• 태양에너지
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• 제14권2호
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• pp.39-50
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• 1994

알루미나 입자(${\rho}_p=2298kg/m^2$)를 유동입자로 사용한 수직이중관식 유동층형 열교환기에서 입자직경($d_p$=0.41, 0.54, 0.65, 0.77mm) 및 초기충진높이($H_o$=50, 100, 150, 200, 250mm)가 전열성능에 미치는 영향을 소요동력의 관점에서 고찰하였다. 내관으로 핀이 달린 관을 사용하는 경우와 평활관을 사용하는 경우의 전열성능을 단상강제대류 열교환기와 비교 검토하였다. 소요동력에 따른 전열성능을 비교한 결과, 입자직경이 작을 수록, 초기충진높이가 높을 수록 전열효과가 증가하며, 실험범위에서 핀이 달린 관을 사용하는 경우가 평활관을 사용하는 경우보다 초기충진 높이에 따라 $2.96{\sim}3.45$배의 전열촉진효과가 있음을 알았다. 또 단상강제대류형 열교환기에 비해 유동층형 열교환기가 열전달효과가 우수한 영역이 존재하며, 평활관을 사용하는 경우에는 최대 91.3%, 핀이 달린 관을 사용하는 경우에는 최대 127.1% 의 전열촉진효과가 있었다.

• International Journal of Air-Conditioning and Refrigeration
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• 제13권3호
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• pp.128-137
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• 2005

In this study, dry and wet surface pressure drop and heat transfer characteristics of heat exchangers having plain fins were investigated. Nine samples having different fin pitches and rows were tested. The wet surface heat transfer coefficient was reduced from experimental data using enthalpy-potential method. The wet surface heat transfer coefficients were approximately equal to the dry surface values except for one row configuration. For one row configuration, the wet surface heat transfer coefficients were approximately $30\%$ lower than the dry surface values. For the pressure drop, the wet surface yielded approximately $30\%$ higher values compared with the dry surface counterpart. Data were compared with existing correlations.

• Nuclear Engineering and Technology
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• 제34권2호
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• pp.165-175
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• 2002

Effects of gap sizes (3.9-44.3 mm) of vertical annuli on nucleate pool boiling heat transfer of water at atmospheric pressure have been obtained experimentally. Through the study, tubes of the closed bottom have been investigated and results are compared with those of a single unconfined tube. According to the results, the annular condition gives much increase in heat transfer coefficient at moderate heat fluxes. The increase is much enhanced 3s the gap size decreases. At the same tube wall superheat (about 3.1 K) the heat transfer coefficient for the least gap size (i.e., 3.9 mm) is more than three times greater than that of the unconfined tube. However, deterioration of heat transfer occurs at high heat flux for confined boiling.

• 설비공학논문집
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• 제16권3호
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• pp.218-229
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• 2004

In this study, dry and wet surface pressure drop and heat transfer characteristics of heat exchangers having plain fins were investigated. Nine samples having different fin pitches and rows were tested. The wet surface heat transfer coefficient was reduced from experimental data using enthalpy-potential method. The wet surface heat transfer coefficients were approximately equal to the dry surface values except for one row configuration. For one row configuration, the wet surface heat transfer coefficients were approximately 30% lower than the dry surface values. For the pressure drop, the wet surface yielded approximately 30% higher values compared with the dry surface counterpart. Data were compared with existing correlations.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권3호
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• pp.153-161
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• 2002

Due to the coupling between momentum and energy transport theoretical analysis of the loop performance is very complicate, therefore it is necessary that these problems be solved by experimental investigation before applying the loop thermosyphon to heat exchanger de-sign. The evaporator and condenser of the loop thermosyphon were made of carbon-steel, and distilled water was used as working fluid in the experiments. From the experimental data correlations of heat transfer coefficient for evaporator and condenser sections were obtained. For heat fluxes in the range of 13000~78000 W/$m^2$, the correlation equations of heat transfer coefficients in evaporator and condenser predict the experimental behavior to within $\pm$5% and $\pm$20% respectively.

