Silvio Barbarelli

A One-Dimensional Numerical Model for Calculating the Efficiency of Pumps as Turbines for Implementation in Micro-Hydro Power Plants

Increasing interest in renewable energy sources makes attractive the exploitation of many small power hydraulic resources (micro-hydro – less than 100 kW). However, the high cost of hydraulic turbines hinders the actual realization of micro-hydro plants. An alternative cheaper solution could be to replace the turbine with a reverse-mode centrifugal pump, developing therefore a pump as turbine (PAT) system. Unfortunately, although a wide number of centrifugal pumps are commercially available for micro-hydro engineering plant, manufacturers do not provide information regarding the performance of centrifugal pumps in turbine mode. In this paper, a simple method based on a one-dimensional numerical code is presented for deriving the turbine efficiency of commercially available centrifugal pumps. The code estimates a sizing of the component using information such as impeller diameter, specific speed, head and flow rate at pump BEP, machine overall dimension which are provided in manufacturer catalogues, to deduce geometrical parameters of the machine, calculating the losses and thus determining PAT performances. The method was validated by a comparison of the predicted characteristic curves with some experimental measurements available on PATs working in a range of specific speed (Head in meters and flow rate in m3 /s) from 9 to 65. The numerical code calculations effectively predicted the measured efficiency of PATs. At BEP, the efficiency was estimated with a relative error of ±10% which is a value much lower than one obtained by using the available in literature correlations. A prediction within this error range is generally accepted for this kind of application.Copyright

Performance Analysis of a Low-Power Tangential Flow Turbine With Rotary Channel

A tangential flow prototype turbine with a rotating channel containing five optimized deflectors is presented. This atypical turbine configuration may be useful for application in the low n s high d s region of the Balje chart, where conventional turbines offer very poor performances. A 70 kW maximum brake power, pressured-air test rig has been used for the analysis of operating characteristics, such as pressure, temperature, flow rate, and brake power. An electronic data acquisition system for automated measurement management was employed. An experimental campaign was carried out to identify the distribution of the pressure in the rotary ducts of the turbine. The results indicate the presence of a pressure gradient in the immediate vicinity of the inlet jet that is strongly attenuated when the ducts are not directly in contact with the jet.

Using a Statistical-Numerical Procedure for the Selection of Pumps running as Turbines to be applied in Water Pipelines: Study Cases

A combined method using statistical and numerical models has been developed by the authors for selecting a pump running as turbine to be applied in micro-hydro plants. The data of the hydrological site chosen for the installation (head and capacity) allow the calculation of two conversion factors which identify the pump to use successfully as turbine in that place. Then, a one-dimensional model, starting from data available on the pumps manufacturers catalogues, reconstructs a virtual geometry of the pump running as turbine, and calculates the performances curves, head vs. capacity, efficiency vs. capacity, useful for identifying the operating point. Two study cases are presented to apply the proposed methodology, concerning the feasibility of the installation of a pump running as turbine in the purifier water plants of Casali and Sersale, located at 1,000 m above sea level (Calabria, South Italy).The assessment of the annual energy yield gives a confirmation of the effectiveness and convenience of using pumps running as turbines.