INFLUENCE OF WATER ACTIVITY ON THE ACOUSTIC PROPERTIES OF BREAKFAST CEREALS

Corn and wheat bran flakes were compressed in a plastic cylinder and the generated vibrations were measured by a piezoelectric accelerometer. Amplitude–time records were thoroughly analyzed and the total acoustic energy in arbitrary units, number of acoustic events and energy of a single acoustic event were calculated. Relationships between the time of compression, frequency and sound intensity are presented as acoustograms. All parameters, except the energy of a single acoustic event, were strongly dependent on water activity (A_w). The flakes differed essentially in their ability to propagate vibrations. At low A_w's, both types of flakes were alike, but at higher A_w's, corn flakes damped high‐frequency waves while wheat bran flakes did not show this property.     

The Effect of Plate Size on the Natural Convective Heat Transfer Intensity of Horizontal Surfaces

Abstract

Natural convective heat transfer from flat horizontal isothermal plates has been investigated for more than a century. In the present study, the influence of the size of the plate on the heat flux is investigated. Two ranges of the heat transfer intensity are proposed for this problem: for the plates with characteristic length smaller than 0.1–0.2 m, the heat transfer coefficient is inversely proportional to the plate width; for plates wider than 0.2 m, the heat flux is not influenced by the plate width. The explanation for the discrepancy between the two ranges of natural convective heat transfer based on analysis and comparison of experimental data available in the literature has been proposed.