• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.237-243
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• 2016

It is necessary to investigate the input power as well as the mass transfer characteristics of the aeration process in order to improve the energy efficiency of an aerobic water treatment. The objective of this study is to experimentally investigate the effect of orifice nozzle design and input power on the flow and mass transfer characteristics of a vertical two-phase flow. The mass ratio, input power, volumetric mass transfer coefficient, and mass transfer efficiency were calculated using the measured data. It was found that as the input power increases the volumetric mass transfer coefficient increases, while the mass ratio and mass transfer efficiency decrease. The mass ratio, volumetric mass transfer coefficient, and mass transfer efficiency were higher for the orifice configuration with a smaller orifice nozzle area ratio. An empirical correlation was proposed to estimate the effect of mass ratio, input power, and Froude number on the volumetric mass transfer coefficient.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1258-1266
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• 2004

It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer. In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to dimensionless parameters such as Sherwood number, Stanton number and Colburn j-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more suitable for turbulent boundary layer. But average Sherwood number and average Colburn j-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar boundary layer as well as turbulent boundary layer.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.22-29
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• 2001

The present study investigates the effects of various rib arrangements and rotating on heat/mass transfer in the cooling passage of gas turbine blades. The cooling passage has very complex flow structure, because of the rib turbulator and rotating effect. Experiments and numerical calculation are conducted to investigate the complex flow structures and heat transfer characteristics; the numerical computation is performed using a commercial code, FLUENT ver.5, to calculate the flow structures and the experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. For the rotating duct tests, the test duct, which is the cross section of is $20mm\times40mm$ (the hydraulic diameter, $D_h$, of 26.7 mm, has two-pass with $180^{\circ}$ turning and the rectangular ribs on the wall. The rib angle of attack is $70^{\circ}$ and the maximum radius of rotation is $21.63D_h$. The partition wall has 10 mm thickness, which is 0.5 times to the channel width, and the distance between the tip of the partition wall and the outer wall of the turning region is 26.7 mm $(1D_h)$. The turning effect of duct flow makes the very complex flow structure including Dean type vortex and high turbulence, so that the heat/mass transfer increases in the turning region and at the entrance of the second pass. The Coriolis effect deflects the flow to the trailing surface, resulting in enhancement of the heat/mass transfer on the trailing surface and reduction on the leading surface in the first pass. However, the opposite phenomena are observed in the second pass. The each rib arrangement makes different secondary flow patterns. The complex heat/mass transfer characteristics are observed by the combined effects of the rib arrangements, duct rotation and flow turning.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2779-2786
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• 1994

This study presents an experimental investigation of the effect of the wake on mass transfer about a circular cylinder in crossflow. The flat-plate wake was generated by merging two mirror images of turbulent boundary layers that were well developed along the both sides of flat plate with a sharp trailing edge. The velocity field was measured by a hot-wire system and the mass transfer rate by a naphthalene sublimation method. The mixing and developing stages of the wake were addressed to identify flow conditions. The mass transfer effects of different developing stages of the wake was discussed in detail. It is noted that a local maximum appears not at the front stagnation point but at a point a little downstream when the cylinder is located in the nearwake region and much more elevated mass transfer rate is obtained compared to effect of free-stream turbulence.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.11
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• pp.888-895
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• 2006

The present study has been conducted to investigate the effects of Reynolds number on heat/mass transfer and pressure drop characteristics in a rotating smooth two-pass duct. For stationary cases, the heat/mass transfer and pressure drop Is decreased on turning region of both leading and trailing surfaces as Reynolds number increases. For rotating cases, increment of Reynolds number affects differently the heat/mass transfer and pressure drop on the leading and trailing surfaces. In the first pass, for example, the heat/mass transfer on the leading surface is greatly increased, though the heat/mass transfer on the trailing surface is almost the same. The reason is that effect of the main flow is more dominant than effect of secondary flow. In particular, it gave decrement of the heat/mass transfer and the pressure drop at turning region and upstream region of second pass for both non-rotating and rotating cases.

