Thermal Analysis With Sauna

Model creation made easy

From the beginning, the Sauna program was created exclusively for the thermal analysis of electronic components and systems. All menus, material libraries and assembly properties were created with this one goal in mind.

Building your model is intuitive and easy. A model is constructed using the building block assemblies of plates and circuit boards. To create a plate you simply define the plate dimensions and choose the material and surface types from menus. In just seconds, the plate appears on the computer screen. You don't have to type in any thermal conductivities or other properties. Furthermore, if you wish to add fins to either side of the plate, this can be accomplished with a single command.

 
A simple heat sink model will appear as shown in the picture on the right. In this picture, which is a wireframe view, you can see the array of nodes and resistors that Sauna uses to define the model characteristics. Although Sauna uses the classic thermal network method, you almost never enter values for the thermal nodes, resistors and capacitors. Sauna calculates model values for you automatically, based on materials and dimensions that you specify. Sauna creates a smart model which is easy for you to check and modify.

 
 
Of course, it is also useful to have a realistic image of your model, instead of the wireframe view. For this, Sauna provides "shade mode". At any time, a single mouse click will switch the display into shade mode, producing a shaded, perspective view of the model. The picture on the left shows the heat sink model in shade mode. If you wish, it is also possible to perform dynamic view rotations and progressive zooms.

You are not restricted to simple heat sinks. Sauna can model heat sinks in a wide variety of shapes and sizes. A more complex heat sink model is shown on the left. Sauna provides you with full 3D modeling capability, so there are many, many other possibilities.

It's also easy to create a circuit board assembly. You use menus to select the number of layers, copper weight, and copper coverage. Very quickly, a complete board model is created and drawn on the screen. All the necessary engineering data, including a library of standard semiconductor packages, is built into the Sauna program.

 
Heat sinks and circuit boards can be analyzed as standalone elements or they can be incorporated into boxes. Sauna provides specialized commands for quickly defining a 6-sided box and for positioning boards and interior walls. These are common tasks when modeling an electronic system, so Sauna makes these tasks easy and error-free.  

Convection and radiation made easy

Convection and radiation heat transfer are both nonlinear, temperature-dependent phenomena. With many thermal analysis packages, dealing with these dissipation modes can become a very time consuming and error prone process.

With Sauna, however, convection and radiation coefficients are automatically calculated for you. You simply connect "float" resistors between the boards and plates and the desired internal or external ambients. For convection, both natural and forced air cooling are available. For radiation, simple (black body) radiation is supported as well as gray radiation inside an enclosure, which includes automatic calculation of view factors.

Sauna uses advanced sparse matrix methods to dramatically reduce model calculation time. For steady state problems, calculation times are typically measured in seconds. Even for transient problems, model calculation times are usually just a minute or two. With Sauna's speed of model creation and temperature calculation, a complete model can be built and analyzed in less time that an average coffee break.

Sauna provides temperature contour capability so you can quickly identify hot spots. To help you interpret transient temperature data, Sauna incorporates a comprehense plotting utility.

Duty cycles and power shutback

In the real world, many products are subjected to duty cycle conditions, where power (or boundary temperatures) vary with time. Sauna provides "control elements" which let you define a variation of wattage (or boundary temperature) with time. You can prescibe simple square waves or you can use Sauna's scripting language to define highly complex power vs. time curves. The same control element feature can be used to define power shutback, which is quite common with contemporary components. There are many other possibilities. Of course, these types of calculations can require significant computation time. Here is another important advantage for Sauna. With Sauna's efficient solver, you can complete duty cycle simulations in minutes, as compared to hours for a competitive FEA or CFD program.

What-if modifications

With Sauna, you can create and analyze a thermal model in a matter of minutes. However, many times you will find that temperatures are not at acceptable levels. An important test of any modeling program is whether modifications are easily performed.

Sauna is the premier tool for what-if thermal design. Powerful edit commands make it a snap to change a housing from ABS plastic to aluminum alloy. Moving heat sources and repositioning circuit boards is quickly accomplished. It is equally easy to change from natural to forced air cooling, or to modify the air velocity. With all these editing features, combined with Sauna's rapid calculation times, it is possible to quickly evaluate a whole series of alternatives. The final result: an optimized final design. And, of course, a savings of many man-hours of engineering time.

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