A small-area, thin-film heat flux sensor that has a large output signal and fast response in a flexible package has been developed at the NASA Glenn Research Center under a Technology Transfer Agreement with the Goodyear Tire & Rubber Company of Akron, Ohio. Heat flux is one of a number of parameters (in addition to pressure, temperature, flow, and others) of interest to engine designers and fluid dynamicists. All heat flux sensors operate by measuring the temperature difference across a thermal resistance. There are various designs of heat flux sensors, such as Gardon gauges, plug gauges, and thin-film thermocouple arrays. The thin-film designs have the advantage of high-frequency response and minimal flow disturbance.
Recently there has been a need for a sensor to measure the heat flux on the sidewalls and within the tread of a tire. These measurements would be on curved surfaces over an area that is smaller than the area of sensors currently available commercially. Thus, a design was developed that retains the fast response of the thin-film thermocouple sensors but that has a larger output and can be made smaller and in a flexible package. This photograph shows the sensor developed to fit in a tire tread.
Heat flux sensor developed at Glenn to fit in a tire tread.
Long description of figure 1.
The new sensor design consists of a resistor bridge fabricated onto a 0.25-mm- (0.010-in.-) thick polyester film. The temperature-sensitive element is sputter-deposited platinum, patterned and applied using a photolithography technique newly developed at Glenn, with line width and line spacing of approximately 60 mm. The variation of platinum’s electrical resistance with temperature is well characterized.
Thus, the ability to measure heat flux magnitude and direction was incorporated into a resistance bridge design fabricated using thin-film techniques to allow fast response. The result is a sensor that does not need the large area and stiff packaging required for the old thermopile design, and that does not have the low output of the thermopile design, but that has a response that is nearly as fast. The development of this sensor offers a new laboratory procedure to establish heat transfer coefficients for different regions of a tire. Testing at the Goodyear Tire & Rubber Technical Center (shown in the following photograph) generated measured heat transfer coefficients that were within the range of values obtained from thermal finite element tire models previously reported in the literature. The experimentally measured temperatures from these data also agree well with the numerically generated values, thus verifying the models.
Tests at the Goodyear Tire & Rubber Technical Center using the new heat flux sensor are validating numerical models of tire heat transfer. (Photograph courtesy of Goodyear Tire & Rubber Company; used with permission).
Long description of figure 2.
The new sensor can be used in components for process control, modeling validation, determination of cooling requirements, and general calorimetry in rocketry, aerospace, and automotive environments. One specific application is to enable thermal control in advanced multiuse extravehicular activity (EVA) pressure suits for future lunar missions. The heat flux sensor is small enough to allow measurement of the heat load on the thermal cooling system as well as the heat flux from various parts of the suit. The correlation of these parameters will give a more accurate estimate of the astronaut’s metabolism and any external thermal loading and will permit a more rapid adjustment of the suit’s cooling system.
Find out more about this research at Glenn’s Sensors and Electronics Branch: http://www.grc.nasa.gov/WWW/sensors/
Glenn contacts:
Gustave C. Fralick, 216-433-3645, Gustave.C.Fralick@nasa.gov
John D. Wrbanek, 216-433-2077, John.D.Wrbanek@nasa.gov
Goodyear contact:
Mahmoud C. Assaad, 330-796-8804, mahmoud.assaad@goodyear.com
Authors:
Gustave C. Fralick, John D. Wrbanek, José M. Gonzalez III, Charles A. Blaha, and Mahmoud C. Assaad
Headquarters program office:
Aeronautics Research Mission Directorate, Exploration Systems Mission Directorate
Programs/projects:
Fundamental Aeronautics, Advanced Extravehicular Systems
Last updated: December 14, 2007
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