Fluid flow measurement assembly

TLDR: In this paper, a fluid flow measurement assembly is described, which consists of two counter-rotating turbines, a pickoff device or pulse detector being provided for each turbine, and a flow conditioning section comprised of a diffuser and straightening vanes, as well as temperature probes, pressure transducers and a metering assembly.

Abstract: A fluid flow measurement assembly is shown and described. In a preferred embodiment, a flow conditioning section comprised of straightening vanes and a diffuser, as well as temperature probes, pressure transducers, and a metering assembly, are all provided in an integral housing. The assembly is provided with different sized flanges on an inlet orifice and an exit orifice, such that the assembly may be installed in a fluid line in only one direction, thereby preventing incorrect installation. The flow conditioning section is comprised of a diffuser and straightening vanes, and serves to ensure that fluid flowing through the measurement assembly is uniformly scrambled and then normalized, such that the metering assembly will be substantially insensitive to upstream flow disturbances and will provide accurate and repeatable fluid flow measurements. The metering assembly is comprised of two counter-rotating turbines, a pickoff device or pulse detector being provided for each turbine. The assembly is provided with a single connector that is coupled to leads of the temperature probes, pressure transducers and pulse detectors, such that these components may be coupled to a processor external to the housing, simply and accurately. In calibrating the measurement assembly and in calculating the volumetric or mass flow rate of a fluid, a K factor for each turbine at a given frequency is determined and added together, the sum of the K factors being plotted against a sum of the frequencies for the two turbines, normalized by the viscosity of the fluid. The turbines are counter-rotating and are hydraulically coupled, such that a change in angular velocity in the upstream turbine will result in an opposite, or compensating change in the downstream turbine. By combining the K factors and frequencies for the turbines, therefore, flow or wear effects are averaged out, and higher resolution or accuracy is achieved given that a higher frequency is used as a reference point. The effects of the hydraulic coupling combined with tracking a calibrated difference in meter turbine frequency at any given flow rate allows for reliable validation of the gathered data, error detection and post measurement data correction.