Book - School of Science and Technology

Air humidification 497Water spray nozzelsCapillary cellsEliminatorsWater in tankFresh water connectionwith water level controlvalveWater pumpFigure 17.25 Air washer, capillary typeor filaments of glass or similar material which provide an extended surface for water andair contact. Water at low pressure is caused to flow over the cells by flooding nozzles froma pump of low power consumption. The water and air have to negotiate the striations ofthe fill together, and are thus intimately mixed so that saturation up to 90% may beachieved. At the same time it may be taken that the filtering efficiency is of a reasonablyhigh order down to 3 mm. It may equally be used with refrigerated water for a full airconditioningsystem. A maximum velocity through the cells of 2 m/s is recommended.Although this form of humidifier is still available from manufacturers, it is not incommon use today.Pan humidifiersA simple pan humidifier consists of a shallow water tray, replenished by a ball valve andheated to improve its effectiveness by an electric immersion element, or a piped heatingsupply. Efficiencies are low, and since the heated water would be at a temperature thatwould present a high riskof bacteriological contamination, this type of humidifier cannotbe recommended. This type of equipment is not in common use.Sprayed coilsCooling coils fitted in air handling plant, sprayed with water from low pressure nozzles,can provide a convenient and effective means of humidification. This arrangement isdescribed later under the heading `Sprayed cooling coils' (p. 500).