• Journal of Advanced Marine Engineering and Technology
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• v.29 no.1
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• pp.25-33
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• 2005

When a circular tube with uniform heat generation within the wall was placed in a cross flow, heat flows by conduction in the circumferential direction due to the asymmetric nature of the fluid flow around the perimeter of the circular tube The circumferential heat flow affects the wall temperature distribution to such an extent that. in some cases, significantly different results may be obtained for geometrically similar surfaces. In the present investigation, the effect of circumferential wall heat conduction is investigated for forced convection around circular tube in cross flow of air and water Two-dimensional temperature distribution $T_w(r,{\theta})$ is calculated through the numerical analysis. The difference between one-dimensional and two-dimensional solutions is demonstrated on the graph of local heat transfer coefficients. It is observed that the effect of working fluid is very remarkable.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.42-47
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• 2001

The heat (mass) transfer characteristics on the blade surface of a first-stage turbine rotor cascade for power generation has been investigated by employing the naphthalene sublimation technique. A four-axis profile measurement system is successfully developed for the measurements of the local heat (mass) transfer coefficient on the curved blade surface. The experiment is carried out at the free-stream Reynolds number and turbulence intensity of $2.09\times10^5$ and 1.2%. The results on the blade surfaces show that the local heat (mass) transfer on the suction surface is strongly influenced by the endwall vortices, but that on the pressure surface shows a nearly two-dimensional nature. The pressure surface has a more uniform distribution of heat load than the suction one.

• Structural Engineering and Mechanics
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• v.32 no.3
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• pp.429-445
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• 2009

Thermal stability of quasi-isotropic composite and polymeric structures is considered one of the most important criteria in predicting life span of building structures. The outdoor applications of these structures have raised some legitimate concerns about their durability including moisture resistance and thermal stability. Exposure of such quasi-isotropic composite/polymeric structures to various and severe climatic conditions such as heat flux and frigid climate would change the material behavior and thermal viability and may lead to the degradation of material properties and building durability. This paper presents an analytical model for the generalized problem. This model accommodates the non-linearity and the non-homogeneity of the internal heat generated within the structure and the changes, modification to the material constants, and the structural size. The paper also investigates the effect of the incorporation of the temperature and/or material constant sensitive internal heat generation with four encountered climatic conditions on thermal stability of infinite cylindrical quasi-isotropic composite/polymeric structures. This can eventually result in the failure of such structures. Detailed critical analyses for four case studies which consider the population of the internal heat generation, cylindrical size, material constants, and four different climatic conditions are carried out. For each case of the proposed boundary conditions, the critical thermal stability parameter is determined. The results of this paper indicate that the thermal stability parameter is critically dependent on the cylinder size, material constants/selection, the convective heat transfer coefficient, subjected heat flux and other constants accrued from the structure environment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.8
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• pp.753-758
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• 2013

In this study, two proposals for the wall heating preconverter of an MCFC are numerically studied to resolve hot temperature generation near the wall by the low thermal conductivity of the catalyst. The numerical results show that the inserted porous cupper plates on the catalyst evidently improve heat transfer and realize more uniform reforming in the preconverter. The calculated results for the preconverter with a circumference empty space of catalyst located at center, 1/2 and 4/5 from center line are compared. The circumference empty space located at 1/2 position shows better results than other cases, but the positive effect on the uniform reforming process is less than in the case of inserted cupper porous plates on the catalyst.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.668-671
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• 2007

A numerical study was conducted on a simplified model of a high-temperature solar receiver which incorporates liquid-metal heat pipe. The objective of this paper is to compare the isothermal characteristics of the heat pipe receiver with the conventional receiver utilizing convection of molten salt as heat carrier. The solar receiver was assumed to be subject to a concentration ratio between 50 and 1,000 to supply high-temperature heat to a stirling engine for electric power generation. For simplicity of the analysis, a cylindrical geometry was assumed and typical dimensions were used based on available literature. The heat pipe had a shape of double-walled cavity and the working fluid was a sodium. The analysis was performed assuming that the radiation heat flux on the inner walls of the receiver was uniform, since the focus of this study was laid on the comparison of the conventional type and heat pipe type receiver. The results showed that the heat pipe type exhibited superior performance when the operating temperature becomes higher. In addition, to explore the advantage of the heat pipe receiver, the channel shape and dimensions should be adjusted to increase the heat transfer area between the wall and the heat trnasfer medium.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.339-344
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• 2005

