• Journal of Advanced Marine Engineering and Technology
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• v.25 no.3
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• pp.552-562
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• 2001

Measurement of average of heat transfer and friction coefficients were obtained with air flowing through electrically heated ducts having square, rectangular(aspect ration, 5), and triangular cross section for range of surface temperature from $540^{\circ}$to $1780^{\circ}$ R and Reynolds number from 1000 to 330,000. The results indicates that the effect of heat flux on correlations of the average heat transfer and friction coefficients is similar to that obtained for circular tubes in previous investigation and was nearly eliminated by evaluating the physical properties and density of the air a film temperature halfway between the average surface and fluid bulk temperatures, With the Nusselt and Reynolds numbers on the hydraulic diameter of the ducts, the data for the noncircular ducts could be represented by the same equations obtained in the previous investigation for circular tubes. Correlation of the average difference between the surface corner and midwall temperatures for the square duct was in agreement with predicted values from a previous analysis. However, for the rectangular and triangular ducts, the measured corner temperature was greater by approximately 20 and 35 percent, respectively, than the values predicted by analysis.

• Journal of Mechanical Science and Technology
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• v.19 no.8
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• pp.1662-1669
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• 2005

Boiling heat transfer characteristics of a two-phase closed thermosyphons with various helical grooves are studied experimentally and a mathematical correlation is developed to predict the performance of such thermosyphons. The study focuses on the boiling heat transfer characteristics of two-phase closed thermosyphons with copper tubes having 50, 60, 70, 80, 90 internal helical grooves. A two-phase closed thermosyphon with plain copper tube having the same inner and outer diameter as those of grooved tubes is also tested for comparison. Water, methanol and ethanol are used as working fluid. The effects of the number of grooves, various working fluids, operating temperature and heat flux are investigated experimentally. From these experimental results, a mathematical model is developed. In the present model, boiling of liquid pool in the evaporator is considered for the heat transfer mechanism of the thermosyphons. And also the effects of the number of grooves, the various working fluids, the operating temperature and the heat flux are brought into consideration. A good agreement between the boiling heat transfer coefficient of the thermosyphon estimated from experimental results and the predictions from the present mathematical correlation is obtained. The experimental results show that the number of grooves, the amount of the working fluid and the various working fluids are very important factors for the operation of thermosyphons. Also, the thermosyphons with internal helical grooves can be used to achieve some inexpensive and compact heat exchangers in low temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.10
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• pp.977-983
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• 2004

An experimental study on saturated flow boiling heat transfer of R113 was peformed in a vertical narrow rectangular channel with offset strip fins. Two-phase pressure gradients and boiling heat transfer coefficients in an electrically heated test section were measured in the range of quality $0{\sim}0.6$, mass flux $17{\sim}43kg/m^{2}s$, and heat flux of $500{\sim}3,000W/m^2$ Two-phase friction multipliers were determined as a function of Lockhart-Martinelli parameter. Local boiling heat transfer coefficients were analysed in terms of mass flux, heat flux and local vapor quality. Correlation for boiling heat transfer coefficients was proposed, which was in good agreement with experimental data.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.5
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• pp.38-44
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• 2002

An experimental investigation was performed to observe the cooling performance of cutting oil and the effect of inclination angle on the transport behaviour of a inclined thermosyphons with low integral-fins. Relatively high rates of heat transfer have been achieved by operating this manner. Water has been used as the working fluid. The inclimation angle of thermoryphon and the ratio of Reynolds number of cooling to hot fluid have been used as the experimental parameters. Heat transfer coefficients at the condenser and the evaporator are estimated from experimental results. The experimental results have been assessed and compared with existing theory. Good agreement with the theory of Yiwei has been found. The maximum heat flow rate in the thermosyphon proved to depend upon the inclination angle.

