International journal of refrigeration-revue internationale du froid vol:26 issue:3 pages:328-336
Convection heat transfer to spherical particles inside a hydrofluidisation freezing unit was investigated. The unit contained a food tank with a perforated bottom plate to create agitating jets. An aqueous solution of 30% ethanol + 20% glucose was used as the refrigeration medium in a temperature range of -20 to 0 degreesC and flow rates from 5 to 15 1 min(-1). The lumped capacitance method was applied on cooling profiles of aluminium spheres of 5-50 mm to obtain surface heat transfer coefficients. Coefficients were within a range of 154-1548 W m(-2) degreesC(-1), and depended on diameter, flow rate, refrigeration temperature and fluid agitation level. The agitation due to jets was accounted for by means of an agitation Reynolds number in a Nusselt correlation A large variability of measured surface heat transfer coefficients was observed. This could be attributed to non-constant flow and turbulence fields in the refrigeration medium. The value of the heat transfer coefficient was compared to values determined on strawberries. (C) 2003 Elsevier Science Ltd and IIR. All rights reserved.