22 October, 2019

Polymer solutions to improve the efficiency of water systems

25 September, 2015

Fluid handling equipment may suffer from multiple problems including physical and mechanical damage as well as general or localised erosion and corrosion. These problems are linked to decreased efficiency and poor performance, leading to increasing operational costs. Minimising performance deterioration is therefore an important factor for pump manufacturers and end users. Indeed, hydraulic losses account for most of the efficiency decrease (9 per cent for a mixed flow pump to 20 per cent for radial flow). Coating technology can help in decreasing these losses, increasing the pump’s performance and reducing operational costs.

Hydrophobic coatings for pump efficiency improvement

In pumping equipment, it is possible to reduce power consumption and improve the hydraulic properties by changing the pump surface finish. In fact, the loss of efficiency is caused by frictional forces created between the fluid and the walls, the acceleration and the slowing down of the fluid, and the change in the fluid flow direction. The smoother the pump walls, the more fluid turbulence will be reduced, thus reducing the energy required for the pump to move the fluid through the hydraulic passage.

In order to get the best performance possible, pump manufacturers seek to create the smoothest surface possible to reduce the turbulence of the fluid. This can be obtained by the polishing of the selected metal, such as stainless steel; however, this method is extremely time consuming and expensive.

A smooth surface finish can also be obtained by applying an erosion-corrosion resistant efficiency coating on the pump’s volute and impeller. These polymeric coatings are specifically designed to improve efficiency on fluid handling systems and protect metals against the effects of erosion-corrosion. Their unique combination of properties such as self-leveling application, hydrophobicity and hydraulic smoothness makes these coatings ideal candidates for lining the hydraulic passages of pumps. These coatings possess a low electronic affinity towards water molecules and result in a smooth glossy finish once applied onto a metallic surface. This allows the water or other aqueous solutions to easily slide on the surface of the coating.

The smoothness of these hydrophobic epoxy coatings is demonstrated on Graph 1, where the surface condition of Belzona 1341 (Supermetaglide), a high performance coating designed to improve efficiency of pumps, pipes, valves and other fluid handling equipment while protecting them from the effects of erosion-corrosion, was measured as 15 times smoother than polished stainless steel.

As a result of the smoother surface and reduction in flow resistance and friction, the hydraulic performance of the pump can be increased. Graph 2 shows the performance curves of a single stage, end suction centrifugal pump with a 250 mm suction and discharge branches before and after being coated with Belzona 1341. This test was performed by the British National Engineering Laboratories (NEL) and the pump, in uncoated condition and running at 1300 rpm, was originally found to deliver 875 m3/h at 26.5 metres head and with overall peak efficiency of 83.5 per cent (overall efficiency defined as the ratio of water power output to mechanical power input at the shaft).

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