4 replies to this topic

[jaffrey]

Hi i'm still in the process of working out how exactly it works. I just have one query which is; when the vapour is used to bubble through the boiling liquid, the temperature of the vapour must be higher than that of the boling point of the liquid to be boiled right. But my problem is how is that proved?

My notes says the T-x-y diagram can be used to explain it, but I though it was just the x-y diagram, but in both cases I just confused myself.

thanks

[afaruque]

Hi i'm still in the process of working out how exactly it works. I just have one query which is; when the vapour is used to bubble through the boiling liquid, the temperature of the vapour must be higher than that of the boling point of the liquid to be boiled right. But my problem is how is that proved?

My notes says the T-x-y diagram can be used to explain it, but I though it was just the x-y diagram, but in both cases I just confused myself.

thanks

Well it is hard to explain without the T-x,y diagram. Just go through page 645-647 of 'Unit operations of chemical engineering ' by McCabe, Smith and Harriot (6th edition ). good luck.

[jaffrey]

thanks for your reply but despite having found the book and reading through the recommended pages my understanding is still very fuzzy.

If the reflux (liquid recycled) back into the column happens, will it not be of a totally different composition? Therefore from this new composition of relux is it possible to locate the new boiling point temperature of this liquid mixture and then find out the temperature of the vapour that is going to be bubbling through it. My problem is just how to find the temperature of the vapour since it is no longer in equilibrium with liquid from the stage directly below the top stage.

from this i can then prove that the Vapour temperature is in fact higher than that of the liquid reflux to be ''bubbled'' which should help with my understanding.

thanks

[Padmakar Katre]

thanks for your reply but despite having found the book and reading through the recommended pages my understanding is still very fuzzy.

If the reflux (liquid recycled) back into the column happens, will it not be of a totally different composition? Therefore from this new composition of relux is it possible to locate the new boiling point temperature of this liquid mixture and then find out the temperature of the vapour that is going to be bubbling through it. My problem is just how to find the temperature of the vapour since it is no longer in equilibrium with liquid from the stage directly below the top stage.

from this i can then prove that the Vapour temperature is in fact higher than that of the liquid reflux to be ''bubbled'' which should help with my understanding.

thanks

Dear,
From you last two posts it seems that you are highly confused or you are not able to express what you actually want to ask us. If I could have understood a little just find my responce below,
1.In any column at any stage (ideal) the vapor leaving has the same temperature of the liquid leaving.
2. If you are interested in the calculations of the enthalpy balance across each stage to calculate the tempearture of incoming vapor and liquid then follow "ponchon-savarit method". Hope this could help you a little else ignore my reply.

[rana680]

hi , i am not very sure but according to me the liquid entering through reflux is in equilibrium with vapor going up. Initially it would not be in equilibrium but after some point of time the whole process works in equilibrium.