• KIEAE Journal
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• v.16 no.6
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• pp.167-172
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• 2016

Purpose: The solar water heater with natural circulation has been used for several decades in the world as it is automatically operated without a pump and controller and is easy to maintain and repair. After the subsidy was offered from 2012, the solar water heater with natural circulation is becoming increasingly popular in Korea. Recently, the development of a wall-integrated solar water heater, which improves the applicability of buildings and prevents the overheating in the summer, is being developed. On the other hand, the design and performance evaluation data of solar water heaters are very inadequate, and analysis of heat and flow is required to develop a new type of solar water heater. Method: Therefore, in this study, we proposed a new simplified system analysis model that reflects heat and pressure loss from the test results of KS B ISO 9806-1 (Solar collector test method), assuming that the collector is a simple pipe system, the validity of which was verified through experiments. Result: As a result, first, the RMSE of the system circulation flow rate and the average temperature of the inlet and outlet of the collector according to the experimental results and the simulation are 0.05563 and 0.88530, respectively, which are very consistent. Secondly, the mass flow rate is increased linearly with the increase of the solar radiation, and the mass flow rate is 0.0104 ~ 0.0180kg/s in the range of $200{\sim}380W/m^2$ of solar irradiance. Compared with the test flow rate 0.0764kg / s of the test collector, it showed a level of less than 20%.

• Journal of the Korean Institute of Gas
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• v.5 no.3 s.15
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• pp.1-8
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• 2001

This study was carried out for the purpose of determination of maintenance period and investigation of weak point due to freeze when the gas heater of KOGAS valve station Is not operated in winter season. 3-dimensional non-linear numerical simulation was conducted in order to predict the time and location which bath water in heater reaches to ice point. FLUENT V 5.0, commercial code, is used for thermal fluid flow analysis. We thought this was problem of heat conduction solving the energy equation and modeled gas heater by using the real geometry and scale for performing the 3-dimensional simulation. It was analyzed complex heat transfer phenomena considering convection due to air on surface, conduction in insulation material, natural convection of liquid in heater and heat loss through the pipe.

• Journal of the Korean Solar Energy Society
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• v.34 no.6
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• pp.49-56
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• 2014

Research about hybrid solar air-water heater that can make heated air and hot water was conducted as a part of improving efficiency of solar thermal energy. At this experiment, ability of making heating air and hot water was investigated and compared with traditional solar air heater and flat plate solar collector for hot water when air or liquid was heated respectively. Comparing hybrid solar air-water heater that used in this experiment to other solar air heater studied already, it has a lower efficiency at same mass flow rate. Air channel structure, fin's shape and arrangement in the air channel result in these difference then the ability of air heating need to be improved with changing these thing. In case of making hot water, performance was shown as similar with traditional system although the air channels were established beneath absorbing plate. But the heat loss coefficient was shown higher value by installing of air channel. Also the performance of hot water making was shown lower value at same liquid mass flow rate with traditional flat plate solar collector for hot water. So the necessity of performance improvement at lower mass flow rate of each heating medium can be confirmed.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1228-1230
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• 2005

This paper deals with design of heater trigger switching in a persistent current system(PCS) by finite element method(FEM) analysis of YBCO coated conductor(CC) tape. Most promising superconducting wire is YBCO coated conductor tape in these days for its high n value and critical current independency from external magnetic field. It is expected to be used many superconducting application such as fault current limiter and cable etc. The superconducting magnet which is operated in persistent current mode in SMES, NMR, MRI and MAGLEV has many advantages such as a high uniformity of a magnetic field and reducing a thermal loss. A PCS system consists of magnet power supply (MPS) which energized current to a magnet, heater, a coated conductor tape for switching, and superconducting magnet. In this paper, the characteristic of thermal quench of the YBCO CC tape and BSCCO tape by heater trigger analyzed by FEM. And optimal length of heater is calculated by temperature and time analysis. This heater trigger analysis is expected to be a basic concept of PCS application design.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.253-261
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• 1987

Thermoacoustic oscillation of an air column induced by heated wires is investigated analytically and experimentally. Acoustic power generation from a single heater wire is estimated based on the result of heat transfer analysis and expressed in terms of the efficiency factor indicating the conversion efficiency from heat to acoustic energy. It is shown that the efficiency factor becomes maximum when the wire radius is the order of the coustic boundary layer thickness and the flow velocity is close to the thermal diffusion velocity. Onset condition of the column oscillation is obtained by equating the acoustic power generation at the heater to the power loss due to thermoviscous dissipation at the tube wall and the convection and radiationloss at the open ends of the tube. In estimating the acoustic power generation, the heater is treated as a stretched single wire by correcting the flow velocity to take into account the interactions between adjacent heater wires. Experiment is performed by using a spiral heater of 1mm diameter in an air column of 37mm diameter. The heat input to drive the oscillation is measured and compared with the theoretical prediction. A good agreement is found between the theory and experiment, which is regarded as a substantial verification of the present analysis.

