Neste trabalho foi determinado o comportamento reológico do suco industrializado de acerola, mediante um reômetro de cilindros concêntricos, em concentrações de sólidos solúveis de 4, 7, 10, 13 e 16ºBrix e no intervalo de temperatura de 5ºC a 85ºC. Os dados experimentais dos reogramas foram ajustados aos modelos reológicos de Ostwald-de-Waele, Herschel-Bulkley, Mizrahi & Berk e Casson. O modelo de Herschel-Bulkley descreveu adequadamente o comportamento reológico do suco industrializado de acerola. Os baixos valores obtidos para o índice de comportamento (0,338 < n hb < 0,759) confirmaram o comportamento pseudoplástico do suco. O efeito da temperatura no comportamento reológico do suco de acerola foi descrito por uma equação análoga a de Arrhenius (etaa = eta0 exp(Eat/RT)). Foi observado que a energia de ativação diminuiu com o aumento da concentração das amostras, expressa em sólidos solúveis, variando desde 3,50kcal/gmol, para as amostras a 4ºBrix, até 1,79kcal/gmol, para as amostras a 16ºBrix. Os dados da viscosidade aparente e da concentração de sólidos solúveis foram ajustados aos modelos potencial e exponencial. O modelo potencial mostrou ser o mais adequado para descrever o efeito da concentração sobre a viscosidade aparente do suco de acerola.

The rheological behavior of the industrialized acerola juice was studied at different soluble solids concentrations 4, 7, 10, 13 and 16ºBrix and temperatures from 5 to 85ºC, using a concentric cylinder rheometer. Rheograms were fitted according to the following models: Ostwald-de Waele or Power Law, Herschel-Bulkley, Mizrahi & Berk and Casson. The best results were obtained using the Herschel-Bulkley model and the low values presented by the behavior index (0,338 < n hb < 0,759) confirm the pseudoplastic behavior of the acerola juice. An equation similar to the Arrhenius one (etaa = eta0 exp(Eat/RT)) described the effect of the temperature on the acerola juice. The results also showed that the activation energy decreases with the increasing in juice concentration, varying from 3.50kcal/gmol (4ºBrix) to 1.79kcal/gmol (16ºBrix). Potential and exponential models were tested considering the apparent viscosity data as a function of the soluble solids concentrations. For this purpose, the potential model showed the best performance.

Continuity and momentum equations applied to the entrance region of an axial, incompressible, isothermal, laminar and steady flow of a power-law fluid in a concentric annulus, were solved by a finite difference implicit method. The Newtonian case was solved used for validation of the method and then compared to reported results. For the non-Newtonian case a pseudoplastic power-law model was assumed and the equations were transformed to obtain a pseudo-Newtonian system which enabled its solution using the same technique as that used for the Newtonian case. Comparison of the results for entrance length and pressure drop with those available in the literature showed a qualitative similarity, but significant quantitative differences. This can be attributed to the differences in entrance geometries and the definition of asymptotic entrance length.

Foi avaliado o estudo reológico do suco de manga - efeito dos sólidos insolúveis a peneiramento com diferentes malhas e no suco centrifugado. Os resultados foram analisados em função do ajuste dos modelos reológicos de Casson e de Mizrahi-Berk. Três conjuntos bem diferenciados foram identificados pelo produto passado em (a) ‘finisher’ de 1,6mm e peneira de 1,8mm; (b) peneira de 0,84mm e 0,59mm e (c) peneira de 0,149mm e material centrifugado.

Mango juice reological study had been evaluated - the effect of unsolvable solids through sifting with different meshes and in the centrifuged juice. The results were analysed according to Casson and Mizrahi - Berk reological models. Three quite different set were identified by the product passed through the (a) "finisher" 1,6mm and sieve of 1,8mm, (b) sieve of 0,84mm and 0,59mm and (c) sieve of 0,149mm and centrifuged material.