• Title/Summary/Keyword: Flow Condensation

Search Result 392, Processing Time 0.028 seconds

Flow Condensation Heat Transfer Coefficients of R22 Alternative Refrigerants in Plain and Microfin Tubes of 6.0 mm Inside Diameter (내경 6 mm 평관과 마이크로 핀관 내에서 R22 대체냉매의 흐름응축 열전달계수)

  • 박기호;서영호;박기정;정동수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.16 no.5
    • /
    • pp.444-451
    • /
    • 2004
  • Flow condensation heat transfer coefficients (HTCs) of R22, R134a, R407C, and R410A were measured on horizontal plain and microfin tubes. The experimental apparatus was composed of three main parts; a refrigerant loop, a water loop and a water/glycol loop. The test section in the refrigerant loop was made of both a plain and a microfin copper tube of 6.0∼6.16 mm inside diameter and 1.0 m length. Refrigerants were cooled by passing cold water through an annulus surrounding the test section. Tests were performed at a fixed refrigerant saturation temperature of 4$0^{\circ}C$ with mass fluxes of 100, 200, and 300 kg/m2s. Test results showed that at similar mass flux the flow condensation HTCs of R134a were similar to those of R22 for both plain and microfin tubes. On the other hand, HTCs of R407C were lower than those of R22 by 4∼16% and 16∼42% for plain and microfin tubes respectively. And HTCs of R410A were similar to those of R22 for a plain tube but lower than those of R22 by 3∼9% for a microfin tube. Heat transfer enhancement factors of a microfin tube were 1.3∼1.9.

A CFD ANALYSIS FOR THERMAL MIXING IN A SUBCOOLED WATER UNDER TRANSIENT STEAM DISCHARGE CONDITIONS (과도상태 증기제트 방출시 과냉각수조 내의 열혼합 해석)

  • Kang H.S.;Kim Y.S.;Chun H.G.;Song C.H.
    • Journal of computational fluids engineering
    • /
    • v.11 no.2 s.33
    • /
    • pp.8-18
    • /
    • 2006
  • A CFD benchmark calculation for a steam blowdown test was performed for 30 seconds to develop the methodology of numerical analysis for the thermal mixing between steam and subcooled water. In the CFD analysis, the grid model simulating the sparger and the IRWST pool were developed by the axisymmetric condition and then the steam condensation phenomena by a direct contact was modelled by the so-called condensation region model. Thermal mixing phenomenon in the subcooled water tank was treated as an incompressible flow, a free surface flow between the air and the water, a turbulent flow, and a buoyancy flow. The comparison of the CFD results with the test data showed a good agreement as a whole, but a small temperature difference was locally found at some locations. The commercial CFD code of CFX4.4 together with the condensation region model can simulate the thermal mixing behavior reasonably well when a sufficient number of mesh distribution and a proper numerical method are adopted.

Modeling of Liquid-Vapor Interfaces of Condensation Flows Based on Molecular Dynamics Simulations

  • Kannan, Hiroki;Teramoto, Susumu;Nagashima, Toshio
    • Proceedings of the Korean Society of Propulsion Engineers Conference
    • /
    • 2004.03a
    • /
    • pp.418-425
    • /
    • 2004
  • Characteristics of a liquid-vapor interface where a nonequilibrium condensation flow exists are considered based on molecular dynamics simulations, The condensation coefficient, the velocity distributions of the reflected and evaporated molecules and the number flux of the evaporated molecules are compared with those under the liquid-vapor equilibrium. The comparison shows that the condensation coefficient under the nonequilibrium condensation is slightly larger and the number flux of the evaporated molecules is considerably smaller than those under the liquid-vapor equilibrium. The net condensation flux under the nonequilibrium condensation is underestimated if it is evaluated from the condensation coefficient and the number flux of the evaporated molecules under the liquid-vapor equilibrium. However the underestimation is relatively small.

  • PDF

Experiments on Condensation Heat Transfer Characteristics and Flow Regime Inside Microfin Tubes (마이크로핀관내 유동 양식과 응축 열전달 특성 연구)

  • 한동혁;이규정
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.13 no.7
    • /
    • pp.602-611
    • /
    • 2001
  • Experiments on the condensation heat transfer characteristics inside a smooth and a microfin tube with R410A/R22 are performed in this study. The test tubes 7/9.52 mm in outside diameters and 3m in length are used. Varying the mass flux of the refrigerant and the condensation temperatures, the average heat transfer coefficients and pressure drop are investigated. Most flows in this study are in the annular and/or wavy flow regime. It is shown that the heat transfer is enhanced and the pressure drops are larger in the microfin tube than the smooth tube. From the heat transfer enhancement coefficients and the pressure drops, it is found that the high heat transfer enhancement factors are obtained in the range of small mass flux while the penalty factors are almost equal. Experiments results show that average heat transfer coefficients of R410A is larger than that of R22 and pressure drop of R410A is less than R22.

