• Journal of the Korean Solar Energy Society
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• v.33 no.6
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• pp.85-91
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• 2013

It is essential to reduce the amount of fossil fuel because facing with the natural problem such as a global warming. To achieve this goal, many of interests in the use of renewable energy is growing. Especially, as one of these renewable energy systems, a solar air heater invention has been conducted for enhancing the efficiency of solar air heater. According to this trend, scale-down sized experiment apparatus was constructed and performed for searching a proper fin and confirming the heat transfer performance by fin shape on constant heat condition to enhance efficiency of solar air heater. In this experiment, heat gain, convection heat transfer coefficient, number of transfer units, Nusselt number, Reynold's number, friction factor, performance factor were investigated in order to evaluate the thermal characteristics based on the real data obtained. By comparison with the each fin performance, a zigzag shape keeping a right angle to the plate had the highest value among them.

• Coupled systems mechanics
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• v.11 no.2
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• pp.107-119
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• 2022

The aim of the work presented in this paper is development of numerical model for prediction of temperature distribution in pavement according to the measured meteorological parameters, with introduction of non-linear heat transfer coefficient which is a function of temerature difference between the air and the pavement. Developed model calculates heat radiated from the pavement back in the air, which is an important part of the heat trasfer process in the open air surfaces. Temperature of the pavement surface, heat radiation together with many meteorological parameters were measured in series during two years in order to validate the model and calibrate model parameters. Special finite element method for temperature heat transfer towards the soil together with the time integration scheme are used to solve the governing equation. It is proved that non-linear heat transfer coefficient, which is a function of time and temperature difference between the air and the pavement, is required to decribe this phenomena. Proposed model includes heat tranfer coefficient callibration for specific climate region, through the iterative inverse procedure.

• Journal of the Korean Solar Energy Society
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• v.23 no.1
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• pp.9-16
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• 2003

For the study of an effect that fin thickness and shape of heat exchanger have on the elevation of heat transfer efficiency, we make models of plate fin type heat exchanger and louvered fin type heat exchanger which was given a transformation of fin thickness in plate f)n type heat exchanger and louvered fin type heat exchanger which are often used now. And the effect of fin thickness on pressure drop and characteristics of heat transfer was experimented and analysed when air velocity and temperature of plate heating was a variable. The results of experiment shows below. Pressure drop shows larger in louvered fin type exchanger than in plate fin type exchanger, size of pressure drop shows like this order that fin thickness is 0.3mm, 0.2mm, 0.1mm. Mean heat transfer coefficient shows higher in louvered fin type exchanger than in plate fin type exchanger, size of mean heat transfer coefficient by fin thickness shows same in both case in louvered fin type heat exchanger and plate fin type exchanger like this order that fin thickness is 0.1mm, 0.2mm, 0.3mm.

• Journal of the Korean Solar Energy Society
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• v.22 no.4
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• pp.77-84
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• 2002

In order to investigate forced convection heat transfer due to the wind from the inner surface of a cavity receiver for a parabolic dish type solar energy collecting system, a two-dimensional rectangular cavity receiver is prepared and installed in a wind tunnel. The convection heat transfer coefficient of the inner surface of the receiver is dependent on the direction and the velocity of the wind. The attack angle of the cavity and the air velocity in the tunnel are controlled in a wide range so that the effects of the attack angle and the wind velocity on the heat transfer coefficient can be studied. The skirt is installed at the aperture of the cavity in order to reduce convective heat loss. The effects of the length and the installation angle of the skirt on convection heat transfer of the cavity are tested. It is found that convection heat loss can be significantly reduced by installing the skirt. Also, it is known that heat transfer from the cavity can be minimized if the angle of the skirt is $90^{\circ}$ to the outer surface of the cavity.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.162-169
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• 2009

In summer electrical energy is consumed in very high rate. It is used to operate conventional air conditioning system. Hot and humid air can germinate mould spores, encourage ill health, and create physiological stress (discomfort). Dehumidifier solar cooling effect is the one alternative solution saving electrical energy. We use surplus heat energy in the summer, to get cooling effect and then to get human reach to comfort condition. These devices have two system, dehumidifier and regeneration system. This paper will be focus in dehumidifier system. Dehumidifier system use for absorbing moisture in the air and decreasing air temperature. When the liquid desiccant as strong solution contact with the vapor air in the packed tower, it works. The heat and mass transfer performances of flow pattern in the packed tower of dehumidifier are analyzed and compared in detail. In this experiment was introduced, the flow patterns are parallel flow and counter flow. The performance of these flow patterns will calculate from air side. Which is the best flow pattern that gave huge mass transfer rate? The proposed dehumidifier flow pattern will be helpful in the design and optimization of the dehumidifier solar cooling system.

• Solar Energy
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• v.20 no.3
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• pp.31-38
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• 2000

In order to study on influence of fin pitch and shape of heat exchanger on the elevation of heat transfer efficiency, we make models of louvered fin type heat exchanger which was given a transformation of fin pitch in louvered fin type heat exchanger which are of en used now. And the influence of fin pitch on pressure drop and characteristics of heat transfer was experimented and analysed when air velocity and fin pitch was a variable. The results of experiment shows below. Pressure drop shows larger in louvered fin type heat exchanger than in plate fin type heat exchanger, size of pressure drop shows like this order that fin space is 4mm, 5mm, 6mm. Mean heat transfer coefficient shows higher in louvered fin type heat exchanger than in plate fin type heat exchanger, size of mean heat transfer coefficient by fin space shows same in both case in louvered fin type heat exchanger and plate fin type like this order that fin space is 4mm, 5mm, 6mm.

