HEAT AND MASS-TRANSFER COEFFICIENTS AT THE SURFACE OF ELLIPTIC CYLINDERS PLACED IN A TURBULENT AIR-FLOW

Heat and mass transfer coefficients were measured at the surface of el liptical cylinders of three different lengths (0.10 m, 0.15 m and 0.20 m) and five ratios of major to minor axis placed in a cross flow of a ir. The flow was characteristic of food pilot plants, i.e. an air velo city ranging from 0.5m s-1 to 2.0 m s-1 and a turbulence intensity, Tu , of about 12%. In agreement with theory, the transfer coefficients me asured at this turbulence intensity were higher than those usually ind icated in chemical engineering literature, which are based on experime nts in 'aeronautic' wind tunnels where the turbulence intensity is clo se to 0%. The airflow properties (air velocity and turbulence intensit y) have a greater effect than body shape characteristics (length and r atio). Velocity and turbulence intensity measurements in a chilling ro om and a dryer showed that the flow is intermittent and highly turbule nt (Tu from 17 to 60%). Thus, the turbulence has to be taken into acco unt in food engineering studies.