How to design a falling film evaporator
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Dear fellow sailors, when designing a falling film evaporator, I encountered 3 problems: (1) The calculation of the liquid film thickness inside the falling film evaporator. For reference, see this forum post: http://bbs.hcbbs.com/thread-970036-1-1.html 〈Design of Falling Film Evaporators〉. By performing calculations related to the falling film, the minimum flow rate per unit length is determined; based on this minimum flow rate, the liquid film thickness is calculated to be 0.2 mm； By increasing the mass flow rate per unit length, the liquid film thickness remains around 0.3 mm and does not increase. How is the thickness of the liquid film calculated? (2) Based on the evaporation rate and the end point of evaporation, the residence time of the material in the evaporator is determined, thereby obtaining the heat exchange area. Then, a heat exchange area is calculated based on the literature linked in (1). How should we view the two calculation results? (3) Can the evaporation conditions inside a falling film be simulated through laboratory experiments (by placing the material in an evaporating dish and heating it to cause evaporation)? It’s a question that has puzzled me for a long time; I hope fellow sailors can give me some guidance. Thank you
Last time, our factory had discussions with the technicians from Kefukai; they were very professional in their explanations, focusing on issues such as distribution, film thickness, gasification rate, and pressure drop. We requested a calculation guide at that time, and it was extremely useful, haha
Could you briefly explain the approach? Thank you:handshake
Calculating the heat exchange area based on residence time is incorrect, resulting in significant errors in the obtained heat exchange area. It should be estimated using the heat transfer coefficient.
Thanks for the reminder! From the beginning of discussions with the management, there was a debate regarding whether to use the residence time to calculate the heat exchange area or the heat transfer coefficient. A request for help was posted at: http://bbs.mahoupao.net/thread-167724-1-1.html. I would like to ask: since the heat transfer coefficient of a falling film evaporator is high, and heat is transferred to the material instantaneously, can it be ensured that the solutes in the material within the falling film will vaporize? That is, can it be ensured that the desired process results will be achieved? Thank you
Evaporation separation is a system; it makes no sense to consider the heat transfer coefficient in isolation