Impinging single nozzle

First, an air jet emerging from a single nozzle is considered. In Fig. 1.3, the generated flow field of a nozzle is shown schematically. From the nozzle with the diameter d, the flow exits with the approximately constant speed w. The jet impinges the surface virtually unchanged with a constant velocity as long as... 

For proper use of the equations, the chamber shape must conform to the spray pattern. With cocurrent gas-spray flow, the angle of spread of single-fluid pressure nozzles and two-fluid pneumatic nozzles is such that wall impingement wiU occur at a distance approximately four chamber diameters below the nozzle therefore, chambers employing these atomizers should have vertical height-to-diameter ratios of at least 4 and, more usually, 5. The discharge cone below the vertical portion should have a slope of at least 60°, to minimize settling accumulations, and is used entirely to accelerate gas and solids for entty into the exit duct. 

Binder liquid should wet the solid particles and not the interior walls or the mixing tools of the equipment. If parts of the mixer are wetted, build-up occurs which is difficult to remove. Different spray patterns are available with commercially available single or two phase nozzles (Fig. 7.22c and 7.23) and a suitable pattern should be selected to assure that liquid impinges only on the moving powder. Since the spray pattern depends critically on the cleanliness of the orifice area, as mentioned before, nozzles must be drip free and installed such that they remain clean or are blown free by the action of atomizing gas. This is particularly important for low capacity nozzles which are often preferred because the binder liquid should be always completely ab-... 

Pautsch A, Shedd T (2005). Spray impingement cooling with single- and multiple-nozzle arrays. Part II visualization and empirical models. International Journal of Heat and Mass Transfer 48 3176-3184. 

Transient cooling rates were measured to study the effect of adding droplets. The cooling time is defined as the time to cool the test plate from 500 C to 35°C. These measurements were made with both the single-phase and two-phase flows. A shutter was used to close the nozzle exit to avoid any flow impingement on tiie test plate. The test plate was heated to 500°C with a constant power input of 310 Watts. The same power input was used for each experiment to msure that, once the plate reached the desired temperature, the insu tion and the heater reached the same conditions for every test Once the piste was heated up to 500°C, the shutter was opened and the heater was turned off to start the cooling process. 

---