Thermal fluid flow in pipe to work out length

Question

Thermal fluid flow in pipe to work out length

m4rjaan (Student)

(OP)

12 Apr 21 12:58

A pipe has outer diameter 0.142m and has ethanol vapour with mass flow rate 108kg/s entering. The temparature of the ethanol entering the pipe is 123celsius and the temperature of the furnace surrounding the pipe is 450celsius. The pipe is stainless steel 304 and thickness 0.2mm.

How do I work out the the length of tube needed for the ethanol to reach 450celsius?

Many thanks.

MacGyverS2000 (Electrical) · Answer 1 · 2021-04-12 15:43:34

Show us your attempted work first...

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onatirec (Mechanical) · Answer 2 · 2021-04-12 15:48:07

Do you know any heat transfer equations? Have you attempted to solve it?

My gut feeling is: the pipe would have to be pretty long. 108kg/s and you want your outflow temperature to reach the same temperature as the furnace... as the delta T decreases, so does the energy transfer. It's asymptotic.

m4rjaan (Student) · Answer 3 · 2021-04-12 16:11:16

Thanks for the responses.

I've attached the working I've done so far, I am not sure if it is correct as the length calculate is quite small.

https://files.engineering.com/getfile.aspx?folder=d512005a-beeb-4167-b5af-7

onatirec (Mechanical) · Answer 4 · 2021-04-12 18:20:19

No units?? What do all the numbers mean? is Do 0.142 as you stated or 0.14241??

I'm not quite sure what you've done there...

It's a flow; did you calculate Re? Mean temp? I don't see that you've used ethanol Cp nor the flow rate at all...

Most heat exchanger problems have the outflow temp lower than the system high temp. To reiterate my first post, it's gonna have to be a long pipe since the flow temp increases at a decreasing rate...

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Thermal fluid flow in pipe to work out length