• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.4
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• pp.577-588
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• 1995

A numerical study is made on the melting process of an unconstrained ice inside an isothermal ice-ball capsule. The unmelted ice core is continuously ascending on account of buoyancy forces. Such a buoyancy-assisted melting is commonly characterized by the existence of a thin liquid film above the ice core. The present study is motivated to present a full-equation-based analysis of the influences of the initial subcooling and the natural convection on the fluid flow associated with the buoyancy-assisted melting. In the light of the solution strategy, the present study is substantially distinguished from the existing works in that the complete set of governing equations in both the melted and unmelted regions are resolved in one domain. Numerical results are obtained by varying the wall temperature and initial temperature. The present results reported the transition of the flow pattern in a spherical capsule, as the wall temperature was increased over the density inversion point. In addition, time wise variation of the shapes for the liquid film and the lower ice surface, the time rate of change in the melt volume fraction and the melting distance at symmetric line is analyzed and is presented.

• FLOWER RESEARCH JOURNAL
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• v.18 no.3
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• pp.186-192
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• 2010

An infrared heating system, installed in a small venlo-type glasshouse ($280m^2$) in Gyeongsang National University, Jinju, Korea, was used to investigate its heating effect with potted Phalaenopsis, Schefflera arboricola 'Hongkong', Ficus elastica 'Variegata', and Rosa hybrida 'Yellow King' as the test plants. Temperature changes in test plants with the system turned 'On' and 'Off' were measured by using an infrared camera and the consumption of electricity by this infrared heating system was measured and analyzed. In potted Phalaenopsis, when the set air temperature of the greenhouse was $18^{\circ}C$, temperature of leaves and the growing medium were $22.8{\sim}27^{\circ}C$ and $21.3{\sim}24.3^{\circ}C$, respectively. In such tall plants as Schefflera arboricola 'Hongkong' and Ficus elastica 'Variegata', the upper part showed the highest temperature of 24.0 and $26.9^{\circ}C$, respectively. From the results of temperature change measurements, the plant temperatures were near or above the set point temperatures with some fluctuations depending on the position or distance from the infrared heating system. When air temperature between night and dawn dropped sharply, plant temperatures were maintained close to the set temperature ($18^{\circ}C$). There was a significant difference between 'On' and 'Off' states of the infrared heating system in average temperatures of root zone and leaf: 21.8 and $17.8^{\circ}C$ with the system 'On' and 20.4 and $15.5^{\circ}C$ with the system 'Off', respectively, in a cut rose Rosa hybrida 'Yellow King'. The heating load was about $24,850{\sim}35,830kcal{\cdot}h^{-1}$, which comes to about 27,000~40,000 won in Korean currency when calculated in terms of the cost of heating by a hot water heating system heated by petroleum. The cost for heating by the infrared heating system was about 35% of that of a hot water heating system. With the infrared heating system, the air temperature during the night was maintained slightly lower than the set point air temperature, probably due to the lack of air tightness of the glasshouse. Therefore, glasshouses with an infrared heating system requires further investigation including the installation space of the heat-emitting units, temperature sensor positions, and convection.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.7
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• pp.711-717
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• 2007

Location information will become increasingly important for future Pervasive Computing applications. Location tracking system of a moving device can be classified into two types of architectures: an active mobile architecture and a passive mobile architecture. In the former, a mobile device actively transmits signals for estimating distances to listeners. In the latter, a mobile device listens signals from beacons passively. Although the passive architecture such as Cricket location system is inexpensive, easy to set up, and safe, it is less precise than the active one. In this paper, we present a passive location system using Cricket Mote sensors which use RF and ultrasonic signals to estimate distances. In order to improve accuracy of the passive system, the transmission speed of ultrasound was compensated according to air temperature at the moment. Upper and lower bounds of a distance estimation were set up through measuring minimum and maximum distances that ultrasonic signal can reach to. Distance estimations beyond the upper and the lower bounds were filtered off as errors in our scheme. With collecting distance estimation data at various locations and comparing each distance estimation with real distance respectively, we proposed an equation to compensate the deviation at each point. Equations for proposed algorithm were derived to calculate relative coordinates of a moving device. At indoor and outdoor tests, average location error and average location tracking period were 3.5 cm and 0.5 second, respectively, which outperformed Cricket location system of MIT.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.2
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• pp.171-179
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• 1997

During the day time in summer, peak of air conditing load, and electric power management system lies under overloaded condition. The reason is the enlarged peak load value of electric power caused by increased air-cooling load in summer. To prevent load concentration during day time and overloaded condition of power management system, some energy storage methods are suggested. One of these methods is ice storage system. Water has some good properties as P.C.M.(Phase Chang Material) : Its melting point is the range of required operation temperature. It has large specific latent heat and is chemically stable compared to other organic or inorganic substances. It is cheap and easy to treat. This study represents experimental results of heat transfer characteristics of P.C.M. under the outward melting process in a vertical cylinder. We experimented with twelve combinations of conditions, i.e., three different inlet temperatures($7^{\circ}C,\;4^{\circ}C\;and\;1^{\circ}C$), two working fluid directions(upward and downward), and two aspect ratios, H/R(4 and 2). At the inlet temperature of $7^{\circ}C$ and $4^{\circ}C$, there was temperature stagnation region where the temperature of P.C.M. remains constant at $4^{\circ}C$ regardless of aspect ratio and direction of working fluid. This temperature stagnation occurs as the water, at its maximum density, flows down to the lower region. The phase change interface formed bell-shaped curve as the melting process continued. With a new set of conditions(4H/R, inlet temperature $4^{\circ}C$ and $1^{\circ}C$, downward/upwerd inlet direction), the movement of phase change interface was faster when the working flued inlet direction was downward. With the same set of conditions, melting rate and total melting energy were larger when the working fluid inlet direction was downward. The results were reversed when the other sets of conditions were applied.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.12
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• pp.2380-2386
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• 2017

