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Title: USMs and Heavy Oil applications -The Woes of Transition and laminar Flow Measurement
Author: T. Cousins
Source: 2017 North Sea Flow Measurement Workshop
Year Published: 2017
Abstract: Heavy oil has three issues that can create measurement problems for liquid USMs. A. High viscosity causes low Reynolds number flows in the transition and laminar flow regimes. B. Temperature gradients, and therefore viscosity gradients, are common in laminar flows. C. High viscosity causes enhanced attenuation of ultrasonic waves. The paper explains these three issues in a practical simple way. By understanding these fundamental phenomena it becomes clear what the underlying implications to measurement are. For example, an USM may be linearized in the laminar / turbulent transition region produced by a volume flow rate at given flow conditions during a laboratory or field prover calibration. However, this transition zone is not fixed by a set volume flow range. The transition region is affected by various influences, such as installation affects, bulk fluctuations in fluid properties (e.g. temperature or composition changes), and local radial temperature / velocity gradients. Hence, a meter calibrated and linearized across one flow conditions volume flow transition region can have significant flow rate prediction biases if the meter is subsequently operated in other flow conditions (which shift the transition region). It is a challenge to predict the point at which a field installed meter will be influenced by transition. Transitional flow adversely affects the path taken by an ultrasound wave, and hence the USM performance.

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