• Asian-Australasian Journal of Animal Sciences
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• v.13 no.11
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• pp.1523-1528
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• 2000

Four Suffolk ewes were used in Latin Square switch over design to study the effects of varying levels and sources of protein on heat production and thermoregulatory responses at daytime high ($33^{\circ}C$ temperature. They were fed Italian ryegrass hay supplemented with fishmeal and/or urea, providing three different levels of crude protein (CP) (low/unsupplemented: 7.9, medium: 11.6, and high: 15.8%) at $1.5{\times}maintenance$. Feeds were distributed at 0900 (30%) and 1700 (70%). Urea diet caused higher heat production and increased vaginal temperature compared to fishmeal and fishmeal-urea mix diets. Time spent standing, skin temperature and respiration rate of sheep fed urea were similar with those of sheep fed fishmeal. Sheep fed diet with low CP level had higher heat production, increased vaginal and skin temperature than sheep fed diet with medium CP content. Sheep on high CP diet produced significantly more heat than sheep fed medium CP diets. Their vaginal temperatures were similar with those of sheep fed medium CP diet but lower than those of sheep fed low CP diet. Respiration rates of sheep and time spent by them for standing on all diets did not differ significantly. These results suggest that urea is inferior protein supplement for thermoregulation of animal at hot environment, as it induced higher heat production than fishmeal and fishmeal-urea mix. Thermoregulatory response on fishmeal-urea mix diet was similar to fishmeal diet. Increasing CP of the diet from low to medium gives advantage for thermoregulation of animal. Increasing CP further to high level was not beneficial as it resulted in the responses of sheep similar to those on low protein diet.

• Journal of the Korean Society of Safety
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• v.12 no.1
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• pp.3-8
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• 1997

It is well known that mechanisms of fracture and fatigue crack propagation depend upon various characteristics such as environmental condition, crack geometry, heat treatment and mechanical properties. It seems to be important for the detailed evaluation of structural components which contain flaws. In this paper, it is studied that the fatigue crack propagation of partly heat treated medium carbon alloy steel(SCM440) by high frequency heat treatment.

• Journal of the Korean Society of Safety
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• v.8 no.1
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• pp.13-20
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• 1993

It is well known that mechanisms of fracture and fatigue crack propagation depend upon various characteristics such as environmental condition. crack geometry. heat treatment and mechanical properties. It seems to be important for the detailed evaluation of structural integrity to investigate the effects of the above factors on the behavior of structural components which contain flaws. In this paper. it is studied that the fatigue crack propagation of partly heat treated medium carbon steel (SM45C) by high frequency heat treatment.

• Journal of the Korean Solar Energy Society
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• v.22 no.4
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• pp.18-25
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• 2002

For application to medium temperature solar collerctors $(80\sim120^{\circ}C)$, a heat pipe should be designed properly to efficiently transfer heat to a hotter condenser than common applications. Among many wick structure candidates for heat pipes of this type, a slab wick was selected based on promising performance data reported previously. The thermal performance of slab wick heat pipes, screen wick heat pipes and thermosyphons with enlarged condenser section were experimentally investigated for comparison purpose. The heat pipes were 8.0 mm O.D. (evaporator section) and 25.4 mm O.D. (condenser section) made of copper. The experimental data of the heat pipes were analysed in terms of thermal resistance against thermal load and coolant temperature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1172-1182
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• 2002

In the present study a general criterion for local thermal equilibrium is presented in terms of parameters of engineering importance which include the Darcy number, the effective Prandtl number of fluid, and the Reynolds number. For this, an order of magnitude analysis is performed for the case when the effect of convection heat transfer is dominant in a porous structure. The criterion proposed in this study is more general than the previous criterion suggested by Carbonell and Whitaker, because the latter is applicable only when conduction is the dominant heat transfer mode in a porous medium while the former can be applied even when convection heat transfer prevails. In order to check the validity of the proposed criterion for local thermal equilibrium, the forced convection phenomena in a porous medium with a microchanneled structure subject to an impinging jet are studied using a similarity transformation. The proposed criterion is also validated with the existing experimental and numerical results for convection heat transfer in various porous materials that include some of the parameters used in the criterion such as a microchannel heat sink with a parallel flow, a packed bed, a cellular ceramic, and a sintered metal. It is shown that the criterion presented in this work well-predicts the validity of the assumption of local thermal equilibrium in a porous medium.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.19 no.1
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• pp.83-102
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• 2015

