Condensation of Water Vapor on Waterproof Breathable Fabrics

8Journa! of Donghua University (Eng. Ed.) Vol. 20, No.2 (2003)Condensation of Water Vapor on Waterproof Breathable FabricsZHOU Xiao-hong(周小红)，WANG Shan-yuan(王善元)T31 ATeatiles Instiue, Donghua Unicersity, Shanghai 200051YUAN Guan-luo(袁观洛)Zhcjiang Technology and Sciente Intituse ，Hanghou 310014Condensation occurs when the local vapor pressurespecific frequency of a strong water vapor absorption andrises above the saturation vapor pressure at the localRuckmanl2] provided a solution to the problem of condensationtemperature in theory. A new measuring apparatuson the inner surface of fabric by perforating metal cylinderwere made to obtain temperature and relativesimulating the perspiring human body to investigate the couplehumidity simultaneously for the purpose ofmechanisms of water vapor transfer and heat trunsfer. Moreinvestigating the mechanism of condensation occurredrecently, Ren and Ruckman'. studied the water vapor ransfern the fabrics. The experiment conducted at therate when condenssation occurs on the surface of difference typestandard condition of temperature of 20C andof waterproof breathable fabrics to ascertain whether therelative humidity of 65%。The result obtained fromamount of condensation will affect the water vapor transferexperiment showed that condensation could occurrate. A method spraying water onto the hot surface of theunder the situation closed to saturation line as thefabric was employed to simulate droplet condensation. Whilst atemperature on fabric may be lower than dew point ofdiscussion of the meris of waterproof breathable fabricswater vapor in the measuring box depending on thefocused on the ability of these fabrics to reduce both heat stressexperiment conducted at an ambient environmentand uncomfortable sensation of wetness while providingtemperature of 20C. The range of fabrics studiedprotection from wind and rainshowed that PTFE laminated fabrics except nylonAll above researches focus on the effect of condensationgingham PTFE laminated fabric facilitates the loss ofon heat and water vapor transfer. Whilst no research has beenwater vapor and therefore prevent condensation. It isconducted to study whether the condensation formed on thenecessary to develop studies from a wide range ofiner surface of a fabric , this paper described the details of thefabrics, especially breathable fabrics and under badmeasuring apparatus investigatedhe mechanismexperiment condition in order to develop fabrics,condensation occured on the fabrics and also presented typicalwhich could eliminate condensation， or transportmeasuring results for representative of fabrics includedwater vapor through the fabric while remainingwaterproof breathable fabrics.waterproof.Keywords: condensaion， roaterproof breathable fabrics ,TheoriessaturationCondensation occurs when the local vapor pressure nisesabove the saturation vapor pressure at the local temperature.IntroductionThe saturation line is described he water vapor pressure-givingrise to 100% relative humidity at a specific temperature, asThe human body through the process of metabolism isshown in Fig.1constandy generating thermal energy and moisture, which12000exchange through the textile layers with its environment. Asperspiration escapes from the human body when the water吧10000vapor ransfer from clothing is low, condensation defined as80000 E. φ= 100%water droplet collected on the inner surface of the clothing may6000 Eoccur, provided that the local vapor pressure ises above thesaturation vapor pressure at the local temperarure.4000Keighley') and Ruckman!2] suggested from theory that2000 Ethe condensation occurring on the fabries may be predicted if a0saturation line and water vapor concenuration line is utilized.5(Keighley'"T devcloped a method that involved measurement ofTemperaure("C)water vapor concentration utilizing infrared absorption at theFig.1 The saturation lineReceived Oct. 22, 2002中国煤化工MYHCNMHGJournal of Donghua University (Eng. Ed.) Vol.20, No.2 (2003) 19This is particularly likely to occur on waterproof fabricssince under such conditions the rate of loss of water vapor fromSamplesthe clothing will be very low with a consequentaly high watervapor pressure within the skin microclimate. The inevitableTo investigate the condensation formed on the innercondensation, which ccurs under these circumstances, leadsfabric surface， 14 fabrics are listed in Table 2. Threeto discomfort with its associated consequence in wear.specimens shall be tested by the same method. They includethe conventional fabrics, tightly woven fabrics; microporousTable 1 Approximate metabolic water vaporproduction for various activitiesfilm fabrics and nonporous flm fabrics. Microporous film:h as PTPE laminatedfabrics ( known as breathableMecabolic Water VaporActivityfabrics) have