Structure influence on jet pump operating limits

Sulfadiazine degradation by combination of hydrodynamic cavitation and Fenton-persulfate: parametric optimization and deduction of chemical mechanism

This paper reports the degradation of the sulfadiazine (SDZ) drug with a hybrid advanced oxidation process (AOP) of heterogeneous α-Fe₂O₃/persulfate coupled with hydrodynamic cavitation. The major objectives of the study are parametric optimization of the process and elucidation of the chemical mechanism of degradation. The optimum conditions for maximum SDZ degradation of 93.07 ± 1.67% were as follows: initial SDZ concentration = 20 ppm, pH = 4, α-Fe₂O₃ = 181.82 mg/L, Na₂S₂O₈ = 348.49 mg/L, H₂O₂ = 0.95 mL/L, inlet pressure = 0.81 MPa (8 atm), orifice plate configuration: hole dia. = 2 mm and number of holes = 4. Density functional theory (DFT) calculations revealed that the atoms of SDZ with a high Fukui index (f ⁰) were potentially active sites for the attack of ^•OH and [Formula: see text] radicals. Fukui index calculation revealed that atom 11 N has a higher value of f ⁰ (0.1026) for oxidation at the α-amine group of the sulfadiazine molecule. Degradation intermediates detected through LC-MS/MS analysis corroborated the results of DFT simulations. Using these results, a chemical pathway has been proposed for SDZ degradation.

Characteristics of a Cavitating Spoiler Mixing Device and Its Performance in a Foam Dust Suppression System

The unsteady foaming-agent mixing ratio in traditional foam-dust-suppression technology limited the dust suppression efficiency. Recent studies proved that the steady mixing ratio could be guaranteed by keeping the jet pumps or Venturis working under cavitation conditions, but the pressure loss of the current devices was over 50%. To decrease the pressure loss under cavitation conditions, we proposed a new mixing device by introducing a spoiler in the Venturi structure. Through computational fluid dynamics (CFD) simulation, the spoiler structure influence on the downstream flow field and the cavitation cloud structure, which affected the total pressure loss of the device, were revealed. For structure optimization, the effect of the other geometric parameters, including the throat length and divergent angle, on the pressure loss was also studied. The proposed device enhanced the cavitation on the suction tube side of the throat; meanwhile, the cavitation in other parts of the device was avoided. Therefore, the cavitation zone in the proposed device was much smaller than that in current devices, and the pressure loss was reduced significantly. When the flow ratio was 0.5-1%, the critical pressure ratio of the proposed mixing device was 0.71-0.68, which indicated that the pressure loss was only 29%-32%. The laboratory experiment verified that when the proposed device worked under cavitation conditions, the accurate and steady mixing ratio was guaranteed. The field experiment indicated that due to the reduced pressure loss of the proposed device, the required water inlet pressure decreased to 0.29 MPa, and the dust suppression rate increased dramatically. This study was of important value in manipulating cavitation cloud structure using a spoiler, clarifying the influence of the cavitation cloud structure on the liquid mixing performance and expanding the application field of the cavitating mixing method.

Research on the Law of Head Loss of Jet Pumps in the Cavitation State

Liquid flow is subject to head loss because of viscous force, surface tension, friction force, and so on. Part of the energy is irreversibly converted into heat, which then dissipates into the environment. Head loss intensifies in the turbulent state. At present, few studies explore the law of head loss caused by secondary flow, cavitation intensity, and turbulence intensity. In this study, the head losses in different sections of a jet pump were studied by controlling the cavitation number σ, the secondary flow rate Q _s, and the inlet pressure p _i. The experimental results were analyzed with the aid of computational fluid dynamics. The results show that an increase in Q _s can weaken the variations of Q _s and suction pressure p _s in the transitional stage of cavitation. Besides, σ, Q _s, and p _i influence head loss to varying extents. Cavitation intensity and turbulence intensity are the main factors for head loss and jet temperature difference. In particular, the influence of Q _s on head loss provides guidance both for reducing the energy loss of the quantitative adding device and jet aerator and for expanding the stable adding range of the jet. More importantly, the main factors of energy loss caused by jet cavitation were analyzed in detail, which can effectively facilitate the pipeline design to reduce the local and frictional head loss.

