• Title/Summary/Keyword: Mass Flux

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Experimental study on the performance of a brazed plate heat exchanger (용접식 판형 열교환기의 성능에 관한 실험적 연구)

  • Kim, Jong-Ha;Yun, Jae-Ho;Kwon, Oh-Kyung;Kim, Jong-Hun;Ryu, Hae-Sung;Lee, Chang-Sik
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.477-482
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    • 2001
  • An experimental study on the performance evaluation of a brazed plate heat-exchanger with 10RT of normal cooling capacity has been carried out. In the present study, a brazed type plate heat exchanger was tested at a chevron angle $25^{\circ}$ with refrigerant R-22. Mass flux was ranged from $23\;to\;58kg/m^{2}s$ in condensation, and from $22\;to\;53kg/m^{2}s$ in evaporation. The heat transfer coefficient and pressure drop increased with the mass flux increases. The water side pressure drop increased with the cooling water flow rate and chilled water flow rate increases, while mass flux has little affect. It is also shown that the system performance can be improved by enlarging condensation heat transfer area.

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Study on the Performance of the Cascade System Using Alternative Refrigerants (대체냉매를 사용한 이원냉동 시스템의 성능에 관한 연구)

  • 박종훈;조금남
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.7
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    • pp.564-571
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    • 2001
  • The present study investigated the effect of key parameters on the performance of a cascade system using R-22 and R-23 refrigerants. Experimental data for the cascade system have been compared with simulation results using thermodynamic analysis. The cascade system tested at the evaporating temperature of $-80^{\circ}C $ and the condensing temperature of$40^{\circ}C $. The key experimental parameters were the evaporating temperature of the HTC(-35, -30, -25, -20, $-15^{\circ}C $) and mass flux of the HTC(200, 250, 300kg/$m^2$s). As the evaporating temperature and the mass flux of the HTC were increased respectively, the COP and the refrigerating efficiency were increased and then decreased while the volume flow rate per unit refrigeration capacity showed the opposite trend. The maximum COP and refrigerating efficiency were obtained at the evaporating temperature of the HTC of $-25^{\circ}C $ and the mass flux of 250 kg/$m^2$s.

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An Experimental Study on the Performance of a Brazed Plate Heat Exchanger (용접식 판형 열교환기의 성능에 관한 실험적 연구)

  • 김종하;권오경;윤재호;이창식
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.1
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    • pp.83-90
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    • 2002
  • An experimental study on the performance evaluation of a brazed plate heat exchanger with 10USRT of normal cooling capacity has been carried out. In the present study, a brazed plate heat exchanger was tested at a chevron angle $25^{\circ}$with refrigerant R-22. Refrigerant mass flux was ranged from 23 to 58 kg/$m^2$s in condensation, and from 22 to 53 kg/$m^2$s in evaporation. The heat transfer coefficients and pressure drops are increased as the mass flux increases. The water side pressure drop is increased as the cooling water flow rate and chilled water flow rate increase, while mass flux has little effect. It is also shown that the system performance can be improved by enlarging condensation heat transfer area.

Enthalpy Flow Loss by Steady Mass Streaming in Pulse Tube Refrigerators (맥동관냉동기의 정상상태 질량흐름에 의한 엔탈피손실)

  • 백상호;정은수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.12 no.7
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    • pp.623-631
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    • 2000
  • Effects of the taper angle and the angular velocity of a pulse tube on the enthalpy flow loss associated with the steady mass streaming were analysis by two-dimensional analysis of a pulse tube with variable cross-section. It was shown that the steady mass flux can lead to a large steady second-order temperature. The enthalpy flow loss associated with the steady mass streaming increases as the angular velocity increases. For a pulse tube where the viscous penetration depth is far thinner than the inner radius, the enthalpy flow loss can be significantly reduced by tapering the pulse tube since both the steady mass flux and the steady second-order temperature decrease as the taper angle increase.

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Temporal and Spatial Variations of Sinking-particle Fluxes in the Northwestern Subtropical Pacific (북서태평양 아열대 해역에서 침강입자 플럭스의 시·공간 변동)

  • Kim, Hyung-Jeek;Hyeong, Ki-Seong;Yoo, Chan-Min;Jeon, Dong-Chull;Jeong, Jin-Hyun;Khim, Boo-Keun;Kim, Dong-Seon
    • Ocean and Polar Research
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    • v.33 no.spc3
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    • pp.385-395
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    • 2011
  • Time-series sediment traps were deployed at 1,000 m water depth of the northwestern subtropical Pacific from July 2009 to June 2010, with the aim of understanding temporal and spatial variations of sinking-particle fluxes. The opening and closing of the traps was synchronized at 18-day periods for 20 events. Total mass fluxes showed distinct seasonal variations with high values for the summer-fall seasons and relatively low values for winter-spring. This seasonal variation at two stations was characterized by a distinct difference in $CaCO_3$ fluxes between the two seasons. The enhanced $CaCO_3$ flux in the summer - fall seasons might be attributed to an increased planktonic foraminiferal flux. Total mass flux at FM10 station was nearly 50% higher than that at FM1 station. The difference in $CaCO_3$ fluxes between two stations contributed nearly 70% of the difference of total mass fluxes. The $CaCO_3$ flux was a major component controlling temporal and spatial variation of sinking - particle fluxes in the western subtropical Pacific Ocean.

