• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.2
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• pp.68-82
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• 2018

Radiant floor heating systems with capillary tubes are energy saving systems in which hot water is circulated into capillary tube with a small diameter. In this study, the heating performance of capillary tube system is investigated in an experimental study and a simulation model. The results of the study showed that, the capillary tube radiant floor heating system maintains a more stable floor surface temperature in comparison a PB pipe system. In terms of energy consumption, the capillary tube radiant floor heating system proved to be more efficient than the PB pipe heating system at $40^{\circ}C$ of low temperature hot water supply. The difference between water temperature and room temperature can be held low for heating which saves energy. Low temperature radiant floor heating system with capillary tubes have significant advantages such as health improvement, low energy cost, optimum use of heat source(boiler) and higher operational efficiency.

• Journal of Power System Engineering
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• v.8 no.2
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• pp.24-30
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• 2004

In this paper, the optimal heating pattern of the furnace is sought to reduce the unnecessary energy loss. A finite difference method was used to estimate the transient temperature field of the billet in a furnace. Heat conduction equations were used in the interior nodes of the billet, while energy balances for conduction, convection, and radiation were considered in the boundary nodes. Several heating patterns for the furnace were tested and subsequently compared each other. The results showed that the temperature in the preheating zone should be set to relatively low. The temperature distributions of the billet are quite different from each other when different heating pattern are used, even though the heating patterns have the same amount of energy consumption. It reveals that there exists an optimal heating pattern to save the energy loss.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.21-25
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• 2009

This study is about heat island as one of the urban climate variation factors in urbanized modern society, which compared and observed the thermal characteristics both the downtown location and the outskirt site in summer. The diurnal air temperature range at each point is $12.6^{\circ}C$ in the downtown location and $14.3^{\circ}C$ in the outskirt site, so, it was found that the diurnal air temperature range in the outskirt site was $1.7^{\circ}C$ higher than in the downtown location. There was 20 minutes difference to reach the highest temperature between globe temperature and air temperature in the downtown location, however, the time spent to reach the highest temperature between globe temperature and air temperature in the outskirt site was the same. When we compared the globe temperature between the downtown location and outskirt site, we found that the temperature in the outskirt site was lower than in the downtown location after sunset due to the sudden temperature drops, although the exposed time to insolation in the outskirt site is longer. The average of globe temperature difference on the sample days was $1.1^{\circ}C$, the average of surface temperature difference on the sample days was $1.0^{\circ}C$, and the average of air temperature difference on the sample days was $2.0^{\circ}C$ Thus, it was found that the average of air temperature difference was higher than the average of globe temperature and the average of surface temperature. The result of this study is that the urban environment factors have more effect on the air temperature difference than globe temperature and surface temperature.

• Journal of the Korean Institute of Gas
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• v.21 no.5
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• pp.1-8
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• 2017

Currently gas safety management in the industrial field has been done by LDAR as contact method or methane leak detector as non-contact method. But LDAR method requires a lot of man-power and methane leak detector have the limitation of methane only. Therefore the Research on the OGI(optical gas image) has big attention by industry. This research was undertaken to see the effect of background temperature difference of gas cloud on the clarity of OGI. The background temperature control panel was constructed to cool down the background temperature. OGI was taken at the various methane gas ejection rate and the designed temperature difference. The experimental results showed that the OGI(when the temperature difference is $-6^{\circ}C$) is more clear thane the OGI(when the temperature difference is zero). To quantify the clarity difference, MATLAB's RGB analysis method was employed. The RGB value of the OGI at ${\Delta}T-6^{\circ}C$ was 20% lower than the OGI at ${\Delta}T0^{\circ}C$. The clarity difference by T difference can be explained by the total radiation law. When the background temperature of the gas is lower than the air temperature, the radiation energy coming into the OGI lens is increasing. As the energy is increasing, the OGI image becomes clear.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.17-23
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• 2004

In the present work, the numerical model was refined to predict the thermal analysis of energy storage in a fixed beds during (charging ,storing, discharging) mode. The governing energy equations of both fluid and the solid particles along with their initial and boundary conditions are derived using a two-phase, one dimensional model. The refined model is carried out by taking into account change of (air density , air specific heat) with air temperature and also by taking into considerations heat losses from bed to surrounding. Finite difference method was used to obtain solution of two governing energy equations of both fluid and solid particles through a computer program especially constructed for this purpose. The temperature field for the air and the solid are obtained, also efficiency of energy stored inside the bed is computed. Finally using refined model the effect of air flow rate per unit area Ga (0.2, 0.3, and 0.4 kg/$m^2$-s), and inlet air temperature (200, 250, 300 $^{\circ}C$) on energy storage characteristics was studied in three mode ( charging ,storing, discharging). The rock particles of diameter 1 em is used as bed material in this research.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.6
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• pp.476-483
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• 2016

