LEDs are increasingly used in automobile headlights because of their small size and reduced energy consumption. But, though they are much more energy efficient than traditional headlights, most of the energy required is converted to heat rather than light — 70 percent, in fact. This presents a challenge to engineers and designers because, since they are semiconductor-based, the diode junction of LEDs must be kept below 120 C. Maintaining temperature below this limit typically involves cooling airflow from an electric fan combined with heat sink fins.
Engineers at Momentive Performance Materials in Strongsville, Ohio, used to spend weeks building and testing a single physical prototype of a heat sink, and it often took many prototypes to arrive at an optimal design. They recently leveraged ANSYS CFD solutions to test a single virtual design in only 15 minutes. By performing heat flow simulations early in the design process, they were able to greatly reduce the development cycle while improving LED performance and cutting costs.
Using a new material they had developed called thermal pyrolytic graphite (TPG), which has four times the thermal conductivity of copper at one-fourth the weight, was one key to this success. However, finding the best structural design to maximize heat dissipation required digital exploration. Digital exploration allows design teams to fully investigate a design space using simulation. Designers and engineers can virtually test the performance of many more designs than would be possible using the traditional build-and-test method, and to arrive at an optimal design faster.
CFD simulations showed the Momentive engineers the bottlenecks for cooling and the determined the steps necessary to protect the TPG from moisture and abrasion. They were able to test new geometries for the heat sink base to increase its surface area and dissipate more heat. Simulation-based digital exploration helped them to explore a wide range of new base geometries in a short time and arrive at an optimal design that increased thermal conductivity by 29 percent. Virtual prototyping using simulation enabled Momentive engineers to wait until they had a viable design before they produced a physical prototype.
The resulting new heat sink base and fin design enabled a large increase in input power to the LED, improving brightness without raising the LED junction temperature. It also eliminated the need for an electric fan for air cooling — a major cost savings. The huge improvement in headlight performance at lower energy consumption helped Momentive to go to market quickly with a superior product.