Abstract
In this study, entropy generation theory based on computational fluid dynamics (CFD) is used to study the influence of a pumping chamber type (guide vane and volute scheme) on the spatial distribution of hydraulic loss in a mixed-flow pump. The CFD data of the mixed-flow pump with a volute is validated by external characteristic test data under Q = 561.4–1598.6 m3/h. The results show that the efficiency and the head of the guide vanes scheme are lower under Q = 800–1200 m3/h, which resulted from a higher total entropy production (TEP) in the pumping chamber and outlet pipe. The high total entropy production rate (TEPR) inside the guide vanes can be found near the leading edge of the hub side and trailing edge of the rim side due to flow separation, which reduces the recovery efficiency of kinetic energy of the guide vanes. The high TEPR inside outlet pipe can be seen near the inlet, caused by back flow. However, the efficiency and head of the volute scheme are lower, under Q = 1200–1600 m3/h, owing to the fact that the volute cannot effectively convert kinetic energy into pressure energy and thus the high TEPR can be found near outlet of volute and inlet of outlet pipe. These results can provide useful suggestions to the matching optimization of the impeller and pumping chamber in a mixed-flow pump.
Highlights
The mixed-flow pump has the advantages of a large flow rate, a widely applicable head variation range, a broad efficient operation area, and difficult cavitation, and they are widely used in agricultural irrigation, urban water supply, and regional water transfer
The results show that the location of high hydraulic loss in the volute shifted from inlet to the baffle and tongue with the increase in flow rate
The velocity fluctuation cannot be obtained by solving the Reynolds time-average equation; Knock [17,18] proposed Equation (8), so that indirect entropy production rate (IEPR) ΦTI can be obtained in computational fluid dynamics (CFD) post-processing
Summary
The mixed-flow pump has the advantages of a large flow rate, a widely applicable head variation range, a broad efficient operation area, and difficult cavitation, and they are widely used in agricultural irrigation, urban water supply, and regional water transfer. Yang [21] studied the distribution of entropy rate in guide vanes of an axial flow pump under different flow rates He found that the area of high hydraulic losses decreased with increase in flow rate, but it increased with the shortening of the axial distance from the outlet. The entropy generation theory based on CFD can visualize the internal energy loss of guide vanes and the volute, and provide a more intuitive reference for optimal designs. There is little public literature that uses entropy production theory to study the recovery efficiency of rotating kinetic energy in the pumping chamber of a mixed-flow pump. A combination of simulation and experiment is used to deeply analyze the internal flow characteristics of guide vane mixed-flow pump and volute mixed-flow pump with the same impeller model, and compares the changes caused by different pressure chamber forms. The different flow loss mechanisms in the mixed-flow pump with guide vanes and a volute are explored
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