Technical Field
The present invention relates to a device which employs thermocouples to determine a void fraction of a two-phase flow of a liquid-gas mixture in a pipe.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
The need for multiphase flow measurement in the oil & gas production and petrochemical industries became prominent in recent years. A number of multiphase flow meters were developed during the last few years by research organizations, meter manufacturers, and oil & gas production companies. These meters use different technologies and the prototypes are varied in design and function.
Reliable measurements of the multiphase flow parameters such as void fraction, phase concentration, phase velocity and flow pattern identification are important for accurate modeling of multiphase systems. These parameters can be measured using a number of techniques, including radiation attenuation (X-ray, gamma-ray or neutron beams) for line or area averaged values, optical or electrical contact probes for local void fraction, impedance technique using capacitance sensors and direct volume measurement using quick-closing valves. The selection of the proper technique depends on the application, and whether a volumetric average or a local void fraction measurement is desired. Accurate measurement of the liquid and gas fractions, also known as void fractions, is essential to the the oil and gas industry, as well as the nuclear energy and chemical processing industries.
Meters from different manufacturers vary in their design, function and capabilities. In the oil industry, the measurement of oil and water flow rate in each production zone of an oil well is very important to monitor and control the fluid movement in the well and reservoir. Therefore, numerous research efforts have been carried out designing accurate multiphase flow meters. A variety of meters are currently under development worldwide. Most of these are equipped with a static mixer or a T-elbow to homogenize the multiphase flow, then the flow rate of each phase is measured using a combination of Gamma-ray densitometer, capacitance water cut meter and cross-correlation type flow meter. However, there are technical challenges in the operation of some of these meters. For example, meters equipped with gamma densitometers that utilize a nuclear source are widely used for measuring the fluid density. The primary drawback of these meters is the environmental and safety issues associated with the nuclear sources.
The Coriolis sensor measures both the mass flow and density by tracking the natural frequency of the vibrating pipe carrying the fluid. These devices, however, require a vibration source which makes them mechanically complex and relatively difficult to maintain.
Optical sensors employing fiber optics have demonstrated high accuracy in addition to being neither intrusive nor invasive, however these sensors are restricted when it comes to monitoring opaque fluids.
Finally, thermal mass flow meters generally use combinations of heated elements and temperature sensors to measure the difference between static and flowing heat transfer to a fluid and infer its flow with knowledge of the fluid's specific heat and density. If the density and specific heat characteristics of the fluid are constant, the meter can provide direct mass flow readout, and does not need any additional pressure temperature compensation over their specified range.
The idea behind using thermal conductivity for the measurement of void fraction in two-phase flows is the sensitivity of heat convection from a solid body to the properties of the flowing fluid (especially the thermal conductivity). It is well established that the rate of heat transfer from a heated cylinder placed in a fluid stream depends on the fluid properties as well as free stream temperature, velocity of the approaching stream, cylinder geometry including surface roughness, cylinder surface temperature, and flow structure of the oncoming stream. The detailed analysis of the heat transfer process from a cylinder in cross flow has been the subject of numerous research investigations [H. M. Badr, “A theoretical study of laminar mixed convection from a horizontal cylinder in a cross-stream”, International Journal of Heat and Mass Transfer, Vol. 26, No. 5, pp. 639-653, 1983; H. M. Badr, “On the effect of flow direction on mixed convection from a horizontal cylinder,” International Journal for Numerical Methods in Fluids Vol. 5, pp. 1-12, 1985; H. M. Badr, “Effect of free-stream fluctuations on laminar forced convection from a straight tube”, International Journal of Heat and Mass Transfer, Vol. 40, No. 15, pp. 3653-3662, 1997; S. Whitaker, “Forced convection heat transfer correlations for flow in pipes, past flat plates, single cylinders, single spheres, and for flow in packed beds and tube bundles”, AIChE Journal, Volume 18, Issue 2, pages 361-371, 1972; B. G. Hegge Zijnen, “Heat transfer from horizontal cylinders to a turbulent air flow”, Appl. Sc. Res., Section A, Vol. 7, pp. 205-223, 1958—Each incorporated herein by reference in its entirety], covering various modes of heat transfer such as constant surface temperature and constant heat flux, along with structures of the approaching stream (laminar and turbulent flow regimes).
In view of the forgoing, the objective of the present invention is to provide an apparatus involving a hollow tube with a plurality of thermocouples for measuring the void fraction of a two-phase flow in a pipe.