Session: 8.3.2 - Pumping Machinery II

Paper Number: 158021

158021 - Improving Functionality of a High-Efficiency Semi-Open 2-Channel Impeller by Connected Leading Edges 

Abstract: 

Wastewater pumps are increasingly clogged by media containing fibers. In order to meet the rising challenges that wastewater pumps are facing nowadays, semi-open impellers with a low number of blades are increasingly developed and used. One of the main reasons for choosing a wastewater pump is its efficiency. The Chair of Fluid System Dynamics at the Technical University of Berlin operates a test rig for evaluating clogging susceptibility of wastewater pumps, on which over 60 different wastewater pumps have already been tested with regard to their susceptibility to clogging by tear-resistant dusters. The semi-open 2-channel impellers in particular show good clogging behavior due to specific geometric properties with comparably high efficiencies in the wastewater sector. The impact of connected leading edges as a geometric feature for semi-open 2-channel impellers on functionality and clear water efficiency is investigated in this publication using a variable impeller.

This publication describes a prototype impeller, which is made out of stainless steel. This prototype is capable of changing the leading edge geometries by inserting 3D-printed parts for the blades to evaluate the deviation in functionality as well as in efficiency for different geometries. The first impeller is an efficiency-optimized semi-open two channel impeller, which has two typical blade leading edges. This basic modification is examined for its maximum efficiency as well as its susceptibility to clogging via two different test procedures. To increase functionality by preserving the highest efficiency possible, further modifications with connected leading edges are presented, which are also installed in the same prototype impeller. Connected leading edges mean for this impeller, that the blade leading edges are directly attached to the hub of the impeller. This eliminates the typical leading edges, which are often responsible for the accumulation of fibrous media, and should allow the dusters to slide off with the aim to still obtain high efficiencies. These variants differ in wrap angle, blade thickness and blade height. For the variants with connected leading edges, the same two test procedures are carried out. In addition to the change in functionality, the deviation in efficiency is also evaluated between the different variants.

Each variant is tested with clear water first to obtain all relevant parameters, for example the best efficiency point and respectively the maximum clear water efficiency. The two tests procedures used for evaluating the susceptibility to clogging are the long-time functional performance test on the one hand, which describes the 60-minute pumping of artificial wastewater in three different contamination classes. The relative change in efficiency due to possible blockages inside the pump is recorded and the amount of dusters accumulated in the impeller and volute casing is evaluated in relation to the added dry weight of the dusters to obtain a degree of long-time functional performance. On the other hand, optical tests are carried out to investigate the interaction between the duster and the suction side of the impeller. These optical tests are realized via a high-speed camera, an endoscope and an LED light ring.

The results show that the efficiency-optimized basic impeller demonstrates a high level of maximum efficiency for the clear water measurement. However, both the optical tests and the long-time functional performance tests clearly show that the impeller is unsuitable for media containing fibers. The variants with connected leading edges significantly increase functionality, as can be seen from the optical and long-time functional performance tests. The clear water characteristics change with slightly reduced efficiencies. Overall, the variants with connected leading edges offer an efficient solution with high efficiency and high functionality for pumping artificial wastewater using tear-resistant dusters.

Presenting Author: David Beck Technische Universität Berlin - Chair of Fluid System Dynamics

Presenting Author Biography: