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MƠ HÌNH HĨA CÁC Q TRÌNH CƠNG NGHỆ HĨA HỌC CƠ BẢN 2017 MASS CONSERVATION NON EQUILIBRIUM SYSTEM FLASH DRUM Consider a model of a flash drum in which it cannot be assumed that the vapour and liquid phases are in phase equilibrium: The vessel can be abstracted as two well-mixed phases constrained within a fixed volume Material and energy fluxes exist between the phases: NON EQUILIBRIUM SYSTEM - FLASH DRUM Control volumes: control volume for gas phase and control volume for liquid phase Both will vary in size and shape as the liquid level rises and falls Assumptions: • individual phases are well-mixed • vessel adiabatic • liquid feed stream well-mixed with the liquid phase • both phases present at all times • bulk flows into and out of vessel specified by user or determined by upstream and downstream models These assumptions are the simplest assumptions that can be made It is interesting to note that to assume anything else would require a detailed knowledge of the internal topology of the vessel and physico-chemical discontinuities (e.g the level of the feed pipe relative to that of the liquid level, the area of heating coil/jacket immersed in the liquid phase, etc.) ... heat is removed by a jacket containing a vaporizing medium, so an energy balance is necessary Assumptions: • vessel contents well mixed • species A and B present in dilute solution • atmospheric... is constant (e.g., P0‡ f (t)) • neglect shaft work of impeller • neglect heat interaction with atmosphere • otherwise, same as above SYSTEM IN WHICH PRESSURE AND VOLUME VARY