3-4. Advanced Concepts for Latent Thermal Energy Storage for Solar Dynamic Receivers KOTARO TANAKA, YOSHIYUKI ABE, KATSUHIKO KANARI, OSAMI NOMURA & MASAYUKI KAMIMOTO Summary The present paper discusses latent thermal energy storage (LTES) systems designed for a closed Brayton cycle (CBC) dynamic power generator. Two new LTES concepts are proposed. The first is the addition of volumetrically variable fins which remain unwetted by the phase change materials (PCM). The use of such fins can reduce mechanical stress on the containment walls. The second is encapsulation of the PCM within a submicron-sized porous ceramic structure. Considerable weight reduction can be achieved by introducing such ceramic-PCM composite systems. A thermal and stress analysis on melting and solidification has been performed. In addition, we cover results from an experiment on void formation and from preliminary cyclic performance tests on receiver LTES components. Introduction A space solar receiver is one of the key components of the solar dynamic power systems (SDPS) used in future space development programs. Energy from sunlight falls on the receiver and is stored in one of the various forms to be used later as necessary. Latent Thermal Energy Storage (LTES) is the most promising energy storage technique because of its high storage density and high efficiency. However, present state-of-the-art LTES systems are large and heavy, massing nearly half of the complete space solar receiver. The specific mass of recent receiver designs has been evaluated to be in the range 50-100 kg/kWe [1,2], mainly due to the weight of the thick metallic containment canisters. If one looks at the components of the conventional receiver recently designed for the 25 kWe space station closed Brayton cycle (CBC), less than 20% of the total weight is associated with the PCM itself, while 40% is from the containment canisters [1], This indicates that the weight of the receiver could possibly be reduced significantly by introducing some new LTES concepts. The authors have conducted systematic screening of PCMs in the temperature range 473-1773 K, evaluating more than 1800 kinds of material [3,4]. Candidate materials for space use are mostly fluoride salts, such as lithium fluoride (LiF), calcium fluoride (CaF2), magnesium fluoride (MgF2) and their eutectic mixtures. The melting temperatures of the selected PCMs match the inlet temperature of the CBC Kotaro Tanaka, Yoshiyuki Abe, Katsuhiko Kanari, Osami Nomura & Masayuki Kamimoto, Energy Materials Section, Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba, Ibaraki 305, Japan. Paper number IAF- ICOSP89-3-4.
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