Spray Cooling Heat Transfer of a Two-Fluid Spray Atomizer

The paper presents an experimental study on the droplet size and velocity, as well as temperature distribution, of a two-fluid atomizer (dj=1.6mm; spray nozzle exit diameter) through optical non-intrusive interferometric particle image (IPI) and particle image velocimetry (PIV) measurements with five different air liquid ratios (Rs) at three spray heights with three target-plate initial temperatures. Cold flow visualization was made for the spray height of 50 mm at 25oC. The Saunter-mean diameter (d32) was measured at the target temperature of 25°C without heating and found to be in the range of 34.22µm to 42.62µm in terms of a correlation with We(dj) Re(dj). The measured impact velocity at the spray height of 50 mm was of 10m/s to 30m/s with three different initial target temperatures. It was found that the impact velocity displayed a strong function of the initial temperature. Furthermore, both the cooling curve and transient boiling curve were obtained with the identified cooling/boiling parameters of the cooling rate, critical heat flux (CHF), Leidenfrost temperature (LFT), as well as the onset of nucleate boiling (ONB). The best cooling performance was found at R=0.242 for a spray height of 50 mm with the corresponding cooling rate of -19.1°/s, CHF of 486 W/cm2, and heat transfer coefficient (HTC) of 2.85 W/cm2K.