Vapor resist

Poly(vinylidene chloride). Poly(viayHdene chloride) [9002-85-1] (PVDC), most of which is produced by Dow Chemical, is best known in its saran or PVC-copolymerized form (see Vinylidene chloride and poly(VINYLIDENE chloride)). As solvent or emulsion coating, PVDC imparts high oxygen, fat, aroma, and water-vapor resistance to substrates such as ceUophane, oriented polypropylene, polyester, and nylon. 

Hoeppe, P, Oohori, T., Berglund, L, and Gwosdow, A. (1985) Vapor resistance, of clothing and its effect on human response during and after exercise. In CLIMA 2000 Indoor Climate, 4, VSS Kongres, Copenhagen, pp. 97-102. 

This parameter helps distinguishing the relative importance of interfacial kinetics and bulk transport. For LpEM < Tpem water transport through the PEM is dominated by interfacial water exchange, whereas for LpEM > bulk permeation of water prevails. The data obtained in Monroe et al. yield Lpem -100-300 im. This indicates that the interfacial vaporization resistance exceeds the resistance due to bulk transport in the membrane when the membrane thickness is LpEM < 100 im. 

Vapor resist has been used to produce 8 nm structures (52) and operating devices with dimensions of 25 nm (Figure 15) (55), but suffers from similar resolution constraints as conventional resists. 

Atomic weight Melting point Boiling point Density Heat of fusion Heat of vaporization Resistivity... 

A bag of vapor resistant fabric is allowed to expand into a housing of much smaller diameter than that of the storage tank. This is a lower cost construction than either of the other two. 

Chemical Surface Modification. In considering the interface, one must contemplate not only the possibility of moisture disrupting the bond but also the possibility of corrosion of the substrate. Corrosion can quickly deteriorate the bond by providing a weak boundary layer before the adhesive or sealant is applied. Corrosion can also occur after the joint is made and, thereby, affect its durability. Mechanical abrasion or solvent cleaning can provide adhesive joints that are strong in the dry condition. However, this is not always the case when joints are exposed to water or water vapor. Resistance to water is much improved if metal surfaces can be treated with a protective coating before being bonded. 

We next examine a simplified expression for the total water vapor resistance that often adequately describes diffusion of water vapor from the sites of evaporation in cell walls to the turbulent air surrounding a leaf and is useful for considering diffusion processes in general. We will consider the case in which nearly all of the water vapor moves out across the lower epidermis and when cuticular transpiration is negligible. By Equations 8.11 and 8.12, the total resistance then is... 

AvenaBustillos, R.D., Krochta, J.M., and Saltveit, M.E. (1997). Water vapor resistance of red delicious apples and celery sticks coated with edible caseinate-acetylated monoglyceride films. J. FoodSci. 62(2), 351-354. 

The reciprocal of permeance is called (unit) vapor resistance and is expressed as... 

Note that vapor resistance represents the resistance of a material to water vapor transmission. 

The overall vapor resistance of a composite building stnicture that consists of several layers in series is the sum of the resistances of the individual layers and is expressed as... 

The condensation and even freezing of moisture In walls without effective vapor retarders is a real concern in cold climates, and it undermines the elfecliveness of insulations. Consider a wood frame v/all that is built around 38 mm x 90 mm (2x4 nominal) wood studs. The 90-mm-wide cavity between the studs is filled with glass fiber insulation. The inside is finished with 13-mm gypsum wallboard and the outside with 13-mm wood liberboard and 13-mm x 200 mm wood bevel lapped siding. Using manufacturer s data, the thermal and vapor resistances of various components for a unit wall area are determined to be... 

SOLUTION The thermal and vapor resistances of different layers of a wall are given. The possibility of condensation or freezing of moisture in the wall is to... 

Assumptions 1 Steady operating conditions exist. 2 Heat transfer through the wall is one-dirnensional. 3 Thermal and vapor resistances of different layers of the wall and the heat transfer coefficients are constant. 

Moisture vapor resistance Excellent Good Fair Fair Poor Good Poor Fair Fair... 

The quantity in square brackets is the film Rayleigh number, and will occur again below. Nu values calculated for the three two-phase systems studied here are listed in Table I for (T -T ) - 10 K and are compared with the experimental values. We see that the experimental values for the supercritical systems are far in excess of this supposed upper bound. Thus, any explanation must not only account for a strongly diminished vapor resistance but must also predict a reduction in the liquid film resistance. 

For distillations, the vapor resistance dominates, whereas for the stripping or absorption of slightly soluble materials, the liquid resistance dominates. In Equation (12.75), m is related to the VLE ratio [Equation (12.19)], and for the binary distillation of an i-j mixture is defined as the slope of the equilibrium line on a y-x diagram ... 

Estimates of the order of magnitude for each of these resistances indicate that several simplifications can be made [33], that is, the axial resistance of both the pipe wall and the liquid-wick combination may be treated as open circuits and neglected and the liquid-vapor interface resistances and the axial vapor resistance can typically be assumed to be negligible, leaving only the pipe wall radial resistances and the liquid-wick resistances at both the evaporator and condenser. 

Hie adiabatic vapor resistance, although usually negligible, can be found as... 

Depending on whether vanadium is vaporized resistively or by means of an electron beam, the experimental procedures for metal preparation and deposition are sufficiently different that each merits a separate treatment. The type of apparatus used is a rotary reactor of the Torrovap design (Fig. 2). 

For collective protection, the army standardized the M20 Simplified Collective Protection Equipment in 1986. This system turned one room of a building into a protected area by (1) lining the walls with a chemical/biological vapor-resistant polyethylene liner and (2) providing 200 cu ft of filtered air per minute. In addition, the army concentrated on modular collective protection equipment for chemical threats to vehicles, vans, and shelters. The Department of the Army identified 43 systems in 1980 that required chemical protection. New systems that were developed each year created a major, longterm project to correct the deficiency that had been discovered after the 1973 Yom Kippur War.207,210... 

Famworth, B., Lotens, W.A., Wittgen, P.P.M.M., 1990. Variation of water vapor resistance of microporous and hydrophilic films with relative humidity. Text. Res. J. 60, 50-53. 

Uses Barrier coating used as basecoat for paper coatings incl. food pkg. Features Rec. where heavier applies, or coatings with different functional props, need to be applied provides some water resist. enhanced grease/vapor resist. 

Features Exc. water/water vapor resist., antibiocking fuiiy repuipabie Regulatory FDA approved for food contact Properties Clear Tykote WTR-AF [Reichhold]... 

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