Document Kz4yn3XBRYGJVY4brmLb7exK

HEATINC VENTILATING AIR CONDITIONING GUIDE 1943 one bank spraying with the air stream and one against it. The number of nozzles required depends upon their design, the quantity of air handled, and the arrangement of the nozzles. Scrubbers generally consist of eliminator-type baffle plates placed in the air stream to cause several reversals of the direction of air flow. The scrubber plates are more effective as air cleaners than as humidifiers. All washer chambers should have inlet diffuser plates to aid in producing more uniform air'flow through the washer spray chamber. These inlet vanes also aid in preventing spray water from being thrown into the air duct ahead of the washer. However, if the water spray is against the air. flow, the ordinary perforated diffuser plate is not sufficient, and specially designed eliminator baffles, must be used to prevent spray from passing f Fig. 1. Typical Single Bank Air Washer Fig. 2. Typical Two Bank Air Washer into the air inlet duct. At the outlet en<J of the washer suitable flooded eliminator plates, which will cause from 4 to 6 reversals of the direction of air flow, should be installed for the purpose of removing drops of unvaporized water from the leaving air. When the air carries certain substances mixed.with it, the spray water may become acidulated and special consideration must be given to the materials used, to reduce the corrosive action. Essential items in air. washer operation are: uniform distribution of the air across the chamber section above the level of the water in the. sump; moderate velocities of air flow, 300 to 600 fpm in the spray cham ber;, ah adequate amount of spray water broken up into a fine mist throughout the air stream; sufficient length of air travel through the water spray and over thoroughly wetted surfaces; and the elimination of free moisture from the air as it leaves the unit. 532 CHAPTER 27. SPRAY EQUIPMENT Washers are sometimes arranged in two or more stages to cool through long ranges or to increase the overall efficiency of heat transfer between the air and the heating or cooling medium. A multi-stage washer is equivalent to a number of washers in a series arrangement. Each stage is in effect a separate washer. Usually the catalog capacity of a washer is expressed in cubic feet of air per minute and is based upon- an air velocity of 500 fpm through the gross inlet area of the unit. At this rating spray type washers handle about 234 gpm f water per bank per square foot of area, that is, about 5 gpm per bank per 1000 cfm. These proportions of air, water, area, and velocity may be departed from to meet the needs of some particular job, but certain limiting relationships should be observed. For a single stage air washer, a 15 F drop in dry-bulb temperature of the air passing through the washer is about the maximum that should be anticipated. For greater decrease in dry-bulb temperature, multi-stage washers should be utilized. A rise of 6 F should be the calculated maxi mum for the spray water. The width and height of a washer may be dictated by space limitations outside the washer, such as headroom, or by the inside space requirements, such as face area needed by a bank of cooling coils. The length of a washer is determined by the number of spray banks, or scrubber plates,' and if cooling coils are installed in the unit, by the number of banks of coils. Roughly, a spray space of about 2 ft 6 in. in length is required for each bank of sprays; leaving eliminators require about 1 ft 6 in., and entering eliminators about 1 ft. The resistance to air flow through an air washer varies with the type of eliminators, number of banks of sprays, direction of spray, air velocity, type of scrubber plates, and size and type of cooling coils if located in the washer. Manufacturers should be consulted to obtain the resistance for a particular installation. HUMIDIFICATION WITH AIR WASHER Air humidification can be accomplished in three ways with an air washer. These are: (1) use of recirculated spray water without prior treatment of the air, (2) preheating the air and washing it with recircu lated spray water, arid'(3) using heated spray water. In any problem of air washing the air should not enter the washer with a dry-bulb tempera ture less than 35 F so that there will be no danger of freezing the spray water. Method 1. Except for the small amount of energy added from outside by the recirculating pump in the form of shaft work, and for the small amount of heat leak from outside into the apparatus, including the pump and its connecting piping, the process would be strictly adiabatic. Evaporation from the liquid spray, would therefore be expected to bring the air immediately in contact with it to saturation adiabatically; and, since the liquid is recirculated, its temperature would be expected to adjust to the thermodynamic wet-bulb temperature of the entering air. It does not follow from the above reasoning that the whole air stream is brought to complete saturation, but merely that its state point should move along a line of constant thermodynarriic wet-bulb temperature as 533 r