Desenvolvimento de um leito vibro-fluidizado e estudos dos coeficientes de transferência de calor de corpos submersos.

Abstract

In this work equipment developments and techniques for aerodynamics and heat transfer studies in a vibro-fluidized bed are presented. The equipment projected and built consists of an acrylic bed with a circular section of 0.12 m diameter and 0.5 m height, with an eccentric mechanism that allowed the amplitude variation, and through the motor speed, variation in the frequency vibration. The aerodynamics study in a vibro-fluidized bed has been carried out through the analysis of the fluidization and standard deviation curves obtained for both systems (conventional and vibrated), in order to verify the pressure drop in the bed and the oscillation around the average, in function of the vibrational frequency and the initial bed height. The bed was constituted of ballotini glass spheres of 700 µm. The global heat transfer coefficient between immersed test body and the bed was obtained from two geometric configurations: cylinder and spheres. For the spherical geometry three different diameters were studied. In both geometries an electric resistances for the bodies heating was used. The local heat transfer coefficient was obtained from a similar cylinder to the one described previously, however equipped with a platinum sensor. This sensor consisted of a quartz piece with a fine platinum film linked to an electric circuit that through appropriate equation and monitor software allowed the obtaining of this coefficient. The influence of the superficial air velocity, vibrational frequency, particle size, forms and size of the tests bodies were analyzed. The aerodynamic results showed that, without vibration, the instantaneous pressure had a significant increase with the intensity vibration, with a maximum value in most of the results. The difference for an experimental condition for another one, is the angular area of the cylinder in which this tendency happens for the coefficient. When compared with the bed without vibration, just fluidized it, was verified that the values obtained in this work for the local coefficient have a similar behavior to the ones found in the literature. oscillation observed in the deviation standard curves are independent of the bed height. In the vibro-fluidized beds these oscillation showed a strong dependence on the bed height and on the dimensionless parameter, in the interval of variables studied. The results of the global heat transfer coefficient showed an increase of h, with the imposition of vibrations, with smaller particle size and for larger air velocity, for both studied geometries. When analyzed locally, it was observed that hθ had a significant increase with the intensity vibration, with a maximum value in most of the results. The difference for an experimental condition for another one, is the angular area of the cylinder in which this tendency happens for the coefficient. When compared with the bed without vibration, just fluidized it, was verified that the values obtained in this work for the local coefficient have a similar behavior to the ones found in the literature.