Drying kinetics and thermodynamic properties of trapia pulp 1 /Cinetica de secagem e propriedades termodinamicas da polpa de trapia

The objective of the research was to study the drying of trapia pulp with the addition of drying aids, determining the drying kinetics and thermodynamic properties of the samples. Formulations of the pulp was treated with the additives monoglycerides, carboxymethylcellulose - CMC and guar gum in different combinations and concentrations (F1 - 0.5% CMC and 0.5% Monoglycerides; F2 - 0.5% Guar Gum and 0.5% Monoglycerides; and F3 - 0.25% Guar Gum, 0.5% CMC and 0.5% Monoglycerides) trapia. Drying was carried out at 50, 60 and 70 [degrees]C with 0.5 cm thick layers. The drying kinetics were determined, and different mathematical models fitted to the data. The Midilli model best represented the drying kinetics, with determination coefficients [greater than or equal to] 0.9985. The effective diffusivities increased with increase in temperature with magnitudes to the order of [10.sup.-10] [m.sup.2] [s.sup.-1]. The enthalpy variations ([DELTA]H) reduced with increase in temperature and were positive. The entropy variations ([DELTA]S) were negative and inversely proportional to the temperature. The variation in Gibbs free energy ([DELTA]G) was positive and increased with increase in temperature. Key words: Crataeva tapia L., mathematical modelling, effective diffusivity, enthalpy, entropy, activation energy O objetivo da pesquisa foi avaliar a secagem da polpa de trapia com a adicao de aditivos de secagem, determinando a cinetica de secagem e as propriedades termodinamicas das amostras. Foram elaboradas formulacoes a partir da polpa e os aditivos monoglicerideos, carboximetilcelulose - CMC e goma guar em diferentes combinacoes e concentracoes (F1 - 0,5% de CMC e 0,5% de Monoglicerideos; F2 - 0,5% de Goma Guar e 0,5% de Monoglicerideos; e F3 - 0,25% de Goma Guar, 0,5% de CMC e 0,5% de Monoglicerideos). A secagem foi realizada a 50, 60 e 70 [degrees]C com camadas de 0,5 cm de espessura. A cinetica de secagem foi determinada e diferentes modelos matematicos foram ajustados aos dados. O modelo Midilli foi o que melhor representou a cinetica de secagem, com coeficientes de determinacao [greater than or equal to] 0,9985. As difusividades efetivas aumentaram com o aumento da temperatura, com magnitudes da ordem de [10.sup.-10] [m.sup.2] [s.sup.-1]. As variacoes de entalpia ([DELTA]H) diminuiram com o aumento da temperatura e foram positivas. As variacoes de entropia ([DELTA]S) foram negativas e inversamente proporcionais a temperatura. A variacao da energia livre de Gibbs (