Unsteady flow in installations with polimeric additional pipe

This paper presents results of a theoretical and experimental study on the reduction of unsteady flow oscillations by using additional pipes of high-density polyethylene (HDPE) inserted at the upstream end of the pipeline in a pumping installation. The experiments generally show a reduction of the oscillations with respect to the case without the additional pipe. The reduction of the oscillations is higher for larger volumes of the device, while oscillations tend to be amplified for very small volumes. Experimental data are used to evaluate the mechanical parameters of the pipe material using a numerical model based on the method of characteristics. The additional pipe is treated as a lumped parameter system. The mechanical behavior of the HDPE is described both by a linear elastic model and by a Kelvin-Voigt viscoelastic model. The numerical tests show that the viscoelastic model better describes the general phenomenon, but the elastic model adequately estimates the maximum and minimum oscillations. An analytical solution for frictionless pipelines with the additional pipe considered as elastic is presented. The case of pipelines with friction is described in graphs that report the results of numerical integrations and allow the design of the device.