Radiation Drying of Textiles

Abstract

This paper deals with radiation drying of woven and matted wool felts, of woven wool crepe, and of absorbent cotton batting. Radiant energy was supplied by R-40 electric lamps, and air conditions at the surface of the samples were controlled. Drying rate curves are analyzed in terms of drying mechanisms, and comparisons are made with convection drying by means of heated air. Among the variables discussed are air conditions, air velocity, intensity of radiant energy, sample thickness, optical properties of the materials being dried, and the initial regain.AS A MEANS of transmitting heat energy, radiation has certain attractive features. It is applied by direct, linear propagation and involves no intermediate heat storage; it lends itself to instantaneous control; and because of the high energy flow rates that may be achieved, equipment sizes may be correspondingly small and process time cycles may be short. Based upon these features, an important infrared heating industry has been developed within the last decade. Heating, to raise the temperature of materials, baking or curing, to cause a chemical reaction to take place, and drying, to remove water or organic solvents, are industrial operations being performed. Typical examples are baking of resins in surface coatings and in textile finishes, softening thermoplastics, shrink-fitting metal parts, softening adhesives, heat-set printing and drying plaster and clay molds, electrical insulation, wood pulp products, and textile materials.Radiation drying of textile materials by means of high-intensity sources such as heat lamps and radiant gas burners, which is the specific subject of this paper, was introduced into the textile industry at about the beginning of World War II. To date, radiation driers have been used mainly to increase the capacity of existing drying equipment such as loop driers and drying cans [7] . Near infrared units are well suited for such booster service because they at OAKLAND UNIV on June 15, 2015 trj.sagepub.com Downloaded from

Some Moisture Relations of Wool and Several Synthetic Fibers and Blends

“…That this arrestation in the evaporation rate decrease is not experimental error or an artifact may be verified by reference to the several figures given by Paul and Wilhelm [20] . It will be seen that all of the wool fabrics employed in the work of these authors exhibited the same type of inflection in the same regain region practically irrespective of the external conditions prevailing during drying.…”

“…After the total moisture content has been reduced below a particular threshold, the rate begins to decrease-first linearly and eventually in some nonlinear manner with the residual moisture content. A number of possible mechanisms which may control the over-all process have been described [3,4,6,10,20,22,27]. The essential features of most of these follow:…”

“…Various explanations have been given for the phenomena occurring at the transition from the first to the second falling rate-periods and during the second falling-rate period. In one version [20], the latter period begins at the instant of total depletion of liquid water and the onset of desorption of regain moisture. For nonhygroscopic granulated solids such as sand [3], this period is believed to coincide with the breaking up of capillary films, when further evaporation is from isolated pockets of liquid between grains.…”

“…The complexity of effects during this period of evaporation (from approximately 50% to approximately 35% regain for wool) may also be inferred from the temperature versus regain curves of Paul and Wilhelm [20] . It will be seen that the meas-ured surface temperature of the fabrics remains constant during both their constant-and first fallingrate periods, but begins to rise at about 55% regain.…”

Heat Gain From Thermal Radiation Through Protective Clothing With Different Insulation, Reflectivity and Vapour Permeability

“…Special attention is paid to the impact of high intensity radiation in the presence of moisture inside the protective clothing of firefighters [23,24]. However, from textile research on drying of wet fabrics by infrared radiation [25,26] one may also expect that moderate thermal radiation might have an influence on the evaporation of moisture from wet clothing and thus on human heat balance.…”