• Journal of Advanced Marine Engineering and Technology
• /
• v.28 no.5
• /
• pp.754-761
• /
• 2004

In this paper, evaporating heat transfer characteristics in the refrigeration and air-conditioning facilities were studied using the environmentally friendly refrigerants R-1270 (Propylene). R-290 (Propane). R-600a (Iso-butane) and HCFC refrigerant R-22 The test tube was surrounded by an annulus with water flowing counter to the refrigerant. The tube is copper. with an outside diameter of 12.7mm and the wall thickness of 1.315mm. The test results showed that the local evaporating heat transfer coefficients of hydrocarbon refrigerants were superior to that of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-1270. The average evaporating heat transfer coefficient increased with the increase of the mass velocity and it showed the higher values in hydrocarbon refrigerants than R-22 Comparing the heat transfer coefficient of experimental results with that of other correlations. the presented results had agood agreement with the Kandlikar's correlation. This results form the investigation can be used in the design of heat transfer exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.

• Proceedings of the SAREK Conference
• /
• 2008.06a
• /
• pp.154-159
• /
• 2008

Two-phase flow boiling heat transfer of R-410A in horizontal small tubes was reported in the present experimental study. The local heat transfer coefficients were obtained over a heat flux range of 5 to 40 kW/$m^2$, a mass flux range of 170 to 600 kg/$m^2s$, a saturation temperature range of 3 to $10^{\circ}C$, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5 and 3.0 mm, and lengths of 330 and 3000 mm, respectively. The section was heated uniformly by applying a direct electric current to the tubes. The effects on heat transfer of mass flux, heat flux, inner tube diameter, and saturation temperature were presented. The experimental heat transfer coefficient is compared with six existing heat transfer coefficient correlations. A new boiling heat transfer coefficient correlation based on the superposition model for R-410A in small tubes was developed with mean deviation of 10.13%.

• Proceedings of the SAREK Conference
• /
• 2007.11a
• /
• pp.241-246
• /
• 2007

The present paper dealt with an experimental study of boiling heat transfer characteristics of $CO_2$. Heat transfer coefficients of the refrigerant flow inside horizontal smooth microchannel were obtained with inner tube diameter of 0.3mm and length of 300mm. The direct electric heating method was applied for supplying the heat uniformly to the refrigerant. The experiments were conducted with $CO_2$ purity of 99.99%, at saturation temperature of $10^{\circ}C$, mass flux ranges of $300{\sim}900\;kg/m^2s$, and heat flux ranges of $15{\sim}45\;kW/m^2$. While heat transfer coefficient increased with the increase of heat flux in the low quality region, the heat transfer coefficient decreased with the increase of quality in the high quality region. The heat transfer coefficients were compared with seven existing correlations with the Gungor-Winterton's(1986) correlation gave the best prediction. A new corelation to predict the two-phase flow heat transfer coefficient was developed based on the Chen(1966) correlation. The new correlation predicted the experimental data well with a mean deviation of 9.69% and average deviation of -3.03%.

• Journal of the Korean Solar Energy Society
• /
• v.35 no.2
• /
• pp.53-62
• /
• 2015

Boiling heat transfer characteristic is very important in the various industries such as solar thermal system, power generation, heat exchangers, cooling of high-power electronics components and cooling of nuclear reactors. Therefore, in this study, boiling heat transfer characteristics such as critical heat flux (CHF) and heat transfer coefficient under the pool boiling state were tested using graphene nanofluids. Graphene used in this study, which have the same thermal conductivity but with different sizes. The experimental results showed that the highest the CHF and boiling heat transfer coefficient increase ratio for graphene nanofluids was at the 0.01 vol.%. At the present juncture, the CHF and boiling heat transfer coefficient increase ratio of the small-sized graphene nanofluids was higher than the large-sized graphene nanofluids.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1998.04a
• /
• pp.353-358
• /
• 1998

