DIRECT CONTACT CONDENSATION OF STEAM ON DROPLETS

An experiment of direct contact condensation of saturated steam on subcooled water sprays characterized by droplets of uniform size has been carried out with the aim of testing the influence of droplet diameter and velocity on the heat transfer rate, up to a pressure of 0.6 MPa. Liquid sprays with a uniform distribution of droplet diameters (in the range 0.3-2.8 mm) were obtained by means of an ad hoc injection system based on the superposition of a high frequency acoustic vibration in the liquid. Continuous measurements of the average droplet temperature along the axis of the spray jet were performed. The condensation efficiency and local heat transfer coefficient were calculated as functions of the main parameters involved (droplet diameter and velocity, thermodynamic condition of the fluids). Comparisons of experimental results with predictions obtained using available models are reported. A method allowing a better data reduction, based on consideration of the turbulence inside the droplet, is proposed.