• Journal of computational fluids engineering
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• v.21 no.1
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• pp.64-71
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• 2016

This research is to numerically investigate the convective cooling performance in the Disk brake. Research concentrates on the heat transfer coefficient and cooling performance which are selected with cooling local locations. Cooling performance of the Hole disk has been compared by Ventilated Disk. According to the results of heat transfer on the disk brake, activated velocity distributions more appear in the Hole disk. This is due to the fact that a number of hole units have exactly 120 on the surface of the hole disk. Therefore, velocity distributions of hole disk brake is better activated than Ventilated disk. According to the calculations of Nusselt number between surface and atmosphere in the interested cooling area, average value of cooling effect has been increased 13.5% by the hole disk at driving of speed 65 km/h situation and grown 18% by the hole disk at driving speed of 100 km/h. Due to the flow of air through the hole route, cooling performance of the hole disk was very excellent. In addition, cooling effect on edge of the bottom is better than the vicinity of center.

• 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 Society of Mechanical Engineers B
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• v.22 no.4
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• pp.510-519
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• 1998

Recently, computer modelling is increasingly used as a design tool, which requires more detailed data for heat transfer coefficients in various regions of the induction motor. But there are little information about those of rotor fan and endring because of difficulty in measuring signals in rotating bodies. In the present studies, the temperature signals were precisely measured with self-developed telemetry system, which had multi-channels and high rotational speed. After some losses were compensated, the heat transfer coefficients of the rotor endring and fan surfaces were measured. Minimum heat transfer region was existed with endcap plate distance and maximum heat transfer was found at some rotor fan width. It was also studied that how the guide plate and endcap inside rib effected on the rotor heat transfer. The higher heat transfer were obtained with decreasing guide plate distance, increasing the number and height of endcap inside rib. The correlation equations of the results were obtained and compared with others. Above results of the heat transfer coefficients can be used as basic data for cooling design of the various kind of motors.

• Journal of computational fluids engineering
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• v.20 no.1
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• pp.92-98
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• 2015

Thermal-fluid analysis is performed numerically to figure out the characteristics of heat transfer in a thermosyphon varying with the aspect ratio of geometry and the filling ratio of working fluid. The computational results are reasonable compared with the experimental data and visualized. The thermal resistance and the convective heat transfer coefficients are evaluated with the aspect ratio of thermosyphon and the filling ratio of working fluid, respectively. In conclusion, the thermal resistance decreases as the length of evaporator increases. However, the variation of a condenser length is nearly independent on the thermal resistance. In order to raise the performance of thermosyphon, the working fluid needs to be filled over 75%. In addition, Nusselt numbers in the evaporator and the condenser show 275 and 304, respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2428-2437
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• 2000

In general, it is known that the portion of leakage loss is more than 20 % of total loss in scroll compressor. So far many studies have been done to improve the leakage problem and volumetric efficiency. In order to do this it is necessary that the leakage is exactly evaluated for conventional scroll model. Almost all studies that have been done were assumed that the clearance remains constant while operating. But in actual operating conditions, scroll wrap is deformed due to elevated refrigerant gas temperature. And this makes the leakage clearance change, so the leakage mass flow and the volumetric efficiency are also changed. In this study we assumed the steady state operating condition and obtain the average temperature and convection heat transfer coefficient in terms of involute angle. With these results, using finite element method we analyzed the heat transfer of scroll wrap, then did thermal deformation analysis. Then we obtain the leakage clearance and do the leakage and volumetric efficiency analysis. Compared with undeformed feature, we examine the effect of the thermal deformation on the leakage. The results say that the leakage mass flow for the case of considering thermal deformation is less than that for the unconsidered one, and this means that the leakage clearance is reduced due to thermal deformation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.6
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• pp.509-517
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• 2006

Present study is concerned with an experimental study on the cooling characteristics of heat-generating components arranged in channels which are made by printed circuit boards. To estimate the thermal performance of the heat-generating components arranged by $5\times11$ in channel flow, three variables are used: the inlet velocity, the height of channel, and row number of the component. The cooling characteristics of the heat-generating components such as the surface temperature rise, the adiabatic temperature rise, the adiabatic heat transfer coefficient, and the effect of thermal wake are compared with the result of the experiment and the numerical analysis. The experimental result is in a good agreement with the numerical analysis. The heat transfer coefficient increases as the Reynolds number increases, while the thermal wake function calculated for each row decreases as the Reynolds number increases. In addition, it is found that Nu-Re correlation equation is Identical to the previous studies, and the empirical correlation equation between the thermal wake function and Re is presented.

