Ewa Radziemska

Thermal performance of Si and GaAs based solar cells and modules: a review

Abstract This review summarizes the recent progress obtained in the field of the temperature performance of crystalline and amorphous silicon solar cells and modules. It gives a general analysis of results and reviews of applications for building integrated photovoltaic (PV) thermal systems that convert solar energy into electrical one and heat as well. Air and water cooled ‘hybrid’ photovoltaic–thermal solar collectors are reported. These include prospective applications of amorphous silicon solar module on flexible plastic film and thin film solar cells. Topics include general results and analysis of the heat transfer mechanisms of the PV modules.

Natural convective heat-transfers from an isothermal horizontal hemispherical cavity

A simplified analytical solution, numerical calculations with the use of the FLUENT/UNS code and experimental studies of laminar free-convection heat transfer from an isothermal hemispherical cavity in unlimited space are presented. The analytical solution is based on an adaptation of the methods used for inclined isothermal plates. In the proposed solution, the control surface of the hemisphere was considered as a small inclined surface. Inclination of this surface was a function of azimuth angle. The results of theoretical analysis, numerical calculation and experimental procedure are presented in the Nusselt and Rayleigh number: relations NuD=0.296 RaD1/4, NuD=0.340 RaD1/4 and NuD=0.316 RaD1/4 respectively. The comparison of theoretical and numerical solutions with experimental results presented in this paper shows good agreement.

Natural convective heat transfer from isothermal cuboids

Abstract The paper presents results of theoretical and experimental investigations of the convective heat transfer from isothermal cuboid. The analytical solution was performed taking into account complete boundary layer length and the manner of its propagation around isothermal cuboid. It arises at horizontal bottom surface and grows on vertical lateral surface of the block. After changing its direction, the boundary layer occurs above horizontal surface faced up and next it is transformed into buoyant convective plume. To verify obtained theoretical solution the experimental study has been performed. The experiment was carried out for three possible positions of the same tested cuboid. As the characteristic linear dimension in Nusselt–Rayleigh theoretical and experimental correlations we proposed the ratio of six volumes to the cuboids surface area, for the analogy to the same ratio using as the characteristic dimension for the sphere, which is equal to the sphere’s diameter. It allowed performing the experimental results independently from the orientation of the block. The Rayleigh numbers based on this characteristic length ranged from 105 to 107. The Nusselt number describing intensity of convective heat transfer from the cuboid can be expressed by: Nu=XRa1/5+YRa1/4, where X and Y are coefficients dependent on the cuboid’s dimensions. For the range of provided experiment the experimental Nusselt–Rayleigh relation can be presented in the form: Nu=1.61Ra 1/5 or 0.807Ra 1/4 with the good agreement with the theoretical one recalculated for the tested cuboid dimensions.

The Effect of Plate Size on the Natural Convective Heat Transfer Intensity of Horizontal Surfaces

Abstract Natural convective heat transfer from flat horizontal isothermal plates has been investigated for more than a century. In the present study, the influence of the size of the plate on the heat flux is investigated. Two ranges of the heat transfer intensity are proposed for this problem: for the plates with characteristic length smaller than 0.1–0.2 m, the heat transfer coefficient is inversely proportional to the plate width; for plates wider than 0.2 m, the heat flux is not influenced by the plate width. The explanation for the discrepancy between the two ranges of natural convective heat transfer based on analysis and comparison of experimental data available in the literature has been proposed.

Free Convective Heat Transfer Structures as a Function of the Width of Isothermal Horizontal Rectangular Plates

Abstract Results are presented for the experimental investigations of free convection heat transfer from upward facing isothermal horizontal rectangular plates as a function of the plate width. Two models of the convective fluid flow structures above horizontal rectangular plates were proposed as a result of flow visualization. Solutions of these models are presented in the form of Nusselt-Rayleigh relations with the aspect ratio as a parameter. Analysis of the visualization results provided a basis for preferring the radial flow pattern at small values of the Rayleigh number, especially for square plates or at the ends of rectangular plates, and a basis for preferring the parallel flow model at large values of the Rayleigh number. From the previous experimental results and the present experimental and interferometric studies, it is shown that the transition Rayleigh number at which the flow changes from the concentric to the parallel flow pattern is a function of the width of the plate.

Experimental investigations of natural convection from circular plates at variable inclination

EAT transfer from circular disk geometry is very important inmanyapplications.Therehasbeensomeexperimentalresearchdevoted to natural convection heat transfer from stationary circulardisks and plates. For a horizontal plate, Kadambi and Drake [1]proposedthecorrelationforexperimentalresultsobtainedinair.Fawand Dullforce [2] made interferometric studies for a round plate inair, and Schulenberg [3] proposed similarity solutions for a regionaround the stagnation point on the isothermal circular plate withspecifiedtemperatureandspecifiedheatflux.Fujiietal.[4]presenteda theoretical study of natural convection heat transfer fromdownward-facing horizontal surfaces with uniform heat flux. For avertical plate, Lewandowski and Kubski [5] obtained the meancorrelationfromtheresultsof25researchers.Inearlierresearch[6,7]the present authors presented the results of theoretical andexperimental investigations for round horizontal plates facingdownward and for vertical ones. Warneford and Fussey [8] madeexperiments in air for a plate inclined at 85 deg from the vertical.In this paper an experimental study of natural convective heattransfer from an isothermal round plate facing up at arbitrary anglesof inclination has been carried out.