Drying Mechanism Of Alginate Geland Numerical Simulation

Alginate is a kind of natural linear polysaccharide copolymers and its repeat unitswas regarded as L-guluronic acid(G) and D-mannuronic acid(M). Guluronic acid unitis the isomer of mannuronic acid unitand vice versa. Two dihedral angles(φ, ψ) in the glycosidic bond between two repeat units determine the molecular conformation. The block composed of GG residueshas higher rigidityand showed higher brittleness. The consistence of the size of negative hole formed by Segment GG appropriate and Ca2+is conducive to the formation of the famous "egg box structure". Bivalentcations(except Mg2+) react with alginic acid to form a kind of hydrogel.To study the differences of the reaction of alginate acid withdifferent types and concentrations of cations, Gaussian09 for Linux were usedwith quantum chemical density functional theory(DFT)-based method to reveal the lowest energy of different state coordination reaction. A kind of presentative cation-diuronate complexes, with GG disaccharide units and without or more water molecules in the coordination shell have been considered. The result suggest that the so-called “lateral association” of alginate chins was reduced by removing excess calcium ions from the gel beads in a process of deionized water treatment. The utilization of calcium ions close to 100% when the calcium chloride’s mass concentration less than 0.04%(m/m), while the concentration of calcium chloride is greater than 0.1%(m/m), the mixed system began to appear insoluble hydrogel.Alginate granulewith high moisture content, porosity, seriously volume shrinkage exhibit unusual drying characteristics. Finite element methods(FEM)were used based on the Fick’s second law, Fourier’s law of heat transfer and shrinkage characteristics equation, to simulate the real drying characters of gel particle.The following works were carried out to explore the drying characters of gel particle:1. Dry-basis moisture content(XDyr) of materiel showed an exponential relationship with drying timebased thin-layer drying experiment; The diameter(Daverage) of materiel showed an linear relationship with dry-basis moisture content: Daverage=13.84*10-4+1.72*10-4*XDyr; The relationship between effective diffusion coefficient(Deff) anddrying temperature obey Arrhenius equation: Deff=4.001*10-9*e(-11447.062/RT);2. The diffusion of moisture in gel was describe by applying the effective diffusion coefficient which was calculated by thin-layer drying experiments to Fick’s second law. The diffusion of heat in gel was describe by applying the Daverage to distance of heat transfer in Fourier’s Law. The shrinkage of gel was describe by linear shrinkage equation deduced by thin-layer drying experiments.3. A numerical model based on Partial Differential Equations(PDE) was built to predict the dry-basis moisture content, temperature and particle size. The maximum error of XDry between predicted results and actual results is 1.16 Kg/Kg, the average error is about 0.30 Kg/Kg.