Ultrasonic flowmeters have been studied widely for the measurement of fluid flow. Various techniques are available, including time-of-flight measurements, Doppler techniques and vortex shedding. While such techniques have been available for some years, it is known that the measurement accuracy is limited by factors such as temperature variation. Typically flow and temperature are measured seperately. Using ultrasound tomographic techniques we have shown that it is possible to measure both temperature and flow variations independently when both are present in the same gas jet.

The experimental arrangement below shows how tomographic ultrasonic data can be collected across a heated gas jet.

  Experimental setup measuring flow and temperature from a hot air gun

The data, in terms of either time-of-flight, amplitude, or spectral content can then be gathered in the form of projections, and used to form images. Either sum of difference data is used, following collection from raypaths in counter-propagation directions (i.e. by swapping source and receiver along the same path). This allows both temperature and flow velocity to be reconstructed concurrently as tomographic images.

Thermocouple measurement (left) compared to temperature variations reconstructed using ultrasonic tomography (right) Results of flow velocity cross-sections from ultrasonic tomographic scan data at a flow angle of 45°