Temperature-Sensitive Hollow Fibers Containing Phase Change Salts

Abstract

Hollow rayon and polypropylene fibers have been modified to change their heat capacity dramatically in an ambient temperature range (270-310 K) by filling them with aqueous solutions of calcium chloride hexahydrate/strontium chloride hexa hydrate capable of producing latent heat gains and losses in the modified fibers during repeated heating and cooling. Both fibers produced large endotherms in the heating cycle (303 K) that were dependent on the relative humidity at which the fibers were previously conditioned; however, only the modified rayon fibers exhibited a significant exotherm in the cooling cycle (282 K). Endotherms and exotherms for modified rayon fibers (previously conditioned at 45% RH) persisted even after 10 heating and cooling cycles. Apparently, hydrophilic differences in the two fiber types require different amounts of water in the salt system of the dried and conditioned fiber to produce reversible latent heat gains and losses caused by heats of fusion and crystallization of the salt system. Neither the unmodified fibers nor another aqueous salt system incorporated into the fibers (sodium sulfate/borax) exhibited any sig nificant endothermic or exothermic changes on heating or cooling.