• Journal of Energy Engineering
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• v.7 no.2
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• pp.209-215
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• 1998

This paper investigated the vertical throughflow effects on natural convection due to heating from below in horizontal porous layer. The motion of the fluid in the porous layer is governed by Brinkman-Darcy equation. And compared Critical Rayleigh number in case of throughflow with no throughflow. Investigated Nusslet number, isothermalline and flow with the variation of the strength of throughflow in a constant Rayleigh number. In the numerical analysis, flow is assumed to be two-dimensional and unsteady. The numerical scheme used is a finite-difference method. In the experimental study, Temperature distribution was measured by use of Liquid Crystal film. As a results, indicated that throughflow influences largely on the temperature field and as the strength of throughflow increased, unstability of natural convection decreased. Also it could predict the strength of natural convection with the measured Nusselt number.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.1
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• pp.1-11
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• 2002

The suitable turbulence model is found to be required in the course of establishing a proper analysis methodology for thermal stripping phenomena which are shown in strong temperature variation area such as reactors and propulsion devices. Three different turbulence models of $\kappa$-$\varepsilon$ model, modified $\kappa$-$\varepsilon$ model, and full Reynolds stress(FRS) model, are applied to analyze unsteady turbulent flows with temperature variation. Three test cases are selected for verification. These are vertical jet flows with water and sodium, and parallel jet flow with sodium. Analysis yields the conclusion that 3-D computation with FRS betters others. However, modified modeling is required to improve its heat transfer characteristic analysis. Further analysis is performed to find momentum variation effects on temperature distribution. It is found that the momentum increase results increase of fluid mixing and magnitude of temperature variation.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1552-1557
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• 2004

This paper introduced about characteristics on the non-steady heat transfer of STS 304 hollow cylinder, In the non-steady state, the specific heat and conductivity are depended on the temperature variations, and these properties affect to the governing equation on heat conduction. But the most of numerical analysis on heat conduction is assumed to constant properties which is conductivity and specific heat. Assuming that conduction is assumed to constant properties which is conductivity and specific heat. Assuming that the properties are reacted sensitively, the numerical results can have the difference of between constant properties with non-constant properties. The main parameters are specific heat and conductivity. The temperature distributions of the STS 304 hollow cylinder became in steady state after 4 minutes in case of the constant properties. As the conductivity in varied with temperature, the temperature distributions became in steady state after 15 minutes. Therefore, a numerical analysis of the non steady state heat transfer will has to apply that conductivity varied with temperature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.9
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• pp.605-612
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• 2016

In this study, numerical simulations were conducted for conjugate heat transfer around ice balls in an encapsulated ice thermal storage system. Four shapes of ice balls were modeled; the default one was a sphere, and the other three shapes were designed to enhance convective heat transfer through the ball surface. The flow around the ball was laminar, for which the Reynolds number was 300, and both forced and natural convections inside and outside the balls were considered. The simulations revealed that the magnitude of convective heat transfer for the different shapes decreased in the following order: bone, dimple, hole, and sphere. For the entire simulation, the maximum difference in the average temperatures of water inside the capsules was found to be $0.9^{\circ}C$. Therefore, it can be said that the effect of ice-ball shape on the performance of the ice thermal storage system is significant, considering that more than 0.3 million balls are used in this system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.95-103
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• 1992

Laminar natural convection heat transfer from an isothermal rectangular beam attached to horizontal and vertical adiabatic plates has been studied for various aspect ratios of the beam and Grashof numbers. The local Nusselt number was increased with decreasing H/B for the constant beam width, B, and with increasing H/B for the constant beam height, H. The total mean Nusselt number of the vertical type was higher than that of horizontal type in the range of H/B.leq.0.52, but reversed in the H/B>0.52 at constant beam width. The total mean Nusselt number of the horizontal type was generally higher than that of vertical type at constant beam height. The total mean Nusselt number of the vertical type was higher than that of horizontal type in the range of H/B.leq.0.43 at constant wetted perimeter, but reversed in the H/B$\leq$0.43.

• Journal of Hydrogen and New Energy
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• v.12 no.4
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• pp.267-275
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• 2001

To clear the differences of heat transfer coefficient of in-cylinder gas with fuel properties, the transient heat transfer coefficient of hydrogen gas is investigated by using the hydrogen fueled engine. The measured results were also compared with those of gasoline engine and several empirical equations. Transient heat transfer coefficients were determined by measurements of unsteady heat flux and instantaneous wall temperature in the cylinder head. As the main results, it is shown that transient heat transfer coefficients have remarkable differences according to fuel properties, and it's value for hydrogen engine is twice higher than that of gasoline engine. It means that equation of heat transfer coefficient that the effect of fuel properties is considered sufficiently, is needed to analyze or simulate the gas engine performance.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.1061-1064
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• 1998

To examine the influence of unsteady wake on the flow and heat transfer characteristics, an experiment has been conducted in a four-vane linear cascade. Flow and heat transfer measurements are made for the inlet Reynolds number of 66000(based on chord length and free-stream velocity). Turbulent intensity and stress were measured using hot wire anemometer, and to measure the convective heat transfer coefficients on the blade surfaces liquid crystal/gold film Intrex technique was used. The disturbance by the unsteady wake is characterized by the unresolved unsteadiness. The unsteady wake enhances the turbulent motion of flow in the cascade passage. It also promotes the boundary layer development and transition. The results show that heat transfer coefficients on the suction surface increase with increasing unresolved unsteadiness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.428-439
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• 1998

Fluid flow and heat transfer have been numerically investigated for an oscillating flow in a tube with a regenerator. The regenerator is placed between hot and cold spaces which are heated and cooled at uniform temperature. An oscillating flow is generated by the piston motion at both ends of a tube. The time dependent, two-dimensional Navier-Stokes equations and energy equation are solved by using the finite-volume and moving grid method. The regenerator is adopted as Brinkmann-Forchheimer extended Darcy model. Numerical results are obtained for the flow and temperature fields, and described the effects of the oscillating frequency and amplitude ratio by the piston motion as well as the aspect ratio. The numerical results obtained indicate that the heat transfer between the tube wall and oscillating flow is increased as the oscillating frequency, amplitude ratio and the aspect ratio are increased.

• Journal of the KSME
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• v.16 no.2
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• pp.116-121
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• 1976

Non-steady hot wire method was adopted to measure thermal coductivity of paraffin wax in the phases of liquid and solid for the utilization of thermal energy storage. The instrument was tested with the measurement of thermal conductivity of water at various temperatures. The reproducibility of the instrumetn was found to be ${\pm}2%$, in which the results for water agree with the literature values. The thermal conductivity of paraffin wax varies from 0.177 W/m C to 0.236 W/m C when the phase changes from liquid to solid near the melting temperature.

• Proceedings of the KIEE Conference
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• 1998.11b
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• pp.713-716
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• 1998

To examine the influence of unsteady wake on the flow and heat transfer characteristics, an experiment has been conducted in a four-vane linear cascade. Flow and heat transfer measurements are made for the inlet Reynolds number of 66000(based on chord length and free-stream velocity). Turbulent intensity and stress were measured using hot wire anemometer, and to measure the convective heat transfer coefficients on the blade surfaces liquid crystal/gold film Intrex technique was used. The disturbance by the unsteady wake is characterized by the unresolved unsteadiness. The unsteady wake enhances the turbulent motion of flow in the cascade passage. It also promotes the boundary layer development and transition. The results show that heat transfer coefficients on the suction surface increase with increasing unresolved unsteadiness.