Relative humidity control

Mixing dry and water vapor-saturated air in defined proportions also can be used to generate constant relative humidity. Control of flow rates and the water vapor content of the dry and saturated air are essential [27,28],... 

Relative humidity controls None None None Heat obviates condensation... 

RHCV = Relative Humidity Control Valve RHE = Relative Humidity Element SA = Supply Air... 

Control of the vapor pressure in the headspace over a solid can also be used to maintain a relative humidity over a solid. As shown in Eq. (4), the relative humidity is directly correlated to the partial pressure of water in the vapor phase. To utilize this technique for relative humidity control, the headspace above the sample must be completely evacuated prior to analysis. Pure water vapor can then be carefully admitted to the vapor phase. Because only water vapor is present, the pressure measured over the system is directly related to the relative humidity over the sample. ... 

Attaining and measuring an equilibrium weight of sorbed water vapor. Gravimetric measurement of moisture uptake can occur continuously or discontinuously. Continuous measurement usually involves placing a sample on a balance in a temperature- and relative humidity-controlled environment. Microbalances in closed systems have been used successfully for this purpose, " and commercial systems are now available that can accurately and precisely control relative humidity and simultaneously monitor sample weight. 

Consideration should be given to temperature and relative humidity control once a significant volume of filtered air is delivered across operators, comfort conditioning is usually found necessary. 

Kinsman, D.J.J. 1976. Evaporites Relative humidity control of primary mineral facies. Journal of Sedimentary Petrology, 46 273-279. 

FIGURE 10.28 Effect of RH on fuel cell internal resistances (RC = electrode resistance, RM = membrane resistance). (Reprinted from /. Power Sources, 184, L. A. M. Riascos. Relative humidity control in polymer electrolyte membrane fuel cells without extra humidification, 204-211, Copyright (2008), with permission from Elsevier.)... 

L. A. M. Fiascos. 2008. Relative humidity control in polymer electrolyte membrane fuel cells without extra... 

Most xenon arc testers simulate the effects of moisture through water spray and/or humidity control systems. The limitation of water spray is that when relatively cold water is sprayed onto a relatively hot test specimen, the specimen cools down. This may slow down the degradation. However water spray is very useful for simulating thermal shock and erosion. In a xenon arc, highly purified water is necessary to prevent water spotting. Because humidity can affect the degradation type and rate of certain indoor products, such as many textiles and inks, control of relative humidity is recommended in many test specifications. Modern xenon test chambers are available with relative humidity control. 

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