heat transfer between two pipes

[Dan_Margulius]

Hello,

I have two pipes one inside another. On the outside pipe wich is steel 5150 there is a generation of heat (0.1Kw,0.5Kw,1Kw,1.5Kw) and so on. the inside pipe is plastic PP and I would like to know at what Watt I will get to the melting point of the PP. How can I do that? I tryed steady state heat transfer with applied temperatures but I want Watts. When I apply total

heat generation on the outside pipe I get weird temp numbers. Help...

R.

Dan

[shakeel.mirza]

Hi Dan,

If I understood it well, you want to apply a heat generation to the outside pipe and get the temperature at the inside part (to ultimately compare that to the melting point of PP). Am I correct in my understanding ?

Steady state heat would be a good point to start where you can apply a wattage value and see the resulting temperature to verify that your approach is working.

Eventually you can choose a Transient heat to go from 0 to max. wattage value and see the variation of temperature on the inner pipe overtime.

However one simple thing to note, Algor takes the values of Internal heat generation in Watt/Volume, so you might need to know the volume of the modeled outer pipe and divide it by the required power in watt. to get per unit volume heat generation value.

Please share the dataset if you need further help.

Regards,

Shakeel

[Dan_Margulius]

Hello 

Shakeel,

You got my problem exactly. I divided the the watts to the volume after taking it from the Weight and COG calculator.

The results I got are not right. I am attaching the algor file with two DS. The first one was done with surface applied temperatures and the results are in the normal scale I think. The second DS is done with surface heat flux and the results are not OK.

Please look at the file on the second DS and tell me where I ma wrong in my inputs.

Thanks,

Dan

[shakeel.mirza]

Dan,

Whats the condition inside the PP pipe ?

In your 2nd DS its modelled as isolated. Does that represent the reality. ? is there any flow inside the inner pipe ?

[Dan_Margulius]

In the inside pipe there is air at 25 C. The customer wants to build like a cap to the outside pipe.

This small model is for selling popouse by the way, to show that Algor can do it. In the first DS I put temperatures. Is it correct from your experience? Because maybe we can show both methods ( Watts and temperatures)

Dan

[Dan_Margulius]

The air inside is not important beacuse we are checking the melting temperature of the PP. If we can see how much time it will take for the plastic to get to the melting point it is even better.

R.

Dan

[shakeel.mirza · Accepted solution]

Dan,

I would suggest to verify the Surface Flux value that you've defined.

To have a 1KW Power dissipated over the surfaces you'll have the following flux value:

Power=  1000

Radius of Cylinderical outer Surf = r =0.014
Length of Cylinder = l=0.035
Outer Pipe Surf  =s= 0.00308m^2

so the Flux should be = Power / s which seems to be very high (I think bc 1KW for a small surface like this is too much.)  On the contrary your given value seems to be tooo low. Please check that value.

I've defined a transient analysis and given a Surf. Flux of 1000 J/s/m2 which seems to give logical results over time. I 

The File is 4Mb and i'm unable to attach it here. let me know your email to recieve that if you are interested. or try with a different flux value.

Regards,

Shakeel

[Dan_Margulius]

Hello,

My email is danm@omnitech.co.il . Please send me the file so I can learn. The 1000W is the maximum the customer wants because he didn't know how much power he needs to melt the PP. we started from 100 W.

Thnank you ,

Dan 

[Dan_Margulius]

I also defined the flux 1000 as you did. Over 60 seconds I get very low temperatures.

picture attached. How much time did you defined? what materials for the pipe did you choose?

Thanks,

Dan