h. l. liu

The objective of this paper is to obtain an excellent structure of a rotational hydrodynamic cavitation reactor (RHCR) by a numerical method and then to investigate the cavitating flow characteristics of the optimized RHCR experimentally. The RNG k-ε turbulence model combined with the Zwart cavitation model was applied to analyze the influence of the straight blade number, the baffle position and the baffle shape on the pressure field, bubble distribution and turbulence kinetic energy of the RHCR. The results show that compared to the original model, an RHCR with a straight blade number of 6, a baffle position of 0.74 and a triangular baffle offers better cavitation performance. Moreover, the energy performance and the cavitation development process of the optimized RHCR were studied experimentally. The results indicate that the multiscale bubbles are induced by straight blades and baffles of the optimized RHCR, accompanied by the twice quasi-periodic shedding dynamics in one cycle. The findings of this study have positive significance for the design and optimization of RHCRs.

To reduce the noise in a pump piping system and increase the usage time of equipment, a new type of porous muffler is proposed in this paper. A water guide cone is incorporated into the muffler structure, which may help to redirect the fluid media in the piping system. The porous structure is adapted from a muffler shell, water cone wall and round bottom plate. According to this structure, the muffler sample is made, and a pump pipeline system test bench is set up. The outlet noise of the pump pipeline system is measured after installing the muffler. At the same time, the muffler is numerically simulated by combining computational fluid mechanics and Lighthill acoustic theory. The characteristics of the flow field and external sound field under three different flow conditions of 200 m3/h, 400 m3/h and 600 m3/h are assessed. The numerical simulation results show the same dominant frequency and trend as the experimental results. The rationality of the numerical simulation is verified. Research shows that: the level of sound pressure at the muffler's outlet is lower than at the inlet, causing muffling, and the characteristics of a quadrupole sound source appear at the outlet. The proposed muffler has a certain effect in reducing noise in the pump pipeline system.

As one of the core components of the fire-fighting water-supply system, the performance of a fire pump directly determines the extent of damage caused by the fire. Compared with conventional pumps, the design requirements of fire pumps not only need to ensure that the head of the pump is at 0Qd, 1.0Qd, and 1.5Qd and its efficiency is at 1.0Qd but also consider the cavitation performance at each flow rate, which presents a greater challenge for the design of high-performance fire pumps. By optimizing the design of a centrifugal fire pump with a specific speed of 24.7, numerical calculations were performed to obtain the best optimized scheme Y4. The results show that at the design flow rate the best optimized scheme improves the efficiency by 9.17% compared with the original scheme, and the head meets the design requirements of the fire pump while avoiding the hump phenomenon. Through a comparative analysis, it was found that the optimized scheme Y4 can reduce the pressure pulsations at the outlet of the pump and improve the cavitation performance at each flow rate. The experiment verifies that the head of the best optimized scheme at the design flow rate is 74.43m, the pump efficiency is 40.22%, and there is no hump in the head curve, which can meet the design and use requirements of the fire pump. The maximum reduction in the outlet pressure pulsations coefficient in the best optimized scheme was 47.12% on average. Compared with the original scheme, the critical net positive suction head (NPSHr) of the best optimized scheme was reduced by 21.5%, 17.6%, 15.7%, and 16.8%, respectively.

To investigate the movement characteristics of cubic particles in a pump, a deep-sea mining lift model pump with a specific speed of 94 is used as the research object in this study. The discrete element method is coupled with the computational fluid dynamics method to simulate the solid–liquid two-phase flow of cubic particles with different densities in the pump while the effect of particle shape on the solid–liquid two-phase flow in the pump is considered. Results show that the cubic particle movement rules for the same flow component are the same. The cubic particle density imposes a more significant effect on the number of particles in the low-velocity zone than in other zones. The number of particles in the low-velocity zone increases with the increase of density. The cubic particle velocity gradient in the impeller decreases as the particle density increases, and the particles exhibit unsatisfactory following performance in the fluid. As the density increases, the collision exhibited by the cubic particles is primarily particle-to-particle collisions, (i.e., more than 37%), and the collision rate between the cubic particles and first-stage guide vane decreases significantly. Compared with cubic particles, spherical particles are likely to obstruct the flow channel in the guide vane. The collision exhibited by the spherical particles in the pump is primarily particle-to-guide vane collision, and the collision rate between the spherical particles decreases by 15.92%.

