Tham khảo tài liệu 'mechanical engineers data handbook episode 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Drag coefficients for various bodies continued Fluid machines FLUID MECHANICS Shape Hollow hemisphere flow on convex face a High-drag car b Medium-drag car c Low-drag car Fluid enters the impeller axially at its centre of rotation through its eye and is discharged from its rim in a spiralling motion having received energy from the rotating impeller. This results in an increase in both pressure and velocity. The kinetic energy is mostly converted to pressure energy in the volute and a tapered section of the discharge branch. Arrangement Hollow hemisphere flow on concave face Centrifugal pump A centrifugal pump consists of an impeller with vanes rotating in a suitably shaped casing which has an inlet at the centre and usually a spiral volute terminating in an outlet branch of circular cross-section to suit a oipe. 166 MECHANICAL engineer s data handbook Some pumps have a ring of fixed diffuser vanes into which the impeller discharges. These reduce the velocity and convert a proportion of the kinetic energy into pressure energy. Symbols used Dj mean inlet diameter of impeller D2 outlet diameter of impeller bl mean inlet width of impeller b2 outlet width of impeller i vane thickness at outlet Pi vane inlet angle p2 vane outlet angle N impeller rotational speed K whirl coefficient 2 flow H head z number of vanes p fluid density 1 refers to impeller inlet 2 refers to impeller outlet 3 refers to diffuser outlet p power K tangential velocity Kw whirl velocity Kf flow velocity V velocity relative to vane v absolute velocity of fluid qh hydraulic efficiency fỊy volumetric efficiency mechanical efficiency 70 overall efficiency a diffuser inlet angle d2 diffuser inlet width d3 diffuser outlet width b diffuser breadth constant a2 diffuser inlet area M2 a3 diffuser outlet area fed 3 K3 diffuser outlet velocity p pressure rise in pump Head Referring to velocity triangles JWa-Wa Theoretical head Hli. ------------ g It is usually assumed .
