• 태양에너지
• /
• 제20권1호
• /
• pp.97-108
• /
• 2000

The purpose of this study is to minimize the heat transfer surface area and cold fluid exit temperature of heat exchanger which applied to the refrigeration and air-conditioning system by utilizing the thermoelectric principle. Both uniform and non-uniform current distribution methods which applied to the analysis of the TE elements that incorporates heat exchanger were investigated. The non-uniform current distribution method had the better coefficient of performance and had the lower cold fluid exit temperature of the TE cooling system than the uniform current distribution method. It was found that if a TE cooling system incorporates a heat exchanger, a non-uniform current distribution should guarantee to the lowest cold fluid exit temperature. Also, the hybrid method (combination of the uniform and non-uniform current distribution method) is investigated to achieve the best results by combining the uniform and non-uniform current distributions. The results show that it can lower the cold fluid exit temperature and reduce the heat transfer surface area for the parallel flow arrangement if we apply the constant current in some entry region and the non-uniform increasing current in the direction of the cold fluid flow afterwards.

• Structural Engineering and Mechanics
• /
• 제57권3호
• /
• pp.543-567
• /
• 2016

This study attempts to address the buckling and free vibration characteristics of an isotropic cylindrical panel subjected to non-uniform temperature rise using numerical approach. Finite element analysis has been used in the present study. The approach involves three parts, in the first part non-uniform temperature field is obtained using heat transfer analysis, in the second part, the stress field is computed under the thermal load using static condition and, the last part, the buckling and pre-stressed modal analysis are carried out to compute critical buckling temperature as well as natural frequencies and associated mode shapes. In the present study, the effect of non-uniform temperature field, heat sink temperatures and in-plane boundary constraints are considered. The relation between buckling temperature under uniform and non-uniform temperature fields has been established. Results revealed that decrease (Case (ii)) type temperature variation field influences the fundamental buckling mode shape significantly. Further, it is observed that natural frequencies under free vibration state, decreases as temperature increases. However, the reduction is significantly higher for the lowest natural frequency. It is also found that, with an increase in temperature, nodal and anti-nodal positions of free vibration mode shapes is shifting towards the location where the intensity of the heat source is high and structural stiffness is low.

• Steel and Composite Structures
• /
• 제22권6호
• /
• pp.1359-1389
• /
• 2016

Buckling and free vibration behavior of a laminated cylindrical panel exposed to non-uniform thermal load is addressed in the present study. The approach comprises of three portions, in the first portion, heat transfer analysis is carried out to compute the non-uniform temperature fields, whereas second portion consists of static analysis wherein stress fields due to thermal load is obtained, and the last portion consists of buckling and prestressed modal analyzes to capture the critical buckling temperature as well as first five natural frequencies and associated mode shapes. Finite element is used to perform the numerical investigation. The detailed parametric study is carried out to analyze the effect of nature of temperature variation across the panel, laminate sequence and structural boundary constraints on the buckling and free vibration behavior. The relation between the buckling temperature of the panel under uniform temperature field and non-uniform temperature field is established using magnification factor. Among four cases considered in this study for position of heat sources, highest magnification factor is observed at the forefront curved edge of the panel where heat source is placed. It is also observed that thermal buckling strength and buckling mode shapes are highly sensitive to nature of temperature field and the effect is significant for the above-mentioned temperature field. Furthermore, it is also observed that the panel with antisymmetric laminate has better buckling strength. Free vibration frequencies and the associated mode shapes are significantly influenced by the non-uniform temperature variations.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.2528-2533
• /
• 2007

Thermoforming is one of the most versatile and economical processes available for the manufacturing polymer products. The drawback of thermoforming is difficult to get uniform thickness of final products. For the distribution of thickness strongly depends on the temperature distribution of sheet, the adjustment of heater power is very important In this paper, an optimization study for getting uniform temperature distribution was carried out using dual optimization steps. At first, the steady state optimal distribution of heater power is searched by numerical optimization to get uniform temperature of sheet surface. In the second step, time-dependent optimal heater inputs have been found out to decrease the temperature difference through the direction of thickness using Rseponse Surface Method and D-optimal method. The optimization results show that the time-dependent optimal heater power distribution gives acceptable uniform sheet temperature in the field of forming temperature..

• 한국의류학회지
• /
• 제29권1호
• /
• pp.35-45
• /
• 2005

The purpose of this study was to evaluate thermal properties of soccer wear with different materials and designs. As a beginning step, the questionnaire survey about the actual condition of soccer wears was conducted. with the results of the questinnaire, two soccer wears with new material and design that were improved in tactile sensations, absorption and ventilation were developed. We evaluated thermal and subjective responses of subjects wearing Korea national soccer team uniform in 1998 World Cup (Uniform 98), soccer wear with new material and same design(New II) and with new material and new design(New I). New I was made with mesh in armhole for improving ventilation. Rectal temperature, skin temperature, clothing microclimate, and heart rate were measured in climatic chamber test(twelve times) and field test(eighteen times). The results were as follows. 1. As the results of the climatic chamber test, rectal temperature was lower in New I and New II than Uniform98, and mean skin temperature was lower in New I than Uniform 98 and New II. Heart rate was lower in New I than New II, and total body weight loss and local sweating were not significantly different by soccer wears. 2. As the results of the field test, rectal temperature was lower in New I than Uniform98 and New II. Mean skin temperature was lower in New II than Uniform98 and New I. Clothing microclimate temperature was lower in New II than Uniform98 and New 1, and clothing microclimate humidity was lower in New I, New II than Uniform 98. Heart rate was lower in New I than Uniform 98, New II and total body weight loss and local sweating were lower in New I, New II than Uniform 98. In conclusion, New I using new design using mesh in armhole and new material using sweat absorbent finishing was excellent from the point of view of physical responses, ventilation and sweat absorption.

