Humidifying towers

In a humidifier in which the make-up liquid is only a small proportion of the total liquid circulating, its temperature approaches the adiabatic saturation temperature Os. and remains constant, so thac there is no temperature gradient in the liquid. The gas in contact with the liquid surface is approximately saturated and has a humidity Jf5. 

From these equations the temperature %2 and the humidity 2 of the gas leaving the humidifier may be calculated in terms of the height of the tower. Rearrangement of euuation 13.61. eives  

Thus the ratio of the actual increase in humidity produced in the saturator to the maximum possible increase in humidity (that is, the production of saturated gas) is equal to (1 - ), and Complete saturation of the gas is reached exponentially. A similar 

Further, the relation between the temperature and the humidity of the gas at any stage 

Calculation of the change in the condition of the liquid and the gas in a humidification tower is rendered more difficult since equation 13.49, which was derived for the air-water system, is no longer applicable. LEWIS and have developed a method of 

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Operating line, humidifying towers 778 Optimum pipe diameter, example 371 — water velocity, heat exchanger 505 Orifice meter 244,246, 248... 

The recently replaced gas purification section was already operating outside its design parameters because of the extra heat load placed on the system as a result of increasing the overbed water usage in the roaster. The plate heat exchangers of the humidifying tower/wash... 

The chamber and humidifying tower temperatures are maintained at 38°C. As described in Annex Al.l, the apparatus may be a water tank with an immersion heater or test chamber with an air dispersion pipe assembly. The key design feature is that condensation is formed on the speci-... 

Hot, humid air is created by bubbling compressed air through a bubble (humidifying) tower containing hot, deionized water. Salt solution is typically moved from a reservoir through a filter to the nozzle by a gravity-feed system (Fig. 11.33). When the hot, humid air and the salt solution mix at the nozzle, it is atomized into a corrosive fog. This creates a 100 percent relative humidity condition in the exposure zone. For a low humidity state in the exposure zone of the chamber, air is forced into the exposure zone via a blower motor that directs air over the energized chamber heaters (Fig. 11.34). 

Cooling towers and other sources of standing water (e.g., humidifiers) are thought to be typical sources of Legionella in buildings. 

Where water is evaporated from a circuit, such as a cooling tower, evaporative condenser, or humidifier, it must be remembered that there is no way of avoiding a steady bleed-off or frequent flushing, to restrict the concentration of dissolved solids. Much trouble arises from the efforts of well-wishing but misguided persons who stop the flow of bleed-off to save water . 

On the large scale, air and water are brought into countercurrent contact in a cooling tower which may employ either natural draught or mechanical draught. The water flows down over a series of wooden slats which give a large interfacial area and promote turbulence in the liquid. The air is humidified and heated as i( rises, while the water is cooled mainly by evaporation. 

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... 

Some workers have attempted to base the design of humidifiers on the overall heat transfer coefficient between the liquid and gas phases. This treatment is not satisfactory since the quantities of heat transferred through the liquid and through the gas are not the same, as some of the heat is utilised in effecting evaporation at the interface. In fact, at the bottom of a tall tower, the transfer of heat in both the liquid and the gas phases may be towards the interface, as already indicated. A further objection to the use of overall coefficients is that the Lewis relation may be applied only to the heat and mass transfer coefficients in the gas phase. 

A number of processes can be considered double alkah processes, but most developmental work has emphasized sodium-based systems, which use lime for regeneration. This system pretreats the flue gas in a prescrubber to cool and humidify the gas and to reduce fly ash and chlorides. The gas passes through an absorption tower where SO2 is removed into a scrubbing solution, which is subsequently regenerated with lime or hmestone in a reaction tank. 

The key properties of mixtures of air and water vapor are described in Section 9.1. Here the interactions of air and water in packed towers under steady flow conditions will be analyzed. The primary objectives of such operations may be to humidify or dehumidify the ait as needed for particular drying processes or other processes, or to cool process water used for heat transfer elsewhere in the plant. Humidification-dehumidification usually is accomplished in spray towers, whereas cooling towers almost invariably are filled with seme type of packing of open structure to improve contacting but with minimum pressure drop of air. 

Air shall be humidified in saturation tower at temperature several degrees higher than that of the cabinet Level of the water must be maintained automatically Atomizers shall be made of inert material Adjustable baffles to obtain uniform distribution of the spray Level of the salt solution shall be maintained automatically... 

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