Investigations of specific modifications in pump as turbine towards performance improvement

ABSTRACT

Centrifugal pumps as turbines offer a proven green energy solution for sustainable development, potentially replacing costly custom turbines in micro-hydro power plants and providing cost savings. But the efficiency of the pump as a turbine is lower than that of the dedicatedly designed pump. In this study, new simple modifications are proposed and evaluated on a developed state-of-the-art PAT test rig with impeller of specific speed 43.7 (m-m³/s). Being simple modifications, cost benefits will remain intact without requiring specially designed turbines and trained manpower. New simple modifications in PAT, like balance holes filling, packing seal optimization with appropriate size, leading edge of impeller blade tips modification making it single curve, and inner shroud widening for increasing the width at the inlet of the impeller, were proposed and performed to investigate the influence of the modifications on PAT performance. The experimental study finds that optimal packing seal size and impeller leading edge modifications notably boost PAT efficiency by 3–3.5%, making it worthwhile to implement for resource conservation and performance enhancement. On the other side, inner shroud widening noticed a 1.2% reduction in efficiency, adversely affecting the performance of PAT. Additionally, balance hole filling is neutral and does not have any effect.

KEYWORDS:

• Pump as turbine (PAT)
• simple modifications
• renewable energy
• experimental investigation
• micro-hydro power plant
• green energy

Nomenclatures

Symbols	=
b	=	Impeller width at inlet (mm)
C	=	Absolute velocity (m/s)
D	=	Diameter of impeller (m)
g	=	Gravitational acceleration (m/s2)
H	=	Head (m)
N	=	Revolution of a machine (rpm)
Ns	=	Discharge based pump mode specific speed $=\mathit{N}\sqrt{\mathit{Q}}/H^{0.75}$ (m, m3/s)
P	=	Power (kW)
Q	=	Flow rate (m3/s)
T	=	Torque (Nm)
t1	=	Blade thickness (mm)
t2	=	Shroud thickness (mm)
u	=	Tangential blade velocity (m/s)
$\mathit{\omega }$	=	Relative velocity (m/s)
z	=	Number of blades
Greek variables	=
Δ/δ	=	Difference
Λ	=	Power Number (P/ρn3D5)
η	=	Efficiency (%)
ρ	=	Mass density (kg/m3)
Φ	=	Discharge Number (Q/nD3, Q in m3/s, n in rps)
ψ	=	Head Number (gH/n2D2)
Subscripts	=
fz	=	Flow zone
L	=	Losses
nfz	=	Non-flow zone
p	=	Pump
u	=	Tangential components

Abbreviations

BEP	=	Best Efficiency Point
PAT	=	Pump As Turbine
PLC	=	Programmable Logic Controller
SCADA	=	Supervisory Control and Data Acquisition
VFD	=	Variable Frequency Drive

Acknowledgements

The authors would like to thank Mr Mohnish, Mr Shivdasan, and Mr Mayank for contributing to developing the PAT test rig.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported that there is no funding associated with the work featured in this article.

Notes on contributors

Rahulkumar Painter

Rahulkumar Painter is a research scholar in the Department of Mechanical Engineering, SVNIT, Surat, India. He completed his Bachelors and masters in the field of Mechanical Engineering from the Gujarat Technology University, Gujarat. His areas of research include Hydro-turbo Machines, Renewable Energy Sources, and Micro-hydro.

Ashish Doshi

Ashish Doshi is faculty, Department of Mechanical Engineering, SVNIT, PhD from the SVNIT, Surat. His areas of research are Hydro-turbo Machines, Micro-hydro and Thermal and Fluid science. He has more than 20 years of teaching and research experience.

Mukund Bade

Mukund Bade is Faculty, Department of Mechanical Engineering, SVNIT, Surat, India. PhD IITB, Mumbai, India. His research interest: Hydro-turbo machines, Energy Modeling, Pinch Analysis, etc. He has more than 20 years of teaching and research experience.