• Title, Summary, Keyword: mass transfer coefficient

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Experimental Study on Heat and Mass Transfer Characteristics in bundles of horizontal absorption tubes (수평관군 흡수기의 열 및 물질 전달특성에 관한 실험적 연구)

  • 설원실;정용욱;문춘근;윤정인
    • Journal of the Korean Society of Marine Engineering
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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.

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Heat and mass transfer analysis in air gap membrane distillation process for desalination

  • Pangarkar, Bhausaheb L.;Sane, Mukund G.
    • Membrane Water Treatment
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    • v.2 no.3
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    • pp.159-173
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    • 2011
  • The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22 ${\mu}m$. A mathematical model is proposed to evaluate the membrane mass transfer coefficient, thermal boundary layers' heat transfer coefficients, membrane / liquid interface temperatures and the temperature polarization coefficients. The mass transfer model was validated by the experimentally and fitted well with the combined Knudsen and molecular diffusion mechanism. The mass transfer coefficient increased with an increase in feed bulk temperature. The experimental parameters such as, feed temperature, 313 to 333 K, feed velocity, 0.8 to 1.8 m/s (turbulent flow region) were analyzed. The permeation fluxes increased with feed temperature and velocity. The effect of feed bulk temperature on the boundary layers' heat transfer coefficients was shown and fairly discussed. The temperature polarization coefficient increased with feed velocity and decreased with temperature. The values obtained were 0.56 to 0.82, indicating the effective heat transfer of the system. The fouling was observed during the 90 h experimental run in the application of natural ground water and seawater. The time dependent fouling resistance can be added in the total transport resistance.

A prediction of indoor pollutant concentration using method mass transfer coefficient in multi-layered building materials (복합 건축자재의 물질전달계수를 이용한 실내 오염물질 농도 예측방법)

  • Kim, Chang Nam;Lee, Yun Gyu;Leigh, Seung Bok;Kim, Tae Yeon
    • KIEAE Journal
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    • v.7 no.5
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    • pp.53-58
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    • 2007
  • In order to predict the indoor air pollutant, the VOCs emission rate is used through small chamber in the design process. However, the small chamber method has limitations as the convective mass transfer coefficient, the most important factor when predicting VOCs contamination of indoor air, is different between the small chamber result and the measured data in the actual building. Furthermore, the existing studies which analyzed mass transfer coefficient in the small chamber were directed on the small chambers developed at the time and FLEC(Field and Laboratory Emission Cell), thus, are different from the current small chamber which has been changed with improvements. The purpose of this study is to determine the emission rate of pollutant in multi-layered building materials, and predict the indoor pollutant concentration through the CFD(Computational of Fluid Dynamics) and CRIAQ2 based on the mass transfer coefficient on singled-layered building material by using the current small chamber widely used in Korea. Futhermore, this study used the new convective mass transfer coefficient(hm') which indicates the existing convective mass transfer coefficient(hm) including VOC partition coefficient(k). Also, formaldehyde was selected as target pollutant.

Characteristics of Gas-liquid Mass Transfer and Interfacial Area in a Bubble Column

  • Lim, Dae Ho;Yoo, Dong Jun;Kang, Yong
    • Korean Chemical Engineering Research
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    • v.53 no.3
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    • pp.315-320
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    • 2015
  • Characteristics of gas-liquid mass transfer and interfacial area were investigated in a bubble column of diameter and height of 0.102 m and 2.5 m, respectively. Effects of gas and liquid velocities on the volumetric gas-liquid mass transfer coefficient ($k_La$), interfacial area (a) and liquid side true mass transfer coefficient ($k_L$) were examined. The interfacial area and volumetric gas-liquid mass transfer coefficient were determined directly by adopting the simultaneous physical desorption of $O_2$ and chemical absorption of $CO_2$ in the column. The values of $k_La$ and a increased with increasing gas velocity but decreased with increasing liquid velocity in the bubble column which was operated in the churn turbulent flow regime. The value of $k_L$ increased with increasing gas velocity but did not change considerably with increasing liquid velocity. The liquid side mass transfer was found to be related closely to the liquid circulation as well as the effective contacting frequency between the bubbles and liquid phases.

An experimental study on cooling characteristics of mist impinging jet on a flat plate (평판에 분사된 분무충돌제트의 냉각특성에 대한 실험적 연구)

  • Jun, Sang-Uk;Chung, Won-Seok;Lee, Joon-Sik
    • Proceedings of the KSME Conference
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    • pp.528-533
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    • 2001
  • An experimental study is carried out to investigate the effects of air and water mass flow rates on cooling characteristics of mist impinging jet on a flat plate. Experiments are conducted with air mass flow rates from 0.0 to 3.0 g/s, and water mass flow rates from 5.0 to 20.0 g/s. An air-atomizing nozzle is used for the purpose of controlling air and water mass flow rates. In this study, a new test section is designed to obtain local heat transfer coefficient distributions. Heat transfer characteristics of the mist impinging jet are explained with the aid of flow visualization. Surface temperature and heat transfer coefficient distributions become more uniform as air mass flow rate increases, and that the increases in water flow rate mainly enhance cooling performance. Air mass flow rate weakly influences averaged heat transfer coefficient when water mass flow rate is low, but averaged heat transfer coefficient increases remarkably as air mass flow rate in case of high water mass flow rate.

