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Proceedings Paper

Toward thermal flow-sensing with pL/s resolution
Author(s): Niels R. Tas; Theo S. J. Lammerink; Pele J. Leussink; J. W. Berenschot; H. E. de Bree; Miko C. Elwenspoek
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Paper Abstract

This paper focuses on the development of highly sensitive calorimetric flow sensors. Both the hydrodynamics of the flow channel, as well as the heat transfer are analyzed in detail. With the expressions for the hydraulic resistance of the flow channel and the hydraulic system requirements for the flow sensor, it is possible to optimize the design of the flow channel. It is theoretically shown why for small v the calorimetric flow sensor output is linear in v. Also it follows from theory that for a symmetrical configuration, in this linear regime the heater temperature is independent of v for constant heating power. This suggests that for low Reynolds Number King's Law has t obe modified. Different configurations and methods are analyzed: absolute, differential, two beam, three beam, CPA, CTA and TBA. The latter is a real thermal balance measurement and allows the use of non-linear sensing elements. From our experience with acoustical measurements it is possible to estimate practical attainable sensitivity. In combination with proper flow channel design, and a fabrication technology for narrow channels, it is shown that pL/s sensitivity is in reach.

Paper Details

Date Published: 15 August 2000
PDF: 16 pages
Proc. SPIE 4176, Micromachined Devices and Components VI, (15 August 2000); doi: 10.1117/12.395619
Show Author Affiliations
Niels R. Tas, Univ. of Twente (Netherlands)
Theo S. J. Lammerink, Univ. of Twente (Netherlands)
Pele J. Leussink, Univ. of Twente (Netherlands)
J. W. Berenschot, Univ. of Twente (Netherlands)
H. E. de Bree, Univ. of Twente (Netherlands)
Miko C. Elwenspoek, Univ. of Twente (Netherlands)

Published in SPIE Proceedings Vol. 4176:
Micromachined Devices and Components VI
Eric Peeters; Oliver Paul, Editor(s)

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