• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.4
• /
• pp.463-473
• /
• 2011

The warm shrink fitting process is generally used to assemble automobile transmission parts (shaft/gear). But the fitting process can cause the dimensions of addendum and dedendum of the gear to change with respect to the fitting interference and the profile of the gear. As a result, there may be additional noise and vibration between gears. To address these problems, we analyzed the warm shrink fitting process according to process parameters; the fitting interference between the outer diameter of the shaft and the inner diameter of the gear, the inner diameter of the gear, addendum and dedendum of the gear, the heating temperature. In this study, a closed form equation for predicting the amount of deformation of addendum and dedendum in the R-direction was proposed. And the FEA method to analyze the cooling process was proposed for thermal-structural-thermal coupled field analysis of the warm shrink fitting process (heating-fitting-cooling process).

• KIEAE Journal
• /
• v.13 no.3
• /
• pp.111-120
• /
• 2013

The purposes of this study were to investigate the actual state of the indoor thermal and air environment in general apartment houses during winter in Cheongju City, to analyze the related factors with the indoor thermal and air environment, and to make suggestions for the improvement. A series of visiting field investigation was conducted in twenty units between 28th December, 2010, and 11th March, 2011. The field investigations included the measurement of physical indoor environmental conditions, the observation of architectural characteristics and resident's behavior, and the on-site questionnaire survey of residents. The measured values of each units were compared to evaluation standard and were categorized to group by the difference between units. Factors related to the difference of the measured values between the groups were analyzed. The findings are summarized as followed. The indoor temperature of apartment houses during winter in Cheongju City was generally suitable. The relative humidity was slightly dry, while the $CO_2$ concentration was found to be excessively high. The factors related indoor environment were analysed as heating operation, ventilation, gas range use, and hanging out the wash to dry in indoors.

• Computers and Concrete
• /
• v.11 no.4
• /
• pp.271-289
• /
• 2013

In this research, a developed microstructural model of cement particles was presented to describe the cement hydration procedure. To simplify the hydration process, the whole hydration was analyzed in a series of sub-steps. In each step, the hydration degree, as well as the microstructural size of the hydration cell, was calculated as a function of the radius of the unreacted cement particles. With the consideration of the water consumption and the reduction of the interfacial area between water and hydration products, the micro-level expressions of the cement hydration kinetics were established. Then the heat released and temperature history of the concrete was carried out with the hydration degree obtained from each sub-steps. The equivalent age method based on the Arrhenius law was introduced in this research. Based on the equivalent age method, a maturity model was applied to describe the evolution of the mechanical properties of the material during the hydration process. The finite element program ANSYS was used to analyze the temperature field in concrete structures. Then thermal stress field was calculated using the elasticity modulus obtained from code formulate. And the risk of thermal cracking was estimated by the comparison of thermal stress and concrete tensile strength.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.18 no.10
• /
• pp.783-790
• /
• 2006

A one-dimensional numerical model coupled with parameter estimation is used to predict the effective thermal conductivities of soil formations and borehole resistances from in situ field test data. In this application a new method of using initial ignoring time (IIT) obtained from error estimation is tried and turned out to be successful in determining soil thermal conductivities. This method is used for single-U and double-U borehole system. The results of this method are compared and agreed well with those of existing software (GPM) in the analysis of single-U borehole data. In the analysis of double-U borehole data this method seems to be better in predicting soil and borehole properties.

• Journal of applied mathematics & informatics
• /
• v.42 no.3
• /
• pp.607-623
• /
• 2024

This article studies the effects of heat generation/absorption and thermal radiation on the unsteady magnetohydrodynamic (MHD) Casson fluid flow past a vertical plate through rotating porous medium with constant temperature and mass diffusion. It is assumed that the plate temperature and concentration level are raised uniformly. For finding the exact solution, a set of non-dimensional partial differential equations is solved analytically using the Laplace transform technique. The influence of various non-dimensional parameters on the velocity are discussed, including the effects of the magnetic parameter M, heat generation/absorption Q, thermal radiation parameter R, Prandtl number Pr, Schmidt number Sc, permeability of porous medium parameter, Casson fluid parameter γ, on velocity, temperature, and concentration profiles, which are discussed through several figures. It is found that velocity, temperature, and concentration profiles in the case of heat generation parameter Q, Casson fluid parameter γ, thermal Grashof number Gr, mass Grashof number Gc, Permeability Porous medium parameter K, and time t have retarding effects. It is also seen that the magnetic field M, Thermal Radiation parameter R, Prandtl field Pr, Schmidt number Sc have reverse effects on it.

• Interaction and multiscale mechanics
• /
• v.1 no.4
• /
• pp.397-409
• /
• 2008

The interfacial thermal resistance of pristine and defective carbon nanotubes (CNTs) embedded in low-density polyethylene matrix is studied in this paper. Interface thermal resistance in nanosystems is one of the most important factors that lead to the large variation in thermal conductivities in literature and the novelty of this paper lies in the estimation of the interfacial thermal resistance for defective nanotubes-systems. Thermal properties of CNT nanostructures are estimated using molecular dynamics (MD) simulations and the simulations were carried out for various temperatures by rescaling the velocities of carbon atoms in the nanotube. This paper also deals with the mesoscale thermal conductivities of composite systems, using effective medium theories by considering the size effect in the form of interfacial thermal resistance and also using the conventional micromechanical methods like Hashin-Shtrikman bounds and Wakashima-Tsukamoto estimates.

