• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1075-1081
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• 2011

A leak-detection method has been developed by measuring the pressure variation between the inner and outer heattransfer tubes of a double-wall tube steam generator. An experiment was carried out to measure the leak rate in the gap between two surfaces pressed with a hydraulic press in order to simulate the phenomena, and a correlation was determined for the leak rate in a micro gap. However, in the correlation, the gap width and friction coefficient were coupled with the surface roughness, which affects the two parameters. The two parameters were separated using a surface-contact model to develop a correlation for the friction coefficient. The correlation was compared with the existing correlations used for crack analysis. Although the applied ranges of Reynolds numbers were different, the developed correlation for Reynolds numbers of 0.1.0.35 showed similar tendencies to existing correlations used for higher Reynolds numbers.

• Solar Energy
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• v.13 no.1
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• pp.11-21
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• 1993

The purpose of this study was to investigate the enhancement of heat transfer without additional external power in the case of rectangular impingement air jet vertically on the flat heating surface. The technique used in the present study was placement of square rod bundles as a turbulence promoter in front of the heat transfer surface. The results obtained through this study were summerized as follws. High heat transfer enhancement was achieved by inserting rods in front of the heating flat plate. According to visulaization, it was examined because of flow acceleration and separation and disturbance of boundary layer. The smaller clerance between rod and heating plate was, the larger heat transfer effect became at each H/B. Arverage Nusselt number reached maximum at H/B=10 and the local augmentation rate of heat transfer became maximum at H/B=2. The maximum average heat transfer enhancement rate increase about 43% for the case of X/B=2 and C=1mm, compared to a flat plate without rods. The correlating equation of average Nusselt number and Reynolds number was obatined. As follws : ${\overline{Nu}}_0=1.249Re^{0.465}(C/A)^{-0.033}(H/B)^{0.013}$.

• 한국가스학회:학술대회논문집
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• 2005.10a
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• pp.123-127
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• 2005

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.9
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• pp.719-726
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• 2015

One method of increasing the heat-transfer rate is to increase the heat-transfer area. In this study, we test a wide louver fin-and-tube heat exchanger with $P_t/P_l$ = 1.03, and we compare the results with those of a louver fin-andtube heat exchanger with $P_t/P_l$ = 0.6. The results obtained show that the heat-transfer capacities of the wide louver samples are larger (16% in one row, 29% in two rows, and 38% in three row samples) than those of the louver samples. Considering the area ratio of 2.17, the increase in the heat-transfer capacity is somewhat small. The reason for this may be due to the smaller heat-transfer coefficient and fin efficiency of the wide louver sample. The effect of the fin pitch on the j and f factors are not profounded. The j and f factors decreased as the number of tube rows increased. We compare the data obtained with existing correlations.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.5
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• pp.687-694
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• 1999

This study was conducted to develop new drying process for automatic control and marine engi-neering system. Air-water tests were carried out to investigate dryer performance. The dispersed flow in he dryer test apparatuses was also simulated by using a numerical code which solves the Dittus-Boelter equation for continuous liquid phase and the Reynolds equation of droplet motion for continuous liquid phase and the Reynolds equation of droplet motion for dispersed phase to predict droplet removal efficiency. Proper conditions for dehumidification were optimized by response ambient conditions. When the selected indexes were constrained in the range of 85-98% moisture content above $15^{\circ}$ and more than mass flow rates of moist air 750kg/h. The numerical results were compared with the experimental data pertaining to the removal effi-ciency at chamber stage and overall pressure drop along concentric tubes Good agreement was obtained as for the efficiency while relatively poor agreement was obtained for the relative humidity. The results also showed that the efficiency depended strongly on the relative humidity at the inlet condition which indicated the importance of estimating the heat exchanger length. Effects of some design parameters in both removal efficiency and breakthrough onset condition are discussed.

• Journal of Energy Engineering
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• v.13 no.4
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• pp.275-280
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• 2004

Augmentation of heat transfer by ultrasonic vibration in pipes are investigated. Measurements of convective heat transfer coefficients on circular pipe walls are made with and without ultrasonic vibration applied to water. These data are compared with each other to quantify the effects of ultrasonic vibration on heat transfer enhancement. Numerical analysis has been also performed in order to extend the ranges of examined temperature and flow rate. FLUENT Ver.6.1 is used to simulate velocity and temperature fields and evaluate heat transfer coefficient with and without ultrasonic vibration. The results show that the ultra- sonic vibration enhances the Nusselt number of forced convection flow and the increase rate strongly depends on flow rate.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.42-50
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• 2015

To evaluate the heat removal capability of a condenser tube in the PCCS of an advanced nuclear power plant, a steam condensation experiment in the presence of noncondensable gas on a vertical tube is performed. The average heat transfer coefficient is measured on a vertical tube of 40 mm in O.D. and 1.0 m in length. The experiments covers the pressures of 2-4 bar, and the mass fraction of air ranges from 0.1 up to 0.7. From the experimental results, the effects of the total pressure and the concentration of air on the condensation heat transfer coefficient are investigated. The measured data are compared with the predictions by Uchida's and Tagami's correlations, and it is revealed that these models underestimate the condensation heat transfer coefficient of the steam-air mixture.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.3
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• pp.113-120
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• 2000

On the absorber of absorption chiller/heater, LiBr solution at high concentration is sprinkled on a bundle of horizontal tube cooled by cooling water. In this case, the conditions of LiBr solution and cooling water have an influence on heat/mass transfer coefficient in this system. Therefor it is important to find optimal operation conditions of absorption chiller/heater to save energy. Heat and mass transfer coefficient increased with the increase of solution flow rate, and also heat and mass transfer rate increased but overall heat and mass transfer coefficient decreased by increasing the solution concentration within the experimental range. The superheating of the solution resulted in superior heat transfer character to a state of equilibrium from the point of heat flux and overall heat transfer coefficient.

• Proceedings of the KSME Conference
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• 2000.04b
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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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.664-675
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• 1990

In this study, the performance test and heat transfer experiment for a 4 cylinder and 4-cycle turbocharged gasoline engine were carried out in order to measure the heat transfer coefficient at the inner wall of the combustion chamber. From the result of heat transfer experiment, the energy balance of the fuel energy and the overall efficiency of the turbocharger were calculated, The variation of them was investigated as well with the engine operation conditions.