Research on Noise-Induced Characteristics of Unsteady Cavitation of a Jet Pump

The dynamic cavitation characteristics of normal-temperature water flowing through a transparent jet pump under different cavitation conditions were experimentally studied by adjusting the pressure ratio. The common results are presented at different pressure ratios, including the temporal and spatial changes of the pressure and noise, together with the visual observation of the cavitation unsteady behaviors using a high-speed camera. The analyses on the measured data and images reveal that the cavitation cloud is generated by periodic oscillations of the jet traveling pressure wave and the bubble traveling pressure wave. The oscillation of the two kinds of interface waves is caused by the collapse of the bubbles, which is the main mechanism of the bubble cloud shedding. As the pressure ratio increases, the maximum length of the jet cloud and bubble cloud linearly decreases, while their oscillation frequency increases gradually. Combined with the cavitation-cloud visualization data and noise frequency analysis, it is proposed that the strong impact between the jet traveling pressure wave and the bubble traveling pressure wave is the main cause of noise. Specially, the acoustic pressure reaches the maximum when the oscillation frequency of the jet traveling pressure wave is the same as that of the bubble traveling pressure wave. Also, the jet traveling pressure wave has a great influence on the migration of bubbles in the cavity. The results can provide guidance for the optimal operating condition in cavitation applications such as jet aerator and quantitative addition.

Numerical Study on the Working Performance of a Streamlined Annular Jet Pump

To improve the working performance of the early annular jet pump (EAJP), a streamlined annular jet pump (SAJP) was proposed. The flow field and working performance of the EAJP and SAJP with an area ratio (m) of 1.75 were numerically studied and compared, separately, by using the combination of the Realizable k-ε turbulence model and the Schnerr–Sauer cavitation model. The results show that the efficiency of the SAJP is higher than that of the EAJP, when the flow ratio (q) is higher than 0.30, with a maximum increase of 1.2%. Furthermore, the high-efficiency area of the SAJP (q = 0.40~0.69) is wider than that of the EAJP (q = 0.36~0.57). There is no flow separation and low local pressure in the SAJP, due to the conjunction part of the suction chamber, throat, diffuser and outlet pipe without the structural mutation. It was found that the incipient cavitation number (σi) of the SAJP and EAJP was 0.541 and 0.578, respectively; therefore, the cavitation performance of the SAJP is better. Meanwhile, the critical flow ratio (qc) of the SAJP is 0.69, which is larger than that of the EAJP (qc = 0.57), implying that the SAJP has a wider normal working range than the EAJP. Importantly, the inception and development of cavitation appeared in the diffuser of the SAJP, different from that in the throat of the EAJP. Hence, it concluded that the cavitation in the SAJP has less influence on the flow field and working performance.

CFD-Based Study of Nozzle Section Geometry Effects on the Performance of an Annular Multi-Nozzle Jet Pump

CFD simulation and analysis of the internal flow field of the annular multi-nozzle jet pump are carried out to study the effects of nozzle section geometries on performance of the pump based on the finite volume method and realizable k-ε model. The results show that the square nozzle peak efficiency is 3% higher than that of the circular nozzle and 4.1% higher than that of the triangular nozzle. According to the simulation results, the mixing mechanism of the working fluid and second fluid is analyzed on the basis of the vortex dynamics. The results show the following: the recirculation area and the friction loss of the non-circular nozzle are reduced, and the mixing effect is improved; the streamwise vortex plays a major role in the mixing process and decays to an extremely small value at the end of the throat after attenuating rapidly in the suction chamber; compared with the streamwise vortex, the strength of the spanwise vortex is relatively stronger; the spanwise vortex still fluctuates after developing to a certain extent in the throat; the maximum streamwise vorticity peak value of the square nozzle is 31% more than that of the circular nozzle and 39% more than that of the triangular nozzle; the maximum spanwise vorticity peak value of the square nozzle is 19% less than that of the circular nozzle and 12% less than that of the triangular nozzle.