• Journal of Power Electronics
• /
• v.13 no.6
• /
• pp.1080-1089
• /
• 2013

In this paper, the superposition principle of a heat sink temperature rise is verified based on the mathematical model of a plate-fin heat sink with two mounted heat sources. According to this, the distributed coupling thermal impedance matrix for a heat sink with multiple devices is present, and the equations for calculating the device transient junction temperatures are given. Then methods to extract the heat sink thermal impedance matrix and to measure the Epoxy Molding Compound (EMC) surface temperature of the power Metal Oxide Semiconductor Field Effect Transistor (MOSFET) instead of the junction temperature or device case temperature are proposed. The new thermal impedance model for the power converters in Switched Reluctance Motor (SRM) drivers is implemented in MATLAB/Simulink. The obtained simulation results are validated with experimental results. Compared with the Finite Element Method (FEM) thermal model and the traditional thermal impedance model, the proposed thermal model can provide a high simulation speed with a high accuracy. Finally, the temperature rise distributions of a power converter with two control strategies, the maximum junction temperature rise, the transient temperature rise characteristics, and the thermal coupling effect are discussed.

• Progress in Superconductivity and Cryogenics
• /
• v.12 no.1
• /
• pp.61-65
• /
• 2010

To develop the thermal analysis method for the thermal behavior of HTS power cable system, cooled with sub-cooled liquid nitrogen, new thermo dynamic model for HTS cable system is introduced. The introduced thermal model is mainly modified from the thermal circuit following to IEC60287 for underground power cable systems such as XLPE or paper wrapped insulation cables. The thermal circuits for HTS cables are similar to the forced cooled underground cable system but the major thermal parameters and the configuration is apparently different to the normal cable systems so there has been no proposals in this field of analysing method. In this paper, 154kV HTS cable system has been introduced as an aspects of thermal models and a thermal circuit is proposed for the fundamentals on the dynamic rating systems for the HTS cable system. By using the thermal circuit developed in this paper, the optimal controls on the sub-cooling system's capacity become possible and it is expected to make the efficiency of HTS cable higher than conventional static controls.

• The Korean Journal of Community Living Science
• /
• v.24 no.4
• /
• pp.543-552
• /
• 2013

Physiological and subjective responses of the farmers and thermal environment during chili harvest in the open field were investigated to evaluate the thermal environments and farmers's workload. Eight career female farmers in their sixties participated as subjects both in morning work(MW, AM 9:00~10:30) and in afternoon work(AW, PM 15:00~16:30) with each lasting about 90 minutes. The results were as follows. 1) Air temperature, air humidity, globe temperature and WBGT of MW were mean $25.54^{\circ}C$, 81.82%RH, $37.72^{\circ}C$, $26.27^{\circ}C$ and AW were mean $30.63^{\circ}C$ 82.50%RH, $40.11^{\circ}C$, $30.02^{\circ}C$, respectively. By the WBGT, we evaluated that the thermal environment in the afternoon in the open field gave a thermal burden to farmers. 2) Mean skin temperature of AW($34.8{\pm}0.8^{\circ}C$) was higher than MW($33.5{\pm}1.2^{\circ}C$)(p<0.05). Clothing microclimate temperature on the chest of each work time were $31.3^{\circ}C$(MW) and $32.7^{\circ}C$(AW). Clothing microclimate humidity on the chest of each work time were over 80%RH. Heart rate were 88.5bpm(MW) and 91.7bpm(AW) respectively. 3) Farmers working in the afternoon felt uncomfortable after 45~60 min. of work and in the morning they felt uncomfortable after 90 min. of work. We evaluated that the harvesting of chilies in the open field was 'moderate work' by the physiological responses but the level of thermal burden increased over time especially in the afternoon work. It is suggested that farm workers should drink fluids between work to stay in homeostasis by sweating and to take frequent rests. Active clothing ventilation and wearing functional garments would help farm workers excrete sweat effectively.

• The KSFM Journal of Fluid Machinery
• /
• v.10 no.5
• /
• pp.54-63
• /
• 2007

A barrel is a high length-to-diameter ratio cylinder that is influenced by environmental factors such as sunlight, precipitation, wind and clouds. Cross-barrel temperature differences caused by uneven heating or cooling lead to thermal deformation that degrades accuracy. Therefore, a barrel is covered by thermal shrouds to minimize the type of thermal deformation, "fall-of-shot". In this paper, an analytical and experimental study is presented to design the thermal shrouds for a gun barrel and to evaluate the thermal shroud effect. First, an analytical study on the thermal shroud effect to minimize thermal deformation of a gun barrel by sunlight and wind is performed. The coupled analysis of thermal fluid dynamics of the air flow between a barrel and thermal shrouds and thermal stresses of a barrel Is performed to clarify both the thermal shroud effect and the drift in gun muzzle orientation by thermal deformation. Second, experiments are carried out to test and evaluate the thermal shroud effect on the performance of a gun barrel. The drift in gun muzzle orientation against the solar radiation is confirmed by the experiments, and the results well agree with the analytical estimation. Third, three principal design factors that are presumed to have an effect on the performance of the thermal shrouds are also analyzed; sorts of shroud materials, wall-thickness of thermal shrouds, and distance of the gap between a barrel and thermal shrouds.