孔数与孔厚对多孔板压损系数的影响机理

多孔板作为管道内节流降压或流量测量元件，在减小管道振动、流动噪声及流动压损等方面较之传统的单孔板具有明显优势。影响多孔板压损系数的结构因素主要有开孔等效直径比、孔数及孔板厚度，其中等效直径比的影响规律已为人熟知，而孔数与孔板厚度的影响机理仍不清晰。本文以均匀布孔的多孔板为研究对象，通过数值模拟方法研究了孔数与孔板厚度对多孔板稳定区压损系数的影响机理。结果表明：在相同的孔板厚度下，压损系数随孔数增多而先快速减小后趋于不变，使压损系数达到稳定的临界孔数随管径减小而减少，但临界孔数对应的孔板相对厚度均接近0.5；在相同的孔数下，随孔板相对厚度增大压损系数先快速降低后趋于不变，使压损系数达到稳定的临界相对厚度为0.5~1.0，临界相对厚度随孔数增多而减小；在相同的相对厚度下，压损系数在薄孔板中随孔数增多先减小后增大，而在厚孔板中随孔数增多而单调增大。这说明除等效直径比外，孔数与孔厚均对多孔板压损系数有影响，应在压损系数关联式模型中予以考虑。

Influencing mechanism of orifice number and thickness on pressure loss coefficient of multi-orifice plates

Multi-orifice plate is often used as a throttling or flow measuring component in pipelines, which has obvious advantages in reducing pipe vibration, flow noise and flow pressure loss in comparison with the conventional single-orifice plate. The structural factors being related with the pressure loss coefficient of multi-orifice plates are mainly the equivalent diameter ratio of orifice to pipe, the orifice number and the orifice thickness. The influence of equivalent diameter ratios had been well identified, while the influences of orifice number and orifice thickness are still unclear. In this paper, the effects of changing orifice number or orifice thickness on the pressure loss coefficient of stable region for multi-orifice plates, in which the orifices were arranged in regular triangle layout, were studied by numerical simulation. The results showed that under the same orifice thickness, the pressure loss coefficient decreases rapidly at first and then tends to be a constant with the increase of orifice numbers. The critical orifice number for reaching a stable pressure loss coefficient is declined with the decrease in pipe diameters, while the relative orifice thicknesses corresponding to the critical orifice numbers are close to 0.50 under different pipe diameter. Under the same orifice number, as the relative orifice thickness increases, the pressure loss coefficient decreases rapidly at first and then tends to be a stable value. The critical relative orifice thickness that makes the pressure loss coefficient stable is in the range of 0.5 to 1.0, which decreases as the orifice number increases. Under the same relative orifice thickness, for thin orifice plates the pressure loss coefficient decreases first and then increases with the increase in orifice number, while for thick orifice plates, it increases monotonously with the increase in orifice number. It revealed that, in addition to the equivalent diameter ratio, both the orifice number and the relative orifice thickness should be considered in the pressure loss coefficient correlation for multi-orifice plates because of their considerable influences.