*1.2.3. Air drier*

The air drier (Fig. 4) is a proprietary designed manufactured in Australia by B.C. Johnson Ltd. It is designed for inlet air conditions of 1.5 ib/sec at a pressure of 115 psig, a maximum temperature of 105 <sup>0</sup> F and an ambient relative humidity at compressor inlet of 100%. The dryer is required to provide an outlet humidity equivalent to -50 0 F at atmospheric pressure after a two hour drying cycle.

**Figure 4.** Air Drier System

The air dryer is of the single tower at a larger stage. Regeneration is accomplished by air pre-heated in an 80 kW electrical heater and forced through the dryer stack in a counterflow direction by a centrifugal blower. The desiccant employed is 800 lb of activated alumi‐ na in a 2 ft diameter by 4.5 ft high bed, preceded by 80lb of buffer desiccant whose purpose is to prevent damage to the main desiccant by liquid carry over from filtration equipment. The dryer is fitted with a water coil for cooling the desiccant bed after regeneration and a felt pad and fibreglass after-filter is installed to prevent any carryover of desiccant dust into the storage vessels.

In operation, dew points of as low as -80 0 F have been obtained after regeneration. With one compressor in operation, drying times of up to six hours have been achieved, although a higher final dew points than -50 <sup>0</sup> F regeneration time is about four hours for heating and four hours for cooling.

#### *1.2.4. Air storage vessels*

*1.2.2. Filtration system*

78 Wind Tunnel Designs and Their Diverse Engineering Applications

automatic water drains.

temperature of 105 <sup>0</sup>

**Figure 4.** Air Drier System

after a two hour drying cycle.

*1.2.3. Air drier*

After compression, air from each compressor is passed through individual shell and tube af‐ ter coolers, centrifugal action water separators, pre-filters and oil-mist filters. The pre-filters consist of a centrifugal action separator combined with a 70 micron porosity, sintered bronze filter element. The oil mist filters are a proprietary design of Daltech Engineering In‐ corporated, USA, and consist of a stainless wire wool pre-filter and a chemical absorption type main element. These filter units are claimed to have a 99.4% filtration efficiency for all oil particulates down to 0.5 microns. Both pre-filters and oil-mist filters operate with a 'col‐ our change' principle in that, as the element becomes saturated with oil, its colour changes from light pink to bright red. All filters, after coolers and water separators are fitted with

The air drier (Fig. 4) is a proprietary designed manufactured in Australia by B.C. Johnson Ltd. It is designed for inlet air conditions of 1.5 ib/sec at a pressure of 115 psig, a maximum

dryer is required to provide an outlet humidity equivalent to -50 0 F at atmospheric pressure

F and an ambient relative humidity at compressor inlet of 100%. The

Four storage vessels (Fig.5 ), each 5 ft diameter by 11 ft 6 ins overall length and designed for a working pressure of 130 psig have been installed with a total storage capacity o f800 cubic feet as mentioned earlier were placed in an overhead structural steel support in the Aerody‐ namics laboratory near which a supersonic wind tunnel was built.

### *1.2.5. Air conditions 105 0 F at atmospheric pressure*

Air conditions in the storage vessels are a volume of 800 cubic feet at ambient temperature and dried to a dew point the equivalent of at least -50 <sup>0</sup> F at atmospheric pressure. For inter‐ mittent operation, maximum pressure is 125 psia. Maximum intermittent mass flow rates are in the region of 10 to 20 lb/sec to limit the system pressure loss to approximately 5 psi. Maximum continuous mass flow is 1.5 lb/sec with a pressure not exceeding 110 psia.

Because the pressure available for supersonic tunnel injection is comparatively low, care was taken in the design and piping and filtration equipment to reduce pressure losses. The overall pressure drop between compressor outlet and storage vessels has been kept between 3 and 5 psi depending upon filter condition.