• KIEAE Journal
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• v.15 no.4
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• pp.29-35
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• 2015

Purpose: Double skin facade is a representative advantageous passive technology of building skin in the aspect of energy saving and environment improvement, reduces heat loss with buffer space in winter season and enhances indoor air and comfort of residents by activating natural ventilation in mid-season. However, in summer season, temperature increase in the intermediate space due to solar energy from exterior transparent skin could be a potential problem; also, relatively weak buoyancy of air caused by low density difference between double-skin facade could increase cooling load as air of intermediate space in high temperature hangs. However, proof data is insufficient to objectify such phenomenon. Method: In this study, researchers surveyed air temperature of intermediate space and airflow and diagnosed its cause targeting on applied multistory facade in the building which gives thermal uncomfort to residents. Also, the researchers produced Solar-air heat transfer coefficient meter, measured thermal boundary condition of double-skin facade, and presented the result of measurement as an objectified verification material regarding overheating phenomenon in the intermediate space of double-skin facade in summer season. Result: Inefficient condition was verified that total heat increases and overheating due to insufficient natural ventilation in multistory facade. In addition, logic behind preceding research was objectified and verified regarding high temperature phenomenon in the intermediate space which could increase cooling load in summer season.

• Journal of Biosystems Engineering
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• v.15 no.1
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• pp.14-22
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• 1990

For efficient use of solar energy in plastic greenhouse, thermal storage system was developed. The system was constructed with the counter-flow type air-water heat exchanger using a thin polyethylene film as a medium of heat exchange parts. Experiments were carried out to investigate the heat exchange rate, optimum water flow rate, overall heat transfer coefficient, and the effectiveness of the counter-flow type air-water heat exchanger with polyethylene film bags. Mathematical model to predict air temperature leaving heat exchanger was developed. The results obtained in the present study are summarized as follows. 1. Heat exchange rate in the counter-flow type air-water heat exchanger with polyethylene film bags was compared to that of polyethylene film. Heat exchange rate was almost identical at air velocity of 0.5m/s on polyethylene film surface. But, heat exchange rate of heat exchanger with polyethylene film bag was $32{\sim}55KJ/m^2$ hr higher than that of polyethylene film at air velocity of 1.0m/s. 2. Considering the formation of uniform water film and the sufficient heat exchange rate of polyethylene film bags, optimum water flow rate in polyethylene film bags was $3.0{\sim}6.0{\ell}/m^2$ min. 3. The overall heat transfer coefficient of polyethylene film bags was found to be $35.0{\sim}130.0KJ/m^2\;hr\;^{\circ}C$ corresponding to the air velocity ranging 0.5 to 4.0 m/s on polyethylene film surface. And the overall heat transfer coefficient showed almost linearly increasing tendency to the variation of air velocity. 4. Mathematical model to predict air temperature leaving the heat exchanger was developed, resulting in a good agreement between the experimental and predicted values. But, the experimental results were a little lower than predicted. 5. Effectiveness of heat exchanger for the experiment was found to be 0.40~0.81 corresponding to the number of transfer units due to the variation of air velocity ranging 0.6 to 1.7 m/s.

• Journal of Biosystems Engineering
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• v.15 no.2
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• pp.123-133
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• 1990

Thermal performance of a solar heating plastic greenhouse designed for a hydroponic system was studied. The system was constructed with the air-water heat exchanger and thermal storage tank that were combined with hydroponic water beds. Experiments were carried out to investigate the daily average heat stored and released in thermal storage tank, average solar energy collection efficiency, average coefficient of performance, average oil reduction factor of thermal storage system, and the heat transfer coefficient during the nighttime in plastic greenhouse. The results obtained in the present study are summarized as follows. 1. Daily average heat stored in thermal storage tank and released from the thermal storage tank was 1,259 and $797KJ/m^2$ day, respectively. 2. The average solar energy collection efficiency of thermal storage tank was 0.125 during the experiment period. And the average coefficient of performance of thermal storage system in plastic greenhouse was 3.6. 3. The average oil reduction factor of thermal storage system and the heat transfer coefficient during the nighttime in plastic greenhouse were found to be 0.52 and $4.3W/m^2\;hr\;^{\circ}C$, respectively.

• 한국태양에너지학회:학술대회논문집
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• 2011.04a
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• pp.195-198
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• 2011

Liquid desiccant material, such as lithium chloride (LiCl) or halide slits are usually used on air conditioning application for controlling the humidity of high Outdoor Air (OA). Solar energy is usually used to heat the liquid in regeneration process of those desiccant. The mass transfer it self is driven by the temperature different between the liquid desiccant and the input air. This experiment study is analyzing the characteristic of the aqueous LiCl-air temperature different in variance specific gravity, especially in range of temperature different using the solar energy as the heat generator. The experiment has done by variating the concentration of the LiCl with specific gravity 1.210 and 1.150. For the comparison the pure water is also used. The result show that the mass transfer rate is increased in every variation as the increases of the temperature different, and the weeker aqueous solution of the LiCl the highest mass transfer coefficient.