• Title/Summary/Keyword: subcooling

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Performance characteristics of the Coil Deposition Type Heat Pump using Geothermal Energy (지열을 이용한 코일 침적형 히트펌프의 성능 특성)

  • Oh, Hoo-Kyu;Lee, Dong-Gun;Jeon, Min-Ju;Son, Chang-Hyo
    • Journal of Advanced Marine Engineering and Technology
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    • v.36 no.4
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    • pp.437-444
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    • 2012
  • This paper describes the experimental characteristics on cooling and heating performance of the coil deposition type heat pump using geothermal energy to optimize the design for the operating parameters of this system. The operating parameters considered in this study include subcooling degree, evaporation and condensation temperature in the coil deposition type heat pump using geothermal energy. The main results are summarized as follows : As the evaporation temperature and subcooling degree of the coil deposition type heat pump using geothermal energy increases, and the condensation temperature decreases, the COP of this system increases. The subcooling degree, evaporation and condensation temperature of the coil deposition type heat pump have an effect on cooling and heating COP of this heat pump. Therefore, it is a necessary to determine the optimum operation conditions for the highest COP of this heat pump presented in this study.

External Condensation Heat Transfer Coefficients of HFC32/HFC152a Mixtures on Enhanced Tubes (열전달 촉진관에서 HFC32/HFC152a 혼합냉매의 외부 응축열전달계수)

  • Lee, Yohan;Kang, Donggyu;Kim, Hyeon-Ju;Lee, Ho-Saeng;Jung, Dongsoo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.26 no.7
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    • pp.315-321
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    • 2014
  • In this study, external condensation heat transfer coefficients (HTCs) of two non-azeotropic refrigerant mixtures of HFC32/HFC152a at various compositions were measured on both 26 fpi low-fin and Turbo-C enhanced tubes, of 19.0 mm outside diameter. All data were taken at the vapor temperature of $39^{\circ}C$, with a wall subcooling of 3~8 K. Test results showed that the HTCs of the tested mixtures on the enhanced tubes were much lower than the ideal values calculated by mass fraction weighting of the pure component HTCs. Also, the reduction of HTCs due to the diffusion vapor film was much larger than that of a plain tube. Unlike HTCs of pure fluids, HTCs of the mixtures measured on enhanced tubes increased, as the wall subcooling increased, which was due to the sudden break-up of the vapor diffusion film with an increase in wall subcooling. Finally, the heat transfer enhancement ratios for mixtures were found to be much lower, than those of pure fluids.

Performance Analysis of Two-stage Compression Refrigeration System with Internal Heat Exchanger Applied Various Refrigerants (다양한 냉매를 적용한 내부열교환기 부착 2단 압축 냉동시스템의 성능 분석)

  • Yoon, Jung-In;Heo, Seong-Kwan;Je, Jae-Myun;Jeon, Min-Ju;Son, Chang-Hyo;Moon, Jung-Hyun
    • Journal of Power System Engineering
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    • v.19 no.6
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    • pp.82-88
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    • 2015
  • In this paper, cycle performance analysis of two-stage compression and one-stage expansion refrigeration system applied various refrigerants is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporation temperature, condensing temperature, mass flow rate ration into inter-cooler, effectiveness of internal heat exchanger. The main results were summarized as follows : The COP of two-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling, mass flow rate ration of inter-cooler, evaporation temperature, but decreases with the increasing condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and 1-stage expansion using substitute refrigerant have an effect on COP of this system. The COP of alternative refrigerants was higher than the COP of R22 in this study, although the COP of some mixed refrigerants were lower than COP of R22.

