Showing papers on "Nanofluids in solar collectors published in 1989"

Chemical Reactions in a Solar Furnace by Direct Solar Irradiation of the Catalyst

Abstract: Concentrated solar radiation has been used to heat air in a volumetric receiver device. Such a receiver, using a wire mesh arrangement placed in the focal zone, can also be used for carrying out a chemical reaction where the catalyst is heated directly by the concentrated solar beam without any intermediary heat transfer fluid. The advantage of such a concept is that the highest temperature of the whole system is at the reaction site and not on the wall of the reactor or in the heat transfer fluid. Thus, higher conversion efficiencies will be obtained. Moreover, as the reaction site is directly irradiated by a very intense solar flux, photochemically enhanced reactions may result under certain conditions. The disadvantage of the approach is the difficulty in insuring uniform insolation and temperature distribution throughout the catalyst surface. Another problem is that a transparent window is required to seal off the reactants from the environment; this may complicate scaling up of the process. In this communication the authors report the results of preliminary experiments demonstrating that catalysed chemical reactions can be carried out by direct solar irradiation of the catalyst.

Spherical solar energy collector

Abstract: A solar collector particularly for receiving concentrated solar energy from a large parabolic reflector and which forms the evaporator of a heat pipe type heat transfer mechanism. The solar collector is formed from a pair of spherical shell portions which are joined at their perimeters such that they are nearly tangent at their joint. This configuration provides low mechanical stresses on the welded joint, making the structure resistant to creep failure. The inside surfaces of the solar collector are preferably covered with wire screens for the transport of liquid heat pipe working fluid. Various finenesses of mesh can be used. Preferably, a coarse mesh is in intimate contact with the inside surfaces of the collector to act as a transport medium with a finer mesh covering it. These mesh layers can be applied to surfaces of sheet metal blanks through sintering or other processes which are thereafter deformed to the desired shell configurations.

Fluid-heating solar collector

Abstract: A fluid-heating solar collector (10) comprises a solar energy absorber (34) characterized by a heat conducting and radiation absorbing material arranged to provide a plurality of angularly bent conduits (38) extending therethrough thus to optimize the heat absorption surface at differing sun angles and also to substantially increase the area for convective heat transfer to passing air or other fluid.

Effect of thermal and optical properties of transparent plates on the collection characteristics of Volume Heat Trap solar collectors

Abstract: This paper describes how the effect of thermal and optical properties of the transparent plate on the collection characteristics of a volume heat trap solar collector was studied theoretically and experimentally. for collectors with transparent plates of different material and thickness, the time changes of the temperature distribution were measured in the indoor and outdoor experiments. The calculated results, taking natural convection within the working fluid layer into consideration, were compared with the experimental data. If was found that the collection characteristics of the volume heat trap collector greatly depended upon both the thermal resistance and the transmittance of the transparent plate.

Utilization of honeycomb structures for a flat-plate solar collector by reduction of natural convection heat loss

Abstract: A most common and economical way of utilizing solar energy is to use a flatplate collector to capture incoming solar energy by heating either liquids or gases. Therefore, a solar collector should be the most critical part of the performance necessary for the system, since maximum available heat depends solely on the collector. In the present investigation, considering that most heat loss from solar collectors results from the natural convection between an absorber plate and a coverglass,it has been demonstrated that this natural convection can be suppressed and heat performances of a solar collector are enhanced by placing thin and poorly conducting honeycomb material between an absorber plate and a coverglass. By suppressing natural convection within collector spacing it has been shown experimentally that honeycomb structures effectively raise critical Rayleigh number, since they provide more shear surfaces.