Case - Multiphase Simulation of a Steam Decontamination Process 

This case study shows how Aerotak™ simulated a ultrasonic steam chicken disinfection process, and helped to optimize the skin temperature of the chicken. 

Objective

For the purpose of improving the the chicken disinfection process, the objective of the CFD study includes an optimization of the steam cloud and the skin temperature of the chickens. Further, the simulation results must be comparable to relevant experimental data and provide both visual and quantitative data for evaluation.

Simulation setup

The steam disinfection process is shown above. Chickens pass through the process from left to right, hanging from a moving conveyer belt. In the disinfection zone, steam is sprayed onto the chickens from the ultrasound nozzles at the bottom. Steam and air exit through four perforated plates before entering the vertical outlet ducts on either side.

The simulation is run in transient state to capture the unsteady flow structures by applying an implicit first-order temporal discretisation scheme. A realisable k-epsilon two-layer turbulence model is adopted for its robustness with respect to convergence and initial conditions. Following simulation techniques are used to simulate the process:

• Chicken motion - Moving Reference Frame and imprinted wall velocity on the chickens.

• Mixture of steam and air - Eulerian multiphase with an air and a steam phase.

• Perforated plates - Modelled as porous regions with a pressure drop corresponding to that of the perforated plates.

• Ultrasound - Neglected, as the objective is to optimise the steam cloud and temperature distribution.

Simulation results

For initial validation of the simulation setup, temperature distributions in the fluid domain and on a selection of chickens were compared to corresponding experimental data. A satisfactory agreement was found between the CFD and the experimental data, allowing for optimization of the steaming process based on the CFD setup. 
Qualitative evaluations of process performance are essential in optimising the steaming process. Specifically, visulisation of the chicken surface temperature is a useful tool for evaluating and improving the heat treatment of the chickens. Such a visualisation is shown in the figure below, with red and blue colors indicating high and low temperature areas, respectively.

The figure below shows an iso-contour of the steam phase at a mass ratio of 0.8. This illustrates the steam motion and concentration in the domain, imperative to the heating and temperature of the chicken skin.

Based on the described simulation setup, Aerotak™ was able to simulate the ultrasonic steam chicken disinfection process and optimize its performance by improving upon the skin temperature of the chickens through quantitative and especially qualitative means, e.g. as the discussed ones. 

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