Technology
New technique for measuring flow patented It may seem that nearly every phenomenon imaginable has been used in devices to measure flow. But with the recent issuance of a patent on a new concept, the polarization flowmeter has joined the list. The concept involved in the patent (U.S. 4,255,976)—it hasn't yet been embodied in a physical device—is an electromagnetic method for measuring velocity of a dielectric material. It combines the principles used in induction and magnetoelectric measurement techniques, which for some time have been used to measure flow. Richard A. Formato of Shrewsbury, Mass., a consultant in electromagnetics and computers, arrived at the new concept serendipitously, while investigating a descaling device for pipes. He was surprised, he says, to find on studying the literature that the induction and magnetoelectric techniques had not been combined before. No commercialization of the new concept has begun yet, but it is under review by a number of instrument companies, Formato says. An advantage of electromagnetic flowmeters is that they are not intrusive; there is nothing to impede flow or add to the pressure drop. The one type of electromagnetic flowmeter—induction—is used with conductive fluids. A stationary magnetic field surrounds the moving fluid. The electric field induced in the fluid according to Faraday's law is proportional to the fluid velocity.
In magnetoelectric flowmeters, a moving nonconducting fluid is subjected to a stationary electric field. This induces a magnetic dipole moment in the fluid that, manifested as an external magnetic induction, is proportional to the fluid velocity. The polarization flowmeter combines the induction and magnetoelectric approaches by applying electric and magnetic fields simultaneously to the moving fluid. The resulting change in the fluid's state of polarization relates to velocity. Formato explains the concept by describing a parallel-plate capacitor filled with stationary water as a dielectric. The capacitance of the system is much greater than the freespace value without water present as a result of reduced electric field between the plates caused by a polarization charge density induced in the water adjacent to the plates. Each water molecule acts as a small electric dipole, all of them aligned along the direction of the applied electric field. This orientation polarization mechanism, Formato explains, is characteristic of polar materials. Distortion polarization is characteristic of nonpolar materials and results from displacement of positive and negative molecular charge centers by an external electric field. Formato explains that if the water in the capacitor is moving and is subjected to a properly oriented magnetic field, in addition to the
C 0 2 replaces hexane in soy oil extraction Using supercritical carbon dioxide, separated from the gas either by rerather than hexane, to extract oils ducing the pressure or by increasing from soybeans and other seeds could the temperature; Friedrich suspects "revolutionize" the oilseed processing that the latter approach would be industry, according to scientists at the more energy efficient in a large-scale Department of Agriculture's North- process. ern Regional Research Center, PeoThe main difference between oils ria, 111. extracted with carbon dioxide and USDA chemist John P. Friedrich with hexane is that the carbon dioxnotes that carbon dioxide, at high ide-extracted oil contains less than pressure and above its critical tem- 10% as much phosphorus "gum." It's perature of 31° C, has the density of essentially equivalent to a degummed a liquid but diffuses as a gas. In ex- hexane crude, Friedrich says, and periments at the center, supercritical doesn't require an extra degumming carbon dioxide at 5000 psi and 50° C, step after extraction. It's also somewhen passed through crushed and what lighter in color than degummed flaked soybeans, absorbed 1.2 to 1.4% hexane crude. of its weight in oil—about the same The process could revolutionize the yield as with conventional hot hexane oilseeds industry, says Timothy L. extraction, Friedrich says. Raising the Mounts, the Peoria center's oilseeds pressure to 8000 psi increased the chief, provided the apparent advanyield to 2.7% by weight. The oil can be tages justified the costs of retooling. 34
C&EN May 25, 1981
electric field between the plates, it exhibits a different degree of polarization than it would if stationary. This effect happens because the tendency of the electric field to produce alignment of the dipole moments may be partially offset or aided by the torque resulting from the magnetic field. This change in polarization depends on the velocity of the water relative to the magnetic field and may be manifested as a change in the material's effective dielectric constant—which can be measured and the velocity deduced. Formato notes that the magnetoelectric flowmeter is limited to extremely good insulators. Because of the large electric field required— typically 1' million volts per m (resulting in a very small induced magnetic field of generally only a few milligauss)—even small levels of conductive contaminants in the fluid can cause signal problems. The polarization flowmeter avoids this. Typically, the polarization flowmeter would require an electric field of only a few tenths of a volt per meter and a magnetic field of a few hundred gauss. Thus the problems associated with intense electric fields are eliminated—to an extent that fairly high conductivities can be tolerated in the measured fluid. Because the system can be implemented with far less sophisticated technology than that of the magnetoelectric flowmeter, Formato expects that costs of the polarization flowmeter would be lower and reliability improved. D He observes that a change from hexane to carbon dioxide would require high-pressure equipment that hasn't even been designed. Friedrich notes that supercritical extraction now is used commercially to remove caffeine from coffee; he says there may be long-range cost and availability advantages to using it for soybeans. The cost of hexane has increased tenfold in less than 10 years. At the current rate of loss of 0.7 gal per ton, oilseed processors use 21 million gal of hexane to extract oil from a billion bushels of soybeans every year. Carbon dioxide is available from fermentation processes, Friedrich points out; the chief cost would be in compressing it. Once compressed, it could be recycled at high pressure. Also, he adds, there would be advantages to using an inert gas instead of a flammable liquid. D
