• Title/Summary/Keyword: air temperature drop

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An Experimental Study on the Performance of the Louver Fin Type Heat Exchanger by the Change of the Driving Condition (운전조건 변화에 따른 루버휜 열교환기 성능변화에 관한 실험적 연구)

  • Kim, Jung-Kuk;Koyama, Shigeru;Kuwahara, Ken;Kim, Dong-Hwi;Park, Byung-Duck
    • Proceedings of the SAREK Conference
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    • 2008.06a
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    • pp.440-445
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    • 2008
  • The present study was investigated the effect of the driving condition on the performance of a louver fin and tube type heat exchanger under frosting condition. Heat transfer rate and pressure drop by frost were experimentally investigated. Effects of the wet blub temperature and the shape of a fin on heat transfer performances has been also investigated. The key parameters were fin type(louver and corrugate fin) and the wet blub temperature of air (0.5, 1.0, $1.5^{\circ}C$). The heat transfer performance of the louver fin and tube type heat exchanger was higher by 0.89% than the corrugate fin type. As the wet blub temperature of air were increased, the heat transfer rate, pressure drop and mass of frost of three test models(Type A, B, C) were increased. Especially, the maximum heat transfer rate and maximum pressure drop were shown for the louver fin and tube type heat exchanger. As a experimental result, the enhancement factor(EF) of louver fin and tube type heat exchanger was $0.2{\sim}0.4$ due to the high pressure drop.

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Prediction and Experiment of Pressure Drop of R22, R407C and R410A on Design Conditions of Condenser (응축기의 설계조건에서 R22, R407C, R410A의 압력강하 예측 및 실험)

  • 김창덕;박일환;이진호
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.1
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    • pp.42-53
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    • 2004
  • An experimental study on the refrigerant-side pressure drop of slit fin-tube heat exchanger has been carried out. A comparison was made between the predictions of previously proposed empirical correlations and experimental data for the pressure drop on design conditions of condenser in micro-fin tube for R22 and its alternatives, R407C (R32/125/134a, 23/25/52 wt.%) and R410A (R32/125, 50/50 wt.%). Experiments were carried out under the conditions of inlet refrigerant temperature of 6$0^{\circ}C$ and mass fluxes varying from 150 to 250 kg/$m^2$s for R22, R407C and R410A. The inlet air conditions are dry bulb temperature of 35$^{\circ}C$, relative humidity of 40% and air velocity varying from 0.68 to 1.43 m/s. Experiments show that pressure drop for R410A and R407C were 17.8∼20.2% and 5∼6.8% lower than those of R22 respectively for the degree of subcooling of 5$^{\circ}C$. For the mass fluxes of 200∼250 kg/$m^2$s, the deviation between the experimental and predicted values for the pressure drop was less than $\pm$20% for R22, R407C and R410A.

Air-Side Heat Transfer in Louvered Fin Heat Exchangers (Louvered fin 열교환기(熱交換器)의 공기측(空氣側) 열전달(熱傳達))

  • Kim, C.S.;Kwon, S.S.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.1 no.1
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    • pp.82-86
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    • 1989
  • A study has been conducted experimentally on heat transfer characteristics of the heat exchangers with louvered fins in air. The experimental results are as follows; 1. Mean heat transfer coefficient is decreased with increasing temperature difference and model III is the best at constant temperature difference. 2. Pressure drop is increased with increasing air velocity, but it is decreased as the heat transfer area increases. 3. $\bar{h}/^{\Delta}p$ is increased and then decreased as air velocity increases.

