On the selection of flow rate for the circulation pump in falling film evaporators

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Our company has two sets of falling film evaporators, designed by Shanghai Shennong. We now plan to use them in other production processes to remove unreacted solvents. The main process parameters are as follows: feed materials (ethyl acetate, ethanol, etc., which serve as solvents), operating pressure (-0.09 MPa, vacuum for solvent removal), operating temperature (to be <100°C), and amount of material (total mass of about 4 t, with 1 t of solvent to be removed). The requirement is to remove the solvent as quickly as possible using existing equipment. Dear experts, what flow rate should be chosen for a circulation pump? How long does it take to evaporate the solvent? In my humble opinion, when the flow rate is low, the wall surface will dry out ； When the flow rate is high, the liquid film thickness increases, resulting in poor heat transfer efficiency. Furthermore, our device is designed for batch production; it is equipped with a buffer tank in conjunction with the foam-reducing heater and separator. The material stored in this buffer tank is pumped to the heater to enable cyclic evaporation of the solvent. The equipment diagram is attached below. Main parameters of the equipment: tube bundles (38*1.2*6000, made of 316L material, 40 tubes), heat exchange area of 28 m2. The separator is also shown in the accompanying drawings