An annular venturi injector (AVI) was proposed to form an intermittent flow structure in airlift pump for a good pump performance. Experiments were conducted to investigate the performance of the airlift pump with this AVI by comparing with pump performance with traditional injectors, at a series of air flow rates . It was found that airlift pump with AVI had higher flow rates of output liquid and particle, than those with the traditional injectors. This AVI promoted the gas core to collapse and formed an intermittent flow structure in rising pipe. For this intermittent structure, its slug length, firstly increased to a maximal value with increasing gas flow rate and then remained stable even under a high gas flow rate, while its slug frequency decreased with gas flow rate and then remained to a minimal value under a high gas flow rate.
An axial piston pump can produce a serious cavitation phenomenon in the high-and low-pressure transition process. Cavitation bubbles expand, compress, rebound and collapse when they enter the high-pressure oil drainage area. This affects the outlet flow ripple as well as the pressure pulsation of the piston pump. However, the effect of the cavitation bubbles is ignored in the current outlet flow ripple model of axial piston pumps. It affects the optimization design of the axial piston pump distribution area structure parameters with the objective of reducing the pressure and flow rate. Therefore, a method of optimizing the fluid dynamic characteristics and the flow distribution area structure parameters of an axial piston pump considering the cavitation bubble evolution is proposed. A single-cavity dynamic model was established to study the bubble evolution as the piston chamber pressure changes. According to the cavitation cloud (group cavitation) characteristics of the axial piston pump, theoretical models of the outlet flow ripple and the pressure pulsation of a piston pump were established considering the cavitation bubble characteristics. The influence of cavitation characteristics on the outlet flow ripples and pressure pulsation of the axial piston pump was analyzed and compared with that without cavitation. Comparison with the experimental results, verified that the outlet flow ripple model becomes more accurate when cavitation bubble characteristics are considered. Based on the multi-agent particle swarm optimization (MAPSO) algorithm, an optimization model of the piston pump outlet flow ripple was established considering the cavitation bubble characteristics. The optimized design parameters for the flow distribution area of the axial piston pump were evaluated. The proposed method can provide theoretical guidance for the design of a low flow ripple axial piston pump.
A cavitator, with a structure of an annular conical aperture, a throat and a collapse cavity, was proposed to form a choking cavitation flow for pollutants degradation in wastewater treatment. Experiment was conducted in this new cavitator to investigate its flow characteristics and pollutant degradation ratio by employing Mythylene blue (MB) as a pollutant in pure water. It was found that choking cavitation flow appears in the throat by controlling the pump pressure and liquid flow rate in a rule. The pollutant degradation ratio in choking cavitation flow is much larger than that in normal cavitation flow, because plenty of cavitation vapours are born, grow up, and finally collapse in this cavitator in the choking cavitation condition. Gemetrical parameters also affect pollutant degradation ratio, and the optimal gemetrical parameters for this proposed cavitator are suggested.
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