Absorptivity water vapor

Test Methods. Tests for water repeUency of concrete and masonry have been described by several authors (72,94). The National Bureau of Standards (NBS) evaluated fifty-five clear water repeUents for masonry surfaces (95). Performance tests included water absorption, water-vapor transmission, resistance to efflorescence, change in appearance, and durability to accelerated and outdoor weathering. More recently, the National Cooperative Highway Research Program conducted a study of several organic and sihcone water-repeUent treatments. The results are communicated in Report 244 (96). The testing procedure used in this study is now a popular method for evaluating water-repeUent treatments on concrete. 

Ashton 117, 118) reported on studies for predicting the durability of clear finishes for wood from the basic properties of the finishes. He reviewed the relationships between composition, water absorption, water vapor permeability, tensile strength, and elongation. Single and multiple regressions were used to establish the relative importance of the different properties in determining the durability of the finishes on wood exposed outdoors. The durability of clear phenolics and alkyds could be predicted from water absorption and permeability properties. Tensile strength and mechanical properties were of less importance. 

Keywords Damages to Building Materials / Water Absorption / Water Vapor / DiBiision / Masonry Protection / Silicon Resin Network... 

Compressive strength Tensile bond adhesion Water absorption Water-vapor permeability Air content Elexural strength... 

Water absorption Water vapor permeability Gas permeability Permeability of packages Oxygen transmission using a coulometric sensor Water vapor transmission Water vapor transmission by dynamic method Water vapor transmission by mfrared spectroscopic methods... 

Cereal Products. Breakfast cereals are susceptible to moisture absorption and require good water-vapor- and fat-barrier packagiag that retains dehcate flavors. Breakfast cereals are packaged in polyolefin coextmsion films in the form of pouches or bags within paperboard carton outer sheUs. 

Significant piopeities of insulation (Table 1) include tliermal conductivity, fite resistance, and ntiniinal production of toxic gases primarily during combustion. Other criteria include water-vapor permeability, resistance to water absorption, and dimensional stability over prolonged periods of submission to extreme environments. 

Such a unique hierarchical stmcture gives leather several advantages (/) transformabiUty into any desired shape, (2) resistance to penetration of wind, water, and other materials, (3) breathabiUty (water vapor and air permeabiUty, and water absorption), (4) flexibiUty, and (5) processibiUty into finished forms having a grain or suede surface. 

The high solubility of the salt and resultant low water vapor pressure (58) of its aqueous solutions ate usehil ia absorption air conditioning (qv) systems. Lithium bromide absorption air conditioning technology efficiencies can surpass that of reciprocal technology usiag fluorochlorocarbon refrigerants. 

Water Vapor The contribution to the emissivity of a gas containing H9O depends on Tc andp L and on total pressure P and partial pressure p . Table 5-8 gives constants for use in evaluating . Allowance for departure from the special pressure conditions is made by multiplying by a correction factor C read from Fig. 5-21 as a function of (p + P) and p ,L. The absorptivity 0t of water vapor for blackbody radiation is evaluated from Table 5-8 but at T instead of Tc and at p LT /Tc instead of p, h. Multiply by (Tc/Ti)° . ... 

Example 6 Solvent Rate for Absorption Let us consider the absorption of acetone from air at atmospheric pressure into a stream of pure water fed to the top of a packed absorber at 25 C. The inlet gas at 35 C contains 2 percent by volume of acetone and is 70 percent saturated with water vapor (4 percent H2O by volume). The mole-fraction acetone in the exit gas is to be reduced to 1/400 of the inlet value, or 50 ppmv. For 100 kmol of feed-gas mixture, how many Idlomoles of fresh water should be fed to provide a positive-driving force throughout the pacldug How many transfer units will be needed according to the classical adiabatic method What is the estimated height of pacldug required if Hqq = 0.70 m ... 

Note that the group on the left side of Eq. (14-182) is dimensionless. When turbulence promoters are used at the inlet-gas seclion, an improvement in gas mass-transfer coefficient for absorption of water vapor by sulfuric acid was obsei ved by Greenewalt [Ind. Eng. Chem., 18, 1291 (1926)]. A falhug off of the rate of mass transfer below that indicated in Eq. (14-182) was obsei ved by Cogan and Cogan (thesis, Massachusetts Institute of Technology, 1932) when a cauTiiug zone preceded the gas inlet in ammonia absorption (Fig. 14-76). 

Mass concentration units for ambient measurements are mass (/xg) per unit volume (m ). Size classification involves the use of specially designed inlet configurations, e.g., PMjq sampling. To determine mass concentration, all the particles are removed from a known volume of air and their total mass is measured. This removal is accomplished by two techniques, filtration and impaction, described in Chapter 13. Mass measurements are made by pre-and postweighing of filters or impaction surfaces. To account for the absorption of water vapor, the filters are generally equilibrated at standard conditions T = 20°C and 50% relative humidity). 

The influence of the absorption oi water vapor from the atmosphere into the fluid... 

Atmospheric attenuation is the consequence of absorption of radiation by the medium present between emitter and receiver. For thermal radiation, atmospheric absorption is primarily due to water vapor and, to a lesser extent, to carbon dioxide. Absorption also depends on radiation wavelength, and consequently, on hie temperature. Duiser approximates transmissivity as... 

The atmospheric attenuation factor takes into account the influence of absorption and scattering by water vapor, carbon dioxide, dust, and aerosol particles. One can assume, as a conservative position, a clear, dry atmosphere for which = 1. 

The total furnace heat absorption may be estimated by using the calculated furnace exit gas temperature and analysis to determine the enthalpy (excluding the latent heat of water vapor) and thus deducting the heat rejection rate from the net heat input rate. 

We have now discussed three types of intermolecular forces dispersion forces, dipole forces, and hydrogen bonds. You should bear in mind that all these forces are relatively weak compared with ordinary covalent bonds. Consider, for example, the situation in HzO. The total intermolecular attractive energy in ice is about 50 kj/mol. In contrast, to dissociate one mole of water vapor into atoms requires the absorption of928 kj of energy, that is, 2(OH bond energy). This explains why it is a lot easier to boil water than to decompose it into the elements. Even at a temperature of 1000°C and 1 atm, only about one H20 molecule in a billion decomposes to hydrogen and oxygen atoms. 

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