Designing a Better Street Luminaire Heatsink with Thermal Simulation

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Without simulations, the R&D team would need at least 6 to 10 physical prototypes, and the team still wouldn’t be able to guarantee they had the best solution. Empirical testing would have cost a minimum of three additional months and at least 500 EUR in prototype costs. By using FloEFD, they cut thermal simulation and management time down to one month.

The team performed the series of simulations in FloEFD based on a parameterized CAD model from CATIA V5, a solid modeler. Their design team had created the original model in CATIA. Because they’re using FloEFD V5, a concurrent CFD product, the model is immediately available for analysis preparation within the CATIA environment.

Figure 1: Thermal simulation of the original heatsink design, showing airflow in FloEFD.
(Image source: BUCK R&D)

Engineers can then use the wizard to prepare a solid model by applying loads and boundary conditions and finally meshing the model before analyzing it. By designing the heatsink model in CATIA as a mechanical model and simulating with FloEFD from the thermal standpoint, the thermal properties can be attached to all the shapes that make the heasink, and the LED set as a source of heat.

After the design optimization of the heatsink, they obtained data on the number, height, and thickness of the fins that would provide the best possible heat dissipation for the LED modules.

As part of the optimization process, they wanted to test the effect of dust accumulation over the top of the heatsink on cooling. Dust/dirt deposition reduces the available surface area for heat transfer, creates additional thermal resistance for heat to get to the ambient, and reduces the amount of airflow that can travel between the heatsink fins (and remove heat). In the simulation, they added a component to represent “dirt/dust” placed over the top of the heatsink.

The desired self-cleaning effect requires relatively high velocities (by natural convection standards) to minimize dirt deposition. This can be simulated using the FloEFD particle study feature. The particle study feature in the simulation software permits injection of virtual particles with a material diameter and mass into the fluid flow to determine where particles will accumulate and erode surfaces. This lets the engineers visualize where dirt will fall out of the flow (or not, which is preferable).

Figure 2: With optimization in the thermal simulation software, the team was able to verify quickly and reliably whether the dirt deposition on the heatsink could lead to malfunction while the luminaire is working.
(Image source: BUCK R&D)

The use of thermal simulation software significantly shortens the development time of a product and provides details difficult to obtain otherwise. This enabled the team to design a new model of heatsink, with vertical fins, which features a higher airflow and a self-cleaning effect that prevents dirt deposition (Figure 3).

The self-cleaning heatsink has a similar mass as the extruded one, but it doesn’t need as much additional work and time on the milling machine. The simpler manufacturing process resulted in not only cost savings, but also significantly reduced maintenance, and longer product life.

With the addition of the new FloEFD LED module, they were able to obtain reliable results effortlessly. The values from the FloEFD simulations were within 3% of the results obtained by measurements on the physical model.

Figure 3: Thermal simulation of the new heatsink design with dirt deposition.
(Image source: BUCK R&D)

The LED module simulates an LED component as a compact package based on either a simple two-resistor model or an advanced measurement-derived model. The detailed model includes a unique solution to the challenge of designing solid state lighting and allows thermal and photometric models of LEDs obtained from testers to be used in FloEFD under constant current operating conditions.The model correctly accounts for power that is emitted as light when calculating the heat dissipation in the LED, with the temperature, power consumption, and light output (hot lumens) predicted by the software. A starter pack of commercially available LED models is provided as part of the module, which also includes the ability to account for absorption of radiation in semi-transparent solids such as a lens in front of the LED, and ability to simulate a PCB as a compact model with biaxial thermal conductivity.

A company-specific LED model can also be input and simulated by specifying forward current for the LEDs; the software calculates the correct thermal heating power and a physically validated operating temperature. It allows building of an accurate thermal radiation analysis that is capable of simulating absorption of radiation in semi-transparent solids such as glass as well as taking into account effects as refraction, specular reflection, and wave-length dependency (spectrum properties of the radiation). Light quality from the LEDs can also be calculated to see whether they meet the design goals for light output and uniformity.

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LED Technology

Designing a Better Street Luminaire Heatsink with Thermal Simulation