Computational Study of a Low Cost Rope Washer Pump for Brine Pumping Application in Rural Areas

The rope washer pump is a hydraulic device in which the rope consisting of equally spaced washers is pulled upward to displace the fluid volume to the desired head before delivering it at the outlet. The straightforward working principle, the ease of manufacture, and the low cost are the main advantages of this pump over a reciprocating pump. The rope washer pump can be either driven by electric motor, by a wind mill, or manually for pumping brine water for salt harvesting in rural areas. In this study computational fluid dynamics (CFD) modeling of the rope washer pump is used to estimate the performance characteristics of the pump. Experimental studies of rope pump can only provide data related to flow rate and head it can achieve, while using CFD it is possible to obtain insight about the flow physics inside the pump. These insights can be used to propose design improvements for more efficient pump operation. Unsteady, incompressible Navier-Stokes equations are solved using a finite volume scheme on unstructured hybrid polyhedral-prismatic overset meshes to obtain flow parameters and the volume of fluid (VOF) interface tracking method is used to capture the free water surface inside the pump by tracking the volume fraction of fluid on each cell. The k-ε turbulence model is used to model turbulence and the motion of the washer is handled by using overset mesh technique for the computation. Leakage between the washer and housing is also considered in this computation. Pump characteristics are calculated for different pump speeds. Thus the flow variables obtained by computation are used to predict the efficiency and flow rate at different washer speed. The pump characteristics define the behavior of the rope washer and are characterized by effective flow rate, volumetric efficiency, power input and the pump torque. These performance characteristics are extracted from the computed flow fields and used for evaluating the optimum range of pump speed, with highest efficiency and flow-rate. This model can serve as a basis for future design optimization studies.