Study of Hot Wire Anemometry and Flow Measurement Elements (original) (raw)
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A New Instrument for the Measurement of the Thermal Conductivity of Fluids
International Journal of Thermophysics, 2006
The transient hot-wire technique is at present the best technique for obtaining standard reference data for the thermal conductivity of fluids. It is an absolute technique, with a working equation and a complete set of corrections reflecting departures from the ideal model, where the principal variables are measured with a high degree of accuracy. It is possible to evaluate the uncertainty of the experimental thermal conductivity data obtained using the best metrological recommendations. The liquids proposed by IUPAC (toluene, benzene, and water) as primary standards were measured with this technique with an uncertainty of 1% or better (95% confidence level). Pure gases and gaseous mixtures were also extensively studied. It is the purpose of this paper to report on a new instrument, developed in Lisbon, for the measurement of the thermal conductivity of gases and liquids, covering temperature and pressure ranges that contain the near-critical region. The performance of the instrument for pressures up to 15 MPa was tested with gaseous argon, and measurements on dry air (Synthetic gas mixture, with molar composition certified by Linde AG, Wiesbaden, Germany, Ar-0.00920; O 2-0.20966; N 2-0.78114), from room temperature to 473 K and pressures up to 10 MPa are also reported. The estimated uncertainty is 1%.
THE PROCEEDINGS OF THE 5TH INTERNATIONAL CONFERENCE ON MARITIME EDUCATION AND TRAINING (The 5th ICMET) 2021
When measuring the temperature of a stream of compressible fluid using a temperature sensor, experimenters must address the problem of the effect of the compressibility of the locally decelerated fluid in the near neighborhood of the sensor on the rendered temperature. Generally said, the temperature rendered by a temperature probe positioned within an airflow depends on the external flow velocity, the specific heat of the fluid, the thermodynamic temperature, and the recovery factor of the probe. A method of measuring the velocity of a flowing compressible fluid that takes advantage of these properties is called Recovery Temperature Anemometry (RTA). This, unfortunately, means there are two unknown properties in real-time measurements-the velocity and the thermodynamic temperature of the fluid. This article is focused on a possible solution to the mentioned problem and the development of appropriate probes. By using two probes with different recovery factors, the need for knowing the thermodynamic temperature is eliminated so that a combination of two temperature probes with different recovery factors can be used for the velocity measurement. As described in this paper, by using multiple temperature sensors with different recovery factors, the temperature of the flowing fluid can be eliminated, leaving only one unknown quantity in the entire problem, which is the velocity of the flowing fluid. The article describes the theoretical basis of the problem, the purpose of multi-element probe, the verification multi-element temperature probe behavior, the measurement technique, and the results.
Investigation on the determination of flow direction using two parallel cylindrical hot film sensors
Measurement, 2010
Measurement of instantaneous air flow velocity with high frequency can be carried out by using a hot wire anemometer (HWA). HWA works on the basis of heat transfer rate from hot wire to the fluid flow, therefore directional identification of the air flow using hot wire anemometer is a difficult task. By using two parallel cylindrical hot film sensors a probe was built. By considering the wake and heat effect of the upstream sensor on the downstream sensor, direction of the air flow can be identified. In this work, the wake and heat effect resulting from the upstream sensor to the velocity measurement, by the downstream sensor was studied. This measured velocity is dependent of the following factors namely; air velocity, upstream sensor overheat ratio, distance between the two sensors and turbulence intensity of the flow. As a result it was found that the manufactured probe with sensor distance of 1 mm apart is capable of measuring reverse flow measurements of up to 20 m/s for a moderate turbulent flow. (M.A. Ardekani), mohamedami-ny@merc.ac.ir (M. Aminy), khoshnevis@Sttu.ac.ir (A. Khoshnevis).
Single Sensor Hot-Wire Anemometer Based on Thermal Time Constant Estimation
IEEE Xplore, 2018
This paper presents a new type of hot-wire anemometer based on its sensor's thermal time constant estimation. In the known types of thermal anemometers, the source of measurement errors is an ambient temperature, which influences the heat exchange between the hot sensor and its surrounding fluid. Therefore, a second sensor is used to compensate the impact of ambient temperature. The solution contemplated here uses the relationship between the sensor's thermal time constant and fluid flow rate. This constant has no relationship to ambient temperature, so there is no need to use a second sensor. The paper presents algorithms for estimating the sensor's time constant, mathematical relationships, the measurement system and sample measurement results obtained.
