Numercial Analysis On Two-phase Flow Performance Of A Micro Hydraulic-turbine

As a high pressure excess energy recovery device,hydraulic turbine is widely used in petrochemical industry,ammonia synthesis and other industrial fields.In some industrial processes,the working medium in turbine inlet contains gas,which results in a drop in turbine characteristics and even affects the stability of the unit operation.In order to reveal the gas-liquid flow characteristics and energy conversion mechanism of the hydraulic turbine under two-phase operating conditions and predict thevariation rules of the external characteristics and internal flow field variation rules,the Eulerian-Eulerian Particle model and the SST turbulence model are used to study the hydraulic turbine model.Firstly,the effects of gas model,two phase model and bubble diameter on turbine performance and flow field prediction are studied.Then the heterogeneous Model,considering the compressibility of the gas,based on PBM(Population Balance Model)Model for turbine operating conditions more gas-liquid flow characteristics are studied,analyzed the different flow rate,inlet gas rate influence on turbine internal two-phase flow characteristics,reveals the rotational speed of the working condition of high rate of gas turbine characteristics and the influence law of flow field.The results show that:(1)Compared with the compressible model,the pressure gradient of the incompressible gas model is larger,and the corresponding hydraulic loss in the runner is also larger.Under the same gas holdup condition,the turbine efficiency and output power of incompressible gas model are lower than that of compressible gas model.At 20%GVF,the efficiency of incompressible gas model is 12%lower than that of compressible gas model,and the output power is 36 kW lower.(2)In the flow channel of the homogeneous flow model,the gas phase working medium and the outlet velocity of the runner are uniformly distributed.Under the heterogeneous flow model,gas-liquid separation has occurred in the volute,resulting in uneven distribution of the gas-phase working medium in the runner.The hydraulic loss in the runner is greater than the homogeneous flow,and the corresponding hydraulic efficiency and output power are smaller than the homogeneous flow model.At 20%GVF,the efficiency of the heterogeneous flow model is 5.6%lower than that of the homogeneous flow model,and the output power is 14 kW lower.(3)The bubble model affects the distribution of the gas phase working medium in the flow channel and the velocity flow line in the runner.Under the model of single bubble diameter,with the increase of bubble diameter,the uneven distribution of gas phase working medium in the flow passage increases,the flow state in the runner becomes worse,the outlet velocity of the runner increases,and the hydraulic loss in the runner increases,resulting in the decrease of turbine output power and hydraulic efficiency.At 20%GVF,the efficiency of the turbine with a bubble diameter of 0.5 mm in the single bubble diameter model was 5.1%lower than that of the turbine with a bubble diameter of 0.1 mm,and the output power was 14.2 kW lower.The external characteristics of the PBM model are between 0.3 mm and 0.5 mm for a single bubble diameter,which is 4.8%lower than the turbine efficiency with a bubble diameter of 0.1 mm,and the output power is 12 kW lower.(4)The gas holdup rate at the inlet affects the distribution of working medium and liquid flow Angle of the inlet breath phase of the runner.the outlet velocity of the runner increases,the hydraulic loss in the runner increases,and the turbine output power and efficiency decrease.At 30%GVF,the efficiency of low flow condition is 34.7%lower than that of pure water condition.(5)The rotation speed affects the operation of the hydraulic turbine in gas-liquid two-phase condition.The increase of rotating speed increases the total pressure head of turbine and improves the efficiency.At different flow conditions,the improvement amplitude is different.At the design flow rate,the turbine efficiency at the working speed of 1660 r/min is 1.9%higher than that at the working speed of 1485 r/min.The hydraulic efficiency of medium flow condition was improved by 1.3%,and that of small flow condition was increased by 1.1%.