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Measurements of pressure pulses from a solid core screen rotor.

Application: The factors that affect pulse characteristics determine how well the pressure screen performs.

Pulp screens would plug quickly if it were not for rotor elements that pass over the apertures and instantaneously backflush the pulp accumulations. The form of the pressure pulse, or its shape and magnitude, determines the minimum aperture An orifice. It often refers to an opening in which light is allowed to pass in optical systems such as cameras and lasers. See f-stop and numerical aperture.  size, and the aperture size determines the capacity of the screen and the extent to which the screen can improve pulp quality.

The researchers examined how the rotor speed, the gap between the rotor and screen cylinder, and the pulp consistency affect the form of the pressure pulse. They measured pressure pulses against a smooth, solid wall, rather than in a slotted, contoured screen basket, to obtain more reliable measurements for comparing pulse shapes.

One of the problems in the overall research study was to develop a fast way to produce rotor elements with specific shapes. To solve this problem, the researchers built rotor elements of aluminium using computer-controlled (CNC (Computerized Numerical Control) See numerical control.

CNC - Collaborative Networked Communication
) machining. With this approach, prototype elements can be rapidly designed, built, and tested.

They found that the pressure velocity increases with tip speed, but the pressure coefficient The pressure coefficient is a dimensionless number used in aerodynamics and fluid mechanics, most often in the design and analysis of an airfoil. The relationship between the coefficient and the dimensional number is:  remains approximately constant. The shape of the pressure pulse does not change significantly with rotor speed. As the gap decreases, the magnitude of the pressure pulse increases, but the pulse shape remains constant. As the pulp consistency increases, the pressure pulse decreases, even at consistencies below 2%.

Pinon Pinon (pī`nŏn), in the Bible, one of the dukes of Edom.  and Olson are with The Pulp and Paper Centre and the Department of Mechanical Engineering, University of British Columbia Locations
The Vancouver campus is located at Point Grey, a twenty-minute drive from downtown Vancouver. It is near several beaches and has views of the North Shore mountains. The 7.
, Vancouver, British Columbia British Columbia, province (2001 pop. 3,907,738), 366,255 sq mi (948,600 sq km), including 6,976 sq mi (18,068 sq km) of water surface, W Canada. Geography
, Canada. Gooding is with Advanced Fiber Technologies (AFT), Montreal, Quebec, Canada. Email Olson at
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Title Annotation:Screening
Author:Olson, James A.
Publication:Solutions - for People, Processes and Paper
Date:Oct 1, 2003
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