very small porous, which allow water vapor toProductiong●m-2●d-1diffuse through but prevent liquid water penetration. Watervapor can be absorbed by another type of breathable fabricsResing350( nonporous hydrophilic film fabric) and be transferred throughBricklaying930the fabrics and emitted into the air spaces by desorptions.Walking a5.5 km . hr-11 305Tightly woven fabrics using the so called microfibers that areless than l decitex per fiber can be woven so densely that noSawing Soft Wood1400interstices can be seen betweea the fibers and thus they resistShoveling Soil1 620 ~2320water penetration.Tree Flling1 860 -2780Table 2 Measuring fabricsDigging Soil2000 .Samples NoMaterialsg. m-2Climging Ladder ( No Load)2090Climging Ladder (20 kg Load)2 780Conventional fabricsNylon/ cotton plain cloth110From a physiological point, comfort can be defined as theCotton canvas33slale that maintains the skin at a temperature of 33土2仁and a .Tightly woven fabricsrelative humidity of less than 100%，i. e. no liquid water onthe skin surface. This state is controlled by the escape of body-Nylon pile face brocade176produced water vapor and the clothing ability to transmit thePE peach face cloth24water vapor. Table 1 lists the amount of water vapor producedMicro-porous fim fabricsby the body in different activities and indicates how muchwater vapor must be lost for comfort to be achievedl.51. Fig.Nylon/ cotton plain cloth + PTFE Laminated1742 shows the model of water vapor ransfer mechanism inCotton poplin + PTFE Laminated22difference fabrics and shows that condensation depends uponNylon gingham + PTFE Laminatedthe properties of the fabrics. The more difficult the water vaportransfer through the fabrics is, the greater are the water vaporPE peach face cloth + PTFE Laminated66concentrations at the inner fabric surface.Nylon pile facc brocade + PTFE Larninated182Non-porous flm fabricsNylon taffeta + Hydropbilic Coated13Inner surface Fabric Outer surface1Nylon oxford + Hydrophilic Coated1801:Nylon gingham + Polyurethane Coated8119Nylon pile face brocade + Polyurethane Coated 12Measuring MethodDistanceFig.2 Water vapor traunsfer mechanismThe water vapor transmission ( WVT) has a directin difference fabricsrelationship to the water vapor transfer through the fabrics, but中国煤化工MYHCNMHG20Jourmnal of Donghua University (Eng. Ed.) Vol. 20, No.2 (2003)wihout reference to condensation though numerous mehodsTable3 Temperatures and relative humidityhave been developed for measuring the water vaporin measuring boxtransmission.A new measuring apparatus for investigating themechanism of condensation is shown in Fig. 3. Data logger .TemperatureRelativeWTCovering Matcrialshumiditywith a smart CMOS chip can be used to examine and recondT(K)and display temperature and relative humidity, simultaneouslyφ(%)JAy~")The mcasuring is conducted under the cootrol of a personalCoaventional fabricscomputer cnnected to the data logger through VO. TheNylon/couon plain cloth28.377.31322 .computer therefore sets the paruneters of data logger andCotton canvas29.579.11239analyzes the measuring data. Main heater and guard heater areTighty woven fabriesusecd for the purpose of keeping a constant water vapor fluxNylon pile face brocade29.475.51008generated in measuring box attached to the heat plate. ThePE peach face cloth28.867.11 189temperature of heat plate is set 32C. During the measurerment,Micro-porous flm fabricsa measuring sample is affixed to the top of measuring box,Nylon/cotton plain clothwhich equipped with temperature and telative humidityPTFE Laninated83.61359sensors. A fabric sanple size of about 10 x 10 cm2 is necessaryCoton poplin + PTFE27.586.51225 .for the measuring materials. The measurements are eried outLaminatedat 2n ambient environment tempenture of 20七and relativeNylon gingham + PTFEhumidity of 65% . The flow velocity over the sarmple, which30.191.3908minimizes the efect of boundary air layer resistance to the testPE peach face clobh + PTFE28.984.01268measurement, is 0.5 m/s.LaninaxedNylon pile face brocade +PTFE Laminated27.285.21 288PC Compuler1/0Data loggerHydrophilie fim fabresand othersr SensorsSample .Nylon uffetAe + HyrophilicCoated30.35.4917Heat Plate一-Nylon oxford + Hydrophie30.094.920- Main HeaterIntegratorNylongingham30.699.8407Polyurethane Coated- Guard HealerNylon ginghanig.3 Masuring ppartus for invstigaing the30.499.5390mechanism of condensationCondensaion on the inner fabric surface is dermnined29.3 .94.4n11from the water vapor fux in the measuring box, theenvironment conditions of temperature and relative humidityAnd saturaion vapor pressure as a function of temperatureand water vapor transmissionWVT) of the sampies. A dishis exressed by the equation'!.with dstilledl wr and covered the opening with the measuringsample is also used to examine the water vapor asmissionP. =614.3exp[ 17.06(号27.1)](2)(WV7). The water vapor tansmision ( wT) is delerminedWhere Tis lemperature (K); P is waler vapor pessre (Pa)from the weight loss during the timeinterval referred to thesamplearea based on the ASTM E00-96 Standard Method notat tmperalure T and P, is sauration vapor pessure (Pa) atdiscussed in this paper.sarme temperature T.Therefore water vapor pressure in measuring box can beResults and Discussioncalculatedusing the cquation (1) and (2) and shown inFig. 