• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.281-287
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• 1999

The turbulent natural convection in the membrane type LNG carrier cofferdam with heating points has been studied by numerical method. As the numerical methods, we introduced the three turbulence model, a standard $k-{\varepsilon}$ model and two case of a low Reynolds number models. The parameters considered for this study ore number and capacity of heating points i.e., $1{\leq}Ns{\leq}12$ and $1.0{\times}10^5{\leq}Qs(W/m^3){\leq}1.0{\times}10^8$. The results of the isotherms and velocity vectors have been represented for various parameters. The temperature and velocity at upper position in the space ore shown to be higher than those at lower position. For obtaining the optimal temperatures, $20{\sim}30^{\circ}C$ in the cofferdam space, the heating capacities show $2.0{\times}10^7W/m^3$ at g-heating points and $1.0{\times}10^7W/m^3$ at 12-points. The mean temperature in the cofferdam space can be expressed as a function of number and capacity of heating points.

• Tribology and Lubricants
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• v.33 no.6
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• pp.296-302
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• 2017

Ball milling of elemental powders in advance and using an induction heating system for intermetallic coatings are known to enhance the reactivity of combustion synthesis. In this work, the effects of simultaneously applying these two incentive methods on the properties of intermetallic coatings are studied. Ni-Al powder compacts ball-milled with three different ball-to-powder weight ratio mixtures are synthesized and coated on mild steel by combustion synthesis in an induction heating system. Consequently, similar to an electrical heating system, the positive effects of ball milling on the combustion synthesis are confirmed in the induction heating system. The enhancement in synthetic reactivity achieved by applying the two incentive methods at the same time is greater than that by applying each incentive method separately. In particular, the enhancement is remarkable at low reaction temperature. However, there are limitations to improving the reactivity by simultaneously applying the two incentive methods to the combustion synthesis, unlike the reaction temperature. The microstructure and hardness of the coating layer are both influenced by the ball-charging ratio employed in the ball-milling process.

• Journal of Bio-Environment Control
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• v.23 no.3
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• pp.192-198
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• 2014

To establish the design criteria for seasonal heating load calculation in greenhouses, standard weather data are required. However, they are being provided only at seven regions in Korea. So, instead of using standard weather data, in order to find the method to build design weather data for seasonal heating load calculation, heating degree-hour and heating degree-day were analyzed and compared by methods of fundamental equation, Mihara's equation and modified Mihara's equation using normal and thirty years from 1981 to 2010 hourly weather data provided by KMA and standard weather data provided by KSES. Average heating degree-hours calculated by fundamental equation using thirty years hourly weather data showed a good agreement with them using standard weather data. The 24 times of heating degree-day showed relatively big differences with heating degree-hour at the low setting temperature. Therefore, the heating degree-hour was considered more appropriate method to estimate the seasonal heating load. And to conclude, in regions which are not available standard weather data, we suggest that design weather data should be analyzed using thirty years hourly weather data. Average of heating degree-hours derived from every year hourly weather data during the whole period can be established as environmental design standards, and also minimum and maximum of them can be used as reference data for energy estimation.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.4
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• pp.27-32
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• 2016

It is estimated that only heating and cooling take about one third of the total energy consumption worldwide. However, the conventional heating and cooling systems have low efficiencies. Also, boilers and electric heaters that are mostly used to generate both domestic and industrial hot water are inefficient and high energy consumers. For this reason, cascade heat pumps which are known to be very energy efficient and have less environmental impact are being promoted to replace conventional heating, cooling and hot water systems. In this study, a newly designed cascade heat pump by two-stage water heating method has been experimentally investigated. By adopting the auxiliary heat exchanger, the performance of the system was increased. The performance enhancement rate of the system could be maximized by adjusting the low stage compressor speed rather than the high stage compressor speed. The performance of the system with the auxiliary heat exchanger was enhanced by 16.5%.

• Journal of Biosystems Engineering
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• v.41 no.2
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• pp.108-115
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• 2016

