Best Practices Overview for Electronics Thermal Simulations - - PowerPoint PPT Presentation

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Best Practices Overview for Electronics Thermal Simulations - - PowerPoint PPT Presentation

Jan 17, 2023 169 likes •390 views

Best Practices Overview for Electronics Thermal Simulations STAR-CCM+ Simulation Process Geometry Preparation Results Mesh Solution Materials Conditions STAR-CCM+ Electronics Thermal Seminars http://www.cd-adapco.com/webcasts (Industry =

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Best Practices Overview for Electronics Thermal Simulations

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Geometry Preparation Mesh Materials Conditions Solution Results

STAR-CCM+ Simulation Process

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http://www.cd-adapco.com/webcasts (Industry = Electronics)

STAR-CCM+ Electronics Thermal Seminars

Natural convection series

– Best practices – Small internal air gaps – Radiation

Forced convection series

– Best practices, part 1 – Best practices, part 2 – Complex heat sinks – Geometry preparation

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  • Assumes 3D-CAD → Parts → Regions
  • Composite parts

Geometry

  • Pre-defined parts-based mesh (PBM) operations

Mesh

  • Air (ideal gas or Boussinesq)
  • Solids (common in electronics)

Materials

  • Pre-defined boundaries
  • Forced & natural convection
  • Field functions for ambient temperature & altitude

Conditions

  • Segregated flow & energy with under-relaxation
  • Gravity & radiation (natural convection)
  • Stopping criteria

Solution

  • Temperature report
  • Geometry & mesh scenes
  • Temperatures with velocity vectors on section planes

Results

STAR-CCM+ Template Simulation File

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Solids

– Eliminate mechanical connectors (screws, rivets, springs, etc.) – Fill holes – Simplify individual parts – Sheet metal modifications – Eliminate interferences – Fill undesired gaps

Best Practices: Geometry Preparation

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Air

– Internal: Fill the empty space – External

  • Natural: Sphere or hemisphere
  • Forced: Short inlet, extended outlet

– Tools (3D-CAD): Extract Internal / External Volume, Boolean

Best Practices: Geometry Preparation

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Best Practices: Geometry Preparation

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Best Practices: Geometry Preparation

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Ideally: Conformal polyhedral mesh

– Strongly recommended for natural convection (because of radiation) – Good for forced convection

Option: Polyhedral (conformal) air, trimmed (non-conformal) solids

– Suitable for forced convection

Part-Based vs Regions-Based

– Preference – Conformal thin mesh not yet available with PBM

Typical mesh: 500,000 – 5,000,000 cells

Best Practices: Meshing

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Best Practices: Meshing

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Air

– Ideal gas with temperature- varying properties always suitable – Boussinesq sufficient for natural convection

Solids

– Isotropic solids – Orthotropic solids (e.g. PCBs)

  • Separate continua
  • Properties in the region
  • Typical PCB: kplanar ~ 10 W/m-K,

kthrough plane ~ 0.5 W/m-K

– Components

  • Can use contact resistances on

interface to model as 2-resistor.

  • Otherwise aluminum oxide (k ~ 25

W/m-K) common.

Best Practices: Materials

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Heat sources

– Temperature on all inlets & outlets – If no air surrounding the enclosure in the model (common in forced convection), to model heat loss to the ambient add convection on boundary:

  • External natural convection: h ~ 5 – 10 W/m2-K
  • External forced convection: h > 20 W/m2-K

– Heat power on all dissipating components*

Best Practices: Conditions

Heat Electrical power supplied Component (e.g. IC, IGBT, MOSFET, LED,…) Electrical power delivered RF energy, visible light

  • “Wall power”
  • Max power (power budget)
  • Measured power?
  • Duty-cycled?
  • What is the efficiency?
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FORCED CONVECTION Flow inlet Flow outlet Flow “pushed” into the system

  • Specified positive flow speed

velocity), positive pressure, positive mass flow rate, or fan pressure jump

  • Ambient temperature
  • Pressure outlet (0 Pa)
  • Ambient temperature (for any

reverse flow) Flow “pulled” through the system

  • Stagnation inlet (0 Pa)
  • Ambient temperature
  • Specified negative flow speed

velocity), negative pressure, negative mass flow rate, or fan pressure jump

  • Ambient temperature (for any

reverse flow) Fan inside the system: Internal Interface fan +

  • Stagnation inlet (0 Pa)
  • Ambient temperature
  • Pressure outlet (0 Pa)
  • Ambient temperature (for any

reverse flow)

Best Practices: Conditions

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Internal Interface Fan

– Only the circular or annular faces used as boundaries in fan definition – Flow direction: From Boundary-0 to Boundary-1 (Swap Boundaries on the interface as needed) – Fan curve

  • Define in the fan interface as a polynomial, OR
  • Input fan curve to Tools > Tables & then select the curve.

Best Practices: Conditions

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Natural Convection: Conditions on the exterior air boundary

– Convection

  • Stagnation Inlet (0 Pa)
  • Total temperature = Ambient temperature

– Radiation

  • Boundary transparency = 1.0
  • Radiation temperature is specified in the air continua

– Inside a room: Radiation temperature = wall temperature – Outdoors: Turn on solar if device exposed to the sun during the day, at night Radiation Temperature = sky radiation temperature

Best Practices: Conditions

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Solvers > Segregated Energy

– Fluid Under-Relaxation = 0.99 (default is 0.9) – Solid Under-Relaxation = 0.9999 (default is 0.99)

Best Practices: Solution

Stopping Criteria

– Often convergence in 300 – 500 iterations. – Observed residuals (non- normalized)

  • Energy residual < 1E-5
  • Momentum residuals < 1E-8

– Convergence requires more iterations for a finer mesh.

Scalability

– For typical size scales well to ~8 cores. – I typically run with 2 or 4 cores.

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Best Practices: Results

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Best Practices: Results

Rthermal = (Tcenter of base – Tambient) Heat power

Report (expression) from field functions:

($ThermocoupletemperatureReport - $Tambient_K)/$Heat_power

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Natural Convection

– Best practices: http://www.cd-adapco.com/webinar/electronics-best-practices-session-1-

simulating-natural-convective-airflow-electronic

– Small gaps: http://www.cd-adapco.com/webinar/electronics-best-practices-session-2-natural-

convection-analyses-thin-air-gaps

– Radiation: http://www.cd-adapco.com/webinar/electronics-best-practices-session-3-natural-

convection-analyses-thermal-radiation

Forced Convection

– Best practices, part 1: http://www.cd-adapco.com/webinar/best-practices-forced-convection-

simulations-series-1-part-1

– Best practices, part 2: http://www.cd-adapco.com/webinar/best-practices-forced-convection-

simulations-series-1-part-2

– Modeling complex heat sinks: http://www.cd-adapco.com/webinar/efficient-modeling-

complex-heat-sinks-series-2-part-1

– Geometry preparation: http://www.cd-adapco.com/webinar/geometry-preparation-electronics-

thermal-simulations-series-2-part-2

More Information: Web Seminar Recordings

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Thank you!

ruben.bons@cd-adapco.com / +1-760-536-8122