Temperature profile stimulation

[114425]

Hi all,

I wonder if it is possible to stimulate a temperature profile of a heat exchanger by only using common software such as matlab, polymath etc. I been looking back in my books but I failed to find a way to do so. If anyone knows, please help me out!

Thank you

 

[iHydrogen]

When you say 'temperature profile' what exactly do you mean? Do you mean a 2-D or 3-D temperature map of HX at steady state? Or a 1-D dynamic profile of temperatures over time at different points (likely inlet and outlet)?

 

[114425]

sorry for the confusion. The temperature profile I meant is just a simple temperature vs. time graph representing the heat exchanging system. For a example, a hot water bath and a coil need to be heated. So the temperature profile for the hot water bath should be constant as time pass, but what I am interested is the temperature change of the coil in the whole process from beginning til end.

I hope I make it better to understand this time, thank you very much for your help.

 

[Latexman]

I'm curious, what useful information would be obtained? You know the incoming T, and you can calculate the outgoing T using the usual heat transfer equations with the known total heat transfer area.

Why not correlate time in the coil to a variable area that the fluid has seen and then calculate the T using the usual heat transfer equations with the known variable amount of heat transfer area.



Good luck,
Latexman

 

[114425]

I want to use this temperature profile for comparison (coil with water bath) with other heat exchange system, and see if I will be able to modify the new system with similar temperature profile.

As Latexman mentioned, I am able to calculate the outlet T using heat transfer equation but I also want to find out the whole process. What I don't understand is how to the correlate the temperature with time during the whole process in my case.

 

[Latexman]

We need a better understanding/more data on your process. Describe the coil. Is it adding heat to or cooling the hot water bath?

Good luck,
Latexman

 

[114425]

To Latexman, here's what I have.
Assume it is a stainless steel 316, ID 10mm OD 12mm, with the water flow rate of 250ml/min. The inital product temperature is about 35C, and the hot water bath is 85C. Coil length is about 2m long. I think that's what I used to calculate the water outlet temperature, but I also want to know how long, and how does the temperature changed with the coil from beginning til end.

 

[IRstuff]

You could probably do a distributed model of the pipe. Assume, say, 0.1-m chunks comprise the full, 2-m length.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[114425]

To IRstuff,

I actually have tried this method before as well, but I ended up getting the product instantly shoot to 80ish already in the first few chunk (0.1m or similar distance). I am not sure if I am doing something wrong in my calculation or the coil just allow such quick heat transfer.

 

[Latexman]

Attach your work and let us look it over.

Good luck,
Latexman

 

[114425]

It is not clearly organized, but please take a look

 

[114425]

Just to clarify, I have tried 2 different Nu correlations. One give much higher number and end up the temperature is very close

 

[Latexman]

The only thing that looked strange to me was the linear velocity (cell B5) - velocity inside the tubing? - you need to use the inside diameter of the tube, not the radius of curvature of the coil. But I don't think this affected your heat transfer calculations.

Good luck,
Latexman

 

[114425]

Ah, thanks for pointing it out. It is just the units problem and I will fix it. but it is just like what you said, it doesn't affect the heat transfer.

 

[Latexman]

I think I see the problem now. You have the forced convection h inside the tube (G8) and the conduction h through the tube wall (C12), but you do not have any term for the outside of the tube. Is the water bath well mixed? I'm wondering if it is forced or natural convection on the outside of the tube? Your U is 276 now; what are the units? What is the new U after incorporating the h for outside the tube? Do you need a h for fouling?

Good luck,
Latexman