Thermal droplet size measurements using a thermocouple

During the investigation on atomization and evaporation of water in steam spray coolers a thermal measuring device has been developed for droplet size measurement. This device consists of a thermocouple on which the droplet evaporates by heat removal from the thermocouple material near the hot junction; it is called: droplet detecting thermocouple (d.d.t.). The principle of a d.d.t. is based on utilization of the correlation between droplet radius and temperature signal of the d.d.t., caused by the evaporating droplet. The d.d.t. proved to be a dependable device for continuous detecting and measurement of water droplets both in air and steam flows, even at high pressures and temperatures. In this paper a theoretical analysis of the d.d.t. behaviour is given together with experimental data of d.d.ts. for water droplets with radii between 3 and 1188 μm. Good agreement between experimental data and theoretically predicted results has been reached.