A TRANSIENTLY HEATED NEEDLE ANEMOMETER

Convective heat transfer from cylinders warmed above ambient temperature is a standard technique for measuring windspeed. Available devices are typically fragile, expensive, and complex. We developed a heat-transfer anemometer that is robust, inexpensive, and simple. Referred to as a needle anemometer, the sensing portion of the device is a 20 mm length of tubing of 0.56 mm diameter, into which a heater and thermocouple are inserted. Needle temperature measured during alternating 5 s heating and non-heating periods allows estimation of the equilibrium temperature rise above ambient temperature for long heating times. This is inversely related to (windspeed)1/2 from 0.05 m s-1 to greater than 14 m s-1. In a field trial, the needle anemometer yielded windspeeds of +/- 0.2 m s-1 (S(y,x)) of those from a cup anemometer. Precipitation striking the needle caused overestimates of windspeed by up to 20%.