Drying of moist food snacks with innovative slot jet reattachment nozzle

Drying of moist porous media such as paper, pulp and food products is one of the most energy intensive processes in industry. Impinging jet nozzles are commonly used in various drying processes. There have been many efforts to improve the transport characteristics of impinging jet nozzles. Utilizing innovative Slot Jet Reattachment (SJR) nozzle is an approach to make the drying process more efficient. This is mainly because these nozzles overcome the high flow rate constraint associated with the traditional Slot Jet (SJ) nozzle. In this paper, the drying characteristics of the SJR nozzle with exit angles of +20˚ and +45˚ are experimentally investigated. The samples used are snack cookies. The results are compared with those of SJ nozzle under the same mass flowrate. The results indicate that significant enhancements in drying rates are achievable with both SJR nozzles compared to SJ nozzle.Keywords: Drying; Porous Food Snack; Slot Jet Reattachment Nozzle; Slot Jet Nozzle

Numerical Simulation on the Pressure Field of Gas Knives

In the continuous galvanizing line, gas knives are used to control the liquid coating thickness. They are based on the principle of turbulent planar impinging jet. The CFD (Computational Fluid Dynamics) method is used to research the turbulent planar impinging jet of gas knives. With the implement of FLUENT software, the realizable k-ε model is adopted to simulate the pressure field. The transverse impact pressure distributions on the steel strip are demonstrated. For gas knives with even nozzle slot, the plot of impact pressure is analogous to parabola, reducing from middle to two ends. This numerical result shows agreement with experimental one. It indicates that the realizable k-ε model can accurately predict the impinging jet. Besides, for gas knives with uneven nozzle slot, the impact pressure is basically equivalent. Furthermore, several main factors having effect on the coating thickness are studied. The numerical results reveal that, the higher the inlet pressure, the thinner the coating; and the longer the distance between jet and strip, the thicker the coating.