• Journal of IKEEE
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• v.25 no.3
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• pp.534-539
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• 2021

Induction heating method that allows the maximum heating power to be delivered by varying switching frequency in the inductance change of the work coil of induction heater was proposed in this paper. Depending on the type of work piece in the work coil and proximity to the work coil, the resonance frequency of the resonant circuit will be changed. It may be difficult to deliver the maximum power due to the damage of the induced heater element or switching loss depending on the resonance frequency and switching frequency operating relationship. The switching frequency was variable to maintain the maximum power transmission by sensing the heating power due to the change of the resonance frequency. Through the result of the proposed method that can be controlled within the required output change range according to the change of the switching frequency corresponding to the change of the resonance frequency, the induction heater having a variable switching frequency characteristic that can transmit almost constant output power (within 0.43 dB) power efficiency was achieved.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.4
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• pp.325-330
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• 2005

A lever type CO micro gas sensor was fabricated by MEMS technology. In order to heat up the gas sensing material, $SnO_2$, to a target temperature, a micro heater was built on the gas sensor. The heater and electrodes were hanged on the air as a bridge type to minimize the heat loss to the silicon base. The sensing material laid on the heater and electrodes and did not contact with the silicons base. The temperature distribution of micro gas sensor was analyzed by a CFD program, FLUENT. The results showed that the temperature of silicon wafer base was almost similar to that of the room temperature, which indicates that the heat generated at the micro heater heated up effectively the sensing material. The required electric current of micro heater to heat up the sensing material to the target temperature could be predicted.

• Journal of the Society of Disaster Information
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• v.10 no.4
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• pp.583-597
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• 2014

Fire caused by heater has various causes as many as the types of heater. also, lots of damage of human life and property loss are caused, since annually continuous fire accident by heater in traditional market is frequently occurring. There are not many cases of fire due to heater in most of residential facilities such as general house, apartments, etc., because they are supplied with heating boiler, however the restaurant, store and office of the market, sports center, factory, workplace, etc. still use heater, e.g. oilstove, electric heater, etc., so that they are exposed to fire hazard. Also, when investigating the number of fire due to heater, it was analyzed to occur in order of home boiler, charcoal stove, oilstove, gas heater/stove, electric stove/heater, the number of fire per human life damage was analyzed in order of gas heater/stove, oil heater/stove, electric heater/stove, briquette/coal heater. Also, gas and oil related heater were analyzed to have low frequency, however, with high fire intensity. Therefore, this research aimed at considering more scientific fire inspection and identification approach by reenacting and reviewing fire outbreak possibility caused by combustibles' contact and conductivity under the normal condition and abnormal condition in respect of ignition hazard, i.e. minimum ignition temperature, carbonization degree and heat flux along with it, due to oilstove and electric stove, which are still frequently used in public use facility, traditional market, and, of which actual fire occurrence is the most frequent. As the result of reenact test, ignition hazard appeared very small, as long as enough heat storage condition is not made in both test objects(oilstove/electric stove), however carbonization condition was analyzed to be proceeded per each part respectively. Eventually, transition to fire is the ignition due to heat storage, so that it was analyzed to ignite when minimum heat storage temperature condition of fire place is over $500^{\circ}C$. Particularly, in case of quartz pipe, the heating element of electric stove, it is rapidly heated over the temperature of $600^{\circ}C$ within the shortest time(10sec), so that the heat flux of this appears 6.26kW/m2, which was analyzed to result in damage of thermal PVC cable and second-degree burn in human body. Also, the researcher recognized that the temperature change along with Geometric View Factor and Fire Load, which display decrease of heat, are also important variables to be considered, along with distance change besides temperature condition. Therefore, the researcher considers that a manual of careful fire inspection and identification on this is necessary, also, expects that scientific and rational efforts of this research can contribute to establish manual composition and theoretical basis on henceforth fire inspection and identification.

• Journal of the Korean Solar Energy Society
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• v.27 no.4
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• pp.121-128
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• 2007

Convective heat loss from solar tower receiver is experimentally investigated in wind tunnel with tilt angles and operating conditions. In order to simulate the receiver, an electric heater, which is made of aluminum (width : 100 mm, height : 100mm) is used and installed in the wind tunnel. The convective heat loss from the receiver is dependent on the direction and the velocity of the wind and the surface temperature of the receiver. The tilt angle and surface temperature of the receiver are varied from 0o (cavity facing straight down) and 90o(cavity aligned horizontally) and from $150^{\circ}C$ to $250^{\circ}C$, respectively. Also, the wind speed is changed from 0 to 4m/s. The convective heat loss is obtained by measuring consumed power to the heater to maintain the desired surface temperature. It is concluded that Nusselt number increases with increasing wind speed for all cases. Especially, it is showed that Nusselt number can be maximized when the tilt angle is 30o.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05a
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• pp.197-201
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• 2002

This paper presents optimized design, fabrication and thermal characteristics of micro-heaters for thermal MEMS (micro electro mechanical system) applications using SOI and trench structures. The micro-heaters are based on a thermal measurement principle and contains thermal isolation regions of 10 ${\mu}m$-thick Si membranes consisting of oxide-filled trenches in the SOI membrane rim. The micro-heaters were fabricated with Pt-RTD on the same substrate via MgO buff layer between Pt thin-film and $SiO_2$ layer. The thermal characteristics of micro-heater with trench-free SOI membrane structure was $280^{\circ}C$ at input power 0.9 W; in the presence of 10 trenches, it was $580^{\circ}C$ due to reduction of the external thermal loss. Therefore, a micro-heater with trenches in SOI membrane rim structure provides a powerful and versatile alternative technology for enhancing the performance of micro-thermal sensors and actuators.