A CFD Study on the Mechanisms Which Cause Cavitation in Positive Displacement Reciprocating Pumps

Abstract

A transient multiphase CFD (computational fluid dynamics) model was set up to investigate the main causes which lead to cavitation in PD (positive displacement) reciprocating pumps. Many authors agree on distinguishing two different types of cavitation affecting PD pumps: flow induced cavitation and cavitation due to expansion. The flow induced cavitation affects the zones of high fluid velocity and consequent low static pressure e.g. the valve-seat volume gap while the cavitation due to expansion can be detected in zones where the decompression effects are important e.g. in the vicinity of the plunger. This second factor is a distinctive feature of PD pumps since other devices such as centrifugal pumps are only affected by the flow induced type. Unlike what has been published in the technical literature to date, where analysis of positive displacement pumps are based exclusively on experimental or analytic methods, the work presented in this paper is based entirely on a CFD approach, it discusses the appearance and the dynamics of these two phenomena throughout an entire pumping cycle pointing out the potential of CFD techniques in studying the causes of cavitation and assessing the consequent loss of performance in positive displacement pumps.

An advanced CFD model to study the effect of non-condensable gas on cavitation in positive displacement pumps

“…According to theory, the valve should get to the seat as soon as the plunger gets to the BDC, however, because of valve inertia, the operating conditions and the fluid properties, there could be a delay in the inlet valve closing time, which would extend the inlet stroke overlapping the first stage of the outlet stroke. This has been observed by Iannetti et al [6] but the influence of the air content on it is still unclear. Solid volumes were utilised to generate the fluid volumes by means of Boolean operations; they were subsequently meshed.…”

“…The authors chose to carry out the investigation by means of the advanced CFD model explained and discussed by Iannetti et al [6] that will be briefly recalled in the next sections. The reason for this choice lies on the higher capability of post processing that a CFD solver has over experimental tests.…”

A CFD and experimental study on cavitation in positive displacement pumps: Benefits and drawbacks of the ‘full’ cavitation model

“…In each test of Figure The plunger stroke in all of the tests was 0.204 m. Figure 3 represents the suction stroke only; the delivery stroke, which is not discussed in this paper, was carried out slowly and only to reposition the plunger to the TDC position again, ready for the next test. The acceleration and velocity were designed to achieve the incipient, partial and full cavitation regimes (Iannetti, Stickland, & Dempster, 2015;Opitz & Schlücker, 2010;Opitz, Schlücker, & Schade, 2011).…”

“…This parameter, in fact, is directly related to the cavitation regimes (Iannetti et al, 2015); the lower the volumetric efficiency, the higher the integral of the vapor generated. It is very simply to calculate volumetric efficiency using CFD but very difficult to measure it in an experimental rig.…”

Numerical methodology for the CFD simulation of diaphragm volumetric pumps

“…In addition, CFD simulations have recently emerged as a powerful tool to analyze in detail the spatial characteristics of the flow patterns within volumetric flow pumps. The performance of plunger pumps as a function of the crank angle [14], the evaluation of its inlet stroke performance [15] and even cavitation inception [16,17] are some examples of the potentiality of computational modelling. The unsteady simulation of airoperated piston pumps [18] and the numerical analysis of axial piston pumps [19,20] are also significant contributions for the study of reciprocating pumps via CFD.…”