基于当地摩擦因数的绝热气动管道流量特性参数计算

在等截面直管绝热有壁面摩擦一维可压缩管道流动模型的基础上,推导以管道进口截面速度因数为自变量的气动管道流量特性参数函数S/A（管道有效截面积与横截面积之比）和临界压力比b的基本表达式。采用基于当地摩擦因数求解管道平均摩擦因数的新方法,直接计算出总压为0.6MPa、总温为300K、长度为1～50m、内径为2.5～9mm尼龙管的流量特性参数S和b,并与经验值进行了比较。S和b的理论计算值与经验曲线变化趋势相同,且计算值与经验值相吻合,表明新方法可以在相当程度上反映气动管道流量特性参数变化的物理本质。将新方法得到的有效截面积S的理论计算值下跌20%、临界压力比b的理论计算值上浮40%,即可作为同等条件下选用气动系统尼龙管的经验推荐值使用。

Computation of the flow rate parameters of adiabatic pneumatic duct based on on-site friction factor

On the basis of the model of 1D compressible flow in the straight constant section adiabatic duct with wall friction,the expression of the flow rate parameter function S/A（the ratio of the effective duct section area to the cross-section area） and b（the critical pressure） of the pneumatic duct was deduced with the velocity in the duct import section as the independent variable.With a new algorithm that calculates the average friction factor of the adiabatic pneumatic duct from on-site friction factor,the flow rate parameters S and b of the pneumatic duct of 1~50 m in length and 2.5~9 mm in diameter under an inlet stagnation pressure of 0.6 MPa and a stagnation temperature of 300 K were calculated directly and compared with the empirical values.It is found that the variable tendency of the calculated curve equates that of the empirical curve,and the calculated values correspond to the empirical values,which implies that the new algorithm can reflect the physical essence of the variation of the flow rate parameters to a certain extent.By reducing the calculated value of S by 20% and increasing the calculated value of b by 40%,the values obtained can be employed for the selection of the pneumatic nylon duct under similar conditions.