• Journal of Energy Engineering
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• v.20 no.4
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• pp.303-308
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• 2011

The present study has been carried out to predict the heat transfer characteristics of reverse heat loss method for a residential refrigerator by using numerical analysis and corresponding experiment. From the measured values of temperature and heat input, one can conclude that, the temperature inside the refrigerator has a nearly linear relationship with heat input. The effect of gasket heat loss was examined with the change of thermal conductivity of gasket region. The appropriate thermal conductivity of gasket region was acquired from the comparison of heat losses with the experimental result and numerical analysis. The result of calculated heat losses had accuracy within 1.8% error with the experimental result. With the selected thermal conductivity of gasket region, the effectiveness of reverse heat loss method was examined with the change of thermal conductivity of vacuum insulation panel.

• Journal of Bio-Environment Control
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• v.22 no.1
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• pp.73-79
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• 2013

An experiment was conducted to study incidences of heat loss in greenhouse in Gyeongnam province using thermal imaging camera in order to determine ways minimizing greenhouse heat loss. Measurements of this work showed that temperature differences between two experiment zones before and after installation of thermal curtains were about $2.0{\sim}3.0^{\circ}C$ and $1.0{\sim}2.0^{\circ}C$ respectively. There was a high correlation between the temperature data measured using a thermal imaging camera and a temperature sensor. There was no serious difference among areas, but between places on the first and second floor with thermal curtains for heat insulation, there was a relatively larger heat loss on the first floor than the second floor. Then in general the greenhouse types had no particular bearing on this matter, there was a relatively large heat loss in the parts of side wall window, the gaps and the parts folded of horizontal thermal curtains, the gutter parts, and the gaps of thermal curtain in the side wall window and facade back side for heat insulation, aren't completely sealed. It was found that there was a substantial heat loss due to infiltration through cracks on covering material, doors, ventilating openings, roof gables and floors, in particular.

• Korean Chemical Engineering Research
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• v.44 no.3
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• pp.270-276
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• 2006

In this study, heat loss through free surface of water contained in bathtub due to conduction and evaporation has been analyzed. As a result of this study, a relational equation has been derived based on the basic theory of heat transfer to evaluate the performance of bath tubes. The derived equation was rational and quantitative. The major heat loss was found to be due to evaporation. Moreover, it has been found out that the speed of heat loss depends more on the humidity of the bathroom than the temperature of water contained in the bathtub. So, it is best to maintain the temperature of bathtub water to be between 41 to $45^{\circ}C$ and the humidity of bathroom to be 95％.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.1
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• pp.45-54
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• 2012

Optimization of the asymmetric trapezoidal fin with various upper lateral surface slope is made using a two-dimensional analytic method. For the fixed fin base height, the optimum heat loss, fin length and effectiveness are represented as inner fluid convection characteristic number, fin base thickness, fin base height, fin shape factor and ambient convection characteristic number. For this optimum procedure, the optimum heat loss is defined as 95% of the maximum heat loss from the fin. One of the results shows that optimum heat loss and effectiveness seems independent of the fin shape factor while optimum fin length decreases almost linearly as the fin shape factor increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.3
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• pp.229-235
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• 2010

Optimum values of fin performance and dimensions for an annular fin with a rectangular profile and a pipe with variable inner radius are determined by using a variable separation method. The range of ambient convection characteristic number that results in optimum heat loss is listed. The optimum heat loss, corresponding optimum fin effectiveness, fin length, and fin height are presented as a function of the inner radius of the pipe, inner fluid convection characteristic number, fin volume, and ambient convection characteristic number. One of the results shows that the optimum heat loss, fin effectiveness and fin length increase linearly with the inner radius of the pipe when both the fin volume and fin-base radius are fixed.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.5
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• pp.14-22
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• 2007

A reversed trapezoidal fin with variable lateral surface slope is optimized using a two-dimensional analytic method. For a fin base boundary condition, convection from the inside fluid to the inside wall and conduction from the inside wall to the fin base are considered. Heat loss from the fin tip surface is not ignored. The maximum heat loss at the practical fin length, the corresponding optimum fin efficiency, fin length and fin base height are presented as a function of the fin inside and outside convection characteristic numbers. One of the results shows that the optimum fin shape becomes 'fatter and shorter' as the ratio of fin tip height to base height increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.7
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• pp.729-738
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• 2010

The characteristics of lifted butane flames diluted with nitrogen have been investigated experimentally in order to elucidate the mechanism of individual flame oscillation modes. Flame oscillations in laminar free-jet lift-off flames are classified into the following five regimes: a stabilized lift-off regime (I), a heat-loss-induced oscillation (II), a buoyancy-induced oscillation along with a heat-loss-induced oscillation (III), a combined form of an oscillation prior to blow-out and a heat-loss-induced oscillation (IV), and a combination of an oscillation prior to blow-out and a buoyancy-induced oscillation along with a heat-loss-induced oscillation (V). The characterization of the individual flame oscillations modes are presented and discussed using Strouhal numbers and their relevant parameters by the analysis of the power spectrum for temporal variation of the lift-off height.

• 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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1465-1472
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• 2009

The effect of heat loss rate on NOx formation of $CH_4/air$premixed flame were examined numerically in a perfectly stirred reactor. The following conclusions were drawn. Under the adiabatic wall condition, an increase in the residence time causes a remarkable increases in NOx emission. Under the heat loss conditions, however, NOx decreases significantly as the heat transfer coefficient and residence time increase. As the heat loss rate increases, Thermal NO mechanism and Re-burning NO mechanism play an important role in the NOx reduction, but Prompt NO mechanism and $N_2O$-intermediate NO mechanism lead to the increase in NOx production. Although the NOx formation is actually related to complex NOx mechanism with the changes in the heat transfer coefficient and residence time, it was found that NOx concentration can be represented by independent Thermal NO mechanism. From these results, new NOx correlation combined with the heat loss rate and residence time was suggested for predicting the NOx concentration in a practical $CH_4/air$premixed combustor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1383-1389
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• 2011

The current study focuses on the consistent analysis of heat transfer in multichannel volumetric solar receivers used for concentrating solar power. Changes in the properties of the absorbing material and channel dimensions are considered in an optical model based on the Monte Carlo ray-tracing method and in a one-dimensional heat transfer model that includes conduction, convection, and radiation. The optical model results show that most of the solar radiation energy is absorbed within a very small channel length of around 15 mm because of the large length-to-radius ratio. Classification of radiation losses reveals that at low absorptivity, increased reflection losses cause reduction of the receiver efficiency, notwithstanding the decrease in the emission loss. As the average temperature increases because of the large channel radius or small mass flow rate, both emission and reflection losses increase but the effect of emission losses prevails.