• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.5
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• pp.149-156
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• 2013

The performances of solar collectors with single and double evacuated tube were experimentally compared. The solar collector with single evacuated tube using surface treatment in this study consists of radiation fin, heat pipe, absorber plate, glass tube, cap and regulating valve, and so on. Surface treatment was conducted for heat pipe and absorber plate with black chrome plating and copper black coating. As the results, the performance of solar collector with single evacuated tube using surface treatment showed good results compared that of double evacuated tube. Absorber plate played a positive role in performance and showed increase of about 28%. Further performance depends on vacuum degree and vacuum degree has to be considered economical efficiency in solar collector.

• Journal of the Korean Solar Energy Society
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• v.24 no.4
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• pp.19-25
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• 2004

A numerical study is performed to investigate the effect of sun tracking on the thermal performance of the evacuated compound parabolic concentrator (CPC) collectors. The evacuated CPC collectors consist of a two-layered glass tube, a copper tube and a reflector. The collector has a copper tube as an absorber and a reflector inside a glass tube. The water is used as a working fluid. The length and the diameter of the glass tube are 1,700mm and 70mm, respectively. The length and the diameter of the copper tube are 1,700mm and 25.4mm, respectively. Ray tracing analysis is carried out in order to compare absorbed heat fluxes on the absorber surface of the stationary and tracking collectors. The collected energy is calculated and compared with that on a fixed surface tilted at $35^{\circ}$ on the ground and facing south. The results indicate that the collected solar energy of the sun tracking system is significantly larger than that of a stationary collector. The sun tracking evacuated CPC collectors show a better performance with an increase in the thermal efficiency of up to 14% compared with an identical stationary collector.

• Journal of the Korean Solar Energy Society
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• v.25 no.1
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• pp.19-25
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• 2005

All-glass evacuated tube solar collectors consist of glass evacuated tubes and absorber tubes. Solar thermal energy from the sun is transferred to the working fluid through the glass evacuated tube and the absorber tube. Several collectors which have different absorber tubes are tested to find the effects of the absorber tube shapes and the operating conditions such as the incident heat flux and the flow rate. As the results, the efficiency of the collector which has a finned tube U tube is about $2{\sim}5%$ higher than that of the others in all cases on an average. And the collector has a finned U tube has the highest efficiency at the high flow rate and the low incident heat flux. In this condition, the outlet mean temperature is low and the heat loss becomes small. Also, it is known that the fin effect is greater than the shade effect.

• Journal of the Korean Solar Energy Society
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• v.23 no.2
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• pp.43-49
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• 2003

The thermal performance of the glass evacuated tube solar collector is numerically investigated. The glass evacuated tube solar collector consists of a two-layed glass tube, a copper tube, and the working fluid. The length and the diameter of the glass tube are 1,200mm and 38mm, respectively. The diameter, thickness, and length of the copper tube and the flow rate of air are considered as the important design and operating parameters of the collector. The effect of these parameters on the thermal performance of the collector are investigated. The results show that as the diameter, the thickness, and the length of the copper tube increase and the flow rate of the air decreases, the thermal performance and the outlet mean temperature increase.

• Journal of the Korean Solar Energy Society
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• v.25 no.2
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• pp.19-26
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• 2005

Concentric evacuated tube solar energy collector has been interested recently since government has driven to install alternative energy systems in new large building. In this paper, testing of the evacuated tube collector is conducted in outdoor during daytime by transient method. The collector thermal efficiencies are plotted in term of $(T_{in}-T_a)/Ic$, where $T_{in}$ is inlet working fluid temperature, $T_a$ is atmospheric temperature and $I_c$ is solar irradiation on the collector surface. The evacuated tube collector efficiency is ranged from 50% to 63% in real outdoor condition. In addition, the total overall heat loss coefficient is found to have an inverse variation to $(T_{in}-T_a)/I_c$ so that the coefficient becomes very high when $(T_{in}-T_a)/I_c$ is small.

• Journal of the Korean Solar Energy Society
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• v.25 no.1
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• pp.35-44
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• 2005

The absorbing rate of solar irradiation on the surface of an absorbing tube in a glass evacuated solar collector is numerically investigated. Four different shapes of the absorbing tubes are considered, and the absorbed solar irradiation on the surface is calculated for several distances between the absorbing tubes and the incidence angle of solar beam radiation. From the calculation, it is known that the absorbing rate of solar irradiation on the tube surfaces depends upon the shape and the arrangement of absorbing tube and the incidence angle.

• 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.

• Journal of the Korean Solar Energy Society
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• v.24 no.1
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• pp.39-45
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• 2004

The thermal performance of glass evacuated tube solar collectors with finned tubes is numerically modelled with code and investigated to see the effect of toe inner tube diameter and incidence angle. The solar collector consists of a two-layered glass tube and an inner tube. Finned tubes are used as the inner tube of the collector in order to improve the performance of the solar collector. Two strip-type fins are attached on the opposite sides of the inner tube surface. The fin is wide enough to be tightly fatted inside the glass tube. The results show that if the incidence angle is small, the effect of the tube diameters is not significant on the thermal performance and the outlet air temperature. If the incidence angle is large, however, the outlet air temperature and the performance increases as the inner tube diameter increases.

• Journal of the Korean Solar Energy Society
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• v.21 no.4
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• pp.63-71
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• 2001

This work has been carried out to find the ideal operating conditions for solar vacuum tube collectors which are widely used at present. Various types of solar collectors including a flat plate one were experimentally tested and examined to determine their thermal efficiencies and operating characteristics. Generally, solar vacuum tubes can be classified into two groups according to their design features. Of these, one is characterized by the insertion of a metallic device(such as a finned heat pipe) in an evacuated glass tube for the collection and transportation of solar energy. The other utilizes double glass tubes where the smaller one is contained inside the bigger one and soldered to each other after the small gap between them is evacuated. Both of these solar collectors are designed to minimize convection heat losses by removing the air which is in direct contact with the absorber surface. The performance of the former type can be readily analyzed by applying the relevant correlations developed for flat plate solar collectors. This has been demonstrated in the present study for the case of a solar collector where a heat pipe is inserted in an evacuated tube.

• Advances in Energy Research
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• v.5 no.3
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• pp.227-237
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• 2017

The continuous increase of emission rates of green house gases and the effects on global warming added a new dimension to the problem of substituting the petroleum and its derivatives by environment friendly and sustainable energy sources for the world. Solar and wind energy appear at the top of the list of renewable of high potential, widely available, of dominated technology and well accepted. Brazil is one of the few countries in the world that receives number hours of sunshine exceeding 3,000 hours per year with a daily average of 4.5 to 6 kWh. However, this potential is largely unexplored and poorly tapped. The number of renewable systems implanted in Brazil has grown in recent years, but still insignificant when compared, for example, with Germany and Spain among others. This paper presents the results of an optical study on small concentration solar collector with evacuated tube enveloping the absorber and internal reflective surface fixed on the bottom part of the evacuated tube. The designed collector has a 2D geometrical concentration ratio between 2.455 and 4.91. The orientation of the solar collector, the ratio of the radius of the receiver to the radius of the absorber, the incidence angle for each period of the year, the collector inclination angle, the aperture angle of the reflective surface, concentration and optical efficiency were determined. The ray traces and flux distribution on the absorber of the evacuated tube solar collector were determined by using the program Ray Optics Simulation. The optical efficiency varies during the year according to the solar declination. For the periods were the solar declination is close to zero the efficiencies are maximum, and the variation during the day is around 25.88% and 99.9%. For the periods were the solar declination is maximum the efficiencies are minimum, and the variation during the day is around 23.78% and 91.79%.