Michel Havet

Computation of the airflow in a pilot scale clean room using K-ε turbulence models

Abstract This work deals with the assessment of the airflow in a food-processing clean room. The flow pattern inside the working area of a pilot scale clean room was numerically investigated using a computational fluid dynamics code based on a finite volume formulation. Two versions of the k-e turbulence model were tested: the standard and the RNG version. The analysis of the velocity magnitude does not reveal sensitive differences between them. Moreover, both models well predict the main features of the flow and numerical results agree with experimental measurements. However, a further examination shows that the RNG k-e turbulence model predicts more swirls and more complex trajectories. As the standard k-e model overestimates the turbulent diffusion, the RNG version seems to be more suitable to calculate the airflow in clean rooms. The influence of initial turbulence intensity is also pointed out. Finally, the study of the airflow below a laminar flow unit confirms that the design of clean rooms can benefit from the numerical approach.

Numerical modeling of high pressure thawing: Application to water thawing

A finite difference scheme model which performs both atmospheric and high pressure thawing simulation is presented. The comparison between numerical simulation and experimental data shows a good level of agreement. This model has been used to predict the performance of the thawing process under a wide range of operation conditions. It clearly shows that high pressure thawing reduces the thawing time.

Conjugate Heat and Moisture Transfer During a Dynamic Thermal Treatment of Food

This work concerns the thermal decontamination of the surface of a food by hot air with the objective of inactivating the bacteria located at the surface. This heat treatment is considered to be intense and short, compared to more conventional drying processes. In order to predict the surface temperature, a coupled heat and mass transfer model was developed taking into account convective and diffusive mechanisms, evaporation, and shrinkage. A pragmatic alternative between Eulerian and Lagrangian formalisms was used in order to perform an efficient model. It was shown that this thermal decontamination process was governed by convection in a first stage, whereas mass diffusion was the limiting phenomenon in the second period. An inverse method was carried out in order to optimize the parameters of the mass diffusivity law.

Transient Exergetic Efficiency of a Forced Convection Drying Process With and Without Electrohydrodynamic (EHD) Enhancement

Electrohydrodynamic (EHD) drying is a novel drying method used to enhance forced convective drying by using a wire-electrode to create an electrostatic field. In this study, it was hypothesized that an EHD enhanced forced convective drying process will not only increase the drying rate, but also the exergetic efficiency over time. A transient exergetic efficiency was defined as the ratio of the exergy use rate in the removing of moisture from the drying product, to the exergy rate of the drying air supplied. In the case of EHD enhanced forced convection, the exergy rate supplied by the wire electrode was also accounted for. Forced convection drying experiments were run on a test specimen simulating a food product (methylcellulose gel) using an air flow channel with and without EHD enhancement with varying air flow velocities. Initial results show that the moisutre loss rate of the methylcellulose gel increased with the application of the electrostatic field. In addition, for low velocities, the exergetic efficiency of EHD enhanced forced convection was higher for the first few hours of drying as compared to conventional forced convection. The exergetic efficiency of both conventional and EHD enhanced forced convection converged at greater air flow velocities.Copyright