Ultrasound induced changes of certain physical and chemical properties of molecules are nowadays exploited at industrial level for food processing and preservation purposes. Deeper knowledge on the mechanisms influencing these changes would contribute to extend implementations of ultrasound to steer structure and functionality of food molecules. In this study the laws of transfer phenomena were applied in order to investigate on the viscosity changes of a pectin-containing fluid flow, i.e. tomato puree in a cylindrical reactor, induced by low frequency, high intensity ultrasound treatments. In particular, the model for fluid motion was associated to a validating rheological investigation. Results showed a good agreement between experimental and computational data for temperature and viscosity progresses with time. A new power law for viscosity has been proposed based on reactor aspect ratio and Rayleigh numbers for natural convection. (C) 2013 Elsevier Ltd. All rights reserved.