Questions for Practice (Module 9)
|Q.1||What are the main differences among evaporation drying, and distillation?|
|Q.2||Define capacity and economy for evaporators.|
|Q.3||What is the difference between natural and forced evaporator?|
|Q.4||Why boiling point elevation is important in evaporators?|
|Q.5||When and why do we prefer to use backward-feed evaporator?|
|Q.6||Single effect evaporator has low heat economy but still we use it in the industries, why?|
|Q.7||Explain Dühring rule.|
A forced circulation evaporator is to concentrate 50,000 kg/h of 40% KOH to 70% KOH using steam at 3 bar pressure. The feed temperature and the condensing temperature are both at 45oC. The density of the feed solution is 1.5 gm/cm3. If the overall heat transfer coefficient is 2 kW/m2 oC, calculate the following,
ii. the heat transfer area required.
A triple effect evaporator is to be used to produce a 60% KOH solution from a feed containing 30% KOH. The available steam is at 160oC, and the vapour from the last stage is condensed at 50oC. Backward feed is used.
If equal amounts of water are removed in each effect, what will be the concentrations in the intermediate effects, the boiling-point elevation in each effect, and the net temperature differences available for heat transfer?
|Q.10||In the problem number 9, what will be the maximum number of effects that could be used with the same terminal temperatures and more than three effects?|