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03/10/2008
ABSTRACT:
In the food industry, fouling stands as a complex and misunderstood phenomena. Heating, holding and cooling operations are carried out in continuous or batch processes and fouling occur in the equipment with a large widespread of kinetics (from minutes up to years) and propensity (from micrometers up to centimeters). The control and understanding of fouling phenomena is of evident industrial interest and various methods have been reported including rheological, electrical, chemical, mechanical, optical, sonic, ultrasonic and thermal methods.
In this context, a thermal sensor named BIOMOSYSTM-HW (INRA patent n°FR2885694) based on the hot wire method associated with heat flux, bulk and wall temperature measurements, was developed to study fouling phenomena. This sensor based on a local measurement was compared to two global methods (overall heat transfer coefficient, pressure drop) during continuous heat processing (pasteurisation and holding) of a dairy fluid. A critical analysis (precision, local and global measurement, deposit thickness, cleaning monitoring) is reported and highlights the advantages and limits of each method.
The sensor exhibits a low thermal inertia, an accurate sensitivity to fouling phenomena and is easily implemented in the process. However, its use should satisfy several criteria like the shape, dimensions, mechanical and chemical resistance, the control of generated heat flux, thermal and hydraulic conditions. Potential scientific and industrial applications concerns the understanding and control of fouling mechanism and nature as well as the geometrical design of process equipment under relatively inexpensive investigation and at small scale.
For instance, the device may be used to analyse deposit (fouling reaction rates) versus controlled conditions (bulk and wall emperatures, heat flux, shear stress) and to determine its properties (thermal conductivity, deposit structure and composition) through on-line and post-process characterisation.
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