Purpose: Radio frequency (RF) heating is a promising thawing method, but it frequently causes undesirable problems such as non-uniform heating. This can occur because of the food shape, component distribution, and initial temperature differences between food parts. In this study, RF heating was applied to the thawing of cylindrically shaped pork sirloin by changing the shape of electrodes and the surrounding temperature. Methods: Curved electrodes were utilized to increase the thawing uniformity of cylindrically shaped frozen meat. Pork sirloin in the shape of a half-circle column was frozen in a deep freezer at $-70^{\circ}C$ and then thawed by RF heating with flat and curved electrodes. In order to prevent fast defrosting of the food surface by heat transfer from air to the food, the temperature of the thawing chamber was varied by -5, -10, and $-20^{\circ}C$. The temperature values of the frozen pork sirloin during RF thawing were measured using fiber-optic thermo sensors. Results: After multiple applications of curved electrodes resembling the food shape, and a cooled chamber at $-20^{\circ}C$ the half-cylindrically shaped meat was thawed without surface burning, and the temperature values of each point were similarly increased. However, with the parallel electrode, the frozen meat was partially burned by RF heating and the temperature values of center were overheated. The uniform heating rate and heat transfer prevention from air to the food were crucial factors for RF thawing. In this study, these crucial factors were accomplished by using a curved electrode and lowering the chamber temperature. Conclusions: The curved shape of the electrode and the equipotential surface calculated from the modeling of the parallel capacitor showed the effect of uniform heating of cylindrically shaped frozen food. Moreover, the low chamber temperature was effective on the prevention of the surface burning during RF thawing.

• Journal of Conservation Science
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• v.30 no.2
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• pp.149-156
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• 2014

Low oxygen treatment and heating treatment are used to prevent insects in the field of food science. These eco-friendly control methods can be applied to biological control technique in conservation treatment of organic cultural properties. To evaluate material stability, low-oxygen treatment and low oxygen treatment are applied to wood, pigment, paper and textile that are related to historical wooden buildings. As a result, wood moisture content declined after low oxygen treatment. But decline rate is a little, so it can be expected to turn back original state as time passes. And test result on pigment, paper, textile of chrominance and strength of test materials are stable. But after heating treatment, pigments are separated.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.1
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• pp.3-9
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• 2010

Titanium and its alloys were brazed in the range of $850-950^{\circ}C$ within 10 min. of brazing time using expensive infra red or other heating methods. However, brazing time needs to be extended to get temperature-uniformity for mass production by using continuous belt type furnace or high vacuum furnace with low heating rate. This study examined effects of holding temperature for 60 min, on microstructure and mechanical properties of titanium alloys. Mechanical properties of titanium alloys were drastically deteriorated with increasing holding temperature followed by grain growth. Maximum holding temperatures for CP (commercial pure) titanium and Ti-6Al-4V were confirmed as $800^{\circ}C$ and $850^{\circ}C$, respectively. Both titanium alloys were successfully brazed at $800^{\circ}C$ for 60 min. with the level of base metal strengths by using Zr based filler metal, $Zr_{54}Ti_{22}Ni_{16}Cu_8$.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2254-2255
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• 2008

Thermoforming is one of the most versatile and economical process to produce polymer products. The drawback of thermoforming is difficult to control thickness of final products. Temperature distribution affects the thickness distribution of final products, but temperature difference between surface and center of sheet is difficult to decrease because of low thermal conductivity of ABS material. In order to decrease temperature difference between surface and center, heating profile must be expressed as exponential function form. In this study, Finite Difference Method was used to find out the coefficients of optimal heating profiles. Through investigation, the optimal results using Finite Difference Method show that temperature difference between surface and center of sheet can be remarkably minimized with satisfying Temperature of Forming Window.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.206-210
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• 2012

Ground source heat pump is a central heating and cooling system that pumps heat to or from the ground. Building Integrated Geothermal system used in this experiment is one of the Ground Source Heat Pump Systems which utilize energy pile. The purpose of this study is to evaluate heating performance of the system. The building is a low-energy experiment apartment in Yonsei University Songdo Campus and the subject is one of the energy reduced houses in this apartment. In the experiment, indoor temperature, outdoor temperature and the inlet and outlet temperature of ground heat exchanger and subject model, were measured. Then the heat pump's Coefficient of performance(COP) of the heat pump was calculated. As a result, the COP of heat pump is 4-5. Although the depth of the ground heat exchanger in this experiment is shallower than usual heat exchanger, the result of heating performance of this system was good as well.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.579-585
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• 2009

Recently, Vertical-Closed Loop system using geothermal which is the most efficient among the building cooling and heating systems is coming into wide spread due to assistance of domestic policies. However, there is a limitation that a design of ground heat exchanger taking 60% of construction cost is done by GLD and GLHEPRO programs without specific guidelines and consideration on Entering Water Temperature(EWT). For getting an optimal EWT, we analyzed the costs for construction of ground heat exchanger and cooling and heating for 15 years. In the results, reduction of construction costs as the length of ground heat exchanger shortens was much greater than increase of the electrical power consumption as COP gets low. EWT that COP of heat pump can be 3.76 or above was below $31^{\circ}C$ in cooling and was over $5^{\circ}C$ in heating.