• Steel and Composite Structures
• /
• 제22권4호
• /
• pp.889-913
• /
• 2016

Vibration analysis of embedded functionally graded (FG)-carbon nanotubes (CNT)-reinforced piezoelectric cylindrical shell subjected to uniform and non-uniform temperature distributions are presented. The structure is subjected to an applied voltage in thickness direction which operates in control of vibration behavior of system. The CNT reinforcement is either uniformly distributed or functionally graded (FG) along the thickness direction indicated with FGV, FGO and FGX. Effective properties of nano-composite structure are estimated through Mixture low. The surrounding elastic foundation is simulated with spring and shear constants. The material properties of shell and elastic medium constants are assumed temperature-dependent. The motion equations are derived using Hamilton's principle applying first order shear deformation theory (FSDT). Based on differential cubature (DC) method, the frequency of nano-composite structure is obtained for different boundary conditions. A detailed parametric study is conducted to elucidate the influences of external applied voltage, elastic medium type, temperature distribution type, boundary conditions, volume percent and distribution type of CNT are shown on the frequency of system. In addition, the mode shapes of shell for the first and second modes are presented for different boundary conditions. Numerical results indicate that applying negative voltage yields to higher frequency. In addition, FGX distribution of CNT is better than other considered cases.

• Agricultural and Biosystems Engineering
• /
• 제3권2호
• /
• pp.65-72
• /
• 2002

Temperature is the most influential environment parameter which affects the quality change of agricultural products in cold storage. Therefore, it is essential to keep the uniform temperature distribution in the storage room. This study was performed to analyze the air movement and temperature distribution in the forced recirculating cold storage facility and to simulate optimum storage method of green groceries using 3-D CFD(three dimensional computational fluid dynamics) computer simulation which applied the standard $textsc{k}$-$\varepsilon$ turbulence model and FVM(finite volume method). The simulation was validated by the experimental results for onion storage and the simulation model was used to simulate the temperature and velocity distribution in the storage room with reference to the change of storage method such as location of storage, no stores, bulk storage, and pallet storage. In case of no stores, internal airflow was circulated without stagnation and consequently air movement and temperature distribution were uniform. In case of bulk storage, air movement was stagnated so much and temperature distribution of onion was not uniform. Furthermore, the inner temperature of onion roses more than the initial temperature of storage. In case of pallet storage, air movement and temperature distribution of onion were so uniform that the danger of quality change was decreased.

• 한국표면공학회지
• /
• 제46권6호
• /
• pp.283-289
• /
• 2013

The experimental study for the temperature uniformity on the wafer using liquid-vapor phase heat transfer mechanism is performed. For the experiment, the heater plate which is consist of stainless steel container, working fluid and electrical heater is designed, manufactured and tested at the range of 600 to $850^{\circ}C$. The results showed that the phase change type heater plate was much more uniform and stable temperature on the heater plate surface and wafer than the uniform heat flux type heater plate at the atmospheric condition. Also, the results of 300 mm outer diameter of heater plate showed that the same temperature uniformity compared with 230 mm.

• 한국세라믹학회지
• /
• 제49권2호
• /
• pp.161-166
• /
• 2012

The temperature-rasing sintering method was used in this study to fabricate the aggregates of uniform pore size and distribution containing reject ash occurred in the thermal power plant. The spheric green aggregates made of reject ash were put into the box furnace of 800~$1000^{\circ}C$, heated with a heating rate of 5~$15^{\circ}C$/min to 1200~$1275^{\circ}C$, sintered for 10 min and then discharged out of the furnace to the room temperature. The input temperature, heating rate and sintering temperature increased the bloating phenomenon of the specimen, and the sintering temperature among them was the most effective factor. The aggregate manufactured at $1275^{\circ}C$ had the specific gravity of about 1.0 and water absorption of 1~2%, and the pores of 500~1,000 ${\mu}m$ were uniformly distributed across the whole specimen. Especially, the aggregates fabricated using the temperature-rasing sintering method in this study showed an excellent bloating properties and uniform microstructure without black core phenomenon which is typical for the bloated ceramics synthesized by direct sintering method.

• ETRI Journal
• /
• 제19권2호
• /
• pp.71-81
• /
• 1997

We report on the room-temperature-growth of highly uniform and ultrathin Ag films on Sb-terminated Si(111) surfaces, as evidenced from a scanning tunneling microscopy (STM) study in an UHV system. With predeposition of one monolayer (ML) of Sb, uniform growth of Ag islands was observed at room temperature. The Sb layer suppresses the surface diffusion of Ag atoms on Si surface and increases the Ag island density, and then the increased island density is believed to cause coalescence of Ag islands before the beginning of multilayer growth in higher coverages, resulting in the growth of atomically flat and uniform islands on the Sb surfactant layer.