. Applied thermodynamics for engineers. inder. The capacity, temperature rise, water con-sumption, power consumption, etc., are computed as before. A considera-ble saving in power follows the change to two stages. 233. Problem. Find the cylinder dimensions and power consumption of adouble-acting single-stage air compressor to deliver 4000 cu. ft. of free air per minute at 100 lb. gauge pres-sure at 80 r. p. m., the intakeair being at lb. absolutepressure, the piston speed640 ft. per minute, clearance4 per cent, and the clearance-expansion and compressioncurves following the law Lay off th
. Applied thermodynamics for engineers. inder. The capacity, temperature rise, water con-sumption, power consumption, etc., are computed as before. A considera-ble saving in power follows the change to two stages. 233. Problem. Find the cylinder dimensions and power consumption of adouble-acting single-stage air compressor to deliver 4000 cu. ft. of free air per minute at 100 lb. gauge pres-sure at 80 r. p. m., the intakeair being at lb. absolutepressure, the piston speed640 ft. per minute, clearance4 per cent, and the clearance-expansion and compressioncurves following the law Lay off the distance GH,Fig. 84, to represent the (un-known) displacement of theDesign of Compressor. ^-^^^^^ ^^^^^ ^,^ ^^.^j ^^11 j) Since the clearance is 4 per cent, lay off GZ = Z>, determining ZP as acoordinate axis. Draw the lines TU, VW, YX, representing the absolute pres-sures indicated. The compression curve CE may now be drawn tlirough C, andthe clearance expansion curve DI through D. The ideal indicator diagram isCEDL We have,. !.OiJ> Fig. M. Art. 233 COMPRESSOR DESIGN 131 Px>Fz>i-3^ = ,i-35 or ^/= (^^) V^ - [jUT 0-0^^= ^F^i-35= P^Fc>35 or F^= (^^^j Fc- (^^) Z>= ). P^TV P«TV-3S or F. E Pa Vd mr- 04 2) = A / P \ /1Q 7\ Vb = f 1^ j Fc = 1^] Z) = Z). But^.B= Vb— Fi = 2) is the volume of free air drawn into the cylinder:AB-^GH =:2 is the volumetric efficiency:* to compress 4000 cu. ft. of free air perminute the piston displacement must then be 4000^ = ^ cu. ft. per the compressor is double-acting, the necessary cylinder area is the quotientof displacement by piston speed or 4973-f-640, giving sq. ft., or (neglectingthe loss of area due to the piston rod), the cylinder diariieter is in. From theconditions of the problem, the stroke is 640 -f- (2 x 80) = 4 ft. For the power consumption, we have W= GDEF+ FECH-JICH-GDTJ PeVe — Pg^c t> ryr ir \ PpVp ~ PiVi 2
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