• Proceedings of the KSME Conference
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• 2001.06d
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• pp.782-789
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• 2001

Local heat/mass transfer and friction loss in a square duct roughened with various types of continuous and discrete rib turbulators are investigated. The combined effects of the gap flows of the discrete ribs and the secondary flows are examined for the purpose of the reduction of thermally weak regions and the promotion of the uniformity of heat/mass transfer distributions as well as the augmentation of average heat/mass transfer. The rib-to-rib pitch to the rib height ratio (p/e) of 8 and the rib angles of 90 and 60 deg are selected with $e/D_{h}=0.08$. The vortical structure of the secondary flows induced by the parallel angled arrays are quite distinct from that induced by the cross angled arrays. This distinction influences on heat/mass transfer and friction loss in all the tested cases. The gap flows of the discrete ribs reduce the strength of the secondary flows but promote local turbulence and flow mixing. As a result, the fairly uniform heat/mass transfer distributions are obtained with two row gaps.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.6
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• pp.651-657
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• 2010

Solute transport through a groove is affected by its vortices. Our laboratory and numerical experiments of dye transport through a single axisymmetric groove reveal evidence of enhanced spreading and mixing by the vortex, i.e., a new kind of dispersion called here the vortex dispersion. The uptake and release of contaminants by vortices in porous media is affected by the flow Reynolds number. The larger the flow Reynolds number, the larger is the vortex dispersion, and the larger is the mass-transfer rate between the mobile zone and the vortex. The long known dependence of the mass-transfer rate between the mobile and "immobile" zones in porous media on flow velocity can be explained by the presence of vortices in the "immobile" zone and their uptake and release of contaminants.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.140-150
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• 2004

In this study, the effect of relative position of the blade for the fixed vane has been investigated on blade surface heat transfer. The experiments were conducted in a low speed stationary annular cascade, and heat transfer of blade was examined for six positions within a pitch. Turbine test section has one stage composed of sixteen guide vanes and blades. The chord length of the tested blade is 150 mm and the mean tip clearance of the blade having flat tip is about $2.5\%$ of the blade chord. For the detailed mass transfer measurements on the blade surfaces, a naphthalene sublimation technique was used. The inlet flow Reynolds number is fixed to $1.5{\times}10^5$. Complex heat transfer characteristics are observed on the blade surface due to various flow characteristics, such as separation bubble, relaminarization, transition to turbulence and leakage vortices. The distributions of velocity and turbulence intensity change significantly with the relative position due to the blockage effect of the blade. This causes the variation of heat transfer patterns on the blade surface. The results show that the flow near the leading edge get highly disturbed and deflected toward the either side of the blade when the blade leading edge is positioned close to the trailing edge of the vane. Therefore, separation bubble disappears on the pressure side and overall heat transfer on the relaminarization region is increased. But, due to reduced tip gap flow at the upstream region, the effect of leakage flow on the upstream region of the blade surface is weakened. Thus, the heat transfer characteristics significantly change with the blade positions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1481-1490
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• 1996

This study is intend to improve flow pattern within evaporator, which is low quality and low mass flux, by installing narrow horizontal annular crevice so that enhance heat transfer coefficient. The motive, which made to study heat transfer enhancement by using narrow annular crevice, came from capillary phenomena and pumping force of generating vapor on refrigerant boiling. Tests were run about 5 models of turbulence promoter with CFC-12, in the range of evaporating temperature (15.deg. C), mass flux (50 to 100 kg/m$\^$2/s), heat flux (3.4 to 6.7 kW/m$\^$2/), quality (0.1 to O.5). It is observed that flow pattern within evaporator is changed closely to semi-annular flow or annular flow, of which refrigerant liquid is reached to the upper side of tube by using narrow annular crevice. When the narrow annular crevice is installed in the evaporator tube, local heat transfer coefficient is generally more improved than that of smooth tube. That fact is according to observed result of flow pattern. It is learned that narrow annular crevice has more efficiency at a low mass flux. At the TP-5, enhancement of heat transfer rate is about 170% compare to that of smooth tube on a low mass flux (50 kg/m$\^$2/s), and it is about 134% on a high mass flux (100 kg/M$\^$2/S), so that we know that it is on a very high condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.937-944
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• 2002

