An economical dual hot-wire liquid water flux probe design

• We designed a new probe that will measure velocity, liquid water content and liquid water flux.
• The probe uses two hot wires, one sensitive to liquid water content and one sensitive to velocity.
• The probe is low cost and suitable for ground-based measurements in sensor networks.
• The velocity measurement uncertainty is about 6%.
• The LWF measurement uncertainty is between 2 and 17%.

The velocity, liquid water content (LWC) and their product, the liquid water flux (LWF), are of interest for research in environmental sciences, fog collection, and free-space communications. This paper provides a design for an economical dual hot-wire LWF probe, which enables the ground-based measurement of velocity, LWC and LWF. The design accounts for the droplet deposition efficiency, prong conduction, saturation and sensitivity. The operating mode and probe configurations are described. Two 125 μm diameter, 5 cm long platinum wires having 2 and 50 °C wire to air temperature offsets would yield measurement uncertainties of about 6% for velocity and from 8 to 22% for the LWC and from 2 to 17% for the LWF given velocities in the range 2 to 8 m/s and LWC in the range 0.2 to 0.8 g/m3. The lower uncertainties correspond to higher LWF, which is of particular interest in fog collection projects. The recurring costs of the instrument's mechanical and electrical components would be about US $150 per unit. Therefore, the design presented herein is a viable option for large-scale sensor networks.