4 replies to this topic

[peaston]

Hey.

Been having trouble tackling a question given to me in class, was wondering if anyone could shed some light on it to maybe point me in the right direction...

the question is as follows:

A heat exchanger accepts a liquid stream consisting of 50.0 mol% n-butane and 50.0 mol% n-pentane at an absolute pressure of 5x10^2 kPa and a temperature of 45.0degree Celsius. Estimate the duty of the heat exchanger if the stream leaves as saturated liquid at an absolute pressure of 5x10^2 kPa (i.e. at the bubble point)

Any help would be great thanks!
Andrew

[pavanayi]

Andrew:

Please describe any approach that you have made to solve the problem.

I am unable to help you presently because
1. I am unaware of what resources you have at your disposal/how you are expected to solve the problem (using simulation software or hand calculations or what)
2. the data itself is incomplete. Please check. I suspect you also would have been given the flow rate.

[peaston]

Hey.

nope that is the question in full... i basically copied it exactly from the sheet the question came from...

he did say is was of first class honours in terms of difficulty and that majority of the class would not be able to solve it.

all we have as an aid is steam tables, he never said we needed anything else other than that... purely a hand calculation, no software has ever been introduced.

hope this helps

andrew

[pavanayi]

Andrew,

In terms of pointing in the right direction, see if the below points help:


1. Define (assume) a flow rate M of the mixture (either in kmol/hr or kg/hr). This is the basis for your design. All designs will have a basis on which it is designed.
2. Find the outlet temperature (what is the bubble point temperature) and thus the delta temperature across the exchanger (K)
3. Find the specific heat (Cp) of the mixture. (Kj/Kmol.K or Kj/Kg.K)

Then, the duty of the exchanger should be a straight forward calculation
Q = M*Cp*delT

That is one of the ways which can give you the heat duty.

Tell me how you get along..


PS: I am still not able to help you 100% because I am not aware of --
i. Which year of university you are in, so that I can understand what skills you are expected to use to solve this question.
ii. What was the course in which this problem was given to you (Thermodynamics/Heat transfer/similar)

Edited by pavanayi, 18 February 2011 - 04:36 AM.

[rowanlim]

I agree with pavanayi, his response is exactly what I would aim to do.

I'm curious, if that's all you were given & your instructor said you need steam tables...I'm gonna assume that the heating medium is steam? Will steam condense in this heat exchanger?

I'm rusty at this, so I may be adding more questions rather than answers, sorry!