Intensification of a flat solar collector efficiency

An experimental study was carried out to investigate the intensification of the efficiency of a flat solar collector. To achieve this aim, we investigated the effect of the thickness of the air gap between the glazing cover and the plate absorber and the effect of presence of transparent partitions in the air gap. Indeed, when the thickness of the air gap is increased, the natural convection is intensified, which induces high thermal losses on the front part of the collector. The result of this study highlights that thicknesses larger than the reference one, given by the manufacturer, decrease the efficiency, while thicknesses smaller than the reference one increase the efficiency. The presence of transparent partitions in the air gap leads to the weakening of the natural convection and thus to the enhancement of the solar collector efficiency. Two situations were studied. In the first one, only transverse partitions were placed in the air gap; in the second one, longitudinal partitions were added to the transverse ones to form a crossed structure of partitions. The obtained results showed that in both situations the enhancement of the efficiency is significant and that the crossed structure induces the better efficiency.

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Numerical simulation of natural convection in the air gap of an inclined flat plat thermal solar collector with partitions attached to its glazing

10.22541/au.160615443.34677441/v1 ◽

2020 ◽

Author(s):

adel laaraba

Keyword(s):

Natural Convection ◽

Solar Collector ◽

Heat Losses ◽

Air Gap ◽

Optimal Length ◽

Fluent Software ◽

Collector Efficiency ◽

Vertical Walls ◽

Optimal Values ◽

Volume Method

In this work, the natural convection in the air gap of an inclined solar collector contains partitions attached to its glazing has been studied numerically. The temperatures of the two horizontal walls are constants and different. The two vertical walls are supposed adiabatic. The equations of the problem are solved with the finite volume method, using of the Fluent software. The necessary objective is to study the influence of the partitions (length and number) on the natural convection in the air gap of the solar collector. The obtained results indicate that the presence of the partitions has important influence on the heat transfer with the decreasing of heat losses with natural convection, so improving of the solar collector efficiency. In this study, it reached that the number of partitions must be higher than 10, and their optimal length is Lp=0.4. The presence of the partitions with the optimal values reduces the heat losses by natural convection with 46 %.

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Higher Order Accurate Transient Numerical Model to Evaluate the Natural Convection Heat Transfer in Flat Plate Solar Collector

Processes ◽

10.3390/pr9091508 ◽

2021 ◽

Vol 9 (9) ◽

pp. 1508

Author(s):

Nagesh Babu Balam ◽

Tabish Alam ◽

Akhilesh Gupta ◽

Paolo Blecich

Keyword(s):

Heat Transfer ◽

Natural Convection ◽

Flat Plate ◽

Solar Collector ◽

Convection Heat Transfer ◽

Air Gap ◽

Convection Flow ◽

Natural Convection Heat Transfer ◽

Convection Heat ◽

Flat Plate Solar Collector

The natural convection flow in the air gap between the absorber plate and glass cover of the flat plate solar collectors is predominantly evaluated based on the lumped capacitance method, which does not consider the spatial temperature gradients. With the recent advancements in the field of computational fluid dynamics, it became possible to study the natural convection heat transfer in the air gap of solar collectors with spatially resolved temperature gradients in the laminar regime. However, due to the relatively large temperature gradient in this air gap, the natural convection heat transfer lies in either the transitional regime or in the turbulent regime. This requires a very high grid density and a large convergence time for existing CFD methods. Higher order numerical methods are found to be effective for resolving turbulent flow phenomenon. Here we develop a non-dimensional transient numerical model for resolving the turbulent natural convection heat transfer in the air gap of a flat plate solar collector, which is fourth order accurate in both spatial and temporal domains. The developed model is validated against benchmark results available in the literature. An error of less than 5% is observed for the top heat loss coefficient parameter of the flat plate solar collector. Transient flow characteristics and various stages of natural convection flow development have been discussed. In addition, it was observed that the occurrence of flow mode transitions have a significant effect on the overall natural convection heat transfer.

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Experimental study of natural convection in PV roof solar collector

International Communications in Heat and Mass Transfer ◽

10.1016/j.icheatmasstransfer.2017.09.022 ◽

2017 ◽

Vol 89 ◽

pp. 31-38 ◽

Cited By ~ 11

Author(s):

Sahachai Phiraphat ◽

Ratthasak Prommas ◽

Withaya Puangsombut

Keyword(s):

Experimental Study ◽

Natural Convection ◽

Solar Collector

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Experimental study on the thermal performance of a solar collector and the effect of the tilt angle on the collector efficiency

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/454/1/012135 ◽

2018 ◽

Vol 454 ◽

pp. 012135

Author(s):

A R Alkumait ◽

F M Abed ◽

Mina A. Nashat

Keyword(s):

Experimental Study ◽

Thermal Performance ◽

Tilt Angle ◽

Solar Collector ◽

Collector Efficiency

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Experimental Investigation of Natural Convection in Partially Divided Enclosures

Journal of Heat Transfer ◽

10.1115/1.3246970 ◽

1986 ◽

Vol 108 (3) ◽

pp. 554-559 ◽

Cited By ~ 3

Author(s):

J. G. Symons

Keyword(s):

Heat Transfer ◽

Experimental Study ◽

Experimental Investigation ◽

Natural Convection ◽

Convective Heat Transfer ◽

Convective Heat ◽

Solar Collector ◽

Heat Transfer Characteristics ◽

Transfer Rates ◽

Slope Direction

An experimental study has been performed on natural convective heat transfer in inclined enclosures heated from below, and with partitions running in the up-slope direction (see Fig. 1). The influence of a clearance between the partitions and the lower heated isothermal surface is considered. This problem is of particular importance in solar collector design. Heat transfer rates have been measured for Ra < 107, enclosure inclination of 0, 30, 60, and 90 deg from the horizontal, and partition end clearances ranging from zero up to half the enclosure height. A flow visualization study which covers the same range of inclinations and end clearances is also reported. It is shown that introducing a small partition end clearance has no significant effect on the flow or heat transfer rates. However, a large end clearance allows up-slope rolls to be established in the unpartitioned region of the enclosure, resulting in an increase in the heat transfer rates. The natural convective heat transfer rates are found to be independent of both partition end clearance and enclosure inclination over certain ranges of these parameters. The convective heat transfer characteristics are also shown to be related to the flow.

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