For complex constructions, you may need to work some of the intermediate
and supplemental exercises. All in all, assume that it takes 1 to 2 days
to learn Sauna. This compares quite favorably with FEM and CFD software.

*I only perform thermal analysis once in a while.
I might be involved with thermal issues for several weeks, then six months
might pass before the next thermal project. Will I
be able to use Sauna on an occasional basis?*

Yes! In reality, there are very few Sauna users that do thermal
analysis on a continuous basis. Since Sauna is easy to learn,
the program is well suited for this intermittent type of use.

Remember, if you are having trouble deciding between Sauna Standard
and Sauna MS, start with Sauna Standard. This is a logical approach
because you can upgrade with full credit during the first year after
purchase.

*What is the numerical method used
by Sauna?*

Sauna is a thermal network (finite difference) program which uses
the thermal/electric
analogy. At the lowest level a Sauna thermal model is composed of
nodes, thermal resistors and thermal capacitors. However, users
rarely specify thermal resistances and capacitances. Instead,
a user specifies a material type and plate or board dimensions.
Sauna then creates the appropriate resistance/capacitance network
based on Sauna's library of material properties and the current
modeling setup.

For calculating steady state temperatures, Sauna uses a sparse,
direct matrix solver which is based on Gaussian Elimination.
Transient temperature calculations are based on either an implicit
or explicit solver, depending on the model parameters
and user settings.

*Sauna includes a flow network feature.
Does Sauna have computational fluid dynamics (CFD) capability?*

No. With the flow network capability, the user can define a flow
path (or paths) and Sauna will calculate the appropriate air
temperature increase as air moves along the flow path. However, it
is up to the user to specify all flow volumes (except for heat sinks,
see next paragraph). If the box has a
straightforward flow path, the flow volume can be readily calculated
by using the fan characteristics and box dimensions (or simply
entered for what-if studies). The Sauna user manual explains how
to perform flow calculations.

For heat sinks, Sauna can perform an integrated fan/flow
calculation. You just need to assign a fan curve to the flow
network and Sauna will handle all of the flow/pressure
calculations. Here again, however, this is handled without
CFD.

*Can AutoCAD files be imported? Can SolidWorks files
be imported?*

At the present time, you cannot import data from AutoCAD, SolidWorks,
etc. Although importing CAD data seems like a great idea, there
are many practical limitations. CAD models tend to have
too much dimensional information and not enough physical data.
For example, a solids model of a molded plastic part can be
quite complicated due to draft angles, blends, etc. But in
a thermal model it isn't critical to know every dimension,
particularly for materials with low thermal conductivity. If
every detail is included, the model might take days to calculate
but the answer won't be much better than a simplified
model.

On the other hand, CAD models frequently lack the necessary
properties such as thermal conductivity, specific heat and
emissivity. This is particularly true for circuit boards.

It's important to realize that an engineering man-week now costs
$3,000 or more. So Sauna will pay off quickly when compared with an
FEM program. Nearly all Sauna customers are also owners of an FEM
software package. But these companies use Sauna for thermal problems
because it is so much more efficient.

*How does Sauna compare with finite element modeling
(FEM, FEA) software?*

The finite element method (FEM), also known as finite element
analysis (FEA), was developed to analyze deflection and stress
in solid mechanical structures. Once the finite element
mesh has been created, it's also possible to solve for heat
flows and temperatures **within the solid material**.

However there are three distinct modes of heat transfer: conduction,
convection and radiation. FEM programs really only deal with the
conduction part of the problem. For the convection part of the
problem, it's usually up to the user to enter a convection
coefficient and, in general, only simple convection to the room is
allowed. For thermal radiation, most FEM packages only include
simple black body radiation to the room environment and there is no
ability for walls of a box to radiate to each other. The result
will be lengthy model creation time and incomplete models.

*How does Sauna compare with computational fluid
dynamics (CFD) software?*

Computation fluid dynamic (CFD) software is a numerical
simulation of the Navier-Stokes equation of fluid motion. This
method is computationally intensive and only became practical within
the last 15 years. The two most popular electronics CFD packages
are ANSYS Icepak and Mentor Graphics FloTHERM.

CFD's primary advantage is the ability to predict flow. If you want
to model a box with 3 fans, and you don't know where the air is
going, then you may wish to consider the CFD approach. With Sauna,
the user must specify the flow rate (Sauna handles all other
aspects of the problem). If the flow path is simple so that flow
volume is readily calculated (details provided in the Sauna user manual),
or for natural cooling, Sauna can be very effective and accurate.
But there are situations where CFD software is useful.

You should be aware of the drawbacks of CFD:

1. CFD programs focus on air flow and convection. CFD programs
are not always effective at handling the conduction and radiation parts
of the problem. For example, a potential purchaser needs to investigate
the way that multilayer circuit boards are modeled and whether the CFD program
has the ability to model radiation networks in complex boxes.
These are very important features for an electronics thermal modeling
program.

2. Details are important in CFD analysis. For example, it's
important in CFD simulations to correctly specify surface roughness
and vent drag coefficients. Sometimes these values must be measured
experimentally. You can't just create a model and assume that
predicted results are on target.

3. CFD analysis is computationally intensive. It's very difficult
to perform duty cycle analysis because the computing time can be
quite significant. What-if analysis is harder because of the
time required for each iteration.

4. CFD software takes time to learn and requires a skilled user.
Since CFD starts with the Navier Stokes equation, it's important
to have a solid background in both heat transfer and viscous fluid
flow. In addition to the proper background, you can expect to
invest at least a week learning the software.

5. CFD software is expensive. Actually, very expensive.

During the comprehensive support period, any questions about thermal
modeling will be answered. When appropriate, technical support will
also review user models to check for proper modeling technique and to
locate obvious flaws. Please be aware that Technical Support does
not provide a "checking" service. The responsibility for "checking"
always resides with the user.

After the initial period, a one year support package can be purchased,
which would include software updates. If this is declined, then
lifetime basic technical support is provided. Basic support means
that Thermal Solutions will respond to phone calls and brief emails
about the operation of Sauna. Questions will not be answered about
modeling assumptions and other thermal issues. Models cannot be
emailed for review and no software updates will be provided.