• Title/Summary/Keyword: Flow Condensation

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A Study of Thermal, Air-flow and Humidity Conditions in an Indoor Swimming Pool (실내수영장의 열, 기류 및 습도환경에 관한 연구)

  • 강석윤;이태구;문종선;이재헌
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.8
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    • pp.683-689
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    • 2003
  • The thermal comfort of an indoor swimming pool is different from that of general indoor space because of the characteristics of large space and the wear conditions of swimmers. Dew condensation by humid air not only makes mold on the floor, wall and roof but also decreases the durability of buildings by penetrating into their structures. In this study, the characteristics of the flow field, the temperature field and the humidity distribution in an indoor swimming pool have been examined by the numerical method to estimate the level of thermal comfort and the generation rate of dew condensation. The results showed that the dew condensation regions were spread widely at the eastern parts of the swimming pool due to the insufficient air flow rate with low velocity and temperature. To prevent the generation of dew condensation in a region, a sufficient warm air flow rate should be supplied to make an air mixing. The values of PMV at horizontal plane of 1.5 m height have the range of -1.0∼1.2, which means the suitable level for swimmers.

IMPROVEMENTS OF CONDENSATION HEAT TRANSFER MODELS IN MARS CODE FOR LAMINAR FLOW IN PRESENCE OF NON-CONDENSABLE GAS

  • Bang, Young-Suk;Chun, Ji-Ran;Chung, Bub-Dong;Park, Goon-Cherl
    • Nuclear Engineering and Technology
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    • v.41 no.8
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    • pp.1015-1024
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    • 2009
  • The presence of a non-condensable gas can considerably reduce the level of condensation heat transfer. The non-condensable gas effect is a primary concern in some passive systems used in advanced design concepts, such as the Passive Residual Heat Removal System (PRHRS) of the System-integrated Modular Advanced ReacTor (SMART) and the Passive Containment Cooling System (PCCS) of the Simplified Boiling Water Reactor (SBWR). This study examined the capability of the Multi-dimensional Analysis of Reactor Safety (MARS) code to predict condensation heat transfer in a vertical tube containing a non-condensable gas. Five experiments were simulated to evaluate the MARS code. The results of the simulations showed that the MARS code overestimated the condensation heat transfer coefficient compared to the experimental data. In particular, in small-diameter cases, the MARS predictions showed significant differences from the measured data, and the condensation heat transfer coefficient behavior along the tube did not match the experimental data. A new method for calculating condensation heat transfer coefficient was incorporated in MARS that considers the interfacial shear stress as well as flow condition determination criterion. The predictions were improved by using the new condensation model.

Condensation processes in transonic two-phase flows of saturated humid air using a small-disturbance model (미교란 모델을 이용한 포화 습공기 천음속 2상 유동에서의 응축현상)

  • Lee, Jang-Chang;Zvi Rusak
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.6
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    • pp.23-29
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    • 2003
  • Transonic two-phase flow of Saturated humid air, in which relative humidity is 100%, with various condensation processes around thin airfoils is investigated. The study uses an extended transonic small-disturbance(TSD) model of Rusak and Lee [11, 12] which includes effects of heat addition to the flow due to condensation. Two possible limit types of condensation processes are considered. In the nonequilibrium and homogeneous process, the condensate mass fraction is calculated according to classical nucleation and droplet growth rate models. In the equilibrium process, the condensate mass fraction is calculated by assuming an isentropic process. The flow and condensation equations are solved numerical1y by iterative computations. Results under same upstream conditions describe the flow structure, field of condensate, and pressure distribution on airfoil's surfaces. It is found that flow characteristics, such as position and strength of shock waves and airfoil’s pressure distribution, are different for the two condensation processes. Yet, in each case, heat addition as a result of condensation causes significant changes in flow behavior and affects the aerodynamic performance of airfoils.

A Comparison of Flow Condensation HTCs of R22 Alternatives in the Multi-Channel Tube (다채널 알루미늄 평판관내 R22와 R134a의 흐름 응축 열전달 성능 비교)

  • 서영호;박기정;정동수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.6
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    • pp.589-598
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    • 2004
  • Flow condensation heat transfer coefficients (HTCs) of R22 and R134a were measured on a horizontal 9 hole aluminum multi-channel tube. The main test section in the refrigerant loop was made of a flat multi-channel aluminum tube of 1.4 mm hydraulic diameter and 0.53 m length. Refrigerant was cooled by passing cold water through an annulus surrounding the test section. Data were obtained in the vapor qualities of 0.1∼0.9 at mass flux of 200∼400 kg/$m^2$s and heat flux of 7.3∼7.7 ㎾/$m^2$ at the saturation temperature of 4$0^{\circ}C$. All popular correlations in single-phase subcooled liquid and flow condensation originally developed for large single tubes predicted the present data of the flat tube within 20% deviation when effective heat transfer area is used in determining experimental data. This suggests that there is little change in flow characteristics and patterns when the tube diameter is reduced down to 1.4 mm diameter range. Thermal insulation for the outer tube section surrounding the test tube for the transport of heat transfer fluid is very important in fluid heat-ing or cooling type heat transfer experimental apparatus.