An Experimental Study on Evaporative Heat Transfer Characteristics in a Small Diameter Tube (미소직경관 내 증발열전달 특성에 관한 실험적 연구)

  • Hwang, Yun-Uk;Kim, Min-Su
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.2
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    • pp.216-224
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    • 2001
  • Experiments have been performed to investigate evaporative heat transfer characteristics of R-134a flowing in a small diameter tube. Test section was made of stainless steel tube with an inner diameter of 2.2mm and was uniformly heated by electric current which was applied to the tube wall. The local saturation temperature of refrigerant flowing in a tube is calculated from the measured local saturation pressure by using an equation of state. Inner wall temperature was calculated from measured outer wall temperature, accounting for heat generation in the tube and one dimensional heat conduction through the tube wall. Mass quality of refrigerant flowing in a tube was calculated by considering energy balance in the pre-heater and the test section. Heat flux was varied from 19 to 64kW/$m^2$, and mass flux was chanted from 380 to 570kg/$m^2$s for each heat flux condition. From this study, heat transfer in a small diameter tube is affected by heat flux as well as mass flux for a wide range of mass quality. Heat transfer coefficient in a small diameter tube is much greater than that in medium sized tubes. Test results in this study are compared with Gungor and Winterton correlation, which gives an absolute average deviation of 27%.

An Experimental Study on Evaperation Heat Transfer and Pressure Drop in Plated cleat Exchangers with Different Chevron Angles (판형열교환기의 세브론각에 따른 증발 열전달특성 및 압력강하에 대한 실험적 연구)

  • Kim, Yun-Ho;Lee, Gyu-Jeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.2
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    • pp.269-277
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    • 2002
  • Experiments on the evaporation heat transfer and pressure drop in the brazed type plate heat exchangers were performed using refrigerants R410A and R22. To investigate the geometric effect, plate heat exchangers with the same pitch and height but different 45$^{\circ}$, 35$^{\circ}$and 20$^{\circ}$chevron angles are used. Tests were conducted fur the ranges of the mass flux of refrigerant from 13 kg/m$^2$s to 34 kg/m$^2$s, the evaporation temperatures of 15$^{\circ}C$, 1$0^{\circ}C$ and 5$^{\circ}C$, vapor quality from 0.15 to 0.95 and the heat flux from 2.5 kW/m$^2$to 8.5 kW/m$^2$. The evaporation heat transfer coefficients and pressure drops were measured. Most of flow patterns are in the chum flow regime and become close to the annular flow for increasing the mass flux and the vapor quality. The heat transfer coefficient increases with increasing the evaporation temperature at a given mass flux in all plate heat exchangers. Also, the pressure drop increases with increasing the mass flux and the quality and decreasing the evaporation temperature and the chevron angle.

An Improved Mechanistic Model to Predict Critical Heat Flux in Subcooled and Low Quality Convective Boiling

  • Kwon, Young-Min;Chang, Soon-Heung
    • Nuclear Engineering and Technology
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    • v.31 no.2
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    • pp.236-255
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    • 1999
  • An improved mechanistic model was developed to predict a convective boiling critical heat flux (CHF) in the vertical round tubes with uniform heat fluxes. The CHF formula for subcooled and low quality boiling was derived from the local conservation equations of mass, energy and momentum, together with appropriate constitutive relations. The model is characterized by the momentum balance equation to determine the limiting transverse interchange of mass flux crossing the interface of wall bubbly layer and core by taking account of the convective shear effect due to the frictional drag on the wall-attached bubbles. Comparison between the present model predictions and experimental CHF data from several sources shows good agreement over a wide range of How conditions. The present model shows comparable prediction accuracy with the CHF look-up table of Groeneveld et al. Also the model correctly accounts for the effects of flow variables as well as geometry parameters.

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R-134a Flow Boiling on a Plain Tube Bundle (평활관군의 R-134a 흐름비등에 관한 연구)

  • 김종원;김정오;김내현
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.1
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    • pp.9-17
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    • 2001
  • In this study, flow boiling experiments were performed using R-134a on a plain tube bundle. Tests were conducted for the following range of variables; quality from 0.1 to 0.9, mass flux from $8\;kg/m^2s$ to $26\;kg/m^2s$ and heat flux from $10\;kW/m^2s$ to $40\;kW/m^2s$. The heat transfer coefficients were strongly dependent on the heat flux. However, they were almost independent on the mass flux or quality. The data are compared with the modified Chen model, which satisfactorily () predicted the data. Original Chen model, however, did not adequately predict the effect of quality. The reason may be attributed to the flow pattern of the present test, where the bubbly flow prevailed for the entire test range. The heat transfer coefficients of the tube bundle were 6~40% higher than those of the single tube pool boiling.

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An Experimental Study of Flow Boiling Heat Transfer inside Small-Diameter Round Tubes (원형 세관내 대류비등열전달에 관한 실험적 연구)

  • 추원호;방광현
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.8
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    • pp.748-755
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    • 2004
  • Flow boiling heat transfer in small-diameter round tubes has been experimentally studied. The experimental apparatus consisted mainly of refrigerant pump, condenser, receiver, test section of a 1.67 mm inner-diameter round tube and pre-heater for control of refrigerant quality at the inlet of test section. To investigate the effect of bubble nucleation site characteristics of different tube materials, three different tubes of copper, aluminum and brass were used. The ranges of the major experimental parameters were 5∼30 ㎾/$m^2$ of the wall heat flux, 0.0∼0.9 of the inlet vapor quality and the refrigerant mass flux was fixed at 600 kg/$m^2$s. The experimental results showed that the flow boiling heat transfer coefficients in small tubes were affected only by heat flux, but independent of mass flux and vapor quality. The effect of tube material on flow boiling heat transfer was observed small.