New portable instrument for the measurement of thermal conductivity in gas process conditions
Review of Scientific Instruments, 2016
The development of high temperature gas sensors for the monitoring and determination of thermophysical properties of complex process mixtures at high temperatures faces several problems, related with the materials compatibility, active sensing parts sensitivity, and lifetime. Ceramic/thin metal films based sensors, previously developed for the determination of thermal conductivity of molten materials up to 1200 • C, were redesigned, constructed, and applied for thermal conductivity measuring sensors. Platinum resistance thermometers were also developed using the same technology, to be used in the temperature measurement, which were also constructed and tested. A new data acquisition system for the thermal conductivity sensors, based on a linearization of the transient hot-strip model, including a portable electronic bridge for the measurement of the thermal conductivity in gas process conditions was also developed. The equipment is capable of measuring the thermal conductivity of gaseous phases with an accuracy of 2%-5% up to 840 • C (95% confidence level). The development of sensors up to 1200 • C, present at the core of the combustion chambers, will be done in a near future.
Energies, 2022
This paper describes a study to expand the knowledge as to whether a thermal wave anemometer can be used to measure the velocity of flowing gases or gas mixtures in situ. For this purpose, several series of measurements were performed in laboratory conditions using both the previously used probe and other probes of similar design. The probes were not modified mechanically or electrically in any way. The obtained results were compared with each other, and on this basis, the optimal, though purely empirical, form of the calibration function was determined (4). The analysis of the relative differences between the measured and set velocity values showed that they do not exceed 1% in the velocity range from 0.05 to 2.5 m/s. Lowering the sensitivity of the method for velocities below approx. 0.05 m/s results in a rapid increase in the observed deviations, reaching 15% for 0.015 m/s. The conducted research also revealed an increased resistance of the proposed measurement method to small fl...
Mass flow-rate control unit to calibrate hot-wire sensors
Experiments in Fluids, 2007
Hot-wire anemometry is a measuring technique that is widely employed in fluid mechanics research to study the velocity fields of gas flows. It is general practice to calibrate hot-wire sensors against velocity. Calibrations are usually carried out under atmospheric pressure conditions and these suggest that the wire is sensitive to the instantaneous local volume flow rate. It is pointed out, however, that hot wires are sensitive to the instantaneous local mass flow rate and, of course, also to the gas heat conductivity. To calibrate hot wires with respect to mass flow rates per unit area, i.e., with respect to (qU), requires special calibration test rigs. Such a device is described and its application is summarized within the (qU) range 0.1-25 kg/m 2 s. Calibrations are shown to yield the same hot-wire response curves for density variations in the range 1-7 kg/m 3. The application of the calibrated wires to measure pulsating mass flows is demonstrated, and suggestions are made for carrying out extensive calibrations to yield the (qU) wire response as a basis for advanced fluid mechanics research on (qU) data in density-varying flows.
Correct Use of the Transient Hot-Wire Technique for Thermal Conductivity Measurements on Fluids
International Journal of Thermophysics
The paper summarizes the conditions that are necessary to secure accurate measurements of the thermal conductivity of fluids using the transient hot-wire technique. The paper draws upon the development of the method over five decades to produce a prescription for its use. The purpose is to provide guidance on the implementation of the method to those who wish to make use of it for the first time. It is shown that instruments of the transient hot-wire type can produce measurements of the thermal conductivity with the smallest uncertainty yet achieved (± 0.2%). This can be achieved either when a finite element method (FEM) is employed to solve the relevant heat transfer equations for the instrument or when an approximate analytic solution is used to describe it over a limited range of experimental times from 0.1 s to 1 s. As well as establishing the constraints for the proper operation of the instrument we consider the means that should be employed to demonstrate that the experiment o...
Development of absolute hot-wire anemometry by the 3ω method
Review of Scientific Instruments, 2010
We have developed hot-wire anemometry applying the 3 method. The approach is based on the same heat transfer process as traditional anemometry, but substituting the constant current by a sinusoidal current and using synchronous detection to measure the conductive-convective exchange coefficient and the gas flow rate. Our theoretical model is tested with air flow at 300 K under atmospheric pressure: The experimental results are in agreement with the numerical simulation, justifying the technical choices in the 3 method and the approximations made. The effectiveness of the 3 method for measuring the flow rate and the conductive-convective exchange coefficient between the hot wire and flowing gas is discussed.
Empirical Correlations for Thermal Flowmeters Covering a Wide Range of Thermal-Physical Properties
1999
Thermal flowmeters can provide direct mass flow measurement of gases and vapors over a wide range of process conditions without the need for density corrections based on pressure and temperature. They are widely used in industrial processes that contain toxic, corrosive, or highly reactive gases. It is often not possible to calibrate the flowmeter on the process gas in which it will be used. In this case a non-hazardous "surrogate" gas is used for calibration, and a theoretical model used to predict the meter's response in the process gas. This can lead to large measurement errors because there are no accurate and straightforward methods for predicting the performance on one kind of gas based on the calibration on another gas because of the complexity of the thermal processes within the flow sensor. This paper describes some of the commonly used models and conversion methods and presents work done at ORNL to develop and experimentally verify better thermal models for predicting flowmeter performance.