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 hexahydrate 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 significant endothermic or exothermic changes on heating or cooling..

We study the equations of isothermal fiber spinning under the assumption that viscous friction in the fiber is balanced by shear stresses. Our discussion gives a rather complete picture of the existence and nonexistence of stationary solutions. The linearization about steady state of the governing equations is analyzed by semigroup methods and shown to have the spectrally determined growth property. Both linear and nonlinear stability of stationary solutions is investigated numerically.