Humidity of the air

Sohd sorbent materials have the abiUty to adsorb water vapor until an equiUbrium condition is attained. The total weight of water that can be adsorbed in a particular material is a function of the temperature of the material and of the relative humidity of the air (see Adsorption). To regenerate the sorbent, its temperature must be raised or the relative humidity lowered. The sohd sorbents most commonly used are siUca (qv), alumina (see Aluminum compounds), and molecular sieves (qv). 

Metal alkoxides are strongly caustic and are decomposed by the humidity of the air or moisture of the skin, requiring the use of protective glasses and gloves. 

Adiabatic-Saturation Temperature, or Constant-Enthalpy Lines If a stream of air is intimately mixed with a quantity of water at a temperature t, in an adiabatic system, the temperature of the air will drop and its humidity will increase. If t, is such that the air leaving the system is in equihbrium with the water, t, will be the adiabatic-saturation temperature, and the line relating the temperature and humidity of the air is the adiabatic-saturation line. The equation for the adiabatic-saturation line is... 

Factors considered to affect pond performance are air temperature, relative humidity, wind speed, and solar radiation. Items appearing to have only a minor effect include heat transfer between the earth and the pond, changing temperature and humidity of the air as it traverses the water, and rain. 

Increasing the relative humidity of the air to 45 to 60% can significantly reduce charging where rates of surface separation are relatively small and... 

Calcium cyanide Ca(CN)2 Reacts with air moisture to release HCN. If finely ground and the relative humidity of the air is >35%, this can occur fairly rapidly Releases HCN slowly on contact with water or CO2, or rapidly with acids Do not handle with bare hands Nonflammable white powder or crystals... 

If you are considering recovering solvent from air, is the relative humidity of the air low enough to allow adsorption ... 

Sling psychrometer An instrument used to measure the dry-bulb and wet-bulb temperatures of the air, from which the humidity of the air can be determined by means of calculations, tables, or charts. 

The humidifier is a means of increasing the absolute humidity of the air although usually controlled from a relative humidity sensor. It should be positioned where shown so that it can correct any over-dehumidification by the cooling coil (see Section 29.8). 

This important fact was first demonstrated by Vernon in a series of classical experiments, some of which are summarised graphically in Fig. 3.1. He showed that rusting is minimal in pure air of less than 100 l o relative humidity but that in the presence of minute concentrations of impurities, such as sulphur dioxide, serious rusting can occur without visible precipitation of moisture once the relative humidity of the air rises above a critical and comparatively low value. This value depends to some extent upon the nature of the atmospheric pollution, but, when sulphur dioxide is present, it is in the region of 70-80%. Below the critical humidity, rusting is inappreciable, even in polluted air. 

Unsealed products will be affected by low humidity of the air in the cooled space and may suffer dehydration. Conversely, some food products such as fresh meat will deteriorate in high humidities. Since the dewpoint of the air approaches the fm surface temperature of the evaporator (see also Chapter 24), the inside humidity is a function of the coil AT. That is to say, the colder the fin surface, the... 

In the cooling tower the temperature of the liquid falls and the temperature and humidity of the air rise, and its action is thus similar to that of an air humidifier. The limiting temperature to which the water can be cooled is the wet-bulb temperature corresponding to the condition of the air at inlet. The enthalpy of the air stream does not remain... 

BS 1339 1965(1981) British Standard 1339 (British Standards Institution, London) Definitions, formulae and constants relating to the humidity of the air. 

Neglecting radiation losses, calculate the mass of dry air passing through the dryer and the humidity of the air leaving the dryer. 

Reacts with air moisture to release HCN. If finely ground and the relative humidity of the air is >35%, this can occur fairly rapidly... 

For organic solvent processes, the humidity of the air can also play a role in the product quality. One particular problem which can arise is that of condensation of water in the bed. In the vicinity of the nozzle, local cooling may be experienced due to solvent evaporation (Smith and Nienow, 1982), as discussed in Sec. 2.3. Asa consequence of this local cooling, the temperature... 

Three color changes were observed blue, violet and red. From the information provided, the blue form appeared to be the anhydride, CoCl2. When exposed briefly to air containing water vapor, the anhydrous cobalt chloride turned violet, CoCl2 2H20. Upon further standing in air, the dihydrate was converted to the fully hydrated form, CoCl2 6 H20. The color of the anhydride-hydrate depended upon the relative humidity of the air to which it was exposed. 

This process is known as efflorescence. It would appear that the relative humidity of the air was rather low for this to occur. When rehydrated and gently dried, the hydrate reappeared indicating a reversible reaction ... 

Soil is hygroscopic. The water content of air dry soil will increase and decrease as the relative humidity of the air it is exposed to changes. The uptake of water by oven dry soil is shown in Figure 7.10. Thus, determination of water content just before analysis is critical. 

Most cabinets incorporate a device whereby the test pieces can be sprayed with water at intervals for various periods of time with or without interrupting irradiation. Distilled water is normally used to avoid any effect of impurities. The humidity of the air between... 

The temperature at which the relative humidity of the air exceeds 100% and water condenses out of the vapour phase to form liquid (dew). 

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