• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.857-864
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• 2012

A linear stability analysis of a diffusion flame with radiation heat loss is performed to identify linearly unstable conditions for the Damk$\ddot{o}$hler number and radiation intensity. We adopt a counterflow diffusion flame with unity Lewis number as a model. Near the kinetic limit extinction regime, the growth rates of disturbances always have real eigenvalues, and a neutral stability condition perfectly falls into the quasi-steady extinction. However, near the radiative limit extinction regime, the eigenvalues are complex, which implies pulsating instability. A stable limit cycle occurs when the temperatures of the pulsating flame exceed the maximum temperature of the steady-state flame with real positive eigenvalues. If the instantaneous temperature of the pulsating flame is below the maximum temperature, the flame cannot recover and goes to extinction. The neutral stability curve of the radiation-induced instability is plotted over a broad range of radiation intensities.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.1 s.256
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• pp.99-108
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• 2007

In this study, the NOx formation characteristics of one-dimensional $CH_4$/Air premixed flame using detailed-kinetic chemistry are examined numerically. The combustor length and the amount of heat loss are varied to investigate the effect of residence time and heat loss on the NOx formation in a post-flame region. In the flame region, NO is mainly produced by the Prompt NO mechanism including $N_2$O-intermediate NO mechanism over all equivalence ratios. However, thermal NO mechanism is more important than Prompt NO mechanism in the post-flame region. In the case of adiabatic condition, the increase of combustor length causes the remarkable increase of NO emission at the exit due to the increase of residence time. On the other hand, NO reaches the equilibrium state in the vicinity of flame region, considering radiation and conduction heat losses. Furthermore the NO, in the case of $\phi$=1.2, is gradually reduced in the downstream region as the heat loss is increased. From these results, it can be concluded that the controls of residence time and heat loss in a combustor should be recognized as an important NOx reduction technology.

• Journal of Mechanical Science and Technology
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• v.14 no.12
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• pp.1403-1411
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• 2000

Heat losses from the receivers for a dish-type solar energy collecting system constructed at Korea Institute of Energy Research are analyzed. The Stine and McDonald's model is used to estimate the convection loss. The Net Radiation method and the Monte-Carlo method are used to calculate the radiation heat transfer rate from the inside surface of the receiver to the surroundings. Two different receivers are suggested here and the performances of the receivers are estimated and compared with each other based on the prediction of the amount of heat losses from the receivers. The effects of the receiver shape and the radiation properties of the surface on the thermal performance are investigated. The performance of Receiver I is better than that of Receiver II, and the amount of solar irradiation that is not captured by the captured by the receiver after being reflected by the concentrator becomes significant if the temperature of the working fluid is low.

• Journal of the Korean Society of Safety
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• v.23 no.6
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• pp.84-90
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• 2008

The mass loss rate and heat release rate of puzzle mats were analysed using variable external irradiation level. Five samples of puzzle mat were tested in this study : Type A, B, C, D and E. Type A, B and C are all general grades whereas Type D and E are both Flame retardant grades. Incident heat fluxs of $25kW/m^2$, $35kW/m^2$, $50kW/m^2$ and $70kW/m^2$ were selected for these experiments. All samples were tested in the horizontal orientation and were wrapped in a single layer of aluminum foil. Each sample was nominally 20mm thick and 100mm square. The combustion heat and mass loss rate were carried out from Oxygen bomb calorimeter and mass loss calorimeter according to ISO 5660-1 respectively. Heat release rates were calculated using the equation ${\dot{Q}}=A_f{\dot{m}}"_X{\Delta}H_c=0.75A_f{\dot{m}}"{\Delta}H_c$. where $A_f$ is the horizontal burning area of the sample, $\dot{m}"$ is mass loss rate per unit area, ${\Delta}H_c$ is complete heat of combustion and 0.75 is combustion efficiency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.29-35
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• 2001

Radiation-induced oscillatory instability in CH$_4$/Air diffusion flames is numerically investigated by adopting detailed chemistry. Counterflow diffusion flame is employed as a model flamelet and optically thin gas-phase radiation is assumed. Attention is focused on the extinction regime induced by radiative heat loss, which occurs at low strain rate. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Depending on the initial strain rate and the amount of perturbed strain rate, transient evolution of the flame exhibits various types of flame-evolution behaviors. Basically, the dynamic behaviors can be classified into two types, namely oscillatory decaying solution and diverging solution leading to extinction.

