Propellers variable-pitch propeller

Recent developments in cooling-tower fan energy management also include automatic variable-pitch propeller-type fans and inverter-type devices to permit variable fan speeds. These schemes involve tracking the loaa at a constant leaving-water temperature. 

Sperry applied for his first patent—a dynamo-electric machine— when he was twenty. His final patent application—for a variable pitch propeller— was submitted in 1930, shortly after his death. In total, 355 of his over 400 patent applications matured as actual granted patents. 

Gordon Aerolite was the result of work on phenolic moulding materials for the manufacture of variable pitch propellers for de Havilland. The use of continuous flax fibres enabled de Bruyne to produce unidirectional prepregs instead of producing reinforced mouldings. 

Axial or propeller blade fatis are eithet Irelt or gear driven. Some drivers are variable speed tnoiors. and some fatis have variable pitch blades. Iti s iecial circumstances, steam turbine, gas or gasolitie etigine drivers are used. Geais should be carefully specilied to avoid overload and should be special ) sealed to prevent moisture entering the case. 

Air is circulated by multiblade propeller-type ns that provide forced or induced drafts. Fans can be supplied with either adjustable-speed or variable-pitch blades. The fen blade pitch can be changed to vary the air-flow rate to compensate for rising or falling air temperatures. Air coolers supplied with multiple fens may be operated with some of the fens shut down. Dampers, baffles, and bypasses can also be tised to further control liquid outlet temperature. For elevated installations, platforms are generally furnished for access to header boxes and motors. 

Pavlushenko et al. (P2) studied the suspension of screened fractions of sand and iron ore in a variety of liquids, with a 1-ft. diameter unbaffled vessel filled to a depth of one foot. Square-pitch three-blade propellers of 3-, 4-, and 5-in. diameter were used, and most of the observations were made with a 1 to 4 weight ratio of solids to liquid. Thief samples were taken at various levels in the vessel. In some cases, the contents did not become uniform at any impeller speed in other cases the contents became uniform at some impeller speed and remained so at higher speeds in a third type of behavior, the upper part of the vessel reached the over-all vessel average and then exceeded it as impeller speed was increased. Using the observations from the second and third types of behavior, a critical speed was defined as the lowest impeller speed at which the solids concentration at each level, or in the upper layers of the liquid, was equal to the over-all average solids concentration. This critical speed Nc in revolutions per second had the following relation to the operating variables ... 

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