A novel single-short-pulse MEMS upstream thermal flow sensor for gases also measuring thermal conductivity and thermal diffusivity

摘要

A prototype thermal flow sensor for gases was designed, fabricated and tested on several distinct specimens. The MEMS sensor is of micro-beam type and consists of one Joule heating element and at least one resistance thermometer. The heater is operated in a single short pulse mode of a duration between 30 mu s and 100 mu s; its excess temperature is limited to 5 K. The velocity of flow is determined from the upstream thermometer. The uncertainty is preliminary assessed to be 1.5% within a range from 0 to 7.2m . s(-1). The sensor not only measures the velocity of flow, but also the thermal conductivity and the thermal diffusivity of the gas under test. The knowledge of the latter two material properties can help to identify an unknown specimen. The report provides empirical working equations for the three measurands mentioned. Additionally, a precise fitting relation is given that effectively supports the evaluation of the acquired data. (C) 2019 Elsevier B.V. All rights reserved.