Fundamentals of Hot Wire Anemometry

Abstract

211 pages Price $5 9. 50.Hot wire (and hot film) anemometry is a subject involving the experimental measurement of fluid flows (usually turbulent) that is approached from a scientific and technical point of view. In hot wire anemometry, a fine metal wire, typically 1 mm long and 5 ttm in diameter (supported between two prongs) is electronically heated by an amplifier in a feedback circuit. Air going past the wire cools it at a rate that is a complicated function of flow speed (known as King's law). This causes the circuit to rebalance by creating more current, which is measured as the hot wire signal. Hot film probes are used in liquids. They have a protective coating, typically quartz, to prevent chemical reactions.Lomas' book reveals the subject from a practical perspective surrounded by the science and engineering discoveries that have extended the instrument from an era--where experimentalists had to build their own--to the present, where commercial equipment is readily available.Chapter 1 gives a good introduction to the instrument, including the various types of probes and electronics. In Chap. 2, the reader gets an appreciation for the wear and tear the probes are subjected to and the engineering designs that are used for best performance and consistent response. Chapter 3 gets back into the physics of the instrument by studying the cooling laws of wires (and metal films) and their calibration. Electronic circuitry and feedback are discussed from the engineering standpoint in Chap. 4. In Chap. 5, Lomas' book becomes invaluable because his discussion on measuring flows in a variety of liquids reveals a wealth of information that could only be learned by years of laboratory experience. Finally, in Chaps. 6 and 7, he puts the subject all together by discussing the methods of measuring the various flow quantities of turbulence (using physics and engineering equations). The material in Chap. 6, entitled "Types of Measurements," is substantial in dealing with topics such as the measurement of mean flow velocity, turbulent flow velocity, vorticity, and temperature. An account on the technique of measurement of gas mixture concentration and heat transfer phenomenon in compressible flow completes this satisfying chapter. With over 225 references and many figures distributed throughout, this compact text is extremely valuable to students and researchers (both experimentalists and theorists) in the field of fluid mechanics and related areas. MURRAYS. KORMAN

Discovery of linear asymptotic behaviour at micro-Kelvin resolution in a modulated Rayleigh–Bénard chamber

“…It stands in sharp contrast with the well-known square-root behaviour of King's law in thermal anemometry (King 1914;Lomas 1986). The excitation in a modulated Rayleigh-Bénard is therefore much more gradual than that of a hot wire or plate in open geometries.…”

Ultrasonic Hot Embossing

“…The wire is heated by an electrical current and the voltage drop over the wire is measured (cf. Figure 8(b)) [14][15][16]. When there is a flow through the channel, the wire is cooled, and, that way, its electrical resistance is decreased.…”

Sensors Characterization and Control of Measurement Systems Based on Thermoresistive Sensors via Feedback Linearization

“…A successful method for measurement using thermoresistive sensor uses feedback control to keep the sensor temperature constant (Sarma, 1993), (Lomas, 1986). Then, the value of the measurand is obtained from the variation of the control signal.…”