Minimization of Problems while Creating Two-Phase Flowmeters for Cryogenics and Their Features: Part I. Diagnostics of Helium Flows

Abstract

The article offers ways to create two-phase helium flowmeters in the range of mass flow rates from approximately 5–6 to more than 1000 g/s. The principle of operation of flowmeters is based on a combination of capacitive void fraction sensors with a uniform electric field inside the sensing elements to determine the average density of the two-phase mixture and conical narrowing devices to find the average flow velocity. In this case, capacitive sensors with sensitive elements of both circular and annular cross sections, which significantly differ in their sensitivity, can be used. The features and problems inherent in two-phase flowmeters of this type are considered, which include, first of all, the influence of a variety of flow patterns on the characteristics of the narrowing device. Another problem is to consider the influence of the structure of a two-phase flow on the determination of its average density. One more problem is related to possible differences between the measured values of the pressure drops in the narrowing device and the expected values, which are estimated using a homogeneous model in one of the limiting cases of a two-phase flow. The ways of minimizing these problems are shown using a combination of individual technical solutions that have already been tested in practice. Specific technical variants of two-phase helium flowmeters, including a flow-through horizontal cryostat, are presented, which are operable in the entire range of the void fractions from 0 to 1 with a relatively small total hydraulic resistance of the flowmeter’s flow part. The differences between the new and previous technical solutions are shown. The uncertainties of determining the flow rate of two-phase helium flows are estimated.