Effect of absorption of solar radiation in glass-cover(s) on heat transfer coefficients in upward heat flow in single and double glazed flat-plate collectors
TL;DR: In this paper, the effects of absorption of solar radiation on inner and outer surface temperatures and consequently on convective and radiative heat transfer coefficients have been studied over a wide range of independent variables.
About: This article is published in International Journal of Heat and Mass Transfer.The article was published on 2012-01-15. It has received 54 citations till now. The article focuses on the topics: Convective heat transfer & Heat transfer coefficient.
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TL;DR: In this article, the effect of using nanofluids as heat transfer fluid, effect of altering absorber plate design for better capture of radiation, methods of heat loss reduction, use of polymer, employing mini channels for fluid flow, using PCM (phase changing materials) to provide heat during night without tank and effect of use of enhancement devices like inserts and reflector have been discussed.
Abstract: Solar flat plate collectors are devices used to trap solar thermal energy and use it for heating applications like water heating, room heating and other industrial applications. Flat plate collectors are popular for low and medium heating applications and there are undergoing constant development in terms of size reduction and enhanced efficiency. This paper presents an overview on the different techniques that are employed to enhance the efficiency of flat late collectors. Effect of using nanofluids as heat transfer fluid, effect of altering absorber plate design for better capture of radiation, methods of heat loss reduction, use of polymer, employing mini channels for fluid flow, using PCM (phase changing materials) to provide heat during night without tank and effect of use of enhancement devices like inserts and reflector have been discussed in this paper. A brief insight on various techniques used to analyse the effects and various designs has also been presented with the development methodology. Some analytical studies and CFD models have also been mentioned. This review paper also deals with the suggestions for the research work which can be carried out in the direction of heat transfer from solar flat plate collectors.
188 citations
TL;DR: The importance and significance of nanofluid on the performance of solar collectors especially on thermal properties are extensively described in this article, where six types of solar collector's viz. flat plate, evacuated tube, direct absorber, parabolic trough, solar dish, and photovoltaic thermal solar collector performance has been extensively reviewed.
Abstract: The upward energy demand along with the depletion of conventional energy sources demands improved utilization of renewable energy resources. Among many energy resources, solar energy is the most appropriate alternative to conventional energy sources owing to its inexhaustibility and green property. Solar collectors are the devices which convert the solar radiation into heat or energy. Solar collector’s efficiency should be improved by nanofluids. The importance and significance of nanofluid on the performance of solar collectors especially on thermal properties are extensively described here. Six types of solar collector’s viz. flat plate, evacuated tube, direct absorber, parabolic trough, solar dish, and photovoltaic thermal solar collector performance has been extensively reviewed here. The nanomaterials such as TiO2, CuO, ZnO, Al2O3, and MWCNTS in base fluids with polymer dispersant or surfactants forming nanofluids for the mentioned types of solar collectors are compiled. Further, the quantification of the improvement in solar collector performance utilizing these nanofluids as working fluid is compiled. Recent problems of these nanofluids performance in the solar collectors are included and a future recommendation of research based on these problems is also covered.
100 citations
TL;DR: In this article, the authors present numerical simulations aimed at optimizing the design of polymer flat-plate solar collectors, which can improve solar collectors economic competitiveness by using polymer absorbers instead of copper or aluminum absorbers.
81 citations
TL;DR: In this paper, the effect of different operating parameters, viz., inlet water temperature, solar insolation, ambient temperature, and mass flow rate on the outlet water temperature and thermal efficiency were studied.
72 citations
TL;DR: In this article, a macro-encapsulated phase change material (PCM) based solar photovoltaic thermal (PV/T) system and micro-channel heat pipes (MCHP) PV/T with a conventional PV/Ts were compared theoretically and numerically.
67 citations
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516 citations
01 Nov 1974
TL;DR: In this article, the spacing between the hot solar absorber and successive glass covers should be in the range 4 to 8 cm to assure minimum gap conductance, based on the theory and some experimental measurements.
Abstract: A useful solar-thermal converter requires effective control of heat losses from the hot absorber to the cooler surroundings. Based upon the theory and some experimental measurements it is shown that the spacing between the tilted hot solar absorber and successive glass covers should be in the range 4 to 8 cm to assure minimum gap conductance. Poor choice of spacing can significantly affect thermal conversion efficiency, particularly when the efficiency is low or when selective black absorbers are used. Recommended data for gap Nusselt number are presented as a function of the Rayleigh number for the high aspect ratios of interest in solar collector designs. It is also shown that a rectangular cell structure placed over a solar absorber is an effective device to suppress natural convection, if designed with the proper cell spacing d, height to spacing ratio L/d and width to spacing ratio W/d needed to give a cell Rayleigh number less than the critical value.
172 citations
Additional excerpts
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TL;DR: In this article, the spacing between the hot solar absorber and successive glass covers should be in the range 4 to 8 cm to assure minimum gap conductance, based on the theory and some experimental measurements.
Abstract: A useful solar-thermal converter requires effective control of heat losses from the hot absorber to the cooler surroundings. Based upon the theory and some experimental measurements it is shown that the spacing between the tilted hot solar absorber and successive glass covers should be in the range 4 to 8 cm to assure minimum gap conductance. Poor choice of spacing can significantly affect thermal conversion efficiency, particularly when the efficiency is low or when selective black absorbers are used. Recommended data for gap Nusselt number are presented as a function of the Rayleigh number for the high aspect ratios of interest in solar collector designs. It is also shown that a rectangular cell structure placed over a solar absorber is an effective device to suppress natural convection, if designed with the proper cell spacing d, height to spacing ratio L/d and width to spacing ratio W/d needed to give a cell Rayleigh number less than the critical value.
169 citations
TL;DR: In this paper, a set of correlations for computing the glass-cover temperatures of flat-plate solar collectors with double glazing is developed, and the results are compared with those obtained by numerical solutions of heat-balance equations.
76 citations
"Effect of absorption of solar radia..." refers background or result in this paper
...The range of variables considered in the analysis is the same as reported in the literature [3–6]....
[...]
...However, the empirical relation for Ut can lead to large errors as shown in the analytical study by Mullick and Samdarshi [3], Samdarshi and Mullick [4] and by Akhtar and Mullick [5,6]....
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...1 However, this exercise is not required for the estimation of top heat loss factor (Ut) because the effect of absorption in glass cover is taken care of by increasing the optical efficiency term without changing Ut [6]....
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TL;DR: In this paper, an improved equation form for computing the glass cover temperature of flat-plate solar collectors with single glazing is developed, and a semi-analytical correlation for the factor f (the ratio of inner to outer heat-transfer coefficients) as a function of collector parameters and atmospheric variables is obtained by regression analysis.
67 citations
"Effect of absorption of solar radia..." refers result in this paper
...The range of variables considered in the analysis is the same as reported in the literature [3–6]....
[...]
...However, the empirical relation for Ut can lead to large errors as shown in the analytical study by Mullick and Samdarshi [3], Samdarshi and Mullick [4] and by Akhtar and Mullick [5,6]....
[...]