Selection of Capillary Tubes for HCFC-22 Alternative Fluids (HCFC-22 대체냉매의 모세관 선정)

  • Jung, D.S.;Kim, C.B.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.7 no.3
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    • pp.435-449
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    • 1995
  • In this paper, pressure drop through a capillary tube is modeled to determine the length of a capillary tube for a given set of conditions. HCFC-22 and its alternatives, HFC-134a, R407B, and R410A are used as working fluids. The conditions on which the model is tested are as follows : condensing temperature; 40.0, 45.0, 50.0, $55.0^{\circ}C$, degree of subcooling;0.0, 2.5, $5.0^{\circ}C$, capillary tube exit condition;choked flow, capillary tube diameter;1.2~2.4mm, mass flow rate;5.0~50.0g/sec. The results justify the use of Stoecker's model which yields the results very close to the values in ASHRAE handbook. While McAdams' method yields much better results than Duckler's in calculating the viscosity of the fluid in 2-phase, the friction factor suggested by Stoecker seems to be the best for capillary tubes of large diameter used in residential air conditioners. For each refrigerant, 372 data with various variables are calculated by the model. The results show that capillary tube length varies very uniformly with changes in condensing temperature and degree of subcooling. Based on this fact, regression analysis is performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and degree of subcooling. Thus determined correlation yields a mean deviation of 2.36% for 1,488 data, showing an excellent agreement.

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

  • Roh, Geon-Sang
    • Journal of the Korean Institute of Gas
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    • v.16 no.3
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    • pp.42-47
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    • 2012
  • In this paper, alternative natural refrigerant R290(Propane), R600(Butane), R717(Ammonia), R1270(Propylene) for freon refrigerant R22 were used working fluids for 2-stage compression and 1-stage expansion refrigeration system. The operating parameters considered in this study included evaporation temperature, condensation temperature, subcooling degree, superheating degree, mass flow rate ratio of inter-cooler. The main results were summarized as follows : The COP of 2-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling degree and mass flow rate ration of inter-cooler, but decreases with the increasing evaporating temperature, condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of 2-stage compression and 1-stage expansion refrigeration system using natural refrigerants have an effect on COP of this system. The COP of natural refrigerants was higher than the COP of freon R22 in this study, so points to be considered are the security, the attached facilities for natural refrigerants than COP.

A Study of Heat Storage System with Phase Change Material - Inward Melting and Solidification in a Horizontal Cylinder - (상변화물질을 이용한 잠열축열조에 관한 기초 연구 - 수평원관내에서의 내향용융 및 응고열전달 실험 -)

  • Kim, I.G.;Cho, N.C.;Kim, J.G.;Lee, C.M.;Yim, C.S.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.1 no.4
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    • pp.319-329
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    • 1989
  • Heat transfer phenomena during inward melting and solidification process of the phase change material were studied expertimentally. The phase change medium was 99% pure n-docosane paraffin ($C_{22}H_{46}$). The solid-liquid interface motion during phase change was recorded photographically. Measurements were made on the temperature, the solid-liquid interface, the melted or frozen mass and the various energy components stored or extracted from the cylinder wall. For melting, the experimental results reaffirmed the dominant role played by the conduction at an early stage, by the natural convection at longer time. For solidification, natural convection effects in the superheated liquid were modest and were confined to short freezing time. Although the latent energy is the largest contributor to the total stored or extracted energy, the aggregate sensible energies can make a significant contribution, especially at large cylinder wall superheating or subcooling, large initial phase change material subcooling or superheating.

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An Experimental Study on the Flow Characteristics Inside an Open Two-Phase Natural Circulation Loop (개방된 2상 자연순환 회로내의 유동특성에 관한 실험적 연구)

  • 경익수;이상용
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.5
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    • pp.1313-1320
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    • 1993
  • Flow patterns inside the riser section and the effects of the heater inlet-and exit-restrictions, liquid charging level and the heater inlet subcooling on the flow characteristics inside an open two-phase natural circulation loop were studied experimentally. Three basic circulation modes were observed ; periodic circulation (A)(flow oscillations with incubation(no boiling) period), continuous circulations(stable operation mode with no flow oscillations), and periodic circulation (B) (flow oscillations with continuous boiling). The circulation rate increases and then decreases with the increase of the heating rate and the maximum circulation rate appears with the continuous circulation mode. The decrease of the inlet-restriction or the increase of the exitrestriction destabilizes the system. When the liquid charging level or the inlet subcooling decreases, the continuous circulation mode starts at the lower heating rate and the system is stabilized.

