Energy dissipation mechanism of a centrifugal pump with entropy generation theory

Abstract

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.

Effect of Volute Collector on the Performance of Centrifugal Pump Based on Entropy Generation Analysis

“…Therefore, the RNG k-ε model was selected. The viscous dissipation value is considerably smaller than the turbulent dissipation value [10,20], as discussed in the numerical result analysis. The power loss and location of loss production regions must be defined in machines.…”

“…At part and design load conditions, minimal and moderate fluctuations of 0.5 and 9% were achieved in the value of the head coefficient, respectively [7]. In contrast, the pump efficiency exhibited deviations of 0.7, 4, and 8% between the simulation and experimental results for the design load, part load, and overload conditions, respectively [9][10]. At the duty flow, the efficiency and head coefficient deviations were in reasonable ranges.…”

“…The grid refinement was verified with six different mesh counts in the range of 3.6-10.5 M and corrected with the head and efficiency of the pump, as presented in Table 2. The data presented in the table reveals that an increase in grid numbers decreases the percentage error in the performance parameters [10,12]. Additionally, the percentage error was less than 1 when the grid size was more than 8.5 M. As refining, the mesh with more grid numbers requires more computational time and does not necessarily provide a unique solution for increasing the accuracy of the results [21], a grid size of 10.5 M was selected in the numerical analysis.…”

“…Simultaneously, Zhang et al [9] applied the entropy production method to define flow losses inside the side-channel pump with different wrapping angles. Huang et al [10] examined the energy loss owing to the direct turbulence and wall friction dissipation. They concluded that the turbulence and wall friction dissipation contribute significantly to entropy generation, whereas the volute contributes to the highest losses at different time steps.…”

Analysis of Energy Loss Characteristics of Vertical Axial Flow Pump Based on Entropy Production Method under Partial Conditions

“…Yu et al [ 4 ] calculated the hydraulic loss of the Francis turbine under different mass flow rates based on entropy production theory and found that the energy loss of the draft tube of the Francis turbine was larger than that of other components. Huang et al [ 5 ] calculated the entropy of ordinary centrifugal pumps and found that the direct dissipation entropy in the pump was very low, accounting for only 0.716%. EPTD and EPWS accounted for 54.629% and 44.654%, respectively, indicating that the influence of average velocity in the pump was small, and the main flow loss was caused by turbulent flow and wall shear stress.…”