Evaporation resistance

Barnes and co-workers have studied mixed-monolayer systems [278,281,283,284] and found some striking nonidealities. Mixed films of octadecanol and cholesterol, for example, show little evaporation resistance if only 10% cholesterol is present [278] apparently due to an uneven granular microstructure in films with cholesterol [284]. Another study of cellulose decanoate films showed no correlation between holes in the monolayer and permeation rate [285]. Polymerized surfactants make relatively poor water evaporation retarders when compared to octadecanol [286]. There are problems in obtaining reproducible values for r [287] due to impurities in the monolayer material or in the spreading solvent. 

Barnes and Hunter [290] have measured the evaporation resistance across octadecanol monolayers as a function of temperature to test the appropriateness of several models. The experimental results agreed with three theories the energy barrier theory, the density fluctuation theory, and the accessible area theory. A plot of the resistance times the square root of the temperature against the area per molecule should collapse the data for all temperatures and pressures as shown in Fig. IV-25. A similar temperature study on octadecylurea monolayers showed agreement with only the accessible area model [291]. 

Fig. IV-25. The evaporation resistance multiplied by the square root of temperature versus area per molecule for monolayers of octadecanol on water illustrating agreement with the accessible area model. (From Ref. 290.)...

ISO EN 9920 C lorhing insulation Estimation of the thermal insulation and evaporative resistance of clothing ensem ble... 

Solution stability. When solution stability after a defined period of time fails due to evaporation of the solution, attempts to diminish the amount of evaporation can be made. Changing the cap on the test tube to a heavier and evaporation-resistant cap can sometimes reduce the speed of evaporation enough to allow for at least 24 h of solution stability. Using the largest volume possible in the test tube will minimize the effect of evaporation. 

G.T. Bames and V.K. La Mer, The evaporation resistances of monolayers of long-chain acids and alcohols and their mixtures, in V.K. La Mer (Ed.), Retardation of Evaporation by Monolayers Transport Processes, Academic Press, New York, 1962, pp. 9-33. 

J. L. Zatz, N. D. Weinder and M. Gibaldi. Monomolecular him properties of protective and enteric film formers. 11. Evaporation resistance and interactions with plasticizers of poly (methyl vinyl ether-maleic anhydride). /. Pharm. Set., 58, 1493-6 (1969)... 

If there is any contact or bond resistance present between the fin and tube or plate on the hot or cold fluid side, it is included as an added thermal resistance on the right side of Eq. 17.5 or 17.6. For a heat pipe heat exchanger, additional thermal resistances associated with the heat pipe should be included on the right side of Eq. 17.5 or 17.6 these resistances are evaporator resistance at the evaporator section of the heat pipe, viscous vapor flow resistance inside heat pipe (very small), internal wick resistance at the condenser section of the heat pipe, and condensation resistance at the condenser section. 

The specific evaporation resistance r for the system described in the problem is about 200 sec/m ... 

A fabric sample measuring 300 x300mm is mounted on a square porous plate which is heated to a constant temperature that approximates body skin temperature (e.g. 35 °C).The plate temperature is measured by the sensor sandwiched directly underneath the plate surface. The whole apparatus is housed in a chamber so that the environmental conditions can be carefully controlled. Air speed above the specimen is regulated at 1 m/s. After steady state conditions are reached, the total evaporative resistance of the fabric is calculated by the following ... 

The intrinsic evaporative resistance of the fabric can be obtained by subtracting the evaporative resistance of the boundary air layer, measured by conducting a test on the bare plate without the fabric ... 

A typical example of reactive evaporation is the deposition of TiN. The source is evaporated resistively or more commonly by electron-beam heating in a nitrogen atmosphere.Deposition rate is reduced with... 

The ASTM F1868 standard method is widely used to evaluate/calculate thermal resistance, evaporative resistance, and THL of fabrics (ASTM F 1868, 2014). However, this standard possesses several limitations. For example, reaching a steady-state condition with some fabrics is often quite difficult during the evaluation of thermal and evaporative resistances the fabric samples may lift off from the plate, especially when tested under an ambient air velocity of 1 m/s, and this can result in abnormally high thermal and evaporative resistance values (resulting in low THL values). The standard does not specify the direction of the ambient air flow or the level of air turbulence to evaluate the thermal and evaporative resistance and the overall THL calculation procedure is very tedious and time consuming. Furthermore, although the ASTM F 1868 standard is the best way to isolate and evaluate thermal resistance and evaporative... 

The ASTM F 1291 and ASTM F 2370 standards are widely used to quantify and compare thermal and evaporative resistance values provided by clothing ensembles having different designs, fabrics, garment layers, closures, and fits (ASTM F 1291, 2010 ASTM F 2370,2010) the thermal and evaporative resistance values of clothing ensembles obtained from these standards can further be used in models to empirically predict the physiological responses of people in different environmental conditions... 

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