串联网式过滤器拦截特性和过滤时间分析

Analysis of the filtration time and interception characteristics of tandem mesh filters

针对网式过滤器在实际灌溉水源条件下易堵塞、使用寿命短等问题,该研究将泵前和泵后网式过滤器串联组合,通过室内原型试验分析各级过滤器对泥沙和木屑的拦截规律。结果表明:过滤器拦截泥沙和木屑的分布情况与各级滤网孔径有关,当水源杂质以泥沙为主时,建议选取0.32和0.20 mm孔径滤网的泵前和泵后过滤器进行过滤,当有机物杂质含量较高时,采用0.25~0.32 mm滤网孔径的泵前过滤器有利于延长过滤时间。对水头损失随过滤时间的变化规律进行分析,明确了水源条件和滤网孔径对过滤时间的影响,极差和方差分析结果表明:不同进水流量条件下,初始水头损失和水头损失峰值分别集中在2.43~5.87和13.92~28.92 m,杂质含量对水头损失影响较小;进水流量越大,过滤器过滤时间越短。建立水头损失计算公式和过滤时间拟合经验公式,拟合与试验结果误差小于7%。各因素对过滤时间影响程度由大到小依次是杂质含量、滤网孔径、含沙量、进水流量。基于多层感知机(multilayer perceptron,MLP)神经网络模型对过滤时间进行预测,预测值与实测值误差基本在10%以内,均方误差和平均相对误差分别为0.32%、5.85%,该模型适用于对复杂水源条件下过滤时间的预测。研究结果可为灌溉工程中串联网式过滤器各级滤网参数的合理配置提供参考。

Easy clogging and short service life of mesh filters have posed great challenges in the irrigation water system.In this study,the pre-and post-pump mesh filters in series were combined to determine the interception of sediment and organic impurities at both pre-and post-pump filters.The indoor prototype tests were also carried out.The results showed that the distribution of the filter interception of sediment and organic impurities was related to the aperture of the mesh at pre-and postpump filters.The smaller the aperture of the post-pump filter was,the shorter the filtration time was.There was basically unchanged in the distribution of sawdust and sediment that was intercepted at pre-and post-pump filters.The smaller the aperture of the pre-pump filter was,the longer the filtration time was,and the smaller the percentage of sawdust intercepted by the filter.The percentage of sawdust intercepted by the pre-pump filter increased under the condition of the same screen aperture,with the increase of inlet water flow rate.It was recommended that the pre-pump filter with the screen aperture of 0.32 mm and the post-pump filter with the screen aperture of 0.20 mm were used for filtration when the content of organic impurities was high.Furthermore,the 0.32 and 0.20 mm mesh apertures of the pre-and post-pump filters were for filtration,when the mass ratio of organic impurities and sediment in the irrigation water source was less than 2.The 0.25-0.32 mm screen aperture of pre-pump filter prolonged the filtration time.There was a variation in the head loss with the filtration time,in order to clarify the influence of water conditions and screen aperture on the filtration time.Combined with the range analysis and multivariate analysis of variance(MANOVA),the initial and peak head loss were concentrated in the 2.43-5.87 and 13.92-28.92 m,respectively,under different inlet flow conditions.The impurity ratio posed a smaller influence on the head loss.Additionally,the larger the inlet water flow rate was,the shorter the filtration time was.The empirical formula of head loss was established to fit the filtration time.The error between the fitting and the test was less than 7%,indicating the better suitable for the filtration time of tandem mesh filters under actual irrigation water.The best combination of the factor level for the orthogonal test was screened as the aperture D1(pre-pump is 0.32 mm,post-pump is 0.20 mm),the sawdust to sediment mass ratio 1:1,sand content 0.12 g/L,and inlet flow 120 m3/h.The influence of each factor on the filtration time was ranked in descending order:the impurity ratio,the screen aperture,the sand content,and the rate of inlet water flow.MLP neural network model was used to predict the filtration time.The error between the predicted and measured values was basically within 10%.The mean square error and the average relative error were 0.32%and 5.85%,respectively,suitable for the prediction of the filtration time under the complex water sources.The finding can also provide a strong reference to configuring the screen aperture of the pre-and post-pump filters in the tandem mesh filters for the irrigation projects.