• International Journal of Air-Conditioning and Refrigeration
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• 제7권
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• pp.79-90
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• 1999

This investigation presents the experimental results of forced convection boiling heat transfer around a circular, electrically heated horizontal cylinder to subcooled water in cross flow. In these experiments, the following primary variables were included: heat flux, flow velocity, pressure and degree of subcooling at inlet. Local surface temperatures were measured at nine peripheral positions. Local surface temperature distributions are classified into four categories depending on the supplied heat flux. The effects of the boiling curve depending on the fluid velocity, degree of subcooling at inlet and pressure are presented.

• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1328-1338
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• 2001

The objective of this study is to present flow and pressure drop characteristics of R22 in adiabatic capillary tubes of inner diameters of 1.2 to 2.0mm, and tube lengths of 500 to 2000mm. Distributions of temperature and pressure along capillary tubes and the refrigerant flow rates through the tubes were measured for several condensing temperatures and various degrees of subcooling at the capillary tube inlet. Condensing temperatures of R22 were selected as 40, 45, and 50$^{\circ}C$ at the capillary tube inlet, and the degree of subcooling was adjusted to 1 to 18$^{\circ}C$. Experimental results including mass flow rates and pressure drops of R22 in capillary tubes were provided. A new correlation based on Buckingham II theorem to predict the mass flow rate through the capillary tube was presented considering major parameters which affect the flow and pressure drop characteristcis.

• 태양에너지
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• 제18권2호
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• pp.91-104
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• 1998

본 연구에서는 냉매 HFC134a를 사용한 배치형 열펌프건조기(Batch type heat pump dryer)에 대하여 수치적 해석을 수행하였다. 즉 냉매의 과열도와 과냉도를 일정하게 유지하고 공기의 질량유량, 공기의 바이패스비(bypass ratio), 압축기의 회전속도, 건조기의 입구건구온도에 따른 건조기의 성능을 분석하였다. SMER에 대하여 수치해와 실험치를 비교한 결과 최대 10%이내에서 잘 일치 하였다. 또한 공기의 질량유량에 대하여 적정공기의 바이패스비가 존재하며, 건조기 입구온도가 $35^{\circ}C$이고, 압축기 회전속도가 1360rpm일 때, 공기질량유량이 0.5kg/s에서는 공기의 바이패스비가 30%, 0.7kg/s에서는 공기의 바이패스비가 40%, 0.9kg/s와 1.1kg/s에서는 공기의 바이패스비가 50%에서 최대의 SMER이 나타다. 그리고 압축기 회전속도가 증가함에 따라 SMER은 감소지만 COP는 증가하고 건조기의 입구건구온도가 증가함에 따라 SMER과 COP는 감소하는 것으로 나타났다.

• 설비공학논문집
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• 제7권4호
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• pp.681-693
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• 1995

A new set of capillary tube selection charts for R-22 is proposed. The set of charts takes into account of the roughness effect on the mass flow rate. For this purpose, a set of numerical model is developed and a series of experiments is conducted to verify the numerical model. A numerical model is used to calculated the mass flow rate for several sets of tube diameter, length, inlet pressures and degree of subcooling. The outlet of the tube is controlled to be at critical condition. The experimental flow rate is compared with calculated values. The calculated values are consistently less than the experimental ones except for the flow rate range below 40kg/hr. The deviation is within 10---. Based on the nunmerical model and results of experiments, the set of capillary tube selection charts for R-22 is constructed. The set of charts consists of standard capillary tube chart(L=2030mm, d=1.63mm, ${\varepsilon}=2.5{\mu}m$), non -standard flow factor(${\phi}_1$) chart, and non-standard roughness factor(${\phi}_2$) chart. The mass flow rate, flow factor, and the roughness factor are defined respectively as; $\dot{m}={\phi}_1{\phi}_2\dot{m}_{standard}\\{\phi}_1=\frac{\dot{m}(L,\;d,\;\varepsilon_{standard})}{\dot{m}_{standard}(L_{standard},\;d_{standard},\;{\varepsilon}_{standard})}\\{\phi}_2=\frac{\dot{m}(L_{standard},\;d_{standard},\;{\varepsilon})}{\dot{m}_{standard}(L_{standard},\;d_{standard},\;{\varepsilon}_{standard})}$.