Processing math: 100%
  • 제목/요약/키워드: mass transfer coefficients

검색결과 360건 처리시간 0.024초

유출홀이 설치된 배열 충돌제트의 유동 및 열전달 특성 (Flow and Heat/Mass Transfer Characteristics of Arrays of Impingement Jets with Effusion Holes)

  • 이동호;윤필현;조형희
    • 대한기계학회논문집B
    • /
    • 제25권11호
    • /
    • pp.1606-1615
    • /
    • 2001
  • The present study has been conducted to investigate heat/mass transfer characteristics on a target plate fur arrays of circular impingement jets with and without effusion holes. A naphthalene sublimation method is employed to determine local heat/mass transfer coefficients on the target plate. The effusion holes are located at the center of four injection holes in the injection plate where the spent air is discharged through the effusion hole after impingement on the target plate. For the array jet impingement without effusion holes, the array jets are injected into the crossflow formed by upstream spent air because the impinged jets must flow to the open exit. For small gap distances, heat/mass transfer coefficients without effusion holes are very non-uniform due to crossflow effects and re-entrainments of spent air. However, uniform distributions and enhanced values of heat/mass transfer coefficients are obtained by installing the effusion holes. For large gap distances, the crossflow has little influence on heat/mass transfer characteristics on the target palate due to the large cross-sectional open area between the injection and target plates. Therefore, the distributions and levels of heat/mass transfer coefficients are almost the same for both cases.

배열충돌제트에서 횡방향유동성분에 따른 열/물질전달 특성 고찰 (Effect of Arrays of Impinging Jets with Crossflow on Heat/Mass Transfer)

  • 윤필현;이동호;조형희
    • 대한기계학회논문집B
    • /
    • 제24권2호
    • /
    • pp.195-203
    • /
    • 2000
  • The local heat/mass transfer coefficients for arrays of impinging circular air jets on a plane surface are determined by means of the naphthalene sublimation method. Fluid from the spent jets is constrained to flow out of the system in one direction. Therefore, the spent fluid makes a crossflow in the confined space. The present study investigates effects of jet-orifice-plate to impingement-surface spacing and jet Reynolds number. The spanwise- and overall-averaged heat/mass transfer coefficients are obtained by numerical integrating the local heat transfer coefficients. The local maximum heat/mass transfer coefficients move further in the downstream direction due to the increase of crossflow velocity. At the mid-way between adjacent jets, the heat/mass transfer coefficients have a small peak owing to the collision of the adjacent wall jets and are affected strongly by the crossflow. The effect of the crossflow occurs strongly at the small orifice-to-impingement surface distance.

Reduction of the Wet Surface Heat Transfer Coefficients from Experimental Data

  • Kim, Nae-Hyun;Sim, Yong-Sub
    • International Journal of Air-Conditioning and Refrigeration
    • /
    • 제12권1호
    • /
    • pp.37-49
    • /
    • 2004
  • Four different data reduction methods for the heat transfer coefficients from experimental data under dehumidifying conditions are compared. The four methods consist of two heat and mass transfer models and two fin efficiency models. Data are obtained from two heat exchanger samples having plain fins or wave fins. Comparison of the reduced heat transfer coefficients revealed that the single potential heat and mass transfer model yielded the humidity-independent heat transfer coefficients. Two fin efficiency models-enthalpy model and humidity model-yielded approximately the same fin efficiencies, and accordingly approximately the same heat transfer coefficients. The heat transfer coefficients under wet conditions were approximately the same as those of the dry conditions for the plain fin configuration. For the wave fin configuration, however, wet surface heat transfer coefficients were approximately 12% higher. The pressure drops of the wet surface were 10% to 45% larger than those of the dry surface.

쐐기형 요철이 설치된 사각덕트에서의 열/물질전달 및 압력강하 특성 (Heat/Mass Transfer and Pressure Drop in A Square Duct with V-Shaped Ribs)

  • 최청;이동호;조형희
    • 대한기계학회논문집B
    • /
    • 제26권11호
    • /
    • pp.1542-1551
    • /
    • 2002
  • The present study investigates the convective heat/mass transfer characteristics and pressure drop inside the rib-roughened cooling passage of gas turbine blades. The internal cooling passage is simulated using a square duct with h- and V-shaped rectangular ribs which have a 60。attack angle. A naphthalene sublimation technique is employed to determine the detailed local heat/mass transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wail. The secondary flow patterns and the local heat transfer in the duct are changed significantly according to the rib orientation. A square duct with ∧ - and V-shaped ribs have two pairs of secondary flow due to the rib arrangement. Therefore, the average heat/mass transfer coefficients and pressure drop of ∧ - and V-shaped ribs are higher than those of the continuous ribs with 90 and 60attack angles. The ∧-shaped ribs have higher heat/mass transfer coefficients than the V-shaped ribs, and the uniformity of heat/mass transfer coefficient are increased with the discrete ribs due to the flow leakage and acceleration near the surface.

