Energy dissipation mechanism of a centrifugal pump with entropy generation theory

From the numerical calculations of a common centrifugal pump, the energy loss characteristics have been investigated by applying entropy generation theory to examine the loss due to the direct, turbulence, and wall friction dissipation rates. The turbulent and wall friction entropy dissipations contribute higher values compared with the direct entropy dissipation rate. The turbulent and wall friction entropy dissipations yielded 54.629% and 44.654%, respectively, at the design flow rate; however, the direct entropy dissipated the least of about 0.716%. This indication proves that these entropy variables affect the irreversible energy losses produced. Meanwhile, the entropy production rate distribution was compared with that pressure fluctuation and vortex characteristics and revealed that the region near the volute tongue interface is associated with high losses at all studied flow rates (0.8Qd, 1.0Qd, and 1.2Qd), especially under part-load conditions. The wall of the volute reveals maximum losses at different time steps at the design point. Furthermore, the trailing edge of the blade records the maximum pressure fluctuation, while the leading-edge records moderate intensities. Most regions in the pressure fluctuation intensity distribution reveal a common tendency with the entropy dissipated; thus, there is a high correlation between entropy production and pressure fluctuation. Moreover, the suction side of the impeller records the maximum entropy coefficient at the leading edge compared to the pressure side under the span view. This indicates that the suction side is also responsible for the high energy loss in the impeller flow passages and corresponds to the flow separation, which leads to vortex patterns recognized close to the hub of the blade. This study widens the assessment of the energy loss and can further contribute to the optimization of the hydraulic structures of centrifugal pumps.