Calibration Of Heat Flux Sensors Research Articles

A Mixed Radiative-Convective Technique for the Calibration of Heat Flux Sensors in Hypersonic Flow

The ability to measure the very high heat fluxes that typically occur during the hypersonic re-entry phase of space vehicles is generally considered a subject of great importance in the aerospace field. Most of the sensors used for these measurements need to be checked periodically and re-calibrated accordingly. Another bottleneck relates to the need to procure thermal sources that are able to generate reliable reference heat fluxes in the range between 100 and 1000 kW/m2 (as order of magnitude). In the present study, a method is presented by which, starting from a calibration system with a capacity of approximately 500 kW/m2 only, heat fluxes in the range of interest for hypersonic applications are generated. The related procedure takes advantage of established standards for the characterization of a radiative heat flux. It also builds on the hybrid radiative-convective nature of typical hypersonic heat fluxes and the yet poorly explored possibility to use convective sources of heat to produce high-intensity fluxes. The reliability of such a strategy has been tested using a high enthalpy supersonic flow facility relying on an electric arc-heater and pure Nitrogen as work gas. Stagnation-point heat fluxes have been successfully measured (with reasonable accuracy) in the range between 600 and 1500 kW/m2 for values of the centerline enthalpy spanning the interval from to 6 to 24 MJ/kg.

Calibration of heat flux sensors based on anisotropic thermoelements and heterogeneous metal structures using a reflected shock wave

The applicability of the calibration method for heat flux sensors based on anisotropic bismuth thermoelements and a heterogeneous copper-nickel structure using a reflected shock wave to determine the volt-watt coefficient is demonstrated. The coefficient obtained for a sensor based on anisotropic thermoelements is close to the stationary calibration data, and for a sensor based on a heterogeneous structure, to the results of numerical simulation. Keywords: heat flux, calibration, shock tube, shock wave, ghfs, hghfs.

The Design and Performance of Heat Flux Sensor Calibration Equipment

This paper introduces the methods of heat flux sensor calibration and gives detailed descriptions of absolute and transfer techniques. The transmission of standard heat flux is realized by comparing the calibrated heat flux sensor with standard heat flux sensor based on a flat plate furnace. Furthermore, we design a heat flux sensor calibration equipment using absolute method which contains a sodium heat pipe blackbody with 50-mm-diam cavities. Thus heat flux sensor calibration can be traceable to the temperature standard using the absolute equipment.

弧光灯热流标定系统光源的仿真设计

弧光灯热流标定系统光源的仿真设计

The Calibration Method of Thermal Heat Flux Sensor Based on Wireless Sensor Networks

This paper analyzed the advantages and disadvantages of existing heat flux sensor calibration methods, proposed a calibration method of thermal heat flux sensor based on wireless sensor networks. Experimental results showed that the detection error was reduced from 6% to 2% after calibration. The proposed method has many advantages, such as short calibration time, accurate results, easy installation as well as batching calibration. In a word, this method is available to calibrate heat flux sensors and will have an important significance for accurate measurement of heat flux.

Adaptation of the in-cavity calibration method for high temperature heat flux sensors

The need for in situ heat flux measurements in hot structures, used in hypersonic vehicle thermal protection system development, combustion and propulsion research, and fire testing requires that heat flux sensors are characterized over their entire operating temperature range. The in-cavity heat flux sensor calibration technique has been adapted to accommodate elevated sensor temperatures, in an effort to develop a primary calibration scheme for high temperature heat flux sensors using an existing blackbody calibration system. The new scheme has been demonstrated through the calibration of a high temperature, thermopile-type heat flux sensor. The output temperature dependence of the high temperature heat flux sensor (HTHFS) has been successfully characterized over the range of 175–960 °C with acceptable uncertainty limits. The calibrated HTHFS sensitivity agrees well with a theoretical sensitivity model, suggesting that the extended in-cavity calibration technique is a viable choice for primary calibration of heat flux sensors at elevated sensor temperatures.

High Heat-Flux Sensor Calibration: A Monte Carlo Modeling

Conventional calibration of heat-flux sensors uses high-temperature blackbody radiation and places the sensors away from the blackbody aperture. This approach limits the achievable calibration heat flux to about 50 kW/m 2 . Recent interest in extension of the calibration to higher heat-flux levels requires placement the sensors inside the heated cavity under nearly hemispherical irradiation environment. The incident flux at the sensor location depends on the effective emissivity, which is a function of the combined cavity and sensor geometry, and the properties of the radiating surfaces. A scheme is presented to compute the effective emissivity for such measurement schemes by the use of the Monte Carlo technique. Typical results presented demonstrate the influence of the cavity wall surface emissivity and diffusity, nonuniform temperature distributions, and the sensor location on the calculated effective emissivity

Radiative Calibration of Heat-Flux Sensors at NIST: Facilities and Techniques.

