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A new method for a simplified comparison of gentle conveyance properties of centrifugal pumps for breweries
P. Zeuschner, J. Fischer, M. Holewa and R. Pahl

It is generally known and accepted that shear forces, which are in the brewing process especially caused by centrifugal pumps, can lead to quality as well as to processing problems. Besides the sensitivity of yeast to mechanical stress, the formation of β-glucan gels is feared by brewers, because of their filter blocking and turbidity increasing properties. For that reason, a test method to evaluate the gentle conveyance properties of centrifugal pumps objectively was developed and the gentle conveyance indices 'φ' and 'Φ', with and without respect to the pump power output were introduced. The method is based on the shear force induced gel formation behavior of barley β-glucans in an aqueous solution and the resulting change in its rheological properties. A detailed comparison between two centrifugal pumps of the same model, with low-speed and with high-speed motor, each with a nominal operation point of 10 m?*h-1 on 20 m hydrostatic head was carried out, using the new method. The slower running pump showed thereby significantly better results by a factor of 1.2 at full load. Additionally, pump curves were developed to demonstrate the gentle conveyance behavior as well on different operation points, where the difference between the two possibilities of flow rate adjustment - throttling and speed control by frequency converter - could be quantified. Besides the possibility to compare pumps according to their gentle conveyance properties, the gained results showed that some theories concerning parameters that are often subjectively made responsible for gentle conveyance of centrifugal pumps could be questioned.

Descriptors: shear forces, gentle conveyance, beta-glucan, beta-glucan gel, pumps, test method

BrewingScience, 74 (January February), pp. 1-9