• Journal of Environmental Science International
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• v.17 no.6
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• pp.689-698
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• 2008

Numerical study is conducted to predict effects of radiative heat loss and fuel composition in synthetic gas diffusion flame diluted with $CO_2$. The existing reaction models in synthetic gas flames diluted with $CO_2$ are evaluated. Numerical simulations with and without gas radiation, based on an optical thin model, are also performed to concrete impacts on effects of radiative heat loss in flame characteristics. Importantly contributing reaction steps to heat release rate are compared for synthetic gas flames with and without $CO_2$ dilution. It is also addressed that the composition of synthetic gas mixtures and their radiative heat losses through the addition of $CO_2$ modify the reaction pathways of oxidation diluted with $CO_2$.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.2
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• pp.67-73
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• 2010

Unlike Urban building, horticultural facilities has a lot of heat loss through plastic or glass covering material which could be much influential to growing plant and consuming energy for heating greenhouse. In many cases, heat loss from a break of cover, a gap of joint sealing, the entrance to greenhouse and windows for ventilation are the main factors considered in calculating the heating load for horticultural facilities. however the normal observation through human eye and digital camera could not recognize where the heat loss occurred. but the infrared thermal image camera with detecting thermal difference could be very effective for noticing heat loss by analyzing infrared thermal image. In this study, greenhouse structure, covering material, internal and external provisions for Horticultural facilities were surveyed in different sites and Infrared thermal camera shooting and image analysis were performed for auditing heat loss from cultivation facilities The results from this study were that unexpected heat loss had been noticed in 7 representative cases of greenhouse such as side wall covered with single or double plastic, and the joint of horizontal thermal curtain, roof without horizontal thermal curtain, entrance to greenhouse, windows for ventilation. the most important factors for keeping heat energy were whether the horizontal thermal curtain with multifold thermal material was installed or not. The internal or external covering using multifold thermal curtain proved to be the most effective ways to keep heat energy from losing through heat transmission, heat radiation. from inside to outside the horticultural facilities.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.54-62
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• 2016

The most efficient system for converting heat to electricity, AMTEC (Alkali Metal Thermal-to-Electric Convertor), is a device that directly converts heat energy to electricity using an alkali metal (sodium) as the working fluid. The AMTEC consists of a low pressure chamber, high pressure chamber, BASE (Beta-Alumina Solid Electrolyte), and artery wick. The main heat loss of the AMTEC system occurs in the low pressure chamber. A high power generation rate is thought to be obtainable by using a high temperature in the BASE. Therefore, to reduce the radiation heat loss, 6 types of radiation shields were examined to reduce the radiative heat loss in the low pressure chamber. The power generation rate of the AMTEC varied depending on the shape of the radiation shield. CFD (Computational Fluid Dynamics) analyses were carried out to optimize the shape of the radiation shield. As a result, the optimum radiation shield was found to consist of a curvature formed at the vertical point, in which case the dimensionless temperature (condenser temperature/BASE temperature) is approximately 0.665 and the maximum power generated is calculated to be 17.69W. Increasing the distance beween the BASE and condenser leads to an increase in the power generated, and the power generated with the longest distance was 17.58 W. The shields with multiple holes and multiple horizontal layers showed power reduction rates of 0.91 W and 2.06 W, respectively.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.11
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• pp.1575-1581
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• 2014

In this paper, eddy current loss, iron loss and heat transfer of PMSG with 2,000kW capacities were analyzed for wind turbine. The PMSG with 3 split magnet was analyzed using ansoft maxwell commercial program and, generator was tested by Back to Back converter with no load condition at laboratory. Rotor surface temperature was measured by Pt100 sensors for investigating heat transfer from rotor to atmosphere. The simulation results shows 27.4kW eddy current loss in no load condition and 50.2kW eddy current loss in rated load condition with 3 split magnet, and also shows 4.3kW iron loss in no load condition and 7.3kW iron loss rated load condition. The heat transfer coefficient of convection between rotor surface and atmosphere was investigated by $9.6W/m^2{\cdot}K$. Therefore the heat transfer from rotor to atmosphere was about 17kW(54%) and from rotor to air-gap was about 14.6kW(46%) in no load condition. It is identified that the cooling system for stator have to include the 46% of iron loss, and heat dissipation structure of rotor surface have to be suggested and designed for efficiency improvement of generator.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.343-349
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• 2006

Systematic experiments in $CH_4/Air$ counterflow diffusion flames diluted with He have been undertaken to study the oscillatory instability in which lateral flame size was less than burner nozzle diameter and thus lateral heat loss could be remarkable at low global strain rate. The oscillatory instability arises for Lewis numbers greater than unity and occurs near extinction condition. The oscillation is the direct outcome from the advancing and retreating edge flame. The dynamic behaviors of extinction in this configuration can be classified into three modes; growing, harmonic and decaying oscillation mode near extinction. As the global strain rate decreases, the amplitude of the oscillation becomes larger. This is caused by the increase of lateral heat loss which can be confirmed by the reduction of lateral flame size. Oscillatory edge flame instabilities at low global strain rate are shown to be closely associated with not only Lewis number but also heat loss (radiation and lateral heat loss).