• Nuclear Engineering and Technology
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• v.36 no.2
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• pp.153-164
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• 2004

A computational fluid dynamics (CFD) analysis has been performed to investigate the turbulent flow and heat transfer in a triangular rod bundle with pitch-to-diameter ratios (P/D) of 1.06 and 1.12. Anisotropic turbulence models predicted the turbulence-driven secondary flow in a triangular subchannel and the distributions of the time mean velocity and temperature, showing a significantly improved agreement with the measurements from the linear standard $k-{\epsilon}$ model. The anisotropic turbulence models predicted the turbulence structure for a rod bundle with a large P/D fairly well, but could not predict the very high turbulent intensity of the azimuthal velocity observed in the narrow flow region (gap) for a rod bundle with a small P/D.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.88-94
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• 1996

The dependence of the node size in the condensation heat transfer coefficient for an inclined surface is eliminated and two correlations applicable for laminar and turbulent regimes are implemented in RELAP5/MOD3.1. The newly implemented correlations are used according to their applicable ranges of the film Reynolds numbers Reps which are calculated recursively to track the condensate film thickness along the condensation length. The modified version is compared with the original one through comparison with an analytical solution and the simulation of the Secondary Condensers (SC). It turns out that the simulation results by this modified version are independent of the node size and are better agreement with the analytical solution than those by the original one.

• Journal of Welding and Joining
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• v.23 no.5
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• pp.55-60
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• 2005

A precise bonding technique, transmission laser bonding using energy transfer, for polymer micro devices is presented. The irradiated IR laser beam passes through the transparent part and absorbed on the opaque part. The absorbed energy is converted into heat and bonding takes place. In order to optimize the bonding quality, the temperature profile on the interface must be obtained. Using optical measurements of the both plates, the absorbed energy can be calculated. At the wavelength of 1100nm $87.5\%$ of incident laser energy was used for bonding process from the calculation. A heat transfer model was applied for obtaining the transient temperature profile. It was found that with the power of 29.5 mW, the interface begins to melt and bond each other in 3 sec and it is in a good agreement with experiment results. The transmission IR laser bonding has a potential in the local precise bonding in MEMS or Lab-on-a-chip applications.

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.74-78
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• 2022

Two β=0.10 cryomodules are required for the China Accelerator Driven Subcritical System (C-ADS) injector II accelerator. Flow design is of great importance in the performance of cryomodules, including thermal design, flow distribution, pressure drop and so on. This paper will study convection heat transfer of helium and relation among the pipe diameter, mass flow rate and Reynolds number. Furthermore, the influence of flow geometries on pressure drop and flow distribution will also be done. It was found that the theoretical flow distribution were in good agreement with the experimental data.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.5
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• pp.687-694
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• 1999

This study was conducted to develop new drying process for automatic control and marine engi-neering system. Air-water tests were carried out to investigate dryer performance. The dispersed flow in he dryer test apparatuses was also simulated by using a numerical code which solves the Dittus-Boelter equation for continuous liquid phase and the Reynolds equation of droplet motion for continuous liquid phase and the Reynolds equation of droplet motion for dispersed phase to predict droplet removal efficiency. Proper conditions for dehumidification were optimized by response ambient conditions. When the selected indexes were constrained in the range of 85-98% moisture content above $15^{\circ}$ and more than mass flow rates of moist air 750kg/h. The numerical results were compared with the experimental data pertaining to the removal effi-ciency at chamber stage and overall pressure drop along concentric tubes Good agreement was obtained as for the efficiency while relatively poor agreement was obtained for the relative humidity. The results also showed that the efficiency depended strongly on the relative humidity at the inlet condition which indicated the importance of estimating the heat exchanger length. Effects of some design parameters in both removal efficiency and breakthrough onset condition are discussed.

• Journal of Mechanical Science and Technology
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• v.20 no.9
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• pp.1492-1501
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• 2006

A transportation system of single wafer has been developed to be applied to semiconductor manufacturing process of the next generation. In this study, the experimental apparatus consists of two kinds of track, one is for propelling a wafer, so called control track, the other is for generating an air film to transfer a wafer, so called transfer track. The wafer transportation speed has been evaluated by the numerical and the experimental methods for three types of nozzle position a..ay (i.e., the front-, face- and rear-array) in an air levitation system. Test facility for 300mm wafer has been equipped with two control tracks and one transfer track of 1500mm length from the starting point to the stopping point. From the present results, it is found that the experimental values of the wafer transportation speed are well in agreement with the computed ones. Namely, the computed values of the maximum wafer transportation speed $V_{max}$ are slightly higher than the experimental ones by about $15{\times}20%$. The disparities in $V_{max}$ between the numerical and the experimental results become smaller as the air velocity increases. Also, at the same air flow rate, the order of wafer transportation speeds is : $V_{max}$ for the front-array > $V_{max}$ for the face-array > $V_{max}$ for the rear-array. However, the face-array is rather more stable than any other type of nozzle array to ensure safe transportation of a wafer.