Flow in centrifugal pumps working at part capacity

The thesis attempts to analyse the flow and energy condition at zero discharge for a simplified radial impeller fitted in a cylindrical casing. Considerable inward and outward flow was observed passing through the impeller and extending along the auction pipe. The discharge area was shared equally between inward and outward flow. Two hydraulic systems were found to exist in the impeller, namely, those corresponding to a pump and a turbine. Part of the impeller was found to act as a pump and part as a turbine. The turbining effect was fairly large and had the effect of reducing the input power considerably. A linear relationship was found between the head and the power coefficients. The geometry of the pump played an important role and had a great effect on the energy and flow conditions at the suction and discharge sides of the pump. Decay of recirculatory flow along the suction pipe was very rapid and depended the geometry of the pump and on viscous forces. Theoretical results based on ideal fluid motion did not give sufficient information about the head reduction coefficient. General behaviour of the head coefficient given by theory was found to follow the experimental results