• Journal of the Korean Society of Industry Convergence
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• v.5 no.3
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• pp.193-200
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• 2002

An experimental study was performed to study heat transfer characteristics for turbulent flow in an axisymmetric annuli. The air flow temperature and the local Nusselt number in turbulent flow were measured or calculated for Re=30,000, 40,000, 50,000, 60,000, 70,000 and 80,000. The local Nusselts number were compared to that obtained from Dittus-Boelter equation with turbulent flow. The results show that the flow enhances the heat transfer in the initial and exit portion of the test tube.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.2042-2052
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• 2003

An experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. The static pressure, the local flow temperature, and the wall temperature with decaying swirl were measured by using tangential inlet conditions and the friction factor and the local Nusselt number were calculated for Re=30000∼70000. The local Nusselt number was compared with that obtained from the Dittus-Boelter equation with swirl and without swirl. The results showed that the swirl enhances the heat transfer at the inlet and the outlet of the test tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.1
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• pp.8-13
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• 2015

The objective of this paper is to provide design data of fin-tube heat exchanger which have a large diameter oval tube for dryer application. In this study, the heat transfer and pressure drop performance characteristics of the fin-tube heat exchanger were compared with Dittus-Boelter and a new correlation equation using Wilson plot method. The simulation results based on section by section method were compared with experimental results. These results showed that a new correlation equation using Wilson plot method provided better prediction, about 3 to 12%, than the Dittus-Boelter equation, from the experiment comparison. Also, the pressure drop of simulation results showed much more deviation with the experimental results.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.7
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• pp.677-684
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• 2013

A lot study of convection heat transfer on internal flow has been extensively conducted in the past decades using of high specific surface area, increasing heat transfer coefficient, swirling flow and improving the transport properties. This study concerned with the application of a tangential slot swirl generator for improving heat transfer in a horizontal circular copper tube. The Al particles(about $100{\sim}130{\mu}m$) was employed for this experimental work. 3D PIV(particle image velocimetry) technique has employed to measure velocity profiles of Al particles with and without swirl flow. The copper tube is heated uniformly by winding of a heating coil for heat transfer work, having a resistance of 9 ohm per meter. Experiments are performed in the Reynolds number range of 6,800~12,100 with swirl and without swirl using Al particles. Experimental data for comparison of Nusselt number is presented that of with swirl and without swirl along the test tube for the Reynolds numbers. The Nusselt number is improved with increasing of Reynolds numbers or swirl intensities along the test tube. The Nusselt number with swirl flow is about 60.0% to 119.0% higher than that obtained by the Dittus-Boelter equation.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.2
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• pp.259-266
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• 2010

The heat flowrate and pressure dorp of $CO_2$ in a multi-tube-in-tube helical coil type gas cooler were predicted using LMTD method and compared with the experimental data. The mass flowrate of $CO_2$ and coolant were varied from 0.06 to 0.075 [kg/s], and the cooling pressure of gas cooler were from 8 to 10 [MPa], respectively. The LMTD method is used to predict the heat flowrate and pressure drop of supercritical $CO_2$ during in-tube cooling. The equations used by LMTD method were Gnielinski correlation for $CO_2$ and Dittus-Boelter correlation for coolant, respectively. The equation used to predict the pressure drop of $CO_2$ and coolant is Blasius correlation. In comparison of heat flowrate and pressure drop of $CO_2$ measured by experiment to that predicted by LMTD method, the experimental heat flowrate and pressure drop of $CO_2$ in the multi-tube-in-tube helical coil type gas cooler shows a relatively good agreement with that predicted by LMTD method.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.3
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• pp.260-274
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• 2005

An experimental investigation was performed to study the characteristics of turbulent swirling flow in the cylindrical annuli. The swirl angle measurements were performed by flow visualization technique using smoke and dye liquid. By using the particle image velocimetry method. this study has found the time-mean velocity distribution and turbulent intensity with swirl for Re=20,000. 30.000. 50.000. and 70,000 along longitudinal sections. The results appear to be physically reasonable. Other experimental study was performed to investigate heat transfer characteristics of turbulent swirling air flow in axisymmetric annuli. The static pressure. the local air flow temperature, and the wall temperature with decaying swirl were measured by using thermocouples and the friction factor and the local Nusselt number were calculated for Re=30,000. 50,000 and 70000. The local Nusselt number was compared with that obtained from the Dittus-Boelter equation with swirl and without swirl, respectively. The results showed that the swirl enhances the heat transfer at the inlet and the outlet of the test tube.

• 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.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.8 no.4
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• pp.213-220
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• 1979

A number of methods has been developed for calculation of heat transfer in the vertical round tube under conditions of forced convection with uniform heat flux at wall. I would like to express hereby one of applications of this study in the design of heat exchanger instruments for water flow at $15.8^{\circ}C(p_r=8)$ used frequently in our daily life. Also all the results are investigated for forced convective heat transfer in the case of heated water-flow at uniform wall heat flux in the vortical round copper tube, where the ratio of length to diameter will be 44. They are well in agreement with Gratz and Kraussold equation respectively in laminar and transition flow range. In turbulent flow in the range from Re=10,000 to 65,000, the experimental formula Is show as follows ; Nu=0.023 $R_e^{0.814}\;P_r^{0.4}$. And this is agreed with Dittus - Boelter equation when Reynolds number exponent increases from 0.80 to 0.814.

• The KSFM Journal of Fluid Machinery
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• v.10 no.5
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• pp.9-19
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• 2007

Fluid temperature fluctuations in a mixing tee pipe were numerically analyzed by LES model in order to clarify internal turbulent flows and to develope an evaluation method for high-cycle thermal fatigue. Hot and cold water with an temperature difference $40^{\circ}C$ were supplied to the mixing tee. Fluid temperature fluctuations in a mixing tee pipe is analysed by using the computational fluid dynamics code, FLUENT, Temperature fluctuations of the fluid and pipe wall measured as the velocity ratio of the flow in the branch pipe to that in the main pipe was varied from 0.05 to 5.0. The power spectrum method was used to evaluate the heat transfer coefficient. The fluid temperature characteristics were dependent on the velocity ratio, rather than the absolute value of the flow velocity. Large fluid temperature fluctuations were occurred near the mixing tee, and the fluctuation temperature frequency was random. The ratios of the measured heat transfer coefficient to that evaluated by Dittus-Boelter's empirical equation were independent of the velocity ratio, The multiplier ratios were about from 4 to 6.