THE EFFECTS OF MACH NUMBER AND THICKNESS RATIO OF AIRFOIL ON TRANSONIC FLOW OF MOIST AIR AROUND A THIN AIRFOIL WITH LATENT HEAT TRANSFER (잠열 전달이 일어나는 얇은 익형주위의 천음속 습공기 유동에서의 마하수와 익형 두께비의 영향)

  • Lee, J.C.
    • Journal of computational fluids engineering
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    • v.17 no.4
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    • pp.93-102
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    • 2012
  • Once the condensation of water vapor in moist air around a thin airfoil occurs, liquid droplets nucleate. The condensation process releases heat to the surrounding gaseous components of moist air and significantly affects their thermodynamic and flow properties. As a results, variations in the aerodynamic performance of airfoils can be found. In the present work, the effects of upstream Mach number and thickness ratio of airfoil on the transonic flow of moist air around a thin airfoil are investigated by numerical analysis. The results shows that a significant condensation occurs as the upstream Mach number is increased at the fixed thickness ratio of airfoil($\epsilon$=0.12) and as the thickness ratio of airfoil is increased at the fixed upstream Mach number($M_{\infty}$=0.80). The condensate mass fraction is also increased and dispersed widely around an airfoil as the upstream Mach number and thickness ratio of airfoil are increased. The position of shock wave for moist air flow move toward the leading edge of airfoil when it is compared with the position of shock wave for dry air.

Velocity and Temperature Profiles of Steam-Air Mixture on the Film Condensation (막응축 열전달에서 공기-수증기 혼합기체의 속도 및 온도분포)

  • 강희찬;김무환
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.10
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    • pp.2675-2685
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    • 1994
  • A study has been conducted to provide the experimental information for the velocity and temperature profiles of steam-air mixutre and to investigate their roles on the film condensation with wavy interface. Saturated gas mixture of steam-air was made to flow through the nearly horizontal$(4.1^{\circ})$ square duct of 0.1m width and 1.56m length at atmospheric pressure, and was condensated on the bottom cold plate. The air mass fraction in the gas mixture was changed from zero(W =0, pure steam) to one(W =1, pure air), and the bulk velocity was varied from 2 to 4 m/s. Water film was injected concurrently to investigate the effect of wavy interface on the condensation. The velocity and temperature profiles were measured by LDA system and thermocouples along the three parameters ; air mass fraction, mixture velocity and film flow rate. The profiles moved toward the interface with increasing steam mass fraction, mixture velocity and film flow rate. The Prandtl and Schmidt numbers were near one in the present experimental range, however there was no complete similarity between the velocity and temperature profiles of gas mixture. And the heat transfer characteristics and interfacial structure were coupled with each other.

Flow Condensation Heat Transfer Characteristic of R245fa in a Horizontal Plain Tube (수평 평활관내 R245fa의 흐름 응축 열전달 특성)

  • Park, Hyun-Shin;Park, Ki-Jung;Jung, Dong-Soo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.20 no.2
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    • pp.87-96
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    • 2008
  • Flow condensation heat transfer coefficients(HTCs) of R123 and R245fa are measured in a horizontal plain tube. The main test section in the experimental flow loop is made of a plain copper tube of 9.52 mm outside diameter and 530 mm length. The refrigerant is cooled by passing cold water through an annulus surrounding the test section. Tests are performed at a fixed saturation temperature of $50\;{\pm}\;0.2\;^{\circ}C$ with mass fluxes of 50, 100, $150\;kg/m^2s$ and heat flux of $7.3{\sim}7.7\;kW/m^2$. Heat transfer data are obtained in the vapor quality range of $10{\sim}90%$. Test results show that the flow condensation HTCs of R245fa are overall 7.9% higher than those of R123 at all mass fluxes. The pressure drop of R245fa is smaller than that of R123 at the same heat flux. In conclusion, R245fa is a good candidate to replace ozone depleting R123 currently used in chillers from the view point heat transfer and environmental properties.

A study on effect of heat transfer of condensation including noncondensable gas over a flat plate (불응축가스가 평판위 응축열전달에 미치는 영향에 관한 연구)

  • 양대일;정형호
    • Journal of Advanced Marine Engineering and Technology
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    • v.24 no.1
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    • pp.25-30
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    • 2000
  • In present paper, mass transfer over a flat plate with film condensation including noncondesable gas is analyzed with the help of similarity methods. Couette flow was assumed in liquid film and boundary-layer approximation was used in the ambient flow. Governing equations were transformed into the ordinary differential equtions by the similarity methods. Runge-Kutta and shooting method were used in order to fine the effect of mass transfer on the velocity and concentrations at the liquid-vapor interface.

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A Study on Characteristics of Condensation for RAC Using Flow Visualization Technique (유동 가시화 기법을 이용한 RAC의 이슬 맺힘 특성에 관한 연구)

  • Lee, A-Mi;Kim, Dong-Won;Na, Seon-Uk;Ko, Han-Seo
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.3092-3097
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    • 2007
  • Although noise of a RAC can be reduced effectively by decreasing RPM, condensation problems can occur to reduce reliability of the RAC for low RPM. Thus, this research has been performed to propose a design guideline of the RAC for low-noise RPM with high reliability. The internal and external flows of the RAC have been visualized and analyzed by a PIV technique to solve the condensation problem at an outlet and impeller. Then, the design guideline has been proposed by the analyzed results and confirmed by wind-tunnel and noise tests to reduce the condensation problem. Finally the shapes of the outlet with reduced condensation problem and the impeller with low noise have been obtained in this study.

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The Effects of Nonequilibrium Condensation on Shock/Boundary Layer Interaction

  • Kim, Heuy-Dong;Lee, Kwon-Hee;Toshiaki. Setoguchi
    • Journal of Mechanical Science and Technology
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    • v.15 no.6
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    • pp.788-795
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    • 2001
  • The effects of nonequilibrium condensation on the shock boundary layer interaction over a transonic bump model were investigated experimentally and numerically. An experiment was conducted using a supersonic indraft wind tunnel. A droplet growth equation was incorporated into two-dimensional Navier-Stokes equation systems. Computations were carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. Computation compared with the experimental results. Nonequilibirum condensation suppressed the boundary layer separation and the pressure fluctuations due to the shock boundary layer interaction. Especially the nonequilbrium condensation was helpful to suppress the high frequency components of the pressure fluctuations.

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