Ansys Tutorial For Thermal Analysis

Getting Started With Thermal Simulations in Ansys

The first thing you need to understand is that Ansys Mechanical (or Icepak, depending on what you're modeling) doesn't care about your beautiful CAD geometry. It cares about volume meshes, boundary condition consistency, and whether your solver will actually converge. I've spent years watching people burn through hours of compute time only to get a result that looks visually impressive but is physically wrong. That usually comes down to two things: incorrect contact definitions and poor mesh quality at interfaces. Before you even open the software, know what type of thermal problem you're solving. Steady-state? Transient? Coupled structural-thermal? Pure conduction, or do you need radiation and convection? Each one takes a different path through the preprocessor. The distinction matters more than most tutorials admit.

Ansys Tutorial For Thermal Analysis

Here's the practical flow I use, stripped of everything that isn't necessary. Launch Workbench, drop a Thermal System into the project schematic, and connect the Geometry cell. Import your CAD. If it came from SolidWorks or Inventor, make sure to clean it up — remove fillets smaller than your intended mesh size, suppress fasteners, and merge small surfaces that won't carry meaningful thermal gradients. I had a board-level PCB simulation once where a 0.3mm chamfer on a mounting hole created a meshing failure that cost me six hours. It was just noise to the thermal problem. Delete it and move on. Now the material assignment. Don't just pick a material from the library and assume it's correct at your operating temperature. Thermal conductivity for most metals drops or rises significantly across temperature ranges. Aluminum 6061 goes from about 167 W/m·K at room temperature down to roughly 130 W/m·K at 400K. If your simulation spans more than a 50-degree delta, define that conductivity as a function of temperature. The solver handles it without extra cost, and your results get materially more accurate. I learned this the hard way on a motor housing analysis where the peak temperature prediction was off by nearly 30 degrees because I used a single-point conductivity value. Mesh generation is where most thermal simulations either succeed or fail. Start with a global sizing that matches your smallest feature of interest. Then apply body sizing or face sizing to regions with steep gradients — heat sinks, near heat sources, thin interface layers. Use curvature-based refinement on surfaces where geometry changes rapidly. For a typical electronics enclosure, I usually target elements around 2-3mm globally, dropping to 0.5-1mm near the hot components and on thin thermal interface materials.

Contact pairs deserve special attention. Default bonded contacts work for most conjugate heat transfer problems, but if you're modeling thermal interface materials, gaps, or assemblies with pressure-dependent contact resistance, you need to set the contact type explicitly and assign a thermal contact conductance value. This is not something to leave at the default. A common mistake I see repeatedly is bonding two mating surfaces and expecting heat to transfer realistically when there's actually an air gap or an TIM layer between them. The solver treats a bonded contact as perfect thermal continuity, which is almost never true in practice. Define the gap, assign the right conductance, and move on.

Boundary Conditions That Actually Matter

Heat generation — this is your power dissipation. Set it in W/m³ for volumetric sources or W for surface loads. If you're simulating a resistor, a power MOSFET, or a PCB trace, the value needs to come from real data, not a datasheet maximum. Use typical operating conditions. Peak power only applies under fault conditions, and mixing the two up will push your temperature predictions into unphysical territory. Convection boundary conditions require a heat transfer coefficient and a bulk fluid temperature. The coefficient is the hard part. Most engineers pull numbers from handbooks or online tables, which gives you a starting point but rarely reflects reality. Natural convection on a vertical flat plate might be 5-10 W/m²·K. Forced convection with a fan could be 25-100 depending on velocity. If you have CFD data or test measurements, use those. If you don't, run a parametric sweep across a reasonable range and check how sensitive your results are. I once validated a laptop thermal model against IR camera measurements and found my convection coefficient was off by a factor of two because the actual airflow path was restricted by a rubber foot I hadn't modeled. Radiation is another area where people either overuse it or ignore it entirely. Surface-to-surface radiation matters when temperatures exceed roughly 100°C and surfaces have line-of-sight to each other. For low-temperature electronics cooling, radiation typically contributes less than 10% of total heat transfer and can often be omitted without significant error. When you do include it, make sure your emissivity values match the actual surface finish. Polished aluminum has an emissivity around 0.05. Anodized aluminum is closer to 0.8. Using the wrong value can shift your radiative heat loss by an order of magnitude.

Solver Settings And Convergence

The solver for steady-state thermal is straightforward — usually the direct MBD (Multi-Boot Domain) solver works fine for most models. For transient analysis, the choice matters more. The Implicit scheme is unconditionally stable but can be slow to converge on problems with steep thermal gradients. The Explicit scheme handles transients better but requires smaller time steps. If your model has both a small thermal mass component and a large solid block, the explicit scheme might force you into time steps measured in milliseconds, which makes a 1-hour simulation take hours of compute time. Stick with implicit unless you have a specific reason not to. Convergence monitoring is essential. Set a residual tolerance of 1E-6 for steady-state. For transient, monitor key node temperatures in addition to residuals. If your max temperature is still drifting after the residuals look converged, your time step is too large. I ran into this on a battery pack simulation where the residuals indicated convergence but the cell temperatures were oscillating between solution steps. Dropping the time step from 60 seconds to 10 seconds resolved it immediately.

Validation And Common Pitfalls

Never trust a simulation result without some form of validation. Even a simple hand calculation or a comparison against published data from a similar configuration will catch most modeling errors. A quick thermal resistance estimate — think of it as a rough nodal model in your head — takes about two minutes and can tell you whether your FEA result is in the right ballpark or completely off. One counter-intuitive thing about Ansys thermal analysis: refining the mesh past a certain point does not always improve accuracy. If your boundary conditions or material properties are uncertain, a finer mesh can actually give you a more precisely wrong answer. I discovered this on a LED thermal simulation where the fin geometry was refined from 2mm elements down to 0.5mm, and the predicted junction temperature shifted by 15 degrees. The real source of error was the contact resistance at the fin base, which I had estimated from a generic table rather than measured. The mesh refinement exposed the sensitivity of the model to an input parameter I didn't actually know well enough. Another pitfall: thermal expansion coupling. If you're running a coupled thermal-structural analysis, make sure your material includes temperature-dependent density, specific heat, and coefficient of thermal expansion. Omitting any of these can produce believable-looking stress results that don't reflect reality. The solver will use whatever data you give it, and missing CTE data means no thermal strain calculation at all, even if your temperature field looks correct.

When transient simulations take too long, the usual culprits are excessive mesh density in low-gradient regions, unnecessary geometric detail, or a time step that's smaller than required. I once cut a 4-hour transient run down to 25 minutes by removing internal threads from a housing model, coarsening the mesh in regions where temperature varied by less than 2 degrees across the entire simulation, and switching to a variable time step with a maximum of 30 seconds and a minimum of 1 second. The peak temperature and thermal profile matched the original within 1 degree. If your model involves phase change materials or latent heat effects, Ansys Mechanical requires the Enthalpy-Porosity method or a custom User Fortran subroutine. This adds significant complexity and is rarely worth the effort unless the phase change is central to your analysis. For most practical purposes, approximating the material with an equivalent specific heat over the transition range gives acceptable results with far less setup time. The software itself is stable, but the learning curve is real. The biggest time investment isn't learning the interface — it's understanding what inputs drive your results and which ones you can safely simplify. Spend your time on material properties, contact definitions, and boundary conditions. Everything else is optimization.