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ISSN Online: 2377-424X

ISBN Print: 1-56032-797-9

International Heat Transfer Conference 11
August, 23-28, 1998, Kyongju, Korea

HEAT TRANSFER IN SOLAR COLLECTORS

Get access (open in a dialog) DOI: 10.1615/IHTC11.2790
pages 325-339

Sinopsis

All energy systems involve processes of heat transfer. This is obvious for thermal applications but it is also true in other energy transfer processes, because there is always at least a secondary effect of heat flow, according to the laws of irreversible thermodynamics (Ohm's law is one example). Solar energy is obviously a field where heat transfer plays crucial role. The energy reaches us from the sun by radiation, first through vacuum and then in the participating atmosphere. The radiation interactions inside the collectors include emission, absorption and transmission, which depend on the temperatures of the collector components and on the wavelength. Heat is then transferred within the collector and from it to the ambient (losses) by conduction and by convection, and forced, natural and mixed modes appear in different systems or various parts of the same one. Furthermore, although the utilization of solar energy practically started about fifty years ago, it has not gained, in general, the widespread market penetration predicted or hoped then. Economically, solar energy systems are at best marginal in most cases. In order to realize the potential of solar energy, a combination of better design and performance and of environmental considerations would be necessary. Here the advancements in heat transfer are crucial for improved thermal characteristics of collectors and systems.
This paper is a survey of heat transfer in solar collectors. The introduction includes brief descriptions of the main types of collectors, the basic principles and the most important features that have been developed and employed to produce high efficiency. The next sections review the treatment of heat transfer analysis of flat plate and concentrating collectors - both the "classical" textbook approaches and new developments, in systems and in methods. Typical results are shown, especially of collector efficiency curves, obtained theoretically and experimentally.