Multi-Parameter Sensing With a Thermal Silicon Flow Sensor

[+] Author and Article Information
M. J. A. M. van Putten, C. R. Kleijn, H. E. A. van den Akker

Kramers Laboratorium voor Fysische Technologie, Faculty of Applied Sciences, Delft University of Technology, Prins Bernardlaan 6, 2628 BW Delft, The Netherlands

J. Fluids Eng 124(3), 643-649 (Aug 19, 2002) (7 pages) doi:10.1115/1.1486471 History: Received June 19, 2000; Revised January 29, 2002; Online August 19, 2002
Copyright © 2002 by ASME
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Top: Schematic drawing of the sensor; both bridges are indicated. Bottom: principle of the double bridge configuration. The measurement bridge is denoted by (M), the heater bridge by (H); ThF denotes thermal feedback, realized by thermal conduction in the silicon substrate. The gradient signal is measured by the operational amplifier, and yields the signal Vout=Vgrad.
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Illustration of the measurement setup. The entrance length to the flow sensor is 1 meter, as well as the exit length. The mass flow controller (MFC) is placed upstream of the entrance length. RM=revolving mechanism. The temperature sensor is a Pt100 element, positioned upstream from the flow sensor.
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Example of the heater voltage, VH, and gradient signal, Vgrad, from the sensor. The labels (a)–(f) denote 6 different flow velocities (0 to 20 SLM) (ReL from 0 to 80) in steps of 4 SLM (or ΔRL≈16). The small spikes, visible in the heater signal, occur at the time that the sensor is turning 180°. During this rotation, it is temporarily positioned at a 90 deg angle with the forced flow component. In this position, the forced convected heat loss is increased, resulting in an increase in the heater voltage. The ADM signal relates to the top-top value of the amplitude of this gradient signal, as indicated in the graph for the flow velocity labeled with (f).
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Response curves for four different temperatures in the temperature range from 18 to 24°C. Only curves corresponding with even values of the temperature are shown. There is an increased density of measured values below Re≈80. Top: The gradient signal, VADM, as a function of Re. Bottom: total heat loss, ΦH, as a function of Re. The detailed behavior of the response curves enclosed by the boxes A and B is shown in Fig. 5. Note, that the gradient signal, VADM is zero at Re=0, contrary to the total heat loss, ΦH.
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Detail of the curves shown in Fig. 4 in the boxes A and B, respectively, showing the behavior of the gradient signal, VADM and the total heat loss, ΦH, near Re=0. The gradient signal becomes a linear function of Re, while the heat loss behaves as an even function, scaling as ∼Re2.
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Relation between the gradient signal, VADM, and the total heat loss, ΦH, for four different temperatures in the temperature range 18–24°C; only values at even temperatures are displayed. Each point in the area enclosed by the VADM and the ΦH axes correspond to a single temperature because the lines shown never intersect.
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Top: Estimated values of Re over the flow range Re=0 to Re=800. Bottom: Temperature estimates. The number of data points estimated was above 1900. The standard deviation of the relative error in the Re estimate is 2.8%. Temperature estimates are accurate within 0.64 K (2 standard deviations).




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