To research the effect of the volute geometry on the radial force characteristics of the centrifugal pump during the starting process, choosing a centrifugal pump with a head of 87m as the research object. The pumping chamber is redesigned into a single-volute and a double-volute with similar external characteristics, and a circulation pipeline system is established. RNG k-ε turbulence model is employed to calculate the unsteady starting process of two kinds of centrifugal pumps. The variation trends of radial force received by the impeller and volute during the start-up process are obtained. The radial force characteristics and internal flow field evolution of two centrifugal pumps are compared and analyzed. The results show that the radial force vector distribution of the impeller changes in spiral periodicity during the startup process, and the spiral geometry is influenced by the number of impeller blades. The direction of the spiral is opposite to the rotational speed. The double-volute geometry can effectively reduce the radial force and pulsation amplitude of the impeller during the start-up process of the centrifugal pump, reducing the radial force by about 80% at rated speed. But the radial force vector distribution of the double-volute is more complicated and disordered than the single-volute.

Cavitation monitoring is particularly important for pump efficiency and stability. It is easy to misjudge cavitation by using a given threshold of a single eigenvalue. In this work, based on the vibration signal, a method for multi-resolution cavitation status recognition of centrifugal pump is proposed to improve the accuracy and universality of cavitation status recognition., wavelet packet decomposition (WPD) is used to extract the statistical eigenvalues of multi-scale time-varying moment of cavitation signal after reducing the clutter, such as root mean square value, energy entropy value and so on. The characteristic matrix is constructed. Principal component analysis method (PCA) is employed to reduce the dimension of the characteristic matrix and remove the redundancy, which constructs the radial basis function (RBF) neural network as the input. The results show that the overall recognition rate of non-cavitation, inception cavitation and serious cavitation by using the vibration signal of one measuring point is more than 97.7%. The recognition rate of inception cavitation is more than 80%. Based on the vibration signal information fusion method of two measuring points, the recognition rate of centrifugal pump inception cavitation status reaches more than 99%, and the recognition rate of vibration signal information fusion method of three measuring points reaches 100% for all three cavitation statuses. Due to the influence of factors such as change of external excitation and abrupt change of working conditions, sensor data acquisition is often subjected to unpredictable disturbance. To study the ability of single-point cavitation status recognition method to resist unknown disturbances, by constantly adjusting the value of the interference coefficient of the interference term. It is found that the recognition rate of cavitation status using single measuring point decreases almost linearly with the increase of the interference coefficient. When five measuring points are used for information fusion cavitation status recognition, the cavitation status recognition rate still reaches over 90% even if the interference factor of one measuring point reaches 50%.

This study investigated the activities of metabolic and immune enzymes in the hepatopancreas and muscle of the banana shrimp Fenneropenaeus merguiensis at different salinities (10, 15, 20, 25, and 30 ‰) and temperatures (21, 24, 27, 30, and 33°C).  The shrimp (mean initial weight, 1.72±0.25 g) were cultured at different salinities or different temperatures for 15 d. All treatments were conducted in triplicate. Results showed that glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT) activities in the hepatopancreas were the highest at a salinity of 20‰ (p<0.05). The GOT and succinate dehydrogenase (SDH) activities in the muscle were the highest at a salinity of 25 ‰ (p<0.05). The GOT and GPT activities in the hepatopancreas at a temperature of 24ºC were significantly higher than those at the other temperatures (p<0.05). The highest SDH activity in the muscle was observed at a temperature of  27 ºC (p<0.05). Different immune enzymes showed different responses to salinity and temperature. The highest superoxide dismutase (SOD) activity in the hepatopancreas, and the highest acid phosphatase (ACP) activity in the muscles was observed at a temperature of 24°C (p<0.05). By contrast, the lowest ACP activities in the hepatopancreas and muscles were observed at salinities of 25 and 20 ‰, respectively (p<0.05). These results indicated that suitable salinity and temperature can increase the metabolic enzyme activities, but the relationship of immune enzymes activities and ambient conditions is indeterminate.