• Journal of Energy Engineering
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• v.5 no.1
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• pp.19-27
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• 1996

Self-pressurization of cylindrical container of cryogen is numerically analyzed. The container is axi-symmetric and heated from side wall with constant heat flux. Natural convection by external heat flux is studied numerically using finite difference method. Oxygen, nytrogen and hydrogen are working fluids in this paper. Liquid is considered incompressible fluid and vapor is assumed to behave as gas meeting with virial equation of gas. The Second virial coefficients of gas are obtained from Lennard-jones model. The important variables which have effects on self-pressurization are external heat flux, heat capacity of wall and initial ullage in container. The most important variable of them is external heat flux. The pressure rise calculated from the virial gas model is slightly different from that calculated using Ideal gas model for oxygen.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.164-170
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• 2001

The influence of unsteady wake on the flow and heat transfer characteristics in a four-vane linear cascade was experimentally investigated. The unsteady wake was generated with four rotating rectangular plates located upstream of the cascade. Tested inlet Reynolds number based on chord length was set to 66,000 by controlling free-stream velocity. A hot-wire anemometer system was employed to measure turbulent velocity components. For the convective heat transfer coefficients measurement on turbine blade surface, thermochromic liquid crystal and gold film Intrex were used. It was found that the unsteady wake enhances the turbulent motion in the cascade passage and accordingly promotes the development and transition of boundary layer. It was found that the heat transfer coefficients on the blade surface increase as the plate rotating speed increases. However, the increasing of heat transfer coefficients is not significant in the case that Strouhal number is higher than 0.503.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.730-740
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• 1996

Boiling heat transfer coefficients of pure refrigerants (R22, R32, R134a, R125, R290, and R600a) and refrigerant mixtures (R32/Rl34a, R290/ R600a, and R32/R125) are measured experimentally and compared with Chen's correlation. The test section is a seamless stainless steel tube with inner diameter of 7.7mm and uniformly heated by applying electric current directly to the tube. Heat fluxes range from 10 to 30kW$^2$. Mass fluxes are set to 424 ~ 742kg/m$^{2}$s for R22, R32, R134a, R32/R134a, and R32/Rl25 ; 265 ~ 583kg/m$^{2}$s for R290, R600a, and R290/R600a. Heat transfer coefficients depend strongly on heat flux at a low quality region and become independent as quality increases. Convective boiling term in the Chen's correlation predicts experimental data of the pure refrigerants fairly well (relative error of 12.1% for the data of quality over 0.2). The correlation for pure substances overpredicts the heat transfer coefficients for nonazeotropic refrigerant mixtures.

• The KSFM Journal of Fluid Machinery
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• v.15 no.1
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• pp.5-12
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• 2012

In this paper, the heat transfer coefficient measurement techniques using TSP(temperature sensitive paint) were introduced and the results of a comparative study on the heat transfer coefficient measurement by steady state and transient TSP techniques were discussed. The distributions of heat transfer coefficient by a single $60^{\circ}$ inclined impingement jet on a flat surface were measured by both techniques. Tested Reynolds number based on the jet diameter (d) was 30,000 and the distance between jet exit and target plate (L) was fixed at 10d. Results showed that the measured Nusselt number by both techniques indicated significant difference except near the center of impingement jet. Also, the heat transfer coefficients measured by the transient TSP technique were affected by the reference temperature of the jet. Based on the measured data, characteristics of both TSP techniques were analyzed and suggestions for applying them were also given.