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Effect of Orifice Nozzle Design and Input Power on Two-Phase Flow and Mass Transfer Characteristics (2 상 유동 및 물질전달 특성에 미치는 오리피스 노즐형상과 소요동력의 영향)

  • Yang, Hei Cheon
    • 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.

A Prediction of Pollutant Emission Rate using Numerical Analysis and CFD in Double-Layered Building Materials (수치해석 및 CFD를 이용한 소형챔버내 복합건축자재의 오염물질 방출량 예측)

  • Kim, Chang-Nam;Leigh, Seung-Bok;Kim, Tae-Yeon
    • Proceedings of the SAREK Conference
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    • pp.277-282
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    • 2006
  • In order to predict the indoor air pollutant, the VOCs emission rate is used through small chamber in the design process. However, the small chamber method has limitations as the convective mass transfer coefficient, the most important factor when predicting VOCs contamination of indoor air, is different between the small chamber result and the measured data in the actual building. Furthermore, the existing studies which analyzed mass transfer coefficient in the small chamber were directed on the small chambers developed at the time and FLEC(Field and Laboratory Emission Cell), thus, are different from the current small chamber which has been changed with improvements. The purpose of this study is to determine the emission rate of pollutant in double-layered building materials through the CFD(Computational of Fluid Dynamics) and Numerical analysis based on the mass transfer coefficient on singled-layered building material by using the current small chamber widely used in Korea. Futhermore, this study used the new convective mass transfer coefficient($h_m'$) which indicates the existing convective mass transfer coefficient($h_m$) including VOC partition coefficient(k). Also, formaldehyde was selected as target pollutant.

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A Naphthalene Sublimation Study on Heat/Mass Transfer for Flow over a Flat Plate

  • Park, Jong-Hark;Yoo, Seong-Yeon
    • 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.

Boiling Heat Transfer Characteristics of R-290 in Horizontal Minichannel (수평미세관내 R-290의 비등열전달 특성)

  • Choi, Kwang-Il;Pamitran, A.S.;Oh, Jong-Taek
    • Proceedings of the SAREK Conference
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    • pp.68-73
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    • 2006
  • The present paper deals with an experimental study of boiling heat transfer characteristics of R-290, and is focused on pressure gradient and heat transfer coefficient of the refrigerant flow inside horizontal smooth minichannel with inner diameter of 3.0 mm and length of 2000 mm. The direct heating method applied for supplying heat to the refrigerant where the test tube was uniformly heated by electric current which was applied to the tube wall. The experiments were conducted with R-290 with purity of 99.99% at saturation temperature of 0 to $10^{\circ}C$. The range of mass flux is $50{\sim}250kg/m^2s$ and heat flux is $5{\sim}20kW/m^2$. The heat transfer coefficients of R-290 increases with increasing mass flux and saturation temperature, wherein the effect of mass flux is higher than that of the saturation temperature, whereas the heat flux has a low effect on increasing heat transfer coefficient. The significant effect of mass flux on heat transfer coefficient is shown at high quality, the effect of heat flux on heat transfer coefficient at low quality shows a domination of nucleate boiling contribution. The heat transfer coefficient of the experimental result was compared with six existing heat transfer coefficient correlation. Zang et al.'s correlation(2004) gave the best prediction of heat transfer coefficient.

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Evaporation heat transfer and Pressure loss in micro-fin tubes and a smooth tube (마이크로핀관과 평활관에서의 증발열전달과 압력손실 특성)

  • 장세환;정시영;홍영기
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.2
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    • pp.215-223
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    • 1999
  • Evaporation heat transfer coefficient and pressure loss were measured for three different micro-fin tubes and a smooth tube. The experiments were carried out with R-22 over a wide range of vapor Quality, mass velocity and heat flux. Heat transfer coefficient of the tube with slightly modified fin shape was found to be higher than that of the commercial reference tube by 60%. The improvement of heat transfer has been achieved without noticeable increase of pressure loss. Heat transfer coefficient was increased with increasing quality, refrigerant mass flux, and heat flux. However, the effect of refrigerant mass flux and heat flux was not great. Heat transfer coefficient at bottom was lower than that at top of the tube in low quality region, which suggested the existence of stratification in the micro-fin tube. Pressure drop was linearly increased with increasing refrigerant quality and was proportional to about square of mass flux.

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