Close the energy balance before trusting local temperatures. If the net heat entering the model does not match the heat leaving plus stored energy for a transient case, local temperature agreement can be accidental.
Problem: the temperature field is physically implausible
Typical symptoms include solid temperatures far above or below expectation, fluid outlet temperature inconsistent with the applied heat load, unexplained hot spots, discontinuities at interfaces, or a model that converges numerically while the global heat balance remains poor.
A CHT model couples conduction in solids with convection in fluids, so errors can enter through either domain or through the interface between them.
Start with a simple energy budget
- Calculate total imposed heat.
Sum volumetric heat sources, wall heat fluxes, prescribed powers and any source terms. Confirm units and whether values are total, per-area or per-volume.
- Calculate fluid enthalpy rise.
For a simple single-phase stream, compare mass flow multiplied by the enthalpy or approximately cpΔT change with the applied heat load.
- Account for other thermal exits.
Radiation, external convection, fixed-temperature boundaries and conductive paths can remove heat before it reaches the monitored outlet.
- For transient cases, include stored energy.
During warm-up, input heat is split between heat leaving the domain and increasing the internal energy of solids and fluids.
Build a quick thermal baseline
Estimate convection, heat rate and temperature difference before debugging the full CHT model.
Likely cause groups
Heat-source definition
Wrong magnitude, wrong region, wrong sign or confusion between total power and volumetric generation.
Material properties
Thermal conductivity, heat capacity or density entered in wrong units or treated as constant when strong temperature dependence matters.
Interfaces / contacts
Missing conjugate interface, accidental adiabatic contact, duplicate boundary, wrong contact resistance or non-conformal coupling problem.
External thermal boundaries
Fixed temperature, convection coefficient, ambient temperature or radiation settings create an unintended heat sink/source.
Fluid-side heat transfer
Wrong mass flow, turbulence treatment, near-wall resolution or recirculation changes the effective convective resistance.
Solid resolution
Thin walls, thermal contact layers or steep gradients are under-resolved, smearing the conduction path.
How to diagnose the thermal error
- List every energy input and output explicitly.
Do not rely on memory of the setup tree. Create reports for each relevant thermal boundary and source.
- Check temperature jumps across interfaces.
A discontinuity can be correct if contact resistance exists, but suspicious when perfect thermal contact is intended.
- Plot heat flux through the thermal path.
Follow energy from source → solid → interface → fluid → outlet. The first unexpected change localizes the issue.
- Check flow rate and outlet enthalpy.
If the fluid carries most of the heat away, its energy rise should be consistent with the applied power.
- Inspect near-wall mesh and y+.
When convection dominates resistance, inaccurate wall treatment can shift the predicted wall temperature and heat-transfer coefficient.
- Run a simplified thermal-resistance model.
Compare CFD temperature differences with an order-of-magnitude conduction/convection network.
Fix order
- Correct heat loads and material units.
These are high-impact errors and easy to verify independently.
- Repair interfaces and boundary ownership.
Confirm every solid-fluid contact is coupled exactly as intended.
- Match flow conditions and thermal exits.
Check mass flow, ambient conditions, radiation assumptions and prescribed temperatures.
- Improve mesh where thermal gradients occur.
Resolve thin solids, boundary layers, jets, recirculation and contact regions rather than refining uniformly.
- Then assess model-form sensitivity.
Investigate turbulence, property dependence, radiation or other advanced physics only after the energy network is internally consistent.
Common mistakes
- Using W/m³ when the intended value is total watts.
- Applying a fixed temperature to a surface that should exchange heat naturally.
- Forgetting a heat-loss path through a support, housing or external boundary.
- Expecting outlet cpΔT to equal total input heat during a transient warm-up.
- Ignoring thermal contact resistance when comparing with hardware.
- Trusting numerical convergence without checking a global energy balance.
Related Abecator resources
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