Adaptive Hydraulics for Improved Centrifugal Pump Efficiency

Centrifugal pumps are used ubiquitously for fluid transport in industrial and municipal systems including: clean and waste water systems, pumped hydro energy storage, closed loop HVAC heating, and irrigation. Globally, pumps consume hundreds of billions of kilowatt hours of electricity each year. In the US, centrifugal pumps consume an estimated 4.4% of electricity generated, equivalent to 232 billion kWh annually. Many pumping applications require operation over a broad range of pressures and flow rates, however traditional centrifugal pumps with fixed geometry are limited in their ability to adjust, resulting in significant energy losses. This research challenged the assumption that volute geometry must be static and showed that by enabling a variable volute geometry greater efficiency can be obtained over a wider operating region. The thesis presents the design and demonstration of a controllable, precision, variable volute mechanism that can expand or contract to adapt to fluctuating operating conditions. Experiments support the hypothesis that adjusting the pump volume shifts the best efficiency point (BEP) creating a best efficiency range (BER). Five initial mechanism topologies were evaluated, and a spiral piston architecture was selected based on structural and hydrodynamic requirements, feasibility, and manufacturability. The engineered variable volute is comprised of a spiral piston integral with a multi start lead screw, rotated by a mating collar with internal multi-start threads and external crowned gear teeth. A non-backdrivable worm actuates the worm wheel integral in the collar. Deterministic design tools were developed, with demonstrated hydrodynamic, structural, and mechanical scalability, to enable future implementation of the variable volute technology in a variety of pump sizes for different applications. Experimental validation of the variable volute characterizes the sensitivity of pump flow, pressure, efficiency, and power to changes in the pump volute volume. Based on the machine design of the pump, error analysis coupled with experimental data demonstrates the ability of the mechanism to accurately and repeatably control the volute height. We achieved a 67% increase in the preferred operating range of the pump for a 160% change in volume. This results in a 30% increase in the energy efficiency at the maximum preferred flow rate. Contextually, significant research and development efforts have been historically dedicated to optimize pump geometry for less than 5% efficiency gains. A case study is presented analyzing a year of hourly resolution, variable operation data from ten, 2600 kW centrifugal pumps in a large wastewater treatment plant to understand the influence of pump design, selection, maintenance and operation on system efficiency. Three feasible interventions were quantitatively compared and show savings up to 4.3% (809,000 kWh) annually. Based on this analysis, an operating space methodology is presented which extends the traditional 2D pump and system curve intersection to a multi-dimensional operating space; connecting pressure and flow performance parameters with control parameters such as variable speed and variable volute.Ph.D