Spray characterisation and heat transfer during cooling processes by intermittent sprays

Spray cooling is used in many technical areas to cool hot materials. There are different boiling phenomena depending on the surface temperature. So the heat flow varies through these boiling ranges. Large local temperature gradients can cause mechanical tensions and also effect material properties strongly. Intermittent spray cooling offers much potential to ensure a uniform cooling, also in the crossing from film to transition boiling. In this work, a high pressure gasoline direct injector (HDEV-5) is used for spray investigations with water and infrared thermography recordings during cooling processes of a heated nickel alloy sheet. Additional measurements of droplet size and velocity by a phase Doppler analyzer (PDA) are conducted to characterise the spray properties. Furthermore, the local mass flux is determined by using a Patternator. The additional setting parameters of an intermittent spray can be expressed by the duty cycle (DC), which is composed of the frequency and the injection duration. This paper offers a basic characterisation of the spray and various physical mechanisms during a cooling process shown in temperature profiles.