Last updated:
4/9/2014

Two-Dimensional,
Steady-State Conduction

**(FREE, NEW (4/9/2014) DOWNLOAD BELOW!)**

The mathematical model for
multi-dimensional, steady-state heat-conduction is a second-order, elliptic
partial-differential equation (a Laplace, Poisson or Helmholtz Equation).
Typical heat transfer textbooks describe several methods to solve this equation
for two-dimensional regions with various boundary conditions. Analytical
solutions usually involve an infinite series of transcendental functions. This
series must be truncated and evaluated at an array of locations to give an
approximate estimate of the temperatures found over the 2-D region. Some
texts also include detailed graphical methods using various paper and pen tools
for estimating temperature and heat-flow lines for 2-D problems, but these
latter methods have become largely obsolete due to the widespread use of
computers and associated numerical algorithms (although the principles on which
graphical methods are based are often useful in checking the validity of
numerical solutions).

**Module Description**

In our software module, HTT_2dss, we employ modern numerical methods to solve for the temperature distribution over a user-specified 2-D region. The region is taken as rectangular, with cutouts possible. The user is asked to:

- specify the nodalization of the heat-conduction region (dynamic array allocation is used, so the problem size is limited only by the memory available),
- derive the appropriate heat-balance equations for specified regions of the solution domain (internal points, boundary edges, corners, interfaces, etc.), and
- input the resulting numerical coefficients on a special input form:

In doing this, they are (without knowing
it) setting up the ranges of numerical Do-loops. The program then uses this
input data to solve the large, sparse system of linear equations using a modern
iterative technique known as the Modified Strongly Implicit Procedure. In just
a few seconds, Htt_2DSS returns a full-color contour-plot of the resulting
isotherms -- for use in further analysis and verification. A sample of the main
user-interface of HTT_2dss is shown in the graphic below. The user may click anywhere on the contour
plot to see the local heat flux vector.

The solution may also be presented as a
raised contour plot:

This main user-interface of Htt_2DSS
includes easy access to two sample problems which have analytical solutions in
the form of an infinite series. For these two samples the color-contour
plot can be enhanced with the overlay of white lines depicting isotherms based
on the analytical solution. The user may specify the number of terms to
be used in the series approximation. (See also our Excel HTTtwodss spreadsheet
that animates the analytical solution of one of these same sample problems by incrementally
adding terms in the infinites series.)

Several PowerPoint presentations are
embedded within this module: One covers analytical solutions for
two-dimensional conduction, including the graphical depiction of results. A
second includes checking and interpreting numerical solutions; while a third
derives all needed governing heat balance equations. The fourth comprises a
step-by-step tutorial for the case shown in the graphic above. The Help Topics
included in HTT_2dss provides an even more thorough discussion of program
operation, as well as the important physical and numerical aspects of this
classical engineering problem.

For this module and several others, our
former laboratory director, Mr. T.C.Scott, developed desktop experiments from
which the whole class takes data. In the one seen here an electric analog is
used to model steady-state conduction in a two-dimensional fin - thus
reinforcing the idea of approximating a continuous system by a
"lumped" one. The brown resistors represent conductive resistance
between adjacent cells; while the turquoise ones represent the convective
resistance between the fin and the ambient air.
Before digital computers, electrical analogs such as this one were a
staple of heat transfer laboratories.

**Software Availability**

Copies of our HTT_2dss module

**Notice to International Users **(in those
countries where decimal points (periods) are used instead of commas to break up
long numbers): If, after you have installed this module, it does not work
properly, then in the International Setting of the Windows Control Panel,
please change the language to English (US).

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