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Characteristics of Pressure-Drop Oscillations in a Boiling Channel (비등유로의 압력강하 요동특성)

  • Kim, B.J.;Shin, K.S.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.7 no.1
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    • pp.132-141
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    • 1995
  • Characteristics of pressure-drop oscillations(PDO) in a boiling channel were studied numerically and compared with experimental data. Effects of initial and boundary conditions on PDO were investigated in terms of oscillation period and amplitude. The period and amplitude of PDO increased with increasing of the compressible volume in the surge tank and the heat input. PDO occurred within the specific range of the fluid temperature, at which oscillation period and amplitude diminished rapidly with the increase of the fluid temperature. The increase of the loss coefficient in fluid supply line resulted in slightly longer oscillation period and larger amplitude. Numerical results showed good agreement with the experimental data.

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Measurement of effective thermal conductivity and permeability on aluminum foam metal (알루미늄 발포금속의 유효열전도도와 침투율의 측정)

  • 백진욱;강병하;김서영;현재민
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.2
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    • pp.185-192
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    • 1999
  • Effective thermal conductivities and pressure-drop-related properties of aluminum foam metals have been measured. The effects of porosity and cell size in the aluminum foam metal are investigated in detail. The porosity of the foam metal, considered in the present study, varies from 0.89 to 0.96 and the cell size from 0.65㎜ to 2.5㎜. The effective thermal conductivity is evaluated by comparing the temperature gradient of the foam metal with that of the thermal conductivity-known material. The pressure drop in the foam metal is measured by a highly precise electric manometer while air is flowing through the aluminum foam metal in the channel. The results obtained indicate that the effective thermal conductivities are found to be increased with a decrease in the porosity while the effective thermal conductivities ire little affected by the cell size at a fixed porosity. However, the pressure drop is strongly affected by the cell size as well as the porosity. It is seen that the pressure drop is increased as the cell size becomes smaller, as expected. The minimum pressure drop is obtained in the porosity 0.94 at a fixed cell size. A new correlation of the pressure drop is proposed based on the permeability and Ergun's coefficient for the aluminum foam metal.

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Comparison of Condenser Characteristics using R134a and R22 under the Same Inlet Temperature Condition (동일한 유입온도조건에서 R134a와 R22 적용 응축기의 특성비교)

  • Kang, Shin-Hyung;Byun, Ju-Suk;Kim, Chang-Duk
    • Journal of Energy Engineering
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    • v.15 no.3 s.47
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    • pp.166-173
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    • 2006
  • R134a is considered as an alternative refrigerant to R22 for air conditioners. An experimental investigation was made to study the characteristics of the heat transfer and pressure drop for R134a flowing in a fin-and-tube heat exchanger used for commercial air-conditioning units. Experiments were carried out under the conditions of inlet refrigerant temperature of $60^{\circ}C$ and refrigerant mass fluxes of $150,\;200,\;and\;250\;kg/m^{2}s$. The inlet air has dry bulb temperature or $35^{\circ}C$, relative humidity of 40% and air velocity varying from 0.68 to 1.6 m/s. Experiments show that air velocity decreased by 5.9% is needed for R134a than that of R22 while pressure drop for R134a was $18.1{\sim}20.4%$ higher than that of R22 for the degree of subcooling $5^{\circ}C$. The results are useful in designing more compact and effective condensers for various refrigeration and air conditioning systems using refrigerant R134a.

Heat Transfer Correlation during Gas-Cooling Process of Carbon Dioxide in a Horizontal Tube

  • Kang Byung-Ha;Choi Yi-Cheol;Kim Suk-Hyun
    • International Journal of Air-Conditioning and Refrigeration
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    • v.14 no.1
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    • pp.19-27
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    • 2006
  • The characteristics of heat transfer and pressure drop have been investigated experimentally during gas-cooling process of carbon dioxide. The results of this study are useful information in the design of a heat exchanger of $CO_2$ refrigerator. The test section consists of 6 series of copper tube, 4.15 and 2.18mm ID, respectively. The inlet temperature, the operating pressure, and the mass flux are varied in the range of $80{\sim}120^{\circ}C,\;{7\sim}10MPa,\;and\;400{\sim}1,900kg/m^2s$, respectively. The heat transfer coefficient of $CO_2$ is affected by temperature, inlet pressure, and mass flux of $CO_2$. At the maximum HTC, the temperature of $CO_2$ nearly accords with the psuedocritical temperature. It is found that the pressure drop is substantially affected by mass flux and inlet pressure of $CO_2$ . The results have been compared with those of previous work. The heat transfer correlation at the gas-cooling process has been also suggested which predicts within the error of 20%.