수평평활관내 탄화수소계 냉매의 응축전열 특성에 관한 연구 (Condensation heat transfer characteristics of hydrocarbon. refrigerants inside horizontal tubes)

  • 이용언;박승준;정진호;장승환;오후규
    • 한국마린엔지니어링학회:학술대회논문집
    • /
    • 한국마린엔지니어링학회 2001년도 추계학술대회 논문집(Proceeding of the KOSME 2001 Autumn Annual Meeting)
    • /
    • pp.15-20
    • /
    • 2001
  • This study investigated the condensation heat transfer coefficients of R-22, R-290 and R-600a inside horizontal tube. Heat transfer measurements were peformed for smooth tube with outside diameter of 12.7 mm Condensation temperatures and mass velocity were ranged from 308 K to 323 K and 51kg/m2ss to 250kg/m2s, respectively. The test results showed that the local condensation heat transfer coefficients increased as the mass flux increased, and also the effects of mass velocity on heat transfer coefficients of R-290 and R-600a were less than R-22. Average condensation heat transfer coefficients of natural refrigerants were superior to that of R-22. The present results had a good agreement with Haraguchi's correlation.

  • PDF

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

  • Pangarkar, Bhausaheb L.;Sane, Mukund G.
    • Membrane and Water Treatment
    • /
    • 제2권3호
    • /
    • pp.159-173
    • /
    • 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 μm. 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.

Estimation of the Chestnut Mass Transfer Coefficient through its Microscopic Structure - Chestnut Mass Transfer Coefficient through its Microscopic Structure -

  • Xu, Hui Lan;Chung, Woo-Yang
    • Journal of the Korean Wood Science and Technology
    • /
    • 제40권5호
    • /
    • pp.352-362
    • /
    • 2012
  • Mass transfer behavior in wood was estimated through its microscopic structure. The diffusion coefficients which were decided by theoretical equations are influenced by different anatomical properties of wood. From the experiment, the moisture flux was linear to the square root of time. The diffusion coefficients had a regular tendency during the time elapse. During the modeling, it is necessary to understand the limitation of parameters and consider the particular situation to be simulated. In hardwood, because the apertures were not considered, tangential mass transfer simulation was totally different from experiment. As a result, a hardwood model design should consider the apertures which are even on the fiber walls.

금망임펠러를 이용한 교반조에서의 기-액 물질이동 (Mass Transfer of Gas-Liquid in Agitated Vessel Using Wire Gauge Impeller)

  • 이영세
    • 한국산업융합학회 논문집
    • /
    • 제11권1호
    • /
    • pp.19-26
    • /
    • 2008
  • The gas-liquid mass transfer volumetric coefficients in gas-liquid agitated vessels with wire gauge impellers were measured to be compared with those in vessels with disk turbine and paddle impellers. Also mass transfer volumetric coefficients for disk turbine, paddle impeller and wire gauge impeller in cylindrical agitated vessel was measured over a wide range of Reynolds number from turbulent flow to transition regions. The effect of geometries on kLa is clarified experimentally. Mass transfer volumetric coefficients kLa depends only on the power consumption (Pgv+Pav) per unit volume.

  • PDF

수평관내 3성분 혼합냉매의 강제대류비등 열전달 (Forced convective boiling heat transfer for a ternary refrigerant mixture inside a horizontal tube)

  • 오종택
    • 설비공학논문집
    • /
    • 제11권6호
    • /
    • pp.912-920
    • /
    • 1999
  • The forced convective boiling heat transfer coefficients of R-407C were measured inside a horizontal tube 6.0mm I.D. and 4.0m long. The heat transfer coefficients increased according to an increase in heat flux at constant mass flux. Because nucleation was completely suppressed in the two-phase flow region with high quality, heat transfer coefficients in forced convective evaporation were higher than those in nucleate boiling region. Average heat transfer coefficients of R-407C were about 30 percent lower than the pure refrigerant correlation, due to mass transfer resistance at the gas-liquid interface. However, the total experimental data shows an agreement with the predicted data for ternary refrigerant mixtures with a mean deviation of 30%.

  • PDF

A Study of the Evaporation Heat Transfer in Advanced Reactor Containment

  • Y. M. Kang;Park, G. C.
    • Nuclear Engineering and Technology
    • /
    • 제29권4호
    • /
    • pp.291-298
    • /
    • 1997
  • In advanced nuclear reactors, the passive containment cooling has been suggested to enhance the safety. The passive cooling has two mechanisms, air natural convection and oater cooling with evaporation. To confirm the coolability of PCCS, many works have been performed experimentally and numerically. In this study, the water cooling test was performed to obtain the evaporative heat transfer coefficients in a scaled don segment type PCCS facility which have same configuration with AP600 prototype containment. Air-steam mixture temperature and velocity, relative humidity and well heat flux are measured. The local steam mass flow rates through the vertical plate part of the facility are calculated from the measured data to obtain evaporative heat transfer coefficients. The measured evaporative heat transfer coefficients are compared with an analytical model which use a mass transfer coefficients. From the comparison, the predicted coefficients show good agreement with experimental data however, some discrepancies exist when the effect of wave motion is not considered. Finally, a new correlation on evaporative heat transfer coefficients are developed using the experimental values.

  • PDF