PREFACEThis report documents research progress during FY 1982 on a class of solid-to-solid phase-change materials.These hydrocarbon molecular crystals were evaluated for possible use as thermal energy storage media in passive solar architectural applications.The research was supported by the U. SUMMARY ObjectivesThe objectives of our research are to evaluate the technical and economic feasibility of using solid-state phase-change materials for thermal energy storage in passive solar architectural applications and to develop a better understanding of the molecular processes involved in solid-state transformations. DiscussionThe temporary storage of solar energy is an essential component of any passive solar heating strategy. Ordinarily such storage is accomplished by the use of massive construction materials such as adobe, concrete, or brick or with the use of water in specially designed storage tanks. Such materials store heat over the entire range of their operating temperatures with a continuous change in temperature as the stored thermal energy content changes.These materials are storing "sensible heat" since their changing state of energy storage can be readily sensed as a changing temperature.Specially designed storage materials called phase-change materials undergo reversible physical/chemical changes while absorbing large amounts of thermal energy over narrow temperature ranges.Phase-change materials combine both sensible and phase-change energy storage; consequently they store much larger amounts of energy per unit mass than the simpler, sensible thermal storage materials.Typical phasechange materials are waxes or salt hydrates (i.e., sodium sulfate decahydrate and calcium chloride hexahydrate), which absorb thermal energy upon melting and subsequently release the same amount of energy upon solidification.The research reported here focuses on a different type of phase-change material--a class of materials that reversibly absorb large amounts of thermal energy during solid-state transformations.These solid-state phase-change materials offer the advantage of storing large amounts of energy per unit mass without the disadvantages of melting and the attendant concerns over leakage of the phase-change material.The solid-state phase-change materials that are the focus of this research are crystalline solid hydrocarbons belonging to the class of compounds called polyalcohols (or polyols). They are similar in molecular structure, having a five carbon atom core and between zero and four hydroxyl (-QH) groups attached to the outer four carbon atoms.The three compounds from this, group having the most practical potential are pentaerythritol S=~II.I -----------------------:;~selected over this range merely by choosing the appropriate proportions' for the binary solid solution.By using differential thermal analysis, we measured a number of the most relevant thermophysical properties of 20 of these solid solutions. These measurements included transformation and melting temperatures, enthalpies, and specific heats.We...

A series of experiments were undertaken using a multiple bar assembly to measure elastic follow-up and relaxation of an initial residual stress. A test rig was designed to permit different levels of elastic follow-up to occur. The general features of the experimental results confirmed predictions provided by simple models. The most reliable measure of elastic followup was obtained by measuring the relaxation of the initial residual stress. The rate of relaxation of the residual stress is found to be proportional to the elastic follow-up factor.