The effect of gas density on the drop trajectory and drop size distribution in high speed gas stream (고속기류에 분사된 액적궤적 및 입경분포에 미치는 주위 기체밀도의 영향)

  • Lee, C.H.
    • Journal of ILASS-Korea
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    • v.5 no.3
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    • pp.37-44
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    • 2000
  • High velocity, gas-assisted liquid drop trajectories were investigated under well-controlled experimental conditions at elevated gas densities and room temperature. A monodisperse stream of drops which are generated by a vibrating-orifice drop generator were injected into a transverse high velocity gas stream. The gas density and air jet velocity were adjusted independently to keep the Weber numbers constant. The Weber numbers studied were 72, 148, 270, 532. The range of experimental conditions included studied the three drop breakup regimes previously referred as bag, stretching/thinning and catastrophic breakup regimes. High-magnification photography and conventional spray field photographs were taken to study the microscopic breakup mechanisms and the drop trajectories in high velocity gas flow fields, respectively. The parent drop trajectories were affected by the gas density and the gas jet velocities and do not show similarity with respect to the either Weber or the Reynolds number, as expected.

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A Design Process for Reduction of Pressure Drop of Air-cooled Condenser for Waste Heat Recovery System (폐열 회수 시스템용 공랭식 응축기의 압력 손실 저감 설계)

  • Bae, Sukjung;Heo, Hyungseok;Park, Jeongsang;Lee, Hongyeol;Kim, Charnjung
    • Transactions of the Korean Society of Automotive Engineers
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    • v.21 no.6
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    • pp.81-91
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    • 2013
  • A novel design process of a parallel multi-flow type air-cooled condenser of a dual-loop waste heat recovery system with Rankine steam cycles for improving the fuel efficiency of gasoline automobiles has been investigated focusing on reduction of the pressure drop inside the micro-tubes. The low temperature condenser plays a role to dissipate heat from the system by condensing the low temperature loop working fluid sufficiently. However, the refrigerant has low evaporation temperature enough to recover the waste from engine coolant of about $100^{\circ}C$ but has small saturation enthalpy so that excessive mass flow rate of the LT working fluid, e.g., over 150 g/s, causes enormously large pressure drop of the working fluid to maintain the heat dissipation performance of more than 20 kW. This paper has dealt with the scheme to design the low temperature condenser that has reduced pressure drop while ensuring the required thermal performance. The number of pass, the arrangement of the tubes of each pass, and the positions of the inlet and outlet ports on the header are most critical parameters affecting the flow uniformity through all the tubes of the condenser. For the purpose of the performance predictions and the parametric study for the LT condenser, we have developed a 1-dimensional user-friendly performance prediction program that calculates feasibly the phase change of the working fluid in the tubes. An example is presented through the proposed design process and compared with an experiment.

The Effect of Operating Conditions on the Frost Formation in a Vertical Plate at a Low Temperature (저온 수직평판에서 착상에 대한 운전조건의 영향)

  • 이관수;이태희;김우승
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.12
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    • pp.3305-3314
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    • 1994
  • In this study, the influence of a frost formed on the vertical plate for different operating conditions(the temperature of the air, the humidity of the air, the velocity of the air, and the temperature of the cooling plate) is investigated. The performance of the heat exchanger is examined by introducing a parameter such as the energy transfer resistance. Correlations which relate frost density, frost thickness and energy transfer resistance to Reynolds number, air temperature and humidity, and cooling plate temperature are developed. Static pressure drop and air flow rate are expressed as a function of free flow area of air.