1、 1 Condensation of Water Vapor on Waterproof Breathable Fabrics Condensation occurs when the local vapor pressure rises above the saturation vapor pressure at the local temperature in theory. A new measuring apparatus were made to obtain temperature and relative humidity simultaneously for the purpo
2、se of investigating the mechanism of condensation occurred on the fabrics. The experiment conducted at the standard condition of temperature of 20C and relative humidity of 65%. The result obtained from experiment showed that condensation could occur under the situation closed to saturation line as
3、the temperature on fabric may be lower than dew point of water vapor in the measuring box depending on the experiment conducted at an ambient environment temperature of 20C. The range of fabrics studied showed that PTFE laminated fabrics except nylon gingham PTFE laminated fabric facilitates the los
4、s of water vapor and therefore prevent condensation. It is necessary to develop studies from a wide range of fabrics, especially breathable fabrics and under bad experiment condition in order to develop fabrics, which could eliminate condensation, or transport water vapor through the fabric while re
5、maining waterproof. Keywords: condensation ；waterproof breathable fabric. Introduction The human body through the process of metabolism is constantly generating thermal energy and moisture, which exchange through the textile layers with its environment .As perspiration escapes from the human body wh
6、en the water vapor transfer from clothing is low .condensation defined as water droplet collected on the inner surface of the clothing may occur, provided that the local vapor pressure rises above the saturation vapor pressure at the local temperature. Keighley and Ruckman suggested from theory that
7、 the condensation occurring on the fabrics may be predicted if a saturation line and water vapor concentration line is utilized .Keighley developed a method that involved measurement of water vapor concentration utilizing infrared absorption at the specific frequency of a strong water vapor absorpti
8、on and Ruckman provided a solution to the problem of condensation on the inner surface of fabric by perforating metal cylinder simulating the perspiring human body to 2 investigate the couple mechanism s of water vapor transfer an d heat transfer .More recently, Ren and Ruckman studied the water vap
9、or transfer rate when condensation occurs on the surface of difference type of waterproof breathable fabrics to ascertain whether the amount of condensation will affect the water vapor transfer rate .A method spraying water onto the hot surface of the fabric was employed to simulate droplet condensa
10、tion .whilst a discussion of the merits of waterproof breathable fabrics focused on the ability of these fabrics to reduce both heat stress and uncomfortable sensation of wetness while providing protection from wind and rain. A1l above researches focus on the effect of condensation on heat and water
11、 vapor transfer .Whilst no research has been conducted to study whether the condensation formed on the inner surface of a fabric .this paper described the details of the measuring apparatus investigated the mechanism of condensation occurred on the fabrics an d also presented typical measuring resul
12、ts for representative of fabrics included waterproof breathable fabrics. Theories Condensation occurs when the local vapor pressure rises above the saturation vapor pressure at the local temperature. The saturation line is described the water vapor pressure giving rise to 100%relative humidity at a
13、specific temperature, as shown in Fig.1. This is particularly likely to occur on waterproof fabrics since under such conditions the rate of loss of water vapor from the clothing will be very low with a consequentially high water vapor pressure within the skin microclimate. The inevitable Condensatio
14、n, which occurs under these circumstances, leads to discomfort with its associated consequence in wear. 3 From a physiological point, comfort can be defined as the state that maintains the skin at a temperature of 332C and a relative； humidity of less than 100%. i.e. no liquid water on the skin surf
15、ace. This state is controlled by the escape of body produced water vapor and the clothing ability to transmit the water vapor. Table l lists the amount of water vapor produced by the body in different activities and indicates how much water vapor must be lost for comfort to be achieved. Fig.2 shows
16、the model of water vapor transfer mechanism in difference fabrics and shows that condensation depends upon the properties of the fabrics. The more difficult the water vapor transfer through the fabrics is .the greater are the water vapor concentrations at the inner fabric surface. Samples To investi
17、gate the condensation formed on the inner fabric surface,14 fabrics are listed in table 2. Three specimens shall be tested by the same method .They include the conventional fabrics, tightly woven fabrics； microporous film fabrics and nonporous film fabrics. Microporous film fabrics .such as PTFE laminated fabrics(known as breathable fabrics)have very small porous, which allow water vapor to diffuse through but prevent liquid water penetration. Water vapor can be absorbed by an other type of breathable
