Thermal Distribution Modeling 2

[Kuhuh]

I am looking to see if you can present a dynamic model with respect of time of the heat distribution from a heated pipe in water. I am trying to model the time it would take to heat a tank of water by means of a copper pipe transporting hot fluid. Can I do this with Matlab? or does anyone else have a good program, student version, or free for this not going to be for school just personal research

 

[IRstuff]

Of course, you can do it with Matlab. Could probably do it in Excel. The only question is how lumpy to make your model. The BFlow CFD for Excel cited in thread997-298781 and located at

http://www.basicnumerics.com/bflow/

may give you some hints as to how to set up your problem.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[zekeman]

You don't need Matlab. All you need to do is solve for Tw as a function of time from the set

1) Rho*a*v*c (Ti-T0) = hpL*[Tw-(Ti+T0)/2]

20 Mc*d(Tw/dt)=Rho*a*v*c (Ti-T0)

dTw/dt)= rate of increase of tank water temperature
rho density
a crossection of pipe
L length of pipe
v velocity of water
c specific heat
h film coefficient tank water to pipe

Ti hot water in
T0 hot water out
Tw water in tank
M weight of tank water

Explanation


2 equations 2 unknowns
Tw, T0 are the 2 unknowns

equation 1 equates the heat transferred from the pipe to the tank water

equation 2 states that the heat transferred is equal to the rate that energy is absorbed in the water .

If you need more help in solving this set I could help.

 

[flash3780]

Matlab is great; Octave would do fine for solving this problem as well and is free. Check out the QtOctave m-file editor if you go that route. I've also heard that Scilab is good, but I haven't tried it. Lots of free tools available that can solve this problem.

I think that zekeman is neglecting the thermal conductivity of the pipe and the HTC between the internal fluid and the pipe, which may be a reasonable assumption. If you want to do something fancier, I think that an iterative solution is necessary.

 

[zekeman]

"I think that zekeman is neglecting the thermal conductivity of the pipe and the HTC between the internal fluid and the pipe, which may be a reasonable assumption. If you want to do something fancier, I think that an iterative solution is necessary. "

Yiou will find that the conductivity thru the pipe and the internal film coefficient are an order of magnitude greater than the external coefficient, so the external film dominates.

 

[flash3780]

"You will find that the conductivity thru the pipe and the internal film coefficient are an order of magnitude greater than the external coefficient, so the external film dominates."
I agree... unless the fluid is creeping through the pipe at a very low flow rate or the pipe is very thick. It's probably a good assumption.

 

[Kuhuh]

I think I have come up with the solution to model this correct me if I am wrong. First I am going to figure out the conduction through a cylindrical wall then use Fourier's law to calculate the speed at which it will spread to the surrounding water. And can some one fill me in on this Film HTC? I am strictly civil not to sure what the films info your all talking about

 

[IRstuff]

The surrounding water. The "film" is the layer of water immediately surrounding the pipe, and the convection currents in the water is what transfers heat from the pipe to the bulk of the water.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Kuhuh]

I got stuck, attached is what I have so far for the heating of air with use of fins. I am using copper pipe and I used a generic number for both thermal conductivity and the heat transfer coefficient. I am using an equation found in the fundamentals of engineering supplied reference book. I can't figure out how to add in the loss of temperature through the length of pipe from the heat extracted from the fins. If you run the program Q=37.11 W so how can I figure the loss in temperature as the pipe continues. I understand that Q out will be dependent on the temperature of the base (pipe) in which the fins are attached. Can anyone help?