• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1681-1691
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• 2002

The heat transfer and pressure drop characteristics of heat exchangers with louver fins were experimentally investigated. The samples had small fin pitches (1.0 mm to 1.4 mm), and experiments were conducted up to a very low frontal air velocity (as low as 0.3 m/s). At a certain Reynolds number (critical Reynolds number), the flattening of the heat transfer coefficient curve was observed. The critical Reynolds number was insensitive to the louver angle, and decreased as the louver pitch to fin pitch ratio (L$_{p}$F$_{p}$) decreased. Existing correlations on the critical Reynolds number did not adequately predict the data. It is suggested that, for proper assessment of the heat transfer behavior, the louver pattern in addition to the flow characterization need to be considered. The heat transfer coefficient increased as the fin pitch decreased. At low Reynolds numbers, however, the trend was reversed. Possible explanation is provided considering the louver pattern between neighboring fins. Different from the heat transfer coefficient, the friction factor did not show the flattening characteristic. The reason may be attributed to the form drag by louvers, which offsets the decreased skin friction at a low Reynolds number. The friction factor increased as the fin pitch decreased and the louver angle increased. A new correlation predicted 92% of the heat transfer coefficient and 90% of the friction factor within $\pm$10%.10%.

• Solar Energy
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• v.12 no.1
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• pp.88-94
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• 1992

A small-scale solar collector and tracking system, using a Fresnel lens of $0.5m^2$, and novel compact fluidized-bed solar receiver[FBR] of closed type has been developed for high temperature solar gas heating. The FBR was improved in carrying over of SiC powder and thermo-siphon effect. The maximum outlet air temperature of 1140K and the maximum thermal efficiency of 64% were obtained. The present FBR's operated efficiently at extremely high temperatures in comparison with conventional solar receivers, composed of flat or tubular solid surfaces.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.130.2-130.2
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• 2011

The application of solar energy in residential building is general and natural in today. And application methods of solar thermal energy is divided in two kind of form, single evacuated tube and flat-plate form. Then in this study, the efficiency of single evacuated tube and flat-plate system is compared by total and effective area considering the time receiving the solar radiation between 24 hours and the specific time(10:00~15:00). As a result of the experiment, single evacuated tube and flat-plate collector's efficiency is varied by the quantity of solar radiation. And especially, the flat-plate system is more affected by outdoor temperature. Therefore the application of solar thermal system should be considered the solar radiation and outdoor temperature.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.480-487
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• 2012

The application of solar energy in residential building is general and natural in today. And application methods of solar thermal energy is divided in two kind of form, single evacuated tube and flat-plate form. Then in this study, the efficiency of single evacuated tube and flat-plate system is compared by total and effective area considering the time receiving the solar radiation between 24 hours and the specific time(10:00~15:00). As a result of the experiment, single evacuated tube and flat-plate collector's efficiency is varied by the quantity of solar radiation. And especially, the flat-plate system is more affected by outdoor temperature. Therefore the application of solar thermal system should be considered the solar radiation and outdoor temperature.

• Solar Energy
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• v.18 no.2
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• pp.19-29
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• 1998

Solar energy is a quantitatively unlimited, clean and non-pollutant source. It has a great potential for industrial commercial usages. For example, solar hot water system for domestic usage has been very popular in many counties. In Korea, the industries consume 47.7% of the total national energy, and the manufacturing sector uses 91.5% out of it. The main energy resoures available in Korea are oils, coals, and gases. There have been continuous efforts among the industries to reduce such energy consumptions by using alternative energy resources, such as solar energy, yet the technology has limited its proper applications to a level of satisfaction. In some advanced countries, research and development programs in solar energy applicable to the industrial usages are very active, and some systems are in the commercial market. Therefore, this paper describes the status and the feasibility for high-efficiency evacuated solar collector which was anticipated to applied for industrial process heat as an alternative of fossil energy.

• Journal of the Korean Solar Energy Society
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• v.28 no.5
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• pp.21-27
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• 2008

In this study, the design of the solar heating system for district heating as well as it's operating characteristics and the performance analysis was carried out. This solar district heating system was composed of two different types of solar collector circuit, flat plate and vacuum tube solar collector, in a system. This system supply constant temperature of hot water without solar buffer tank. For this, the proportional(variable flow rate) control was used. The experimental facility for this study was used the Bundang district solar heating system which was installed in the end of 2006. The operating characteristics and behaviour of each collector circuits are investigated especially for the system design and control. The yearly solar thermal efficiency is 47.5% on the basis of aperture area and 39.8% on the basis of gross area of collector. As a result this solar heating system without solar buffer tank and with proportional controller was testified a very effective and simplified system for district heating. It varied especially depend on the weather condition like as solar radiation and ambient temperature.