An organic Rankine cycle for ocean thermal energy conversion system is a generating cycle using the temperature difference between surface water and deep water of the ocean. The working fluid is an important factor in the thermodynamic performance of an organic Rankine cycle. There is pinch point analysis as thermodynamic analysis of an organic Rankine cycle. This study performed a thermodynamic performance analysis according to variation in the pinch point temperature difference in heat exchangers and variation of outlet temperature of heat source and heat sink. It analyzed the thermodynamic performance by applying seven types of simple working fluids in a simple Rankine cycle for ocean thermal energy conversion that was designed according to pinch point analysis. As a result of the performance analysis, cycle irreversibility and total exergy destruction factor more decreased, and second law efficiency more increased in the lower pinch point temperature difference and temperature variation of heat source and heat sink in heat exchangers. In addition, the irreversibility changed greatly at a point that occurred in the thermodynamic variation. Among the selected working fluids, RE245fa2 showed the best thermodynamic performance, and the performance of all working fluids was observed to be similar. It needs a strict theoretical basis about diverse factors with thermodynamic performances in selecting heat exchangers and working fluids.

• New & Renewable Energy
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• v.6 no.3
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• pp.22-29
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• 2010

The concept of Ocean Thermal Energy Conversion (OTEC) is simple and various types of OTEC have been proposed and tried. However the location of OTEC is limited because OTEC requires $20^{\circ}C$ of temperature difference as a minimum, so most of OTEC plants were constructed and experimented in tropical oceans. To solve this we proposed the modified OTEC which uses condenser discharged thermal energy of existing fossil or nuclear power plants. We call this system CTEC (Condenser Thermal Energy Conversion) as this system directly uses $32^{\circ}C$ partially saturated steam in condenser instead of $20{\sim}25^{\circ}C$ surface sea water as heat source. Increased temperature difference can improve thermal efficiency of Rankine cycle, but CTEC should be located near existing plant condenser and the length of cold water pipe between CTEC and deep cold sea water also increase. So friction loss also increases. Calculated result shows the change of efficiency, pumping power, net power and other parameters of modeled 7.9 MW CTEC at given condition. The calculated efficiency of CTEC is little larger than that of typical OTEC as expected. By proper location and optimization, CTEC could be considered another competitive renewable energy system.

• Geosystem Engineering
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• v.21 no.6
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• pp.309-317
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• 2018

We employ a three-dimensional indirect boundary element method (BEM) to simulate temperature change around an underground liquefied natural gas storage cavern. The indirect BEM (IBEM) uses fictitious heat source strength on boundary elements as basic variables which are solved from equations of boundary conditions and then used to compute the temperature change at other points in the considered problem domain. The IBEM requires evaluation of singular integration for temperature change due to heat conduction from a constant heat source on a planar (triangular) region. The singularity can be eliminated by a semi-analytical integration scheme. However, it is found that the semi-analytical integration scheme yields sharp temperature gradient for points close to vertices of triangle. This affects the accuracy of heat flux, if they are evaluated by finite difference method at these points. This difficulty can be overcome by a combination of using a direct numerical integration for these points and the semi-analytical scheme for other points distance away from the vertices. The IBEM and the hybrid integration scheme have been verified with an analytic solution and then used to the application of the underground storage.

• Journal of Energy Engineering
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• v.26 no.1
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• pp.9-22
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• 2017

A combined thermal and flow analysis was carried out to study the behavior and performance of a small, commercial LTD (Low-Temperature-Differential) heat engine. Laminar-flow solutions for annulus and channel flows were employed to estimate the viscous drags on the piston and the displacer and the pressure difference across the displacer. Temperature correction factors were introduced to account for the departure from the ideal heat transfer processes. The analysis results indicate that the work required to overcome the viscous drags on engine moving parts and to move the displacer is much smaller than the moving-boundary work produced by the power piston for temperature differentials in the neighborhood of $20^{\circ}C$ and engine speeds below 10 RPS. A comparison with experimental data reveals large degradations from the ideal heat transfer processes. Thus, heat-transfer devices inside the displacer cylinder are recommended.

• Proceedings of the SAREK Conference
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• 2004.06a
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• pp.231-231
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• 2004