Humidification humidifier types

Humidification. For wiater operation, or for special process requirements, humidification maybe required (see Simultaneous HEAT and mass transfer). Humidification can be effected by an air washer which employs direct water sprays (see Evaporation). Regulation is maintained by cycling the water sprays or by temperature control of the air or water. Where a large humidification capacity is required, an ejector which direcdy mixes air and water in a no22le may be employed. Steam may be used to power the no22le. Live low pressure steam can also be released directly into the air stream. Capillary-type humidifiers employ wetted porous media to provide extended air and water contact. Pan-type humidifiers are employed where the required capacity is small. A water filled pan is located on one side of the air duct. The water is heated electrically or by steam. The use of steam, however, necessitates additional boiler feed water treatment and may add odors to the air stream. Direct use of steam for humidification also requires careful attention to indoor air quahty. 

Figure 11-69 describes a typical central system. Either water or direct-expansion refrigerant coils or air washers may be used for cooling. Steam or hot-water coils are available for heating. Humidification may be provided by target-type water nozzles, pan humidifiers, air washers, or sprayed coils. Air cleaning is usually provided by cleanable or throwaway filters. Central-station air-conditioning units in capacities up to about 50,000 cu ft/min are available in prefabricated units. 

Many different types of humidifiers are in common use the humidification process is simply achieved by adding moisture into the air to be conditioned. 

In this type of humidifier, the water required for the humidification process is stored within the unit and is normally fed automatically from the water mains. However, smaller portable units do not have this automatic facility and have to be manually filled with water as required. 

Humidification can be done at the system level by having humidifier section at the air-handling unit supplying fresh air. The humidifier can be electric or gas type. Another method is to use evaporative pads such as GLASdek from Munters. This eliminates the use of gas or electricity for humidification. 

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. 

Another type of process of some importance occurs when adiabatic cooling or humidification takes place between air and water that is recycled as illustrated in Fig. 4.25. In this process the air is both cooled and humidified (its water content rises) while a little bit of the recirculated water is evaporated. At equilibrium, in the steady state, the temperature of the air is the same as the temperature of the water, and the exit air is saturated at this temperature. By making an overall energy balance around the process Q = 0), we can obtain the equation for the adiabatic cooling of the air. 

Fig. 4 (a) Try type bioreactor (i) chamber, (2) trays (5) water valve, (4) UV tube, (5) humidifier, (6) air inlet, (7) airflow meter (S, 10) air filter (9) air heater and humidifier, (77) air outlet, (72) tray holder, (b) Column bioreactor (7) water-bath where humidification occurs, (2) air inlet, (i) air filter, (4) sparger, (5) filter paper, (6) solid substrate, (7) cotton... 

Methods of Active Humidification Active humidification requires a discrete, external humidification system. In a laboratory environment, a sparge-type humidifier, as illustrated in Figure 6.9, is often used. In this system, gas is sparged through a porous rock and into heated water to absorb moisture before entering the fuel cell. This system is not useful outside the laboratory because it is dependent on orientation and almost never 100% efficient. Care must be used to ensure proper humidification is achieved and careful calibration is neccessary. 

The humidification conditions have a big impact on the water content of membrane. Ciureanu [32] took an experiment on Nafion under various types of humidification cathodic (Ch Ad), anodic (CdAh), anodic and cathodic (Ch Ah), and no humidification at all (CdAd). It is indicated that the resistance of membrane is small and relatively insensitive to the anodic humidification when the fuel cell stack is cathodic humidified (ChAd and ChAh). On the contrary, the resistance is high and strongly dependent on current density and anodic humidification when the stack is not cathodic humidified (CdAh and CdAd). 

Fig. 16 Various types of humidification (six diagrams showing conventional fuel cell humidification methods used in research (a) the self-humidifying fuel cell with no active external humidification of the reactant streams, (b) the setup featuring liquid water injection into an inactive portion of the fuel cell, (c) a typical dew point humidifier, (d) the evaporation setup, (e) the steam injection system and (f) the flash evaporation method (from Evans, 2003).

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