In general, we have used the finite element method(FEM) to find natural frequencies of plates. In this method, however, it is necessary to use a large amount of computer memory and computation time because the FEM requires many degrees of freedom for finding natural frequencies of plates correctly. Therefore it was very difficult to analyze the free vibration of plates correctly on personal computer. For overcoming this disadvantage of the FEM, the authors have developed the finite element-transfer stiffness coefficient method(FE-TSCM) which is based on the concept of modeling techniques in the FEM and the transfer of the stiffness coefficient in the transfer stiffness coefficient method. In this paper, we formulate free vibration analysis algorithm of rectangular plates using the FE-TSCM. Some numerical examples of rectangular plates are proposed, and their results and computation times obtained by the FE-TSCM are compared with those by the FEM and the finite element-transfer matrix method in order to demonstrate the accuracy and efficiency of the FE-TSCM.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.9 no.2
• /
• pp.92-98
• /
• 2001

We determined the transfer coefficient through the analysis of three dimensional temperature distribution in comparison with the measured temperature on the piston in the turbocharged diesel engine. And we analyzed the thermal stress and the thermal deformation with that heat transfer coefficient by using finite element method. According to this results, we found that maximum tempetature range of the piston appeared at the upper part of the piston crown and that the heat transfer coefficient of the upper part of the piston is smaller than that of the lower one. It showed that the maximum thermal deformation is shown at the edge of the upper part of piston and that the maximum thermal stress was shown on the lower part of the piston crown. Finally, we defined the method of determination of a piston heat transfer analysis by using measured temperature on the piston and analyzed temperature with finite element method.

• Food Science and Biotechnology
• /
• v.14 no.3
• /
• pp.328-333
• /
• 2005

Finite difference model and dynamic thermal property evaluation system were developed to estimate convection heat transfer coefficient by modeling temperature-time profile of beef cube in continuous flow sterilizing system. As input parameters of the model, specific heat and thermal conductivity values of beef frankfurter meat were independently measured from 20 to $80^{\circ}C$. Convection heat transfer coefficient was estimated by comparing simulated and measured temperature-time profiles. Actual temperature-time profiles of meat cube were measured at flow rates of 15, 30, and 45 L/min and viscosities from 0 to 15 cp, and mean values of convection heat transfer coefficients ranged from 792 to $2107\;W/m^2{\cdot}K$. Convection heat transfer coefficient increased with increase in flow rate and decreased as viscosity increased.

• Journal of Power System Engineering
• /
• v.16 no.2
• /
• pp.11-16
• /
• 2012

In this paper, the authors formulate the sensitivity analysis algorithm for the natural frequency of a torsional shafting by expanding the transfer stiffness coefficient method. The basic concept of the present algorithm is based on the transfer of sensitivity stiffness coefficient, which is the derivative of stiffness coefficient with respect to design parameter, at every node from the first node to the last node in analytical model. The effectiveness of the present algorithm is confirmed by comparing the results of the sensitivity analysis and those of the reanalysis for the natural frequencies of a torsional shafting with a constant cross section. In numerical calculation, the design parameter is the diameter of the shaft element of the torsional shafting.

• Journal of Power System Engineering
• /
• v.17 no.6
• /
• pp.33-39
• /
• 2013

It is very important to analyze the dynamic responses of the shell structures from the viewpoint of the design of shell structures with a variety of axisymmetric loadings. In this paper, the computational algorithm for the dynamic response analysis of an cylindrical shell with axisymmetric loading is formulated by the transfer mass coefficient method based on the transfer of mass coefficient. After the computational programs for obtaining the dynamic responses of cylindrical shells with axisymmetric loading are made by the transfer mass coefficient method and the finite element method, the computational results by both methods are compared. From the computational results, we can confirm that the transfer mass coefficient method has the effectiveness in the dynamic response analyses of cylindrical shells with a variety of axisymmetric loadings.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2039-2042
• /
• 2008

Recently, Electronic & Electrical Products have problems how to reduce heat in trend reducing size and increasing speed. heat pipes worked by latent heats can solve problems for effective and quiet electronic applications. Heat Pipes have to be suitably designed for the external conditions due to showing optimum performance. it has influence on efficiency of heat pipes to the exterior structure changed by length, bending angle, diameter. Designing heat pipes has depended on experience from trial and error. this method wasted too many resources, but can't guarantee efficiency. to prevent those wastes, this study aims at making the thermal transfer coefficient predicting efficiency. In this study, the thermal transfer coefficient has been made from experimental results that used variables - lengths between heat source and radiation, bending angles, diameters of heat pipes. variables become non-dimensional in modeling process for making the coefficient.