水力学2015 7 1 pump第7课泵特性.pdfVIP

Lesson 7. Pump Characteristics Pumps Operating characteristics of a pump depend on: Q- pump flow rate (gal/min, m3/s) H- head added by the pump (ft, m) P- power delivered by the pump = γ QH (hp, kW) n (or ω ) - impeller speed (rpm, rad/s) 3 3 - density of the fluid (slugs/ft , kg/m ) D-impeller diameter (ft, m) - viscosity Performance of a pump is measured: a) by the head added by the pump H(Q). Typically H = H 0 − βQ 2 H H0 Q The relationship H=H(Q) is given by the manufacturer b) by the efficiency p ower delivered to the fluid η = (also given by the manufacturer) p ower d by the shaft gH,η= f( ρ,μ , D , n, Q) Using dimensional ysis (choose ρ, n, D as primary variables) ρnD2 C ,η = f (C , ) H Q μ ρnD2 (where accounts for the viscous influence neglect at high Re) μ Q CQ=discharge coefficient= 3 nD gH CH=head coefficient= 2 2 n D H Obs: In practice, dimensional form is used CH= 2 2 n D gH  Q  So for gH: CH = f 1(CQ ) 2 2 = f 1 3  n D nD   Q  For : C = f (C ) η = f   η 2 Q 2 3 nD  ρ C C γ QH P