Published in:
Journal of Food Process Engineering, 40 (2017) 1
Language:
English
DOI:
10.1111/jfpe.12317
ISSN:
0145-8876;
1745-4530
Origination:
Footnote:
Description:
AbstractWe investigated two different sized pressure‐swirl nozzles and two twin‐fluid nozzles (external and internal mixing) spraying food liquids with different viscosities (0.001 Pa s ≤ µ ≤ 0.308 Pa s). Liquid pressures in the range of 0.2 MPa ≤ pL ≤ 30 MPa and gas‐to‐liquid ratios of 0.01 ≤ GLR ≤ 2.92 were applied. To compare the nozzles, we used two energy based approaches: The spraying efficiency e and the energy density EV. The spraying efficiency of all investigated nozzles was within reported ranges from literature. When described as a function of EV, the Sauter mean diameter (SMD) of the spray drops showed a power‐law dependency. Further, the SMD was independent of the size of the pressure‐swirl nozzles and the location (internal or external) of mixing in twin‐fluid nozzles. The pressure‐swirl nozzles were superior over the twin‐fluid nozzles when low viscous fluids were sprayed. However, only the twin‐fluid nozzles were able to spray viscosities of µ ≥ 0.143 Pa s satisfactorily. Overall, the EV concept showed to be an appropriate method for the prediction of SMD in dependency of energy relevant process parameters.Practical ApplicationIn spray‐drying of foodstuffs, the spray drop size is a crucial parameter. It depends on the physical properties of the liquid, on the type of nozzle and on the chosen process parameters. The nozzle comparison by means of the energy density EV enables the operator to quickly choose the needed energy, i.e. the process parameters, which has to be supplied to the nozzle at a specific viscosity and liquid volume flow rate to obtain the desired mean spray drop size. This facilitates the operation of spray dryers and the scale up of spraying nozzles.