4.The resuls invoved temperature (T) and rlaiveFrom Fig.4 it is clear that condensation occurs on thehumidiy (φ) obtained simulancously from exerimentsfabrics expressed in the Area 1 under the situation are closed toconducted using data logger are shown in Table 3.Water vaporsaturation line.It is not identical to the theory thattransmission: WVT) is also shown in Table 3. Relativecondensation occurs when the local vapor pressure nises abovehumidity is defined as:the sturation vapor pressure at the local temperatore. Kelvinhass described the rlainsip betwen the water vapor presureφ=卡x10%(1)and water droplet radial when condensation occurs(i10].中国煤化工MHCNMH GJournal of Donghua University (Eng. Ed.) Vol.20, No.2 (2003) 21Other result obtained from this experiment is that waterInp=p_RT，(3)vapor transmission of fabrics associated with the Area 2 iswhere r is water droplet radial, σ is surface force of water, Pwsufficient to prevent condensation. It includes conventionalfabrics, tightly woven fabrics, and microporous flm fabrics.is density of water, R is constant.In fact, the poor water vapor permeability of these fabricsThe most interesting result is that PTFE laminated fabrics havemakes both the water vapor pressure and temperature withinachieved the permeability without condensation. This result ismeasuring box increase. When the temperature o fabric outerto be expected because, the use of such fabrics facilitates thesurface is lower than dew point of water vapor in the measuringloss of water vapor through the clothing system and thus avoidbox, depending on the experiment conducted at an ambientcondensation. It is however, noted that condensation is likelyenvironment temperature of 20t, condensation occurs. In useto occur on nylon gingham PTFE laminated fabric. This resultsituation, of course, an ambient environment temperature ismay partly be due to the properties of nylon and makelikely to be much lower than 20C. This result indicales thatconsideration of material of fabrics for coating or laminatingstudies on condensation of water vapor lransfer through theessential.fabrics are necessary for the purpose of the development offabrics, which will transport water vapor through the fabricConclusionwhile remaining waterproof.To investigate the mechanism of condensation occurred on7015the fabrics, a new measuring apparatus were made to obtain.φ=100%.temperature and relative humidity simultaneously. The6015Area Iexperiment conducted at the standard condition of temperatureof 20C and relative humidity of 65%. The result obtained5015from experiment showed that PIFE laminated fabrics except4015。nylon gingham PTFE laminated fabric facilitate the loss ofwater vapor and therefore prevent condensation. However the3015range of fabrics studied showed that condensation could occurunder the situation closed to saturation line. It is necessary to2015Area 2develop studies from a wide range of fabrics, especiallybreathable fabrics and under bad experiment condition in order1 015to develop fabrics, which could eliminate condensation, ortransport water vapor through the fabric while remainingwaterproof.1035 30252015temperature("C)References■1 Nylon/cotton plain cloth[ 1 ] Heighiley, J.H, J. Coated Fabric, 1985, 15(10), 89 - 104▲2 Cotlon canvas[2] Ruckman, J.E, 1. Coated Fabrics, 1997, 26(4). 293 -307[3] Ren, Y.J & Ruckman, J. E, J. coared fabries, 1999, 29.◆3 Nylon pile face brocade(1), 20-36●4 PE peach face cloth[ 4] Pause, B, J. Coated Fabrie, 1996, 25 (4), 311 -320口5 Ny1on/cotton plain cloth +PTFE LaminatedTanner, J. C, J. Coated Fabric, 1979, 8 (4), 312 - 322◎6 Cotton poplin +PTFE Lami natedLomax,.R, J. Coated Fabric, 1985, 15<7). 40-48△7 Nylon gingham+PTFE l.aminated[7 ] Rocy, M. V,J. Coared Fabric, 1991 , 21<7). 20-31人8 PE peach face cloth +PTFE LaminatedWeder, M, J. of Coated Fabric, 1997, 27(10), 146 - 168Gibson,P, ect, J Coalted Fabrics, 1995, 24(4), 322 -345*9 Nylon pile face brocade +PTFE Laminated[10] Cai, Y. N, & Wang N. N, Two-phase sysem of wer vapor口10 Nylon taffetaHydrophilic Polyurethane coatedfuid, University of Xi'an Jiao Tong Publisher, 1985.τ 11 Nylon oxford+ Hydrophilic Pol yurethane coated■12 Nylon gingham +Po] yurethane coaled- 13 Nylon gingham iPolyurethane coatedB14 Ny1on pile face brocade +Polyurethane coatedFig.4 Temperatures and walter vapor pressure in measuring box中国煤化工MYHCNMHG