Heat transfer problem

[mfqd13]

Hi,

In attach i put an image with my heat transfer problem.
Please take a look...
Until now, i made 2 simulations:

1- assuming heat transfer problem for parallel flows A and B, assuming B2 as 40ºC and B2 as 9ºC i've obtained a water flow of 6kg/h
2 - assuming radial conduction from surface of E as 500ºC and D1 as 9ºC and D2 as 12ºC and i've obtained 7kg/h.

Apparently this are similar results but i'm affraid i'me not doing this right.

The main gold is to determine the optimal water flow so that the main stream ends at 40ºC.

I'm not asking anyone to solve the problem but to give me ideas how can i compute this in a certain sequence of calculations so that i test diferent values of water flowrate and see what is the final A2 temperature....

NOTE: Streams B and D are the same. i'm analysing jusr 1m length, but at the end the flow returns back

THANKS!!!!

 

[mfqd13]

The attached file is here!

 

[TD2K]

Maybe I'm misreading your sketch since the intermediate water layer comes in at 7C and leaves at 12C, how you expect to heat the main fluid stream from 30C to 40C?

 

[mfqd13]

Dear TD2K,

You are right the given data is that the main fluid enters at 30ºC and it can not override the 40ºC. Lets say, i have to find a water flowrate so that the main fluid doesn't override 40ºC at the outlet.

I have solved the problem, but i need to have a second opinion about my calculations:

What i did was:
1-Assume 500ºC as the surface temperature of the refractory, and use the heat transfer formula for conduction through a cilinder wall and forced convection of the water at layer C (return line). To calculate this heat transfer power i need to estimate a water flowrate and the medium temperature between points C2 and C1.

2-The same for layers C to E and forced convection in both and conduction in D. The flowrates are the same as i mentioned before. Here i assumed a medium temperature between E1 and E2 and calculate the power rate. But, i needed to perform an iteration so that the assumed medium temperature corresponds at the DT value calculated.

3-At the end i played with: water flowrate, medium temperature at C and medium temperature at E to obtain what i wanted.

I didn't calculate the heat transfer from the water stream to the main fluid, because i assumed that if the water has temperatures between 7-12ºC and the main fluid never enters at a temperature greater than 30ºC it will never increase it's temperature.

It maybe be confuse but if someone could give me an opinion it will be great!
Thanks