The present paper analyses the radiation effects of mass transfer on steady nonlinear MHD boundary layer flow of a viscous incompressible fluid over a nonlinear porous stretching surface in a porous medium in presence of heat generation. The liquid metal is assumed to be gray, emitting, and absorbing but non-scattering medium. Governing nonlinear partial differential equations are transformed to nonlinear ordinary differential equations by utilizing suitable similarity transformation. The resulting nonlinear ordinary differential equations are solved numerically using Runge-Kutta fourth order method along with shooting technique. Comparison with previously published work is obtained and good agreement is found. The effects of various governing parameters on the liquid metal fluid dimensionless velocity, dimensionless temperature, dimensionless concentration, skin-friction coefficient, Nusselt number and Sherwood number are discussed with the aid of graphs.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.612-620
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• 2001

The optimum design of a heat exchanger with porous media insertion is studied in this paper. It is considered that the aluminum foam metal is inserted in a flat plate channel and air flows through it. The influence of the microstructure of the foam metal on the pressure drop and heat transfer is investigated utilizing previous analytical results and existing correlation equations. Design parameters are identified as the unit-cell size and the ligament thickness of the porous medium, and their effects are examined. The results show that there exists optimum microstructure of the porous media maximizing heat transfer with a constant pressure drop. When the increase in the pressure drop is within a practically acceptable range, the increase in the heat transfer is dominated by the increase in the heat transfer area due to the porous medium insertion. Consequently, among the porous media with a constant pressure drop, the heat transfer is maximized with a microstructure with maximum specific surface area.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.3 no.2
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• pp.1-7
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• 2007

This paper is concerned with the selection of proper working fluids for medium temperature range heat pipe. The heat pipe which is made of SUS 316L has a total length of 700 mm as well as an outside diameter of 27.2 mm and a thickness of 2.1 mm respectively. Working fluids used in this study were Naphthalene, Biphenyl and Dowtherm A. Their charge amounts were about 40% of the inside volume of evaporator section. Experimental results shows that the Dowtherm A is good for $200^{\circ}C{\sim}300^{\circ}C$temperature range, while the Naphthalene is proper for $300^{\circ}C{\sim}430^{\circ}C$. In the case of the Naphthalene heat pipe, the heat transfer rate reaches 1500 W along with a vapor temperature of $430^{\circ}C$.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.776-781
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• 2001

To enhance thermal efficiency of thermal facility through recovery of low and medium temperature waste heat, 1MW organic Rankine cycle system was designed and developed. The exhaust gases of $175^{\circ}C$ at two 100MW power plants in pohang steel works were selected as the representative of low and medium temperature waste heat in industrial process for the heat source of the organic Rankine cycle system. HCFC-123, a kind of harmless refrigerant, was chosen as the working fluid for Rankine cycle. The organic Rankine cycle system with selected exhaust gases and working fluid was designed and constructed. From the operation, it was confirmed that the organic Rankine cycle system is available for low and medium temperature waste heat recovery in industrial process. The optimum operating manuals, such as heat-up of hot water, turbine start-up, and the process of electric power generation, were derived. However, electric power generated was not 1MW as designed but only 670kW. It is due to deficiency of pump capacity for supply of HCFC-123. So it is necessary to increase the pump capacity or to decrease the pressure loss in pipe for more improved HCFC-123 supply.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.6
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• pp.338-343
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• 2010

Mechanical properties and microstructures of medium carbon high manganese steels were investigated in terms of alloying elements such as Mn, C contents, and heat treatment condition. Austenite volume fraction was increased with increasing Mn content, leading to hardness decrease in the range of Mn content of above 10% after quenching and tempering. Such results are also supported by microstructural analysis and X-ray diffraction in that the increase in mangaese content results in the increase in austenite fraction. Studies on tempering condition indicated that not only hardness and tensile strength but also charpy impact values were reduced as tempering temperature were raised in the range of $250^{\circ}C$ to $600^{\circ}C$. It was also observed that fracture mode was changed from dimple to intergranular fracture. Such results are thought to be due to very fine carbide precipitation or impurity segreagation at grain boundaries as tempering temperature goes up. Heat treatment of Fe-5Mn-2Si-1Al-0.4C can be optimized by austenitizing at $850^{\circ}C$, air cooling and tempering at $250^{\circ}C$, resulting in 1950 MPa in Tensile strength, 17% in elongation and 23.3 $J/cm^2$ in charpy impact energy with high work hardening characteristics.