THE COLLIERY GUARDIAN . . AND / ■ ' JOURNAL OF THE COAL AND IRON TRADES Vol. CXI. FRIDAY, FEBRUARY 4, 1916. No. 2875 Turbo Blowers and Compressors.* By H. L. GUY and Lieut. PL. JONES, B.Sc. Perhaps the most marked feature in the recent history of power production has been the replacing of reciprocating machinery by that of the rotary type. The steam turbine has invaded and captured a considerable portion of the fields of usefulness of the reciprocating steam engine. The centrifugal water pump has largely replaced the reciprocating pump; rotary condenser auxiliaries are rapidly superseding reciprocating plant, and rotary blowers and compressors have entered into a successful contest with reciprocating compressors. ; ; The factors which have decided the issue in favour of rotary plant zhold for all the types mentioned. They The turbo blower is really a multi-stage centrifugal air pump. Air is drawn into the eye of the first impeller A, fig. 1, and delivered at the periphery B in a compressed condition. It can be shown that if the compression is performed without loss, the equivalent of half the work done is transformed into pressure energy of the air the remaining half (MC 2\ ■ J ’ On leaving the impeller the air now enters the diffuser D, the object of which is to convert the kinetic energy into potential from 8 to 151b. per sq. in., it is necessary to employ three, four, or even five stages. ; (2) In a water pump the density, and therefore ,the increase in pressure per stage, is constant, but in a blower the pressure and temperature of the air change, Fig. 1.—Sectional Elevation of Turbo-blower. A energy. [Rise of pressure = J so that in a perfect blower at the point diffuser, the pressure energy in the air 0 outside the would be equal to the work done in the impeller. The air now passes through the guide blades E which direct it into the eye of the second impeller, where the process is repeated. Although the operation is very similar to that in a centrifugal water pump, there are important differences in the working of the two classes of machines. (1) For a given peripheral speed, the terminal pressure is proportional to the density of the medium, hence the pressure produced in the impeller of the blower is about of the pressure which would be produced with Variation in Temperature $ Pressure \ 'fN A 4'57Ab'L B lOA/ER. 12 180 <0 70 2 ■ — too !4O /OO 00 /2O d 80 Fig. 2. ____— J’epnper'r^hjr'e ------—— Constant Speed Characteristics or a .Blower 14 72 8 6 4 2 <5 ■ ; // - - ■ J $ 7 lc. £ \- 0- 2400 2000 Qt ' £ 7600 § 1200 8 12 16 20 24 28 32 36 40 4 yp/ume of Fr-ee A/r' Discharged, IQPOO Ou fT/M/n- Fig. 3. O Cl A COtfCGNSB are-:--Small; space- occupied and; light weight—a fact water being 800 times as heavy as air. For this reason resulting from high speed ;, excellent balance, due'to it is always necessary to build blowers, even for such the elimination of reciprocating elements ; light fouh da- low terminal pressures as 5 lb. per’sq. in., with more tions; low first cost; simplicity (no valves arid valve .than one impeller, and for the more usual pressures of gear other than the governor)maintenance o f efficiency owing to absence of valves and rubbing parts, the wear of the 'former, being responsible for much of the heavy drop in efficiency in reciprocating plant; reliability, resulting from extreme simplicity; accessibility, as all internal parts can be examined by raising top casing; efficient lubrication, the rotary bearings of. the machine being fed by a self-contained lubricating system which uses the same oil continuously; and low maintenance costs. Machinery which can be driven by a steam turbine has the additional and valuable advantage that a mixed pressure turbine can be employed utilising waste steam, a large quantity of which is usually available. * From a paper published in the Proceedings of the South Wales Institute of Engineers, January 18, 1916. * c = absolute velocity of air in. feet per second ; Dx = diameter of impeller in inches ; ,D2 = diameter of diffuser in inches ; — mean density of air in pounds per cubic foot; F = area at throat of nozzle.in square feet; g = gravitational constant = 32'2 ft. per second ; J = Joule^s equivalent — 778 foot-lb. per B.T.IL; M = weight of air com- pressed in pounds per second; Mc = weight of circulating water in pounds per second ; n = speed in the revolutions per minute; PB = barometric pressure ; po = gauge pressure at blower or compressor suction; Po = absolute pressure at blower or compressor suction = PB — Po; Pf — gauge pressure at blower or compressor discharge ; Py = absolute pressure at blower or compressor discharge = pf + PB ; pn = gauge pressure measured by a Pitot tube before measuring nozzle on discharge side ; Pw = absolute pressure measured by a Pitot tube after measuring nozzle on dis- charge side = pn + PB; p' = gauge pressure measured by a static tube after measuring nozzle on suction side; P' = absolute pressure measured by a static tube after measuring nozzle , on suction side = PB + p'; Q = volume of free air in cubic feet per minute; E = constant in relation PV = Fig. 4. Diagrammatic Arrangement of Governor Gear for Constant Quantity. resulting in a change of density, so that the increase in pressure per stage is continually increasing. T-lie rise in temperature is due to two .causes (a) The rise .associated with adiabatic compression which is given by the* expression— ■ ‘ Tf _ ' /D/ X __ /B/ \ °291 T7 • \Po7 • \Po/ . 5 (5) the rise due to the fact that the compression is ET, andE = 53*3 for air; t0 = initial temperature in degs. Fahr.; To = absolute initial temperature = 461 + to; tf = final temperature at discharge' Tn> degs. Fahr.; T/ = absolute final temperature = 461'+ ■'£/; tn = temjerature before measuring nozzle in degs. Fahr.;; T^ = absolute temperature before measuring nozzle =. 461 + tn ; V = specific volume of air in cubic: feet per- pound ; W = work in brake-horse power; Waez = work done in adiabatic com- pression in B.H.P.; W& = work done in isothermal com- pression in B.H.P.; a = used to indicate an angle; yaa = efficiency relatively to adiabatic compression; yis = efficiency relatively to isothermal compression ; = internal effi- ciency, neglecting bearing losses; X = ratio of specific heat at constant pressure to that at constant volume = 1'41 for air. When “free' air.” is referred to, air measured at 30 in. Hg barometer and 60 degs. Fahr, is to be understood.