E-Book, Englisch, 326 Seiten
Auer / Douglas Advances in Energy Systems and Technology
1. Auflage 2013
ISBN: 978-1-4831-9129-4
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark
Volume 5
E-Book, Englisch, 326 Seiten
ISBN: 978-1-4831-9129-4
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark
Advances in Energy Systems and Technology: Volume 5 present articles that provides a critical review of specific topics within the general field of energy. It discusses the fuel cells for electric utility power generation. It addresses the classification of fuel cell technologies. Some of the topics covered in the book are the major components of the fuel cell; the phosphoric acid fuel cells; molten carbonate fuel cells; solid oxide fuel cells; electric utility fuel cell systems; and the integration within fuel cell power plants. The analysis of the solar ponds is covered. The operational problems with salt-gradient solar ponds are discussed. The text describes the membrane-stratified solar ponds. A study of the household demand for conservation is presented. A chapter is devoted to the construction of the insulation index. Another section focuses on the use of Box-Cox transform for both dependent and explanatory variables. The book can provide useful information to scientists, engineers, students, and researchers.
Autoren/Hrsg.
Weitere Infos & Material
Solar Ponds
N.D. Kaushika, Centre for Energy Studies, Indian Institute of Technology, New Delhi, India
Publisher Summary
This chapter provides an overview of solar ponds. The solar pond is a unique development in renewable energy resource technology. It utilizes a body of still water to collect solar energy and stores it as thermal energy, which is suitable for a variety of applications, including electric power generation, industrial process heating, and space conditioning. The mechanism of heat accumulation in a nonconvective solar pond may be appreciated by comparing it with a normal convective pond. Both the ponds absorb solar radiation in the water and in the material at pond floor and convert it to heat. In the convective pond, loss of heat is large because each small element of water, when heated, rises to the surface and exchanges heat with the atmosphere. In contrast, in the nonconvective pond, only the upper layer of water can exchange heat with the atmosphere, with consequent low loss of heat. Heat loss from lower regions is by conduction only and is meager because nonconvective water is a poor conductor of heat. Thus, the regions of water near the bottom of the solar pond attain a high temperature, and if there is enough sunshine, this temperature can reach the boiling point while the pond surface remains close to that of ambient air.
III. Salt-Gradient Solar Ponds: Basics
IV. Thermal Models of the Salt-Gradient Pond
V. Construction of the Salt-Gradient Pond
VI. Management of the Salt-Gradient Pond
I INTRODUCTION
The solar pond is a unique development in renewable energy resource technology. It utilizes a body of still water to collect solar energy and stores it as thermal energy, which is suitable for a variety of applications, including electric power generation, industrial process heating, and space conditioning.
As a practical matter, all ponds, lakes, oceans, and other expanses of water in nature collect solar energy and convert it to thermal energy, but their heat-retention efficiency is poor. This is because the water near the surface is quickly cooled as the heat is rapidly dissipated to the environment. The warmer and more buoyant water in the lower region rises to the surface; this movement of water is called natural convection. Therefore, a water-pond system will be more effective in the collection and storage of solar energy if convection is suppressed. Several means of convection suppression have been suggested. By far the most common approach is the establishment of a salt density gradient (increasing density with depth), so that the water in the lower regions can be warmer than the water above it without simultaneously acquiring lower density and rising to top by convection. Artificial salt-gradient ponds were first investigated in Israel in the late 1950s and have since been constructed as solar thermal energy sources in several countries. They are usually referred to as “salt-gradient solar ponds” or “solar ponds.”
The mechanism of heat accumulation in a nonconvective solar pond may be appreciated by comparing it with a normal convective pond. Both the ponds absorb solar radiation in the water as well as in the material at pond floor and convert it to heat. In the convective pond, loss of heat is large because each small element of water, when heated, rises to the surface and exchanges heat with the atmosphere. In contrast, in the nonconvective pond, only the upper layer of water (at low temperature) can exchange heat with the atmosphere, with consequent low loss of heat. Heat loss from lower regions is by conduction only and is meager because nonconvective water is a poor conductor of heat. Thus, the regions of water near the bottom of the solar pond attain a high temperature, and if there is enough sunshine, this temperature can reach the boiling point while the pond surface remains close to that of ambient air.
II HISTORICAL BACKGROUND
The physical phenomenon of the salt-gradient solar pond occurs in nature in some salt lakes which may have existed for a million years. The first documented description of these lakes was given by a Russian scientist (Von Kalecsinsky, 1902). He reported that during the summer the Madve Lagoon in Transylvania (Hungary) acquired temperatures in excess of 70°C at a depth of 1.32 m for a surface temperature close to that of ambient air. In more recent times several authors, including Anderson (1958), Wilson and Wellman (1962), Hoare (1966), Por (1970), Melack and Kilham (1972), Hudec and Sonnefeld (1974), and Cohen (1977), have reported that salt lakes with elevated bottom-region temperatures occur in many parts of the world. The most remarkable seems to be Lake Vanda (Wilson and Wellman, 1962) in Antarctica. It exhibits a temperature of 25°C in the bottom region, while the annual mean atmospheric temperature at the lake site is -20°C and the lake is perennially covered with 3 to 4 m of ice. These lakes invariably have been observed to be characterized by salt leaching at the bottom of the lake and a supply of fresh water (low-salinity brine) at the surface provided by a river (or other means). The natural diffusion of salt gives rise to a downward increase in salt concentration which prevents convection and renders the upper region of lake a partially transparent insulator. Consequently, the lake acts as a solar heat trap and becomes heated in the lower region. Typical temperature and salt profiles for Lake Madve are illustrated in Fig. 1.
Fig. 1 Vertical profiles of temperature and salinity in Lake Madve. [After Kalecsinsky (1902) and Hull (1979).]
The idea of an artificial solar pond and its practical utilization as a solar thermal energy resource was proposed in Israel by Rudolph Bloch. The first laboratory-size solar pond was operated around 1959 (Tabor, 1959, 1961). Pioneering outdoor solar pond experiments were conducted by Tabor (1963) at Sdom on the shores of the Dead Sea; concentrated end brine primarily composed of magnesium chloride was used for generating the gradient. Subsequently, many investigations on the physics and engineering of the solar pond were reported (Weinberger, 1964; Elata and Levin, 1965; Tabor and Matz, 1965) and the technical feasibility of solar ponds was established. Temperatures up to 96°C were recorded, and the importance of careful site selection as well as the use of a liner to seal the pond’s bottom and sides were stressed. Due to the massive thermal storage capacity of the system, the main emphasis was placed on the power production application. However, at that time, due to the availability of cheap fossil fuel-based electricity, such an application could not be demonstrated to be cost attractive. Solar pond research in Israel, therefore, suffered a setback after 1965, and for...
