Abstract
This paper introduces a simple theoretical model for the response time of thermal flow sensors. Response time is defined here as the time needed by the sensor output signal to reach 63.2% of amplitude due to a change of fluid flow. This model uses the finite-difference method to solve the heat transfer equations, taking into consideration the transient conduction and convection between the sensor membrane and the surrounding fluid. Program results agree with experimental measurements and explain the response time dependence on the velocity and the sensor geometry. Values of the response time vary from about 5 ms in the case of stagnant flow to 1.5 ms for a flow velocity of 44 m/s.
Highlights
Micro-machined thermal flow sensors are used for many applications, especially ones that need a fast response time such as medical and automotive applications
Micromachines 2011, 2 response time behavior is an important issue for such applications
The thermal flow sensors considered in this study are those developed by IMSAS [2,3,4]
Summary
Micro-machined thermal flow sensors are used for many applications, especially ones that need a fast response time such as medical and automotive applications. The thermal flow sensors considered in this study are those developed by IMSAS [2,3,4] These sensors are based on silicon as substrate material. Sosna et al investigate an electrical measurement of thermal response time and present a model for that measurement. According to this method, an electric heating impulse is applied to the sensor heater which causes a heat transfer through the membrane. The two thermopiles detect a rising in temperature (measured as an electric voltage) that leads to estimate the thermal response time. Results meet the experimental results of the response time, and provide the sensor output signals (thermopiles) in the steady state case
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