Mathematical modelling of internal heat recovery in flash tank heat exchanger cascades

Andrei Korobeinikov, John McCarthy, Emma Mooney, Krum Semkov, James Varghese


Flash tank evaporation combined with a condensing heat exchanger can be used when heat exchange is required between two streams and where at least one of these
streams is difficult to handle (tends severely to scale, foul, causing blockages). To increase the efficiency of heat exchange, a cascade of these units in series can be used. Heat transfer relationships in such a cascade are very complex due to their interconnectivity, thus the impact of any changes proposed is difficult to predict. Moreover, the distribution of loads and driving forces in different stages and the number of designed stages faces tradeoffs which require fundamental understanding and balances. Addressing these problems this paper offers a mathematical model of a single unit flash tank evaporator combined with a condensing heat exchanger unit. This model is then developed for a chain of units. The purpose of this model is to allow an accurate study of the factors influencing efficiency of the system (maximum heat recovery) and evaluation of the impact of any alteration of the system, thus allowing for guided design or new or redesign of existing system.

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