Untitled in english

Author(s)

Fernando Bacaneli

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 1998-12-08

Examining board members

Julio Cezar Adamowski; Eduardo Tavares Costa; Celso Massatoshi Furukawa

• Advisor: Julio Cezar Adamowski

Abstract

This paper presents an analysis of the characterization of bovine milk using ultrasound, a non-destructive method that can be applied to a processing line. Models of propagation of acoustic waves in non-homogeneous liquids are presented. Several types of standard milks used in the dairy industry are described, such as: in natura, pasteurized (B e C) and UHT, which differ in the processing and in the fat contente. Using an optical microscope, the behavior and distribution of the fat particles were observed. Measurements of the propagation velocity, attenuation coefficient and density as a function of the fat contente were accomplished. It was used a measurement cell that rmploys multiple reflections and a double-element transducer. The operating frequency was 10MHz and the temperature was around 20°C. The acoustic parameters as a function of frequency (8 11MHz) and temperature (5 40°C) were measured, for several the samples of UHT milk. It was observed that the behavior of the attenuation coefficient depends on the size of the particles. For the samples with fat contente uniformly distributed, as in the UHT milk, the attenuation coefficient showed a linear dependence upon the fat contente. In these cases, the experimental results agreed well with the theoretical model described. For the samples with non-uniform particle distribution, as in the pasteurized and in natura, the linearity was not observed. (AU)