How is the velocity of liquid in a falling film calculated?

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For process requirements, a set of external falling-film equipment was designed. The length of the falling film tube is 12 m. The film is formed using a sleeve method: a concentric falling film head is fitted over the outer wall of the falling film tube. The inner diameter at the outlet of the falling film head is 2 mm larger than the outer diameter of the falling film tube, meaning that the gap between the falling film tube and the falling film head is 1 mm. The height at the feed inlet and the film-forming outlet of the falling film head is 5 cm; according to Bernoulli’s equation, ignoring friction, the velocity of the liquid film at the outlet of the falling film head is 1 m/s. Now I want to know: Since the entire 12m-long falling film tube is placed vertically, how long does it take for the film to flow from the top to the bottom? My idea is as follows: the fluid just as it forms a film has a velocity of about 1 m/s. This velocity will definitely increase, because at that point the gravity acting on the liquid film is greater than the resistance to its flow; as a result, there is an acceleration and the velocity of the flowing liquid film increases. As the speed increases, since drag is related to speed, the drag also increases; eventually, gravity and drag reach equilibrium, and the liquid film flows down at a constant speed. Personally, I think it should take a relatively short time to reach this speed, with the liquid falling in a uniform film. The key is not knowing the formula to describe this resistance. By checking textbooks on chemical engineering principles, the formula for the resistance in straight pipes seems unsuitable for this situation. Moreover, there is a difference between falling film and sedimentation; sedimentation refers to the relative movement of particulate substances within a fluid, which is primarily determined by the balance between buoyancy and gravity. Therefore, the settlement velocity formula seems unable to be applied either. I was really poor at Chemical Engineering Principles; I barely passed back then. I earnestly ask for the guidance of experts; I am extremely grateful! (My falling film tube has an outer diameter of 76 mm; the thickness of the film formed on its surface is 1 mm. It is made of 316L stainless steel seamless tubes, with a length of 12 m. The medium used for the falling film process is heat transfer oil, and I can provide data such as its viscosity and surface tension. Experts could help me perform calculations using water at 30°C as the medium.) ) Additionally, there is another question: a inclined tube with an angle of 30° to the horizontal line, an inner diameter of 25 mm, containing 1/3 fluid volume, and a length of 3 m. Fluid is continuously and steadily poured into the tube from an external container (with a height difference of 10 cm). How long will it take for the fluid to flow out? What is the flow velocity? This flow velocity should also accelerate first and then maintain a constant speed, right? May I ask how much can be achieved in the end? Since it is an industrial device in operation, it cannot be disassembled to measure its speed; therefore, we can only rely on theoretical calculations for our current purposes of modification and scaling up. Thank you again!