A Study of External Condensation Heat Transfer of Flammable Refrigerants (가연성 냉매의 외부 응축 열전달에 관한 연구)

  • 배동수;하종철;유길상;정동수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.6
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    • pp.522-529
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    • 2004
  • In this study, external condensation heat transfer coefficients (HTCs) of flammable refrigerants of propylene, propane, isobutane, butane, DME, and HFC32 were measured on a horizontal plain tube, 26 fpi low fin tube, and Turbo-C tube. All data were taken at the temperature of 39$^{\circ}C$ with a wall subcooling of 3∼8$^{\circ}C$. Test results showed a typical trend that condensation HTCs of flammable refrigerants decrease with increasing wall subcooling. HFC32 had the highest HTCs among the tested refrigerants showing 44% higher HTCs than those of HCFC22 while DME showed 28% higher HTCs than those of HCFC22. HTCs of propylene and butane were similar to those of HCFC22 while those of propane and isobutane were similar to those of HFC134a. Based upon the tested data, Nusselt's equation is modified to predict the plain tube data within a deviation of 3%. For 26 fpi low fin tube, Beatty and Katz equation predicted the data within a deviation of 7.3% for all flammable refrigerants tested. The heat transfer enhancement factors for the 26 fpi low fin and Turbo-C tubes were 4.6∼5.7 and 4.7∼6.9 respectively for the refrigerants tested indicating that the performance of Turbo-C tube is the best among the tubes tested.

Critical Heat Flux for Low Flow in Vertical Annulus under Various Pressure Conditions

  • Chun, Se-Young;Jun, Hyung-Gil;Chung, Heung-June;Moon, Sang-Ki;Chung, Moon-Ki
    • Proceedings of the Korean Nuclear Society Conference
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    • 1997.05a
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    • pp.386-391
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    • 1997
  • It is important to understand correctly a CHF under low flow condition for the purpose of enhancing the reactor safety and performance in the LWRs. The CHF experiments have been carried out for an internally heated vertical annulus in RCS loop facility. The experimental conditions cover ranges of pressure from 1.82 to 12.08 MPa, mass flux from 300 to 550kg/$m^2$. s and inlet subcooling of 210kJ/kg. The CHF data decrease with increasing pressure at high value of mass flux. For mass flux of about 300kg/$m^2$. s, the CHF rue little influenced by pressure. The CHF data are correlated well by using the dimensionless heat flux and dimensionless mass flux for a fixed inlet subcooling except the data group of 12.08 MPa. It seems that the Doerffer correlation and Katto correlation overestimate the CHF for low pressure and lower value of mass flux within this experimental ranges. The Bowling correlation gives a better prediction than the other two correlations.

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An Empirical Correlation for Subcooled Two-Phase Critical Flow Rates in Short Tubes, Nozzles, and Orifices

  • Park, Choon-Kyung;Seok Cho;Won, Soon-Yeun;Min, Kyung-Ho;Chung, Moon-Ki
    • Proceedings of the Korean Nuclear Society Conference
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    • 1997.05a
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    • pp.273-278
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    • 1997
  • Critical two-phase flow rates of subcooled water through very short tube (L=20 mm) with small diameters (D=1.0 mm) has been measured for wide ranges of subcooling(0~186$^{\circ}C$) and pressure (0.5~2.0 MPa). Experimental results show that subcooled critical two-phase flow rates can be expressed in terms of two scaling parameters for geometries and initial conditions. They are discharge coefficient of cold water, ( $C_{d}$ )$_{ref}$, and dimensionless subcooling, $\Delta$ $T^{*}$$_{sub}$, respectively. A new empirical correlation expressed in terms of ( $C_{d}$ )$_{ref}$ and $\Delta$ $T^{*}$$_{sub}$ is obtained for subcooled two-phase flow rates through very short length tube. Comparisons between the mass fluxes calculated by Present correlation and a number of experimental data show that the agreement is very good.ood.ood.ood.

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