An experimental study has been conducted to investigate the heat/mass transfer characteristics within a square film cooling hole with asymmetric inlet now condition. The asymmetric inlet now condition is achieved by making distances between side walls of the secondary now duct and the film cooling hole different; one side wall is $2D_h$ apart from the center of the film cooling hole, while the other side wall is $1.5D_h$ apart from the center of the film cooling hole. The heat/mass transfer experiments for this study have been performed using a naphthalene sublimation method and the now field has been analyzed by numerical calculation using a commercial code. Swirl now is generated at the inlet region and the heat/mass transfer pattem with the asymmetric inlet now condition is changed significantly from that with the symmetric condition. In the exit region, the effect of mainstream on the inside hole now is reduced with the asymmetric condition. The average heat/mass transfer coefficient is higher than that with the symmetric condition due to the swirl now generated by the asymmetric inlet condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.435-442
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• 2000

The present study is conducted to investigate the local heat/mass transfer characteristics for flow through perforated plates. A naphthalene sublimation method is employed to determine the local heat/mass transfer coefficients on the effusion plate. Two parallel perforated plates are arranged for the two different ways: staggered and shifted in one direction. The experiments are conducted for hole pitch-to-diameter ratios of 6.0, for gap distance between the perforated plates of 0.33 to 10 hole diameters, and for Reynolds numbers of 5,000 to 12,000. The result shows that the high transfer region is formed at stagnation region and at the mid-line of the adjacent impinging jets due to secondary vortices and flow acceleration to the effusion hole. For flows through the perforated plates, the mass transfer rates on the surface of the effusion plate are about six to ten times higher than for effusion cooling alone (single perforated plate). More uniform and higher heat/mass transfer characteristic is obtained in overall region with small gap between two perforated plates.

• The KSFM Journal of Fluid Machinery
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• v.11 no.4
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• pp.7-13
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• 2008

The computational investigation is performed to find out the interaction of arc plasmas with surrounding materials and the thermal flow characteristics in a PASB (Puffer-Assisted Self-Blast) chamber, which is one of new breaking concepts in $SF_6$ switchgears. It is very important to define the flow and mass transfer happened during the full arcing history for further understanding complex physics inside the chamber. In this study, we have considered two diffusion processes by the hot arc plasma, one is PTFE nozzle ablation and the other is Cu electrode evaporation, simultaneously. It was found that the principle of the pressure-rise inside the chamber is confirmed by the computational results and the increase of the electrical conductivity of the residual gas near current zero is critical to the chamber design.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.93-96
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• 2006

The heat transfer enhancement by pulsatile flow in the plate heat exchanger has been investigated numerically in the present study. The numerical study was performed in the range of the mass flux from 0.04 to 0.12 kg/s. The results showed that the pulsatile flow produces resonating vortex shedding at the groove sharp edges and a strong transient vortex rotation within the grooved channels. As a result, the mixing between the trapped volume in the grooved cavity and the main stream was enhanced. Good agreements between the predictions and measured data are obtained in steady flow. And the heat transfer of pulsatile flow is about 2.4 times than steady flow when frequency is 10 Hz and the mass flux of cold side is 0.04 kg/s.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.8
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• pp.690-696
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• 2003

This paper presents the heat recovery performance of water fluidized-bed heat exchanger. Temperature and humidity ratio of waste gas are considered as important parameters in this study. Therefore, the heat recovery rate through water fluidized-bed heat exchanger for exhaust gases with various temperatures and humidity ratios can be estimated from the results of this study. Mass flow ratio (the ratio of mass flow rate of water to that of gas) and temperature of inlet water are also considered as important operating variables. Increase of heat recovery rate can be obtained through either high mass flow ratio or low temperature of inlet water with resultant low recovered temperature. The heat recovery performance with the mass flow ratio of about up to 10 has been investigated. The effect of number of stages of water fluidized-bed on the heat recovery performance has been also examined in this study.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.4 no.1
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• pp.121-131
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• 2000

Melt flow, heat and mass transfer of oxygen have been analyzed numerically in the process of Czochralski single crystal growth of silicon under the influence of misaligned cusp magnetic fields. Since the silicon melt in a crucible for crystal growth is of high temperature and of highly electrical-conducting, experimentation method has difficulty in analyzing the behavior of the melt flow. A set of simultaneous nonlinear equations including Navier-Stokes and Maxwell equations has been used for the modelling of the melt flow which can be regarded as a liquid metal. Together with the melt flow which forms the Marangoni convection, a flow circulation is observed near the comer close both to the crucible wall and the free surface. The melt flow tends to follow the magnetic lines instead of traversing the lines. These flow characteristics helps the flow circulation exist. Mass transfer characteristics influenced by the melt flow has been analyzed and the oxygen absorption rate to the crystal has been calculated and turned out to be rather uniform than in the case of an aligned magnetic field.