This research experimentally studied the effect of operational parameters on spray characteristics of flash evaporation system which is the key component of the discharge thermal energy combined desalination (DTECD) system. For this purpose, initially the effect of superheat degree, inlet pressure, and inlet temperature on the spray angle of three different types of full cone spray nozzles was investigated using a high speed camera. Moreover, a force balanced mathematical model was developed to calculate droplet sizes and the results were compared with experimentally measured values using shadowgraph technique. The results show that the spray angle was largely affected by the superheat degree regardless of nozzle type. In addition, an empirical equation was suggested to correlate inlet pressure, saturation pressure, and spray angle. Further, a model was proposed to estimate the variation of droplet sizes along the spray centreline and concluded that the spray capacity significantly influenced the droplets' lifetime. (C) 2019 Elsevier B.V. All rights reserved.