topic Re: Automatic solution of multilayer stady heat transfer as a function of layers number in Mathcad

Automatic solution of multilayer stady heat transfer as a function of layers number

wzelik — Thu, 03 May 2018 13:20:25 GMT

Hi,

I'm looking a way of automatic solution of HT problem with multilayer steady heat transfer with numbers of layer dependency.

I'd like to put n variable as number of materials layer then put thicknes and thermal conductivity as a consequences of layer namber and finally get a solution for n=2,3...k layers.

Thank you in advance for any idea

I enclose MP 4.0 file.

wzel

Re: Automatic solution of multilayer stady heat transfer as a function of layers number

ValeryOchkov — Sun, 07 Jan 2018 14:02:48 GMT

May by this Mathcad-Websheet is any help for you

http://twt.mpei.ac.ru/MCS/Worksheets/Thermal/T-T-2-Chapter-3-3-3-1.xmcd

Re: Automatic solution of multilayer stady heat transfer as a function of layers number

DJF — Sun, 07 Jan 2018 14:48:49 GMT

I think this is similar to a problem I posted here (N orifices in series).

https://community.ptc.com/t5/PTC-Mathcad-Questions/Solve-block-for-N-inputs/m-p/484610#M173308

See MJG's solution - the trick is in the 'stack'ing of the pressures.

Re: Automatic solution of multilayer stady heat transfer as a function of layers number

wzelik — Sun, 07 Jan 2018 18:44:18 GMT

Thank you both, Valery and DJF.

The problem is that I have to solve the non-linear equation due convecting and radiation therms which are set as outflow boundary condition.
This is a first step to get interlayer and inflow temperatures.

wzel

Re: Automatic solution of multilayer stady heat transfer as a function of layers number

DJF — Sun, 07 Jan 2018 21:15:26 GMT

I think the link did that, although yours is complicated by having different equations at the start and end. But the concept is the same. Since I can probably use something similar someday, I took a stab at it. Seems to work - you can add or delete rows to the table. But user beware, etc.

T_start is the temp at the start of a 'plate', and T_end is the temp at the end of a plate.

Re: Automatic solution of multilayer stady heat transfer as a function of layers number

Fred_Kohlhepp — Mon, 08 Jan 2018 20:28:55 GMT

Note that your solution changes the value of Q. Might try taking it out of the Find statement

Re: Automatic solution of multilayer stady heat transfer as a function of layers number

DJF — Mon, 08 Jan 2018 20:39:04 GMT

I thought that finding Q was the (eventual) point. If I define the temperatures then Q is a result, not an input. Otherwise I'd need to change thicknesses or heat transfer. Original post solved for Q, but never called it that - they just set the equations for Q equal to each other. But I didn't study it very hard so maybe I'm not understanding their question.

Re: Automatic solution of multilayer stady heat transfer as a function of layers number

Fred_Kohlhepp — Mon, 08 Jan 2018 21:26:56 GMT

I understand the confusion.

If you have the inside/outside temperatures given, then solving for Q and the layer by layer makes sense and should work.

If you set Q (and wither the inside OR the outside temperature), then you can solve for the whole temperature set.

I didn't realize you were solving the first problem. Sorry!

Re: Automatic solution of multilayer stady heat transfer as a function of layers number

wzelik — Tue, 09 Jan 2018 17:18:49 GMT

Hi,

Thank you DJF, your solution work perfectly.

I have overlooked my own mistake in first post. In quadratic part of radiation therms should be plus instead minus.

I have checked solution with my old maple mathapps. The results are the same.

Below comparison of 3 and 4 layer solution done in MathCad and Maple.

Q vaule is also correct. it is no surpise beocuse Q=4000W is starting point for looking solution.

Thank you once again.

wzel