  • PDF

An Experimental Study on the Characteristics of Generated Particle using Homogeneous Condensation Particle Generator (응축입자 발생기에서의 입자 발생특성에 관한 실험적 연구)

  • Kim, J.H.;Kim, S.S.
    • Proceedings of the KSME Conference
    • /
    • 2000.04b
    • /
    • pp.392-397
    • /
    • 2000
  • Mono-disperse particles generated by a condensation particle generator are widely used to meet the experimental and industrial needs. The characteristics of particles generated by homogeneous nucleation have been studied experimentally using a laminar flow condensation particle generator. Dry nitrogen gas saturated with oleic acid vapor was cooled well below the saturation temperature causing the highly supersaturated vapor to nucleate. The dependence of GSD(Geometric Standard Deviation), GMD(Geometric Mean Diameter), and the mass concentration of particles on the temperature at the evaporator, flow rate and the temperature condition at condenser was studied. The experimental results show that the mass concentration of particles is affected by the radial temperature profile at condenser. Nucleation at the center of the condenser causes the mass concentration of particles to increase. The experimental results also show that the suppression of additional nucleation by a constant temperature condition at the condenser increases the mean diameter of particle.

  • PDF

Condensation Heat Transfer Coefficient in Horizontal Stratified Cocurrent Flow of Steam and Cold Water (물-증기 동방향 성층이상 유동에서의 응축 열전달 계수)

  • 김효정
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.10 no.5
    • /
    • pp.618-624
    • /
    • 1986
  • Some studies on direct-contact condensation in cocurrent stratified flow of steam and subcooled water were reviewed. Several approaches have been performed to develop the condensation heat transfer coefficient relationshipo. The local Nusselt number is correlated in terms of the local water Reynolds and Prandtl numbers as well as the steam Froude number. In addition, a turbulence-centered model, developed principally for gas absorption in several geometries, is modified by using calculated interfacial paramters for the turbulent velocity and length scales. These approaches result in a fairly good agreement with the data, whereas, the turbulence-centered model is here rexcommened since it is based on the turbulent properties which may be closely related to the condensation phenemena.

An Experimental Investigation of the Interfacial Condensation Heat Transfer in Steam/water Countercurrent Stratified Flow in a Horizontal Pipe

  • Chu, In-Cheol;Yu, Seon-Oh;Chun, Moon-Hyun;Kim, Byong-Sup;Kim, Yang-Seok;Kim, In-Hwan;Lee, Sang-Won
    • Proceedings of the Korean Nuclear Society Conference
    • /
    • 1998.05a
    • /
    • pp.565-570
    • /
    • 1998
  • An interfacial condensation heat transfer phenomenon in a steam/water countercurrent stratified flow in a nearly horizontal pipe has been experimentally investigated. The present study has been focused on the measurement of the temperature and velocity distributions within the water layer. In particular, the water layer thickness used in the present work is large enough so that the turbulent mixing is limited and the thermal stratification is established. As a result, the thermal resistance of the water layer to the condensation heat transfer is increased significantly. An empirical correlation of the interfacial condensation heat transfer has been developed. The present correlation agrees with the data within $\pm$15%

  • PDF

Experimental Study to Evaluate the Thermal and Condensation Performance of Steel Stud Walls in Steel-Framed Schools (철골조학교(鐵骨造學校) 스틸스터드 벽체(壁體)의 단열(斷熱) 및 결로방지(結露防止) 성능(性能) 평가(評價)를 위한 실험적(實驗的) 연구(硏究))

  • Yu, Young-Dong;Kim, Gap-Dug
    • Journal of the Korean Institute of Educational Facilities
    • /
    • v.6 no.4
    • /
    • pp.16-23
    • /
    • 1999
  • The thermal and condensation performance of steel stud walls are monitored in steel-framed schools of Ee-Wol Elementary School and kindergarten using temperature and humidity sensors installed. The monitoring process carried out during the summer and winter period, shows decrement effect of the external heat flow to be quite remarkable and excellent. And steel stud walls provides a highly efficient time-lag effect in spite of its light weight property, with 30 minutes to 4 hours time-lag for external heat flow, which variation mainly depends on its location of each part of the wall. Any condensation phenomena are not observed in either external or internal surfaces.

  • PDF

RELAP5 Analysis of a Condensation Experiment in an Inverted U-tube

  • Park, Chul-Jin;Lee, Sang-Yong
    • Proceedings of the Korean Nuclear Society Conference
    • /
    • 1995.10a
    • /
    • pp.383-388
    • /
    • 1995
  • Two-phase transient phenomena in the noncondensable gas-filled closed loop was investigated numerically using the RELAP5/MOD3 version 3.1 computer code. The condensation heat transfer correlation for noncondensable gases was studied in detail. Two modes of the reflux condensation which can be characterized by countercurrent flow of steam and its condensed water and the oscillatory between reflux condensation and natural circulation were predicted well. However, the natural circulation mode which the condensed water carried over the U-bend concurrently with steam was failed to predict.

  • PDF

An Analysis on Direct-Contact Condensation in Horizontal Cocurrent Stratified How of Steam and Cold Water (동방향 성층이상유동에서의 직접접촉 응축현상에 대한 해석)

  • Lee, Sukho;Kim, Hho-Jung
    • Nuclear Engineering and Technology
    • /
    • v.24 no.2
    • /
    • pp.130-140
    • /
    • 1992
  • The physical benchmark problem on the direct-contact condensation under the horizontal occurrent stratified flow was analyzed using the RELAP5/MOD2 and /MOD3 one-dimensional model. Analysis was peformed for the Northwestern experiments, which involved condensing steam/water flow in a rectangular channel. The study showed that the RELAP5 interfacial heat transfer model, under the horizontal stratified flow regime, predicted the condensation rate well though the interfacial heat transfer area was underpredicted. However, some discrepancies in water layer thickness and local heat transfer coefficient with experimental results were found especially when there is a wavy interface, and those were satisfied only within the range.

  • PDF