximately 120% to 170% higher than those of the dry surface. Both the heat transfer coefficient and the friction factor of the wet surface increased as the relative humidity increased, fin pitch decreased, and the number of row decreased, although the difference was not large.

• 설비공학논문집
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• 제24권7호
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• pp.553-559
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• 2012

A plate-fin heat exchanger is a type of heat exchanger widely used in air conditioners, and tubes and fins are tightly assembled by the mechanical expansion process of tubes. The tube expansion process deforms the grooves inside the tube, and the groove shapes also affect the adhesion between tubes and fins. In this study, the adhesion and heat transfer performance affected by the tube expansion of the non-uniform groove shape tube with different heights are investigated by both analysis and experiments. From the analysis method, it was shown that the contact pressure of non-uniform groove tube is higher than that of the uniform groove tube, and the most appropriate high groove number of the non-uniform groove tube is designed for the maximum contact pressure. From the experimental results, the decreasing rate of the condensation heat transfer coefficient is smaller in the non-uniform groove tube with different heights, compared to the conventional uniform groove tube. Also, the air-side heat transfer coefficient of the non-uniform groove tube with different heights is higher than that of the uniform groove tubes.

• Journal of Advanced Marine Engineering and Technology
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• 제27권1호
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• pp.108-116
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• 2003

In this paper, the experimental results of condensation heat transfer were reported for the plate and shell heat exchangers(P&SHE) using R-l34a. An experimental refrigerant loop has been established to measure the condensation heat transfer coefficient of R-l34a in a vertical P&SHE. Two vertical counter flow channels were formed in the P&SHE by three plates of geometry with a corrugated trapezoid shape of a chevron angle of 45$^{\circ}$. Downflow of the condensing R-l34a in one channel releases heat to the cold up flow of water in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality of R-l34a on the measured data were explored in detail. The results indicate that at a higher vapor quality the condensation heat transfer coefficients are significantly higher. Condensation heat transfer coefficients were increased when the refrigerant mass flux was increased. A rise in the average heat flux causes an slight increase in the hr. Finally, at a higher system pressure the hr is found to be lower. Correlation is also provided for the measured heat transfer coefficients in terms of the Nusselt number.