Arab J Sci Eng (2014) 39:7241–7250 DOI 10.1007/s13369-014-1283-4 RESEARCH ARTICLE - MECHANICAL ENGINEERING Visual Characterization of Airless Water Spray Jet Breakup and Vortex Clouds Formation at Elevated Temperature and Pressure M. Y. Naz · S. A. Sulaiman · B. Ariwahjoedi · Ku Zilati Ku Shaari Received: 8 May 2013 / Accepted: 30 November 2013 / Published online: 6 July 2014 © King Fahd University of Petroleum and Minerals 2014 Abstract Most of the Newtonian fluids when heated close to their boiling points exhibit very complex spray structures where vortex clouds may occur due to turbulence in the flow. The objective of the study was to observe the spray jet dynam- ics and the vortex cloud formation during the atomization of the water at elevated temperature and pressure. For this pur- pose, visual and comparative studies were conducted on full cone water spray pattern generated by three axi-symmetric spray nozzles of different exit diameters. Using a high-speed camera, the jet breakup dynamics were visualized as a func- tion of water heating temperature and load pressure. The image analysis confirmed the strong influence of the nozzle orifice diameters and processing parameters on spray struc- ture and characteristics. The spray cone angle and width did not vary significantly with increasing Reynolds and Weber numbers at early injection phases leading to increased macro- scopic spray propagation. The discharge coefficient, mean flow rate and mean flow velocity were significantly influ- enced by the load pressure, but less affected by temperature. The fine-scale image analysis also predicted the formation and decay of the semi-torus-like vortex clouds in the spray structures near the water boiling point. For smallest used ori- M. Y. Naz (B ) · B. Ariwahjoedi Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia e-mail: yasin603@yahoo.com S. A. Sulaiman Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia K. Z. Ku Shaari Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia fice diameter, these vortex clouds were seen clearly above 1 bar water pumping pressure and at 90 ◦ C heating temperature. Keywords Airless sprays · Thermal energy · High-speed imaging · Vortex clouds 1 Introduction The liquid jet breakup is an ubiquitous phenomenon in nature and is a classic problem in hydrodynamics. The academic and research interest in problems related to liquid jet breakup dates back to the nineteenth century. The liquid sprays and the corresponding atomizing systems have many industrial applications. Therefore, the delightful accounts of the ear- 123