Modeling of fixed bed heat storage units utilizing phase change materials
- PDF / 751,249 Bytes
- 8 Pages / 583.28 x 777.28 pts Page_size
- 45 Downloads / 196 Views
I.
INTRODUCTION
ECONOMIC heat storage systems are used for heat recovery and for load leveling under circumstances where the demand for and availability of energy do not coincide chronologically. Consequently, load leveling in a power plant with the utilization of stored heat for power generation during peak demand hours, utilization of alternative sources of energy (e.g., solar), and waste heat recovery are areas with potential for cost reduction using efficient heat storage. Heat storage systems that utilize only the sensible heat of a storage material (no phase change) may be one of two types. The first one is a system in which the energy transporting fluid itself serves as the storage medium. The other system has an enthalpy transporting fluid which exchanges heat with a separate storage medium. Domestic hot water heating systems using water as both the transporting and heat storing fluid fall into the first category. An example of the second type is a system utilizing the sensible heat of solids such as a firebrick checkerwork. A storage medium utilizing sensible heat should have high values for its heat capacity per unit volume and for thermal diffusivity; it should be chemically and geometrically stable under conditions of reversible heating and cooling. It should be noncombustible and nontoxic, have a low vapor pressure, and be inexpensive. 1 Storage systems that utilize the latent heat of transformation are currently receiving considerable attention. The storage media used by these systems, called Phase Change Materials (PCMs), offer advantages such as a small temperature difference between the storage and retrieval cycles, small unit sizes, and low weight per unit storage capacity. Selection of the storage material depends largely on the mean storage temperature. Some desirable characteristics of a PCM for use as a heat storage medium are a high latent heat of transformation (usually fusion), a narrow freezing range or a congruent melting point, nontoxicity, long term chemical stability, inertness with respect to a suitable container material, low cost, and ready availability. 1 Inorganic salts such as halides, nitrates, sulfates, carbonates, etc. in multicomponent eutectic systems have been V. ANANTHANARAYANAN, Graduate Student, Y. SAHAI, Associate Professor, C. E. MOBLEY, and R. A. RAPP, Professors, are with the Department of Metallurgical Engineering, The Ohio State University, Columbus, OH 43210. Manuscript submitted January 8, 1986. METALLURGICALTRANSACTIONS B
studied for a long time as PCM alternatives to sensible heat storage in water, fused salts, or bricks. Tye, Bowine, and Desjarlis 2 specified PCM salts with temperature ranges to match principal heat generating sources: LiNO3 at 527 K (254 ~ for a pressurized water reactor, 63LiOH-37LiC1 at 533 K (260 ~ for a boiling water reactor, LiOH at 743 K (470 ~ for a fossil-fueled supercritical steam reactor, and Na2B407 at 1015 K (742 ~ for a high-temperature gascooled graphite moderated reactor. Thus lithium salts were the basis for most workable P
Data Loading...
