The tank size for 0.9 m3 capacity can be 1.1 m in diameter with a 1.2 m height.  The 1.25 m diameter and 1.25 m height tank would also work.  The tank does not need baffles if an off-center, angle-mounted portable mixer is used.  A typical portable mixer is mounted on or near the top edge of the tank, angled vertically about 10 to 15 degrees away from the side of the tank.  With an axial flow impeller, pumping downward and rotating clockwise as viewed from the motor, the mixer should be aimed about 15 degrees to the right of the centerline across the tank.  The mixer should be aimed to minimize the rotational flow and surface vortex, to provide good vertical mixing and uniformity.  Solid-body rotation and a strong vortex provide poor vertical and horizontal mixing.
 Assuming 50 Hz electric power, portable mixers will operate at either 1170 rpm for direct drive or 235 rpm for gear drive models.  In any case a 0.2 kW mixer is adequate for either speed.  Different selections would be recommended if 60 Hz power is standard. The axial flow impeller can be either a hydrofoil (propeller) or a pitched-blade turbine.  The hydrofoil impeller typically has three narrow blades at a shallow angle, equivalent to a 3-blade, 1:1 pitch left-hand marine-style propeller.  The pitched-blade turbine would have four blades mounted at a 45-degree angle.
The combination of impeller types, rotational speeds and one or two impellers gives several options:
A 0.2 kW direct-drive portable operating at 1170 rpm could have any of the following:

one 125 mm diameter hydrofoil impeller or two 100 mm diameter hydrofoil impellers

or  one 100 mm diameter pitched-blade turbine or two 88 mm diameter pitched-blade turbines
A 0.2 kW gear-drive portable mixer operating at 235 rpm could have any of the following:

one 350 mm diameter hydrofoil impeller or two 300 mm diameter hydrofoil impellers

or  one 250 mm diameter pitched-blade turbine or two 225 mm diameter pitched-blade turbines
Depending on available standard mixers or custom built mixers, these combinations will give similar results.  Two impellers may cause more splashing as the tank is filled or empties.  If surface addition of ingredients is difficult, two impellers may work better.

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