Heat transfer in tubular heat exchangers for particulate containing liquid foods

Abstract

By measuring the temperatures before and after the cooling- and heating sections in a tubular heat exchanger, inner heat transfer coefficients for a starch solution without and with different particle concentrations were determined. The liquid phase consisted of a 4% starch solution, which is a pseudoplastic fluid and can be described by the power-law model. The particles were made of alginate and the concentrations used were 0, 10, 20 and 30%. The particles had an average diameter of 5–6 mm. When increasing the particle concentration from 0 to 10%, the inner heat transfer coefficient increased approximately 100%. An increase of particle concentration from 10 to 20% and 20 to 30% gave an increase of 25% for the heating section and 35% for the cooling section. A plausible explanation is that the particles are sweeping liquid as they rotate in the boundary shear field, causing an exchange of liquid. The heating section showed higher inner heat transfer coefficients through all experiments compared with the cooling section.