• 제목/요약/키워드: Condensing Flow

검색결과 111건 처리시간 0.03초

Local Heat Transfer Coefficients for Reflux Condensation Experiment in a Vertical Tube in the Presence of Noncondensible Gas

  • Moon, Young-Min;No, Hee-Cheon;Bang, Young-Seok
    • Nuclear Engineering and Technology
    • /
    • 제31권5호
    • /
    • pp.486-497
    • /
    • 1999
  • The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate, A single vertical tube has a geometry which is a length of 2.4m, inner diameter of 16.56mm and outer diameter of 19.05mm and is made of stainless steel. Air is used as a noncondensible gas. The secondary side has a shape of annulus around vertical tube and the lost heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 11 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348∼3.282kg/hr, of inlet air mass fraction 11.8∼55.0%. The investigation of the flooding is preceded to find the upper limit of the reflux condensation. Onset of flooding is lower than that of Wallis' correlation. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the increase of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed by 165 data of the local heat transfer. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17.7% between the results by the experiment and by the correlation.

  • PDF

EV 상용차용 히트펌프 시스템 냉방 운전 특성에 관한 연구 (A Study on Performance Characteristics of Heat Pump System on Cooling Mode for Light-duty Commercial Electric Vehicles)

  • 전한별;김정일;원헌주;이호성
    • 한국산학기술학회논문지
    • /
    • 제20권12호
    • /
    • pp.69-75
    • /
    • 2019
  • 본 연구의 목적은 EV 경상용차에 적용되는 히트펌프 시스템에 대한 냉방 성능 특성을 실험적으로 분석하는 것이다. EV 경상용차가 운전되는 냉방 운전조건인 외기온도 35 ℃, 내기온도 25 ℃ 상황에서, 히트펌프 시스템의 냉방 특성을 분석하고자, 냉각수의 온도조건, 전동식 압축기 회전수 조건 변화에 대해서, 실험을 진행하였고, 그 결과를 분석하였다. 전동식 압축기 회전수가 증가할수록 냉방 성능이 평균 8.0 %가 증가하였고, 전동식 압축기 소비전력은 27 %가 증가하여서, 시스템 효율은 16.4 %가 감소하는 결과를 보여주고 있다. 전자장비 냉각을 위한 냉각수의 폐열을 활용하기 위하여서, 냉매랑 냉각수가 열교환 하는 칠러를 본 시스템에 적용하였다. 칠러에 적용되는 냉각수의 온도를 35 ℃에서 55℃로 변화시켰을 때, 응축 열원의 증가로 인하여서, 시스템 효율이 평균적으로 18.2 %가 떨어지는 결과를 보여주고 있다. 냉각수 유량 변화 측면에서, 운전 조건을 변화시켰지만, 냉방 성능에는 큰 변화를 보이고 있지 않았다. 향후, 냉각수 폐열을 사용하여서, 히트펌프 시스템에 대한 난방 성능 향상을 위한 연구가 필요한 상황에서, 관련 연구에 추가 할 예정이다.

CFD ANALYSIS OF TURBULENT JET BEHAVIOR INDUCED BY A STEAM JET DISCHARGED THROUGH A VERTICAL UPWARD SINGLE HOLE IN A SUBCOOLED WATER POOL

  • Kang, Hyung-Seok;Song, Chul-Hwa
    • Nuclear Engineering and Technology
    • /
    • 제42권4호
    • /
    • pp.382-393
    • /
    • 2010
  • Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

R744-R404A 캐스케이드 냉동시스템의 최적 냉매 충전을 위한 질량유량비 분석 (Mass flow rate ratio analysis for optimal refrigerant charge of a R744 and R404A cascade refrigeration system)

  • 오후규;손창효;조환;전민주
    • Journal of Advanced Marine Engineering and Technology
    • /
    • 제37권6호
    • /
    • pp.575-581
    • /
    • 2013
  • 본 논문은 R744-R404A 캐스케이드 냉동시스템의 최적 냉매 충전을 위해 과냉도, 과열도, 내부열교환기 효율 등에 대한 영향을 분석한 것이다. 연구에 사용된 캐스케이드 냉동시스템의 고온 사이클에는 R404A, 저온 사이클에는 R744를 적용하였다. 그 주요 결과는 다음과 같다 : 고온 사이클의 과냉도, 과열도, 내부열교환기 효율과 저온 사이클의 증발온도와 압축효율은 크게 할수록 질량유량비가 작게 나타났다. 그리고 캐스케이드 온도차와 고온 사이클의 증발온도, 응축온도와 저온 사이클의 과냉도, 과열도, 내부열교환기 효율은 작을수록 질량유량비가 작게 나타났음을 확인하였다.

