8 replies to this topic

[cheminst]

Can anyone please tell me how to calculate the LMTD value for this shell and tube heat exchanger.

 

Shell side has two separate inlets which are considerably far from each other. One is a gas stream sparged at 187 ⁰C temperature and other is a liquid stream at 106 ⁰C.The gas stream is continuously sparged through a pool of liquid,(with the continuous liquid stream coming) and an exothermic chemical reaction happens between the gas and the liquid.I have calculated the heat load of the heat exchanger.

 

Both gas and liquid streams mix ,react and leave at two outlets in same place ,where gas and liquid are in same temperature at 175 ⁰C.

 

Tube side is a U tube bundle submerged in the pool of liquid. Inlet is saturated water at 4.5 bar pressure (at 147.9 ⁰C) and outlet is saturated steam at 4.5 bar pressure (at 147.9 ⁰C)

 

I'm puzzled about how to get the inlet temperature of the shell side to calculate LMTD value, Should I use the average temperature ? or is there any other way.

Edited by cheminst, 01 January 2016 - 06:09 AM.

[srfish]

It would help if you would provide a sketch of the location of the shell side nozzles. There is not going to be a single LMTD. The LMTD will have  to be weighted.

[cheminst]

Here is the sketch of the location of the shell side nozzles. Can you please tell me now how to calculate the LMTD value?

 

 

 sketch.JPG   33.54KB   3 downloads

[cheminst]

Please forgive me for the mistake. It won't happen again.

[cheminst]

I'm in urgent need for the answer. Can anyone please post a reply about how to solve this or name any reference

[srfish]

I don't believe you will find anything like this setup in the literature. What is that in the outlet ? How are you separating the gas and liquid? I suggest a kettle reboiler to separate the liquid and gas.

 

The inlet temperature for a LMTD calculation could be the temperature after the exothermic reaction and the gas and liquid mix.

[cheminst]

Actually this is the pool condenser used in stamicarbon process for urea production as depicted by the following diagram. Gas and liquid just flows by overflowing as I assume.

 

So if I take inlet temperature as you said, is it okay not to use multiple LMTDs and weight them as you said early ?

Attached Files

•  pc.JPG   49.36KB   2 downloads

[srfish]

That is right. You do not need to weight the LMTD since the liquid mixes with the gas before it reaches the heat exchanger tubing. The sketch shows a large space behind the bundle. There should be very little space there where the fluid could bypass the bundle.

[S.AHMAD]

1. I strongly believe that the problem in this scenario is not to determine LMTD.

2. The main issue is to determine the film heat transfer coefficient of the shell since it is a two phase stream.

3. Since the inlet and outlet temperatures are known then the LMTD can be calculated,.is it not?

 

S.Ahmad