A PEMFC system model for FCEV was constructed and simulated numerically to examine the heat/water flow of the system and air/fuel humidification process for various operation conditions (ambient pressure /temperature/humidity, operating temperature, power load). We modeled PEMFC stack which can generate maximum electricity of about 80 kW. This stack consists of 400 unit cells and each unit cell has $250cm^2$ reacting area. Uniform current density and uniform operating voltage per each cell was assumed. The results show the flow characteristics of heat and water at each component of PEMFC system in macro-scale. The capacity shortage of the radiator occurred when the ambient was hot $(over\;40^{\circ}C)$ and power level was high (over 50 kW). In spite of some heat release by evaporation of water in stack, heat unbalance reached to 20kW approximately in such a severe operating condition. This heat unbalance could be recovered by auxiliary radiators or high speed cooling fan with additional cost. In cold environment, the capacity of radiator exceeded the net heat generation to be released, which may cause a problem to drop the operating temperature of stack. We dealt with this problem by regulating mass flow rate of coolant and radiator fan speed. Finally, water balance was not easily broken when we retrieved condensed and/or unused water.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.440-448
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• 1998

This paper considers the influence of circumferential wall heat conduction for the case of forced convection around a circular cylinder in cross flow of air. Keeping uniform heat generation from the inner surface of the cylinder in radial direction, heat is transferred by wall conduction in the circumferential direction due to the asymmetric nature of the temperature distribution of the cylinder and by convection around the perimeter of the cylinder. The wall conduction depends on conductivity of the cylinder and size of the cylinder radius and thickness and affects the local convective heat transfer rate significantly for geometrically similar surfaces and flow conditions. A nondimensional conjugation parameter K. (=k$_t$R/k$_w$b) has been used to characterize the effect of the circumferntial wall heat conduction. The small values of conjugation parameter K are found to be associated with large effect of wall conduction on the local convective heat transfer rate.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.1-8
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• 2001

With uniform heat generation within the wall of the cylinder placed in a cross flow, heat flows by conduction in the circumferential direction due to the asymmetric nature of the fluid flow around the perimeter of the cylinder. The circumferential heat flow affects the wall temperature distribution to such an extent that in some cases significantly different results may be obtained for geometrically similar surfaces. In the present investigation, the effects of circumferential wall heat conduction on local convective heat transfer is investigated for the case of forced convection around horizontal cylinder in cross flow of air. Two-dimensional temperature distribution $T_w$/(${\gamma}$,${\theta}$) is presented through the numerical analysis. The one-dimensional and two-dimensional solutions are in good agreement with experimental results of local heat transfer coefficients.

• 전기의세계
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• v.25 no.5
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• pp.79-87
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• 1976

This paper is to investigate the A.C generation of MHD engine, converting directly the kinetic energy of conductive gas in high temperature to electric power by the effect of magnetic field. It is known that there are at least two kinds of method in A.C MHD power generation; one, by sending stationary plasma flow in an alternating or rotating magnetic field and the other, by transmission of pulse type plasma flow in uniform and constant magnetic field, former method is adopted here. In order to raise the total efficiency of close cycle in combination with nuclear power and MHD genertaion, an argon plasma jet is utilized as heat source, which is not mixed with the seed material, and the design data are obtained for A.C MHD generation in small capacity, but induced voltage and power output have the maximum values, 15 voltages and 7.5W respectively due to plasma flow with low conductivity and weak magnetic field.

• Journal of Hydrogen and New Energy
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• v.22 no.4
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• pp.546-551
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• 2011

The corrosion on steam generator tubes of the secondary side of pressurized water reactor inhibits heat transfer. One of the most efficient techniques improving the heat transfer performance of a nuclear electric generation is a corrosion control. The environmental parameters mostly affecting corrosion are materials and chemical additives. It seems that no further corrosion occurs in steels with Polyacrylic acid polymer dispersant treatment. Polyacrylic acid forms a protective coating with uniform thickness on metal surface. Polyacrylic treatment appears to be the most convenient way to enhance the thermal performance by the thermal conductivity improvement in steam generators.