원형관 코팅장치에서 연소 입자의 응축성장에 미치는 2차원 열 및 물질전달의 영향 (Effects of Two-dimensional Heat and Mass Transports on Condensational Growth of Soot Particles in a Tubular Coater)

  • 박성훈
    • 한국입자에어로졸학회지
    • /
    • 제9권3호
    • /
    • pp.163-171
    • /
    • 2013
  • Soot particles emitted from combustion processes are often coated by non-absorbing organic materials, which enhance the global warming effect of soot particles. It is of importance to study the condensation characteristics of soot particles experimentally and theoretically to reduce the uncertainty of the climate impact of soot particles. In this study, the condensational growth of soot particles in a tubular coater was modeled by a one-dimensional (1D) plug flow model and a two-dimensional (2D) laminar flow model. The effects of 2D heat and mass transports on the predicted particle growth were investigated. The temperature and coating material vapor concentration distributions in radial direction, which the 1D model could not accounted for, affected substantially the particle growth in the coater. Under the simulated conditions, the differences between the temperatures and vapor concentrations near the wall and at the tube center were large. The neglect of these variations by the 1D model resulted in a large error in modeling the mass transfer and aerosol dynamics occurring in the coater. The 1D model predicted the average temperature and vapor concentration quite accurately but overestimated the average diameter of the growing particles considerably. At the outermost grid, at which condensation begins earliest due to the lowest temperature and saturation vapor concentration, condensing vapor was exhausted rapidly because of the competition between condensations on the wall and on the particle surface, decreasing the growth rate. At the center of the tube, on the other hand, the growth rate was low due to high temperature and saturation vapor concentration. The effects of Brownian diffusion and thermophoresis were not high enough to transport the coating material vapor quickly from the tube center to the wall. The 1D model based on perfect radial mixing could not take into account this phenomenon, resulting in a much higher growth rate than what the 2D model predicted. The result of this study indicates that contrary to a previous report for a thermodenuder, 2D heat and mass transports must be taken into account to model accurately the condensational particle growth in a coater.

Local Heat Transfer Coefficients for Reflux Condensation Experiment in a Vertical Tube in the Presence of Noncondensible Gas

  • Moon, Young-Min;No, Hee-Cheon;Bang, Young-Seok
    • 한국원자력학회:학술대회논문집
    • /
    • 한국원자력학회 1999년도 춘계학술발표회요약집
    • /
    • pp.104-104
    • /
    • 1999
  • The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate. A single vertical tube has a geometry which is a length of 2.4m, inner diameter of 16.56mm and outer diameter of 19.05mm and is made of stainless steel. Air is used as a noncondensible gas. The secondary side is installed in the form of coolant block around vertical tube and the heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 15 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348 -3.282kg/hr, of inlet air mass fraction 11.8 -55.0%. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the decrease of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed represented with the 165 sets of local heat transfer data. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17. 7% between the results by the experiment and by the correlation.

  • PDF

암모니아 대체 자연냉매를 이용하는 2단압축 1단팽창 냉동시스템의 성능예측 (Performance Analysis of 2-Stage Compression and 1-Stage Expansion Refrigeration System using Alternative Natural Refrigerants)

  • 노건상
    • 한국가스학회지
    • /
    • 제16권3호
    • /
    • pp.42-47
    • /
    • 2012
  • 본 논문에서는 규제 프레온냉매 R22의 대체 자연냉매의 후보인 R290(프로판), R600(부탄), R717(암모니아), R1270(프로필렌)을 작동유체로 사용하는 2단압축 1단팽창 냉동시스템의 성능 특성을 비교하였다. $-20^{\circ}C{\sim}-50^{\circ}C$ 정도의 저온을 얻기 위해 사용되는 2단압축 1단팽창 냉동장치에서의 증발온도, 응축온도, 과열도 및 과냉각도의 변화에 따른 성능계수(COP) 변화를 규명하고자 하였다. 성능특성 규명 결과, 과냉각도 및 중간냉각기에서의 냉매유량 증가에 따라 시스템의 COP는 증가하였으나, 증발온도, 응축온도 및 과열도가 증가할수록 COP는 저하되는 결과를 나타내었다. 또한, 자연냉매를 사용하는 2단압축 1단팽창 냉동시스템의 COP는 규제 프레온냉매 R22를 사용하는 경우보다 높기 때문에 자연냉매를 사용하고자 하는 냉동시스템의 안전성이 확보되면 충분히 대체 냉매로서의 경쟁력이 있을 것으로 판단되었다.