We present an overview of the National Institute of Standards and Technology high temperature blackbodies, both in operation and in development, suitable for heat-flux sensor calibration. Typical results of calibrations using the transfer technique in the 25 mm Variable-Temperature Blackbody are presented to demonstrate the long-term repeatability of the calibration technique. A comparative study of the absolute and transfer calibrations of a Gardon gage in a spherical blackbody with a cooled enclosure surrounding the gage housing was conducted. Results of this study demonstrated the influence of convection associated with absolute calibration of sensors in a cooled enclosure. Plans for further development of the transfer technique to higher heat-flux levels and the associated technical issues are discussed.

Comparative calibration of heat flux sensors in two blackbody facilities

This paper presents the results of heat flux sensor calibrations in two blackbody facilities: the 25 mm variable temperature blackbody (VTBB) primary facility and a recently developed 51 mm aperture spherical blackbody (SPBB) facility. Three Schmidt-Boelter gages and a Gardon gage were calibrated with reference to an electrical substitution radiometer in the VTBB. One of the Schmidt-Boelter gages thus calibrated was used as a reference standard to calibrate other gages in the SPBB. Comparison of the Schmidt-Boelter gages calibrations in the SPBB and the VTBB agreed within the measurement uncertainties. For the Gardon gage, the measured responsivity in the SPBB showed a gradual decrease with increasing distance from the aperture. When the gage was located close to the aperture, a distance less than the aperture radius, the responsivity in the SPBB agreed with VTBB measurements. At a distance of about three times the aperture radius, the responsivity showed a decrease of about 4 %. This is probably due to higher convection loss from the Gardon gage surface compared to the Schmidt-Boelter sensor.

Aperture Proximity Effects in High Heat Flux Sensors Calibration.

In the transfer calibration of heat flux sensors, a correction for the irradiance distribution across the sensing area may be required when the sensing areas of the reference and test sensors are different. A method to calculate this correction using well-known equations for the configuration factors is presented. Also, estimates of the correction for test conditions corresponding to the transfer calibration technique in use at the National Institute of Standards and Technology are given.

Calibration of High Heat Flux Sensors at NIST.

An ongoing program at the National Institute of Standards and Technology (NIST) is aimed at improving and standardizing heat-flux sensor calibration methods. The current calibration needs of U.S. science and industry exceed the current NIST capability of 40 kW/m2 irradiance. In achieving this goal, as well as meeting lower-level non-radiative heat flux calibration needs of science and industry, three different types of calibration facilities currently are under development at NIST: convection, conduction, and radiation. This paper describes the research activities associated with the NIST Radiation Calibration Facility. Two different techniques, transfer and absolute, are presented. The transfer calibration technique employs a transfer standard calibrated with reference to a radiometric standard for calibrating the sensors using a graphite tube blackbody. Plans for an absolute calibration facility include the use of a spherical blackbody and a cooled aperture and sensor-housing assembly to calibrate the sensors in a low convective environment.

High-Frequency Heat Flux Sensor Calibration and Modeling

A new method of in-situ heat flux gage calibration is evaluated for use in convective facilities with high heat transfer and fast time response. A Heat Flux Microsensor (HFM) was used in a shock tunnel to simultaneously measure time-resolved surface heat flux and temperature from two sensors fabricated on the same substrate. A method is demonstrated for estimating gage sensitivity and frequency response from the data generated during normal transient test runs. To verify heat flux sensitivity, shock tunnel data are processed according to a one-dimensional semi-infinite conduction model based on measured thermal properties for the gage substrate. Heat flux signals are converted to temperature, and vice versa. Comparing measured and calculated temperatures allows an independent calibration of sensitivity for each data set. The results match gage calibrations performed in convection at the stagnation point of a free jet and done by the manufacturer using radiation. In addition, a finite-difference model of the transient behavior of the heat flux sensor is presented to demonstrate the first-order response to a step input in heat flux. Results are compared with shock passing data from the shock tunnel. The Heat Flux Microsensor recorded the heat flux response with an estimated time constant of 6 μs, which demonstrates a frequency response covering DC to above 100 kHz.

Sources of Error in Vacuum Calibration of Heat Flux Sensors

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