Several questions about evaporators
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In the evaporation process, 1. The heating steam is usually saturated steam; can superheated steam be used instead? Why? 2. When the material being evaporated is an inorganic salt solution, its boiling point increases, becoming higher than that of pure water at the operating pressure. In this case, is the temperature of the secondary steam generated equal to the boiling point of the solution? If it equals the boiling point of the solution, is it superheated steam or saturated steam at that pressure? 3. Effective heat transfer temperature difference = Temperature of the heating steam – Boiling point of the material? Is it still the effective heat transfer temperature difference = temperature of the heating steam – temperature of the secondary steam? 4. When performing calculations for multi-effect evaporation, the overall heat transfer temperature difference coefficient is equal to the temperature of the heating steam minus the saturated steam temperature of the final condenser. How should this saturated steam temperature of the final condenser be understood? Is the secondary steam that exits the final stage and enters the condenser superheated? And why does it mention the condenser? What does it have to do with the condenser? There are too many questions, and they’re rather scattered; it’s very frustrating when reading, as it’s difficult to understand. I hope my friends will kindly offer their guidance! Thank you! :$
This post was last edited by TNQYG on 2016-11-9 at 15:52. 1. Superheated steam won’t work, because as we know, when steam at 100°C turns into distilled water at 100°C at room temperature, there is a phase change latent heat involved, and this latent heat is quite large. Therefore, the reason we ensure that the steam is saturated is to make use of this latent heat. 2. The vapor produced is always the saturated vapor corresponding to that pressure; as per the equation PV/T = constant, this is why the liquid temperature in the separator is higher than the vapor temperature.