Fluid flow measurement using correlation techniques
Abeysekera, Sunanda A.
Abeysekera, Sunanda A.
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End of Embargo
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The University of Bradford theses are licenced under a Creative Commons Licence.
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Accepted for publication
Institution
University of Bradford
Department
School of Control Engineering
Awarded
1971
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Additional title
Measurement of steady and pulsating flow, by transit time analysis of temperature fluctuations
Abstract
The applicability of the temperature cross correlation method to measurement of flow under steady and pulsating flow conditions is investigated. The factors to be considered in applying this technique to different flow systems are discussed and its advantages over the conventional techniques are highlighted. The method involves monitoring random temperature variations in the flow at two points along the pipe and determining the transit time between the two points using the cross correlation technique. The velocity of flow is thus determined by the time and distance between the two points.
The method is proved in the laboratory to be an absolute, reliable and accurate method of volumetric flow measurement in laminar flow of highly viscous liquids (e.g. oils) and for the turbulent flow of liquids under steady and pulsating flow conditions. For low viscosity liquids (e.g. water) under laminar flow conditions the measurement is dependent on the flow characteristics and fluid properties and hence sensitive to upstream effects and pulsations. The flow characteristics of laminar and turbulent flow under steady and pulsating flow conditions and their influence on the heat transport mechanism are examined. Theoretical models are presented for developed and developing flow conditions and the experimental results show fair agreement with theory. Errors in the measurement technique are discussed and design conditions are recommended so as to minimise these errors.
It is shown theoretically and experimentally that an important parameter called the ‘frequency parameter’ (KR) governs the applicability of the technique to measurement of pulsating laminar flow. Only if KR<1 can the flowmeter, calibrated for steady flow measurement, meter pulsating flow accurately. This condition is satisfied easily by highly viscous liquids and hence this method is an accurate method for metering highly viscous liquids under pulsating flow conditions. The measurement of developing laminar flow with moderate amplitude pulses (<50% of mean) and turbulent flow with small and large amplitude pulses, is independent of the frequency parameter.
This technique of flow measurement offers minimum pressure drop, no mechanical wear, no blockage of pipe lines and can be used under adverse environmental conditions using a simple and robust sensing element. The flowmeter gives a linear output and accuracy better than +/- 2% can be achieved. The temperature signals used have rather narrow bandwidths and therefore averaging times of between 2 and 4 mins are required. However a better heat injection technique is described which will provide wider band width signals which should give a quicker response flowmeter.
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Thesis
Qualification name
PhD