설비공학 분야의 최근 연구 동향 : 2013년 학회지 논문에 대한 종합적 고찰 (Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2013)

  • 이대영;김사량;김현정;김동선;박준석;임병찬
    • 설비공학논문집
    • /
    • 제26권12호
    • /
    • pp.605-619
    • /
    • 2014
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2013. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of fluid machinery, pipes and relative parts including orifices, dampers and ducts, fuel cells and power plants, cooling and air-conditioning, heat and mass transfer, two phase flow, and the flow around buildings and structures. Research issues dealing with home appliances, flows around buildings, nuclear power plant, and manufacturing processes are newly added in thermal and fluid engineering research area. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results for general analytical model for desiccant wheels, the effects of water absorption on the thermal conductivity of insulation materials, thermal properties of Octadecane/xGnP shape-stabilized phase change materials and $CO_2$ and $CO_2$-Hydrate mixture, effect of ground source heat pump system, the heat flux meter location for the performance test of a refrigerator vacuum insulation panel, a parallel flow evaporator for a heat pump dryer, the condensation risk assessment of vacuum multi-layer glass and triple glass, optimization of a forced convection type PCM refrigeration module, surface temperature sensor using fluorescent nanoporous thin film. In the area of pool boiling and condensing heat transfer, researches on ammonia inside horizontal smooth small tube, R1234yf on various enhanced surfaces, HFC32/HFC152a on a plain surface, spray cooling up to critical heat flux on a low-fin enhanced surface were actively carried out. In the area of industrial heat exchangers, researches on a fin tube type adsorber, the mass-transfer kinetics of a fin-tube-type adsorption bed, fin-and-tube heat exchangers having sine wave fins and oval tubes, louvered fin heat exchanger were performed. (3) In the field of refrigeration, studies are categorized into three groups namely refrigeration cycle, refrigerant and modeling and control. In the category of refrigeration cycle, studies were focused on the enhancement or optimization of experimental or commercial systems including a R410a VRF(Various Refrigerant Flow) heat pump, a R134a 2-stage screw heat pump and a R134a double-heat source automotive air-conditioner system. In the category of refrigerant, studies were carried out for the application of alternative refrigerants or refrigeration technologies including $CO_2$ water heaters, a R1234yf automotive air-conditioner, a R436b water cooler and a thermoelectric refrigerator. In the category of modeling and control, theoretical and experimental studies were carried out to predict the performance of various thermal and control systems including the long-term energy analysis of a geo-thermal heat pump system coupled to cast-in-place energy piles, the dynamic simulation of a water heater-coupled hybrid heat pump and the numerical simulation of an integral optimum regulating controller for a system heat pump. (4) In building mechanical system research fields, twenty one studies were conducted to achieve effective design of the mechanical systems, and also to maximize the energy efficiency of buildings. The topics of the studies included heating and cooling, HVAC system, ventilation, and renewable energies in the buildings. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which can improve the energy efficiency of the buildings. (5) The field of architectural environment is mostly focused on indoor environment and building energy. The main researches of indoor environment are related to infiltration, ventilation, leak flow and airtightness performance in residential building. The subjects of building energy are worked on energy saving, operation method and optimum operation of building energy systems. The remained studies are related to the special facility such as cleanroom, internet data center and biosafety laboratory. water supply and drain system, defining standard input variables of BIM (Building Information Modeling) for facility management system, estimating capability and providing operation guidelines of subway station as shelter for refuge and evaluation of pollutant emissions from furniture-like products.

배압터빈을 사용하는 열병합발전소의 열 회수 온도에 따른 성능특성 분석 (Performance Analysis on CHP Plant using Back Pressure Turbine according to Return Temperature Variation)

  • 임신영;이종준;전영신;김형택
    • 한국유체기계학회 논문집
    • /
    • 제19권6호
    • /
    • pp.26-33
    • /
    • 2016
  • Combined heat and power (CHP) system is one of the power generation system which can generate both electricity and heat. Generally, mid-size and big-size CHP plant in Korea generate electricity from gas turbine and steam turbine, then supply heat from exhaust gas. Actually, CHP can supply heat using district heater which is located at low pressure turbine exit or inlet. When the district heater locates after low pressure turbine, which called back pressure type turbine, there need neither condenser nor mode change operating control logic. When the district heater locates in front of low pressure turbine or uses low pressure turbine extraction steam flow, which calls condensing type turbine, which kind of turbine requires condenser. In this case, mode change operation methods are used for generating maximum electricity or maximum heat according to demanding the seasonal electricity and heat.

낮은 핀 관의 응축 열전달 성능에 관한 연구 (A Study on the Condensation Heat Transfer of Low Integral Fin Tubes)

  • 한규일;박성국
    • 수산해양기술연구
    • /
    • 제32권1호
    • /
    • pp.67-77
    • /
    • 1996
  • The heat transfer performance of R - 11 vapor condensing on integral fin tubes has been studied using fin tubes having the fin density from 748 to 1654 fins per meter. Electric heater supplied heat energy to the boiler to generate R - 11 vapor over the range of 25-60W. Condensation rates of each tubes were tested under the condition of cooling water flow rate from 400l/h to 2500l/h. For the seven fin tubes tested, the best performance has been obtained with a tube having a fin density of 1417fpm and a fin height of 1.3mm. This tube has yielded a maximum value of the heat transfer coefficient of 16500W/$m_2$K, at a vapor to wall temperature difference of 3K. Experimental results of integral fin tubes have been compared with available predictive models such as Beatty - Katz's analysis, Webb's analysis, Sukhatme's analysis and Rudy's empirical relation. The experimental results were shown to be in good agreement with that of the Sukhatme's analysis.

  • PDF