Steam generator type is either internal or external circulation. External circulation type is used in the so called thermosyphon processes. This is a process where a mixture of vapour and liquid exits the evaporating side of the heat exchanger. The mixture is then guided to an external droplet separator.
Circulation of fluid can be by pump, but more typically it is naturally driven. A static head of a liquid and the temperature difference forces the coldest fluid to enter the heat exchanger.
With Vahterus PSHE, a thermosyphon evaporator is designed in the same way as a flooded evaporator. Vahterus calculate the circulation ratio as 1 from a thermotechnical point of view. Circulation ratio 1 means that the entire stream coming out from the evaporator is in vapour phase. In reality there are will always be some liquid present which will increase the evaporating side pressure drop slightly.
Benefits of Vahterus Plate & Shell for Thermosyphon
- Eccentric design
- Compact design
- Possibility for high temperature differences caused by batch processes