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Titre du document / Document title

Minimum wetting and distribution rates in falling film evaporators

Auteur(s) / Author(s)

MORISON K. R. (1) ; WORTH Q. A. G. (1) ; O'DEA N. P. (1) ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

(1) University of Canterbury, Christchurch, NOUVELLE-ZELANDE

Résumé / Abstract

Falling film evaporators are used extensively in the food industry for their ability to process heat sensitive liquids. A coherent liquid film is required to maintain heat transfer efficiency and minimize fouling. It is likely that most evaporator fouling occurs after film breakdown as the substance within the evaporator dries out. The minimum flow rate required to maintain a film is known as the minimum wetting rate which is defined as the minimum mass flow rate per unit circumference. In this work, minimum wetting rates were determined in a 1 m long, 48 mm internal diameter, vertical, stainless steel tube. Water and aqueous solutions of glycerol, alcohol and calcium chloride were used. These substances were chosen so as to give a wide range of properties such as viscosity (0.5-39 mPa s), density (950-1410 kg m-3), surface tension (35-90 mN m-1) and contact angle (64-98°). In a separate set of experiments, the minimum flow rate required to distribute liquid and completely wet the top of industrial evaporator tubes was measured using a range of sucrose solutions. The tube wetting results obtained fitted a dimensionless power law relationship well. Surface tension and contact angle had a strong influence on the wetting rate but viscosity and density were found to have very little effect. The minimum flow rates for distribution were found to nearly always exceed the minimum wetting rates showing that more attention needs to be given to distributor design.

Revue / Journal Title

Food and bioproducts processing    ISSN  0960-3085 

Source / Source

2006, vol. 84, no 4 (121 p.)  [Document : 9 p.] (1/4 p.), pp. 302-310 [9 page(s) (article)]

Langue / Language

Anglais

Editeur / Publisher

Institution of Chemical Engineers, Rugby, ROYAUME-UNI  (1991) (Revue)

Mots-clés anglais / English Keywords

Film evaporator

;

Falling film

;

Rate

;

Distribution

;

Mots-clés français / French Keywords

Evaporateur film

;

Film tombant

;

Taux

;

Distribution

;

Mots-clés espagnols / Spanish Keywords

Evaporador película

;

Película caediza

;

Tasa

;

Distribución

;

Localisation / Location

INIST-CNRS, Cote INIST : 4284 D, 35400015963409.0080

Nº notice refdoc (ud4) : 18449857



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