Design and force analysis of stirred digester with curved full blade turbine using mathematics and finite element by abacus software

In this research a stirred digester with curved full blade turbine was designed and analyzed using mathematical equations and ABACUS software according to needed biogas / methane for a village with 1000 persons. The results of designing showed that mixer diameter, digester diameter and shaft length were 1.38, 3, and 2.385 m, respectively, steel density existing in mixer structure was 8000 kg/m3, liquid density was 1000 kg/m3 and rotational speed was 0.25 rev/s. The engine power and torque was 0.39 kw and 250 Nm, respectively with confidence coefficient of 1.5. Its vanes included blade and T shape arm, which corresponding dimensions were 4×276×320 and 20+320) ×90×18 mm, respectively. Equivalent force from liquid on the blade was 78 N and its moment was 46 N-m. Equivalent bending moment on shaft calculated using Van Maize law was 1414.3 Nm. The shaft diameter calculated by true and error method was 60 mm. A 3 dimensional design of mixer was drawn by CATIA software according to calculated parameters in this research and it was analyzing by ABACUS software. The software results showed that however the stress in T shape arms was higher than the other parts of mixer, but it was lower than critical selected stress for mixer. Furthermore the stress in the other parts of mixer was very low. Therefore the mixer with these parameters can truly work in digester with no problem.