D4.4 - Calibration-Free Volume Flow Measurement Principle Based on Thermal Time-of Flight (TTOF) for Gases, Liquids and Mixtures

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
D4 - Gas Sensors II
E. Engelien, O. Ecin, R. Viga, B. Hosticka, A. Grabmaier - Universität Duisburg-Essen (Germany)
589 - 594


A novel flow measurement principle based on the Thermal Time-of-Flight (TTOF) is applied with the methods of heat transfer including heat source and heat sinks. Therefore, an appropriate flow meter is designed which can be deployed to any kind of fluid considering gases, liquids and mixtures. With this significant advantage the TTOF flow meter is calibration-free. A low-maintenance usage is intended by introducing steady thermocouples as heat detectors.
The presented investigation includes a discontinuous heat source associated with minimum two thermal sensors arranged downstream. The heat source is used to generate a signal code by injection of local thermal pulses into the flow stream. The thermal sensors detect the time-dependent thermal gradients in the fluid at different positions. Using signal processing methods the time delay between the thermal signals obtained from the serially arranged thermal sensors is calculated. Herewith, a measurement technique is aimed for the determination of the flow velocity of any kind of fluid with unknown properties (volume flow measurement). Accordingly, it is feasible to draw conclusions from thermal transfer functions between the thermal sensors to the fluid properties.
An important characteristic of the sensor is the behaviour of the temperature and velocity boundary layer. Consequentially, for the gas measurement (δth >> δv) a heat radiation source is adopted to avoid an influence of the flow stream through contactless heating and to produce the signal code. Due to the high absorption coefficient in the flow velocity measurement for liquids and mixtures (δth ≤ δv) a filament is used to facilitate the generation of the local thermal pulse.
The authors report on a measurement principle in a flow velocity range from Re ≈ 26 - 2600 for gases, liquids and mixtures. Therefore, a flow sensor construction is developed, which can be applied likewise to any composition of fluids. The simplified sensor model allows an absolute accuracy down to 10 % and relative accuracy down to 4 %. Further enhancements are the modification of the TTOF flow sensor concerning its application to fluids containing solid particles/fractions and its miniaturisation as well as the integration of signal detection and signal processing into the sensor assembly.