Parâmetros hidrodinâmicos de vegetais fatiados em geometrias definidas.

Abstract

This research has objective of studying the hydrodynamics parameters of sliced chayote, potato and carrot, at defined geometries forms. The follow parameters were determined to achieve these results: a) the physical characteristics (mass, volume, specific mass) of chayote, carrot and potato, sliced as follow, disks whose diameters measured 8,10 and 12 mm respectively, and 5 mm of height; square planes whose sides were8, 10 and 12 mm respectively and 5 mm of height; cylinders whose diameters were 8 and 12 mm and height of 20 and 30 mm, respectively; rectangular shapes whose sides measured 8 and 12 mm and height was 20 and 30 mm , respectively; b) water terminal speed, drag coefficient and wall effect of these particles. That were submitted to falls in tubes whose diameters were 50, 100 and 150 mm and the height was 1000 mm; c) the study of the effects of the shape and size of the pieces of chayote, potato and carrot and of the size of the fall tube at the terminal speed of these particles in water. PVC cylindrical tubes, with transparent acrylic, whose were 50,100 and 150 mm, respectively, and height of 1,0 m were used to the determination of the terminal speed. The samples of each kind of geometric shape (disks, plane plates, cylinders and rectangular) were also used to the determination of the terminal speed. The experiment was followed by a VHS camera. The chronometer, placed near the tube, was filmed simultaneously to the experiment. The data removing was done through the slow camera resources of a video cassette apparel. The equations that were given by MOHSENIN (1978), CLIFT et al. (1978) and ISAACS and THODOS (1967)were used to analyze the experimental data. It was concluded that: the unitary specific mass (real) of chayote, potato and carrot, whose water contents were 89,84%, 81,93% and 92,48% w.b., respectively, was 1007; 1073 and 1006 Kg.m"'; the terminal speed increases when the size of the fall tube at the terminal speed of water particles; the cylinders and the rectangular shapes of chayote and potato, in general, presented bigger speeds than the disks and plates, independently of the size of the fall tube, evidencing the influence of the shape of the particle at the terminal speed in water; the terminal speed, calculated through the equation suggested by ISAACS and THODOS (1967), offered a good approximation of the terminal speed, mainly to the geometric shapes of chayote; the equation cited by MOHSENIN (1978), with the CD suggested by HEISS and COULL (1952), supply values much near to the experimental ones for the potato ; the drag coefficient of the circular and square planes of chayote, potato and carrot, that was obtained through the equation proposed by ISAACS and THODOS (1967) were 1,35,1,41 and 1,46; and were 0,91 to the cylindrical pieces and rectangular shapes; the wall effect was more present at the tubes of 50 mm, to the cylindrical pieces and rectangular shape ones (P = 0,34) and the minor effect was verified to disks and square plane plates of 8 mm, in the tube of 150 mm (P = 0,05).