• 설비공학논문집
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• 제13권6호
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• pp.462-473
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• 2001

Due to the coupling between momentum and energy transport theoretical analysis of the loop performance is very complicate, therefore it is necessary that these problems be solved by experimental investigation before applying th loop thermosyphon to heat exchanger design. The evaporator and condenser of the loop thermosyphon were made of carbon-steel, and distilled water was used as working fluid in the experiments. From the experimental data correlations of heat transfer coefficient for evaporator and condenser sections were obtained. For heat fluxes in th range of 13~78kW/$m^2$, the correlation equations of heat transfer coefficients in evaporator and condenser predict the experimental behavior to within $\p$\pm$5% and\;\pm20$% respectively.

• 설비공학논문집
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• 제19권3호
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• pp.263-268
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• 2007

The pressure drop and heat transfer coefficient were measured at room temperature in a CFB heat exchanger with multiple vertical tubes. The circulation rate of solid particles was also measured. The theoretical model for predicting heat transfer coefficient using the solid flowrate was developed in this study. The model predictions were compared with the measured heat transfer coefficient to show relatively good agreement.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.138-143
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• 2005

Finite Element analysis is widely applied to elevated temperature forging processes and shows a lot of information of plastic deformation such as strain, stress, defects, damages and temperature distributions. In highly elevated temperature deformation processes, temperature of material and tool have significant influence on tool life, deformation conditions and productivities. To predict temperature related properties accurately, adequate coefficients of not only contact heat transfer between material and dies but also convection heat transfer due to coolants are required. In most F.E analysis, too higher value of contact heat transfer coefficient is usually applied to get acceptable temperature distribution of tool. For contact heat transfer coefficients between die and workpiece, accurate values were evaluated with different pressure and lubricants conditions. But convection heat transfer coefficients have not been investigated for forging lubricants. In this research, convection heat transfer coefficients for cooling by emulsion lubricants are suggested by experiment and Inverse method. To verify acquired convection and contact heat transfer coefficients, tool temperature was measured for the comparison between measured tool temperature and analysis results. To increase analysis accuracy, repeated analysis scheme was applied till temperature of the tool got to be in the steady-state conditions. Verification of heat transfer coefficients both contact and convection heat transfer coefficients was proven with good accordance between measurement and analysis.

• 대한기계학회논문집B
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• 제25권2호
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• pp.171-179
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• 2001

Experimental study has been carried out on the characteristics of pressure drop and heat transfer of brazed plate heat exchangers using R-22. Data are presented for the following range of variables: the mass flux (40∼90kg/$m^2$s), chevron angle ($20^{\circ}$, $35^{\circ}$, $45^{\circ}$) and inlet pressure of the refrigerant (1.4 and 1.6MPa). For both subcooled and two-phase flow, as chevron angle increases, pressure drop and heat transfer coefficient decrease. Condensation heat transfer coefficient and pressure drop were compared with the previously proposed correlations. Among therm, Traviss correlation agreed with experimental results within -40%∼-84% for heat transfer coefficient and -59%∼62% for pressure drop.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.436-439
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• 2008

This paper is to research the heat transfer performance of the sintered pipe. Recently, oil prices is to be 127 $ per barrel, we expect higher costs this summer. We promote alternative fuels, after oil and gasoline prices reached record highs. The governments have made efforts to avoid future crisis by continuing the move toward renewable energy and energy saving. In this paper, we have fabricated a sintered pipe, the heat transfer performance of sintered pipe is achieved experimentally. The pipe is copper tube of outer diameter of 15.88 mm, the length of the pipe is 800 mm. Based on the experimental results, it is shown the overall heat transfer coefficient of sintered pipe is increased as compared with that of a straight pipe, is equal as compared with that of a spiral pipe. The overall heat transfer coefficient was $0.075{\sim}0.09\;kW/^{\circ}C$