• Membrane and Water Treatment
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• v.2 no.2
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• pp.75-89
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• 2011

The predicting equations for mass transfer rate in cross-flow rectangular dialyzers with double flow and recycle, have been derived by mass balances. The recycling operation has two conflicting effects. One is the desirable effect of the increase in fluid velocity, resulting in an increased mass transfer coefficient. The other is the undesirable effect of the reduction in concentration difference due to remixing, resulting in decreased mass-transfer driving force. In contrast a single-pass device without recycling, considerable improvement in mass transfer is achieved if the cross-flow rectangular dialyzer of same size is operated with double pass and external recycling. It is concluded that recycle can enhance mass transfer, especially for larger reflux ratio.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2002.05a
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• pp.41-47
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• 2002

A model of simultaneous heat and mass transfer process in absorption of refrigerant vapor into a lithium bromide solution of water-cooled vertical plate absorber was developed. The model can predict temperature and concentration profiles as well as the absorption heat and mass fluxes, the total heat and mass transfer rates and the heat and mass transfer coefficients. Besides, the effect of operating condition on absorption mass flux has been investigated, with the result that the absorption mass flux is increased as the inlet cooling water temperature decreases, the system pressure increases and the inlet solution concentration increases. And among the effects of operating parameters on absorption mass flux, the effect of inlet solution concentration is dominant.

• Journal of computational fluids engineering
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• v.17 no.3
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• pp.59-67
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• 2012

Large Eddy Simulation(LES) of turbulent mass transfer in fully developed turbulent pipe flow has been performed to study the effect of Reynolds number on the concentration fields at $Re_{\tau}=180$, 395, 590 based on friction velocity and pipe radius. Dynamic subgrid-scale models for the turbulent subgrid-scale stresses and mass fluxes were employed to close the governing equations. Fully developed turbulent pipe flows with constant mass flux imposed at the wall are studied for Sc=0.71. The mean concentration profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The effects of Reynolds number on the turbulent mass transfer are identified in the higher-order statistics(Skewness and Flatness factor) and instantaneous concentration fields. The budgets of turbulent mass fluxes and concentration variance were computed and analyzed to elucidate the effect of Reynolds number on turbulent mass transfer. Furthermore, to understand the correlation between near-wall turbulence structure and concentration fluctuation, we present an octant analysis in the vicinity of the pipe wall.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.7 s.238
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• pp.828-836
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• 2005

Impingement/effusion cooling technique is used for combustor liner or turbine parts cooling in gas turbine engine. In the impingement/effusion cooling system, the crossflow generated in the cooling channel induces an adverse effect on the cooling performance, which consequently affects the durability of the cooling system. In the present study, to reduce the adverse effect of the crossflow and improve the cooling performance, circular pin fins are installed in impingement/effusion cooling system and the heat transfer characteristics are investigated. The pin fins are installed between two perforated plates and the crossflow passes between these two plates. A blowing ratio is changed from 0.5 to 1.5 for the fixed jet Reynolds number of 10,000 and five circular pin fin arrangements are considered in this study. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The results show that local distributions of heat/mass transfer coefficient are changed due to the installation of pin fins. Due to the generation of vortex and wake by the pin fin, locally low heat/mass transfer regions are reduced. Moreover, the pin fin prevents the wall jet from being swept away, resulting in the increase of heat/mass transfer. When the pin fin is installed in front of the impinging let, the blockage effect on the crossflow enhances the heat/mass transfer. However, the pin fin installed just behind the impinging jet blocks up the wall jet, decreasing the heat/mass transfer. As the blowing ratio increases, the pin fins lead to the higher Sh value compared to the case without pin fins, inducing $16\%{\~}22\%$ enhancement of overall Sh value at high blowing ratio of M=1.5.

• The KSFM Journal of Fluid Machinery
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• v.11 no.6
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• pp.24-30
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• 2008

In order to enhance the heat/mass transfer, a turbulator has been installed at the exit of injection hole for the impingement/effusion cooling system. The local heat/mass transfer coefficients have been obtained by a naphthalene sublimation method. Experiments have been carried out at the fixed jet Reynolds number of 10,000. Two turbulators with different diameter have been used in the current study. The result presents that the turbulator leads to the increase in flow mixing and jet velocity, consequently enhancing the heat/mass transfer at a stagnation region. Further, the stagnation region is divided into four small areas with peak value. In the existence of initial crossflow, the stagnation regions move downstream and low heat/mass transfer regions are formed regardless of the installation of turbulator. However, the increased jet velocity by turbulator reduces the crossflow effect against the jet, resulting in decrease of low heat/mass transfer regions. Compared to the case without turbulator, the installation of turbulator yields $5{\sim}10%$ augmentation in averaged Sh value.