Fresh agricultural product in Korea are currently being exported overseas through expensive air transportation, supported by the governments's farm export subsidies. However all members of the World Trade Organization(WTO) must halt government subsidies by 2023. Accordingly, it is necessary to use marine transport capable of carrying freight at low cost. Reefer containers are used for marine transportation of fresh produce but it have a problem due to the temperature difference inside the reefer container which causes of fresh cargo and drop in freshness during sea transportation. In order to solve the problem, we developed a temperature control algorithm for reefer container that maintain a constant temperature and minimizes the deviation inside reefer container. The result showed that the maintained a constant temperature within a maximum of $0.5^{\circ}C$ based on the set-point of $4.0^{\circ}C$ inside reefer container.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.1
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• pp.34-41
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• 2006

The objectives of this study were to investigate the affecting factors on streaming current(SC) and to evaluate set point(SP). For the study, a pilot scale apparatus with a capacity of 12 L/min was operated at Guui water intake of Seoul. SC was monitored with varying poly aluminium chlorides(PACs) dose and water quality parameters like conductivity, turbidity, temperature, and pH. The removal efficiencies were evaluated in terms of turbidity and dissolved organic carbon(DOC) with varying coagulation conditions. The effects of affecting factors on SC and SP were also estimated. According to the result observed from the variation of SC with water quality parameters during the experimental period, tendencies of SC and conductivity were very similar, and SC and conductivity had a strong linear relation. At the optimum condition of coagulation, SP decreased as the rainy season changed to the dry season, during the experimental period. Especially, in condition of low turbidity, conductivity had relatively more effect on SC than turbidity. As conductivity increased, SP decreased and coagulant dose per unit increase of SC gradually increased. In view of the results so far obtained, it may be possible to determine the SP range considering the real time variation of water quality, especially conductivity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.3
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• pp.371-379
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• 1997

A theoretical study for a forced uniform flow impinging on a rotating disk, typically involved in Chemical Vapor Deposition(CVD) and Vapor-phase Axial Deposition(VAD) processes, has been carried out. A set of exact solutions for flow and temperature fields are developed by employing a similarity variable obtained from force balance on a control volume near the disk. The solutions depend on the rotating speed of the disk, .omega., and the forced flow speed toward the disk, a. For constant forced flow speed, the overall boundary layer thickness decreases when the rotating speed increases. Approximately 5%, 15%, and 30% decreases of the thickness are obtained for .omega./a = 2, 5, and 10, respectively, compared to the case of .omega./a = 0 (axisymmetric stagnation point flow). For constant rotating disk speed the boundary layer thickness immediately decreases as the forced flow speed increases, compared to the case of .omega./a .rarw. .inf. (induced flow near a rotating disk). Effects of .omega. and a on heat transfer coefficient are studied and explained with the boundary layer characteristics.

• Journal of KIISE:Databases
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• v.34 no.4
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• pp.369-377
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• 2007

Histogram is one of tools that efficiently summarize data, and it is widely used for selectivity estimation and approximate query answering. Existing histogram construction algorithms are applicable to point data represented by a set of values. As often as point data, we can meet interval data such as daily temperature and daily stock prices. In this paper, we thus propose the histogram construction algorithms for interval data by extending several methods used in existing histogram construction algorithms. Our experiment results, using synthetic data, show our algorithms outperform naive extension of existing algorithms.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.452-455
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• 2004

MSC (Multi-Spectral Camera) system is a remote sensing instrument to obtain high resolution ground image. EOS (Electro-Optic System) for MSC mainly consists of PMA (Primary Mirror Assembly), SMA (Secondary Mirror Assembly), HSTS (High Stability Telescope Structure) and DFPA (Detector Focal Plane Assembly). High performance of EOS makes it possible for MSC system to provide high resolution and high quality ground images. Temperature of the EOS needs to be controlled to be in a specific range in order not to have any thermal distortion which can cause performance degradation. It is controlled by full redundant CPU based electronics. The validity of thermistor readings can be checked because a few thermistors are installed on each control point on EOS. Various kinds of thermal control logics are used to prevent 'Single Point Failure'. Control logic has a few set of database in order not to be corrupted by SEU (Single Event Upset). Even though the thermal control logic is working automatically, it can also be monitored and controlled by ground-station operator. In this paper, various ways of thermal control logic for EOS in MSC will be presented, which include thermal control mode and logic, redundancy design and status monitoring and reporting scheme.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.206-211
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• 2016

Various applications require dry air at low temperature, such automation equipment, semiconductor manufacturing, chemical production lines, and coating processes for the shipbuilding industry. Four evaporators for low temperature (below $0^{\circ}C$) were installed for a dehumidification system. Moist air is cooled sequentially over three evaporators. The first evaporator has an evaporation temperature of $13^{\circ}C$, that of the second evaporator is $5^{\circ}C$, and that of the third evaporator is maintained at $-1.3^{\circ}C$. In the fourth evaporator implantation thereby the moisture contained in the moisture air. A pressure regulator (CPCE 12) is used at this point and is defrosted when the vapor pressure is below a set value. The non-implantation moisture of the air is a heating system that uses the waste heat of a condenser with high temperature. It develops the cooling type's dehumidifier, which is important equipment that prevents the destruction of protein and measures the temperature and humidity at each interval by changing the front air velocity from 1.0 m/s to 4.0 m/s. The cooling capacity was also calculated. The greatest cooling capacity was 1.77 kcal/h for a front air velocity of 2.0 m/s