Nozzle specific energy consumption

In Fig. 1.19, specific energy consumption is shown separately as a function of the evaporation rate, with the nozzle diameter as a parameter. The nozzle exit velocity is assumed to be constant at 50 ms. It is evident that the specific energy consumption is less with smaller nozzles, with the maximum being displaced towards higher evaporation rates. However, the lowest possible value of nozzle diameter is limited, first by the increase in production costs, and second through the minimum distance of the nozzle to the product. This distance should not be greater than approximately five-times the nozzle diameter otherwise the heat transfer will be decreased. Rather, the smaller the nozzle the closer the field must be shifted towards the product. 

In Fig. 1.20, specific energy consumption is shown as a function of the drying rate, with the nozzle discharge velocity as a parameter as an example, a nozzle... 

For hole channels, analogous results are valid, and a pitch of t = 6d is again recommended. A larger pitch will result in a decrease in the heat transfer, which will remain constant with lower pitches however, the number of nozzles and thus the flow rate, will be increased. The specific energy consumption and the required gas temperatures are slightly higher for hole channels than for single-nozzle arrays, because the heat transfer is somewhat lower. 

Another way to balance out the temperature in the manifold (and even in the nozzles) is the use of a specific fluid, located between the heating element and the flow channel (Schottli AG). The fluid absorbs heat from the heater and transports it (by convection) to places of lower temperature. The energy consumption is much less than in traditional systems and the system is well suited for heat sensitive plastics. 

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