White Papers
State of the Art in Solid State Lighting Thermal Design
Unlike incandescent lighting that relies on heat to cause a filament to glow and produce light as hot black body, light emitting diodes (LEDs) are semiconductors and as such must be kept cool. When LEDs produce light, heat is a by-product. Heat generated in an LED increases its temperature. As the LED’s temperature increases, the light output decreases, the light changes color, and the lifetime of the LED reduces. Temperature adversely affects both the functional performance of the LED and its longevity. As a consequence, thermal management has become the most predominant issue in solid state lighting (SSL) design.
State of the Art in LED Thermal Characterization
Using the JEDEC standard static test method for transient thermal measurements in accordance with JESD51-14 and CIE 127-2007 has increased the level of accuracy in light-emitting diodes (LEDs) thermal characterization. These higher standards have resulted in increased customer confidence and market share. In compliance with these standards, the Mentor Graphics T3Ster system can complete more than 100 LED thermal measurements in a single day, and it is the most accurate. The T3Ster post-processing software fully supports the latest thermal testing standard (JEDEC JESD51-14) for junction-to-case thermal resistance measurement. This paper discusses the importance of more accurate thermal characterization to the rapidly evolving marketplace and how the T3Ster and TERALED systems are meeting this challenge for lighting manufacturers and their customers.
Thermal transient measurement of high power bipolar transistors: chances and challenges
Transient thermal testing becomes more and more important for discrete power transistors (BJTs), IGBTs and MOSFETs. While reaching proper power levels is relatively simple for the two latter, measuring BJTs is more challenging. Existing standards such as the JEDEC JESD51 and MIL-STD-750 give general guidelines on their transient measurements, i.e. powering and transient recording. However, the typical realization of the standard needs two high current power supplies with fast switching capabilities. Furthermore, BJTs operate as high frequency amplifiers in the circuit scheme needed for thermal testing, which may cause unwanted oscillations. This paper proposes an exact realization of the existing standards with a more cost effective instrumentation and better stability. Also a small add-on to the T3Ster line facilitating the standard measurements is presented in a case study.
Optical Characterization of Power LED
Besides their electrical properties the optical parameters of LEDs also depend on junction temperature. For this reason thermal characterization and thermal management play important role in case of power LEDs, necessitating both physical measurements and simulation tools. The focus of this paper is a combined electrical, thermal and optical characterization of power LED assemblies. In terms of simulation a method for board-level electrothermal simulation is presented, for measurements a combined thermal and radiometric characterization system of power LEDs and LED assemblies is discussed.
Optimizing Gas Mixing Processes with CAD-Embedded Engineering Fluid Dynamics Simulation
Best practices for CFD analysis in gas mixing with new CAD-embedded tools.
Understanding electronic IP: common issues and how to find them
Using IP blocks in designs requiring DO-254 compliance is becoming more popular as a way to reduce costs and schedules. However, the use of IP comes with its own problems and pitfalls. A good methodology to better screen this IP before its usage can significantly reduce unexpected problems and lower risk, especially on safety critical designs. The most important soft IP screening technologies are automatic formal check and clock domain crossing analysis. This paper will provide a background explanation of IP, including: what types exist in the market; caveats to their usage; and suggestions to better analyze IP before it is used in a design, thus lowering risk and improving product safety. (Note: This paper does not address IP compliance issues. For more information on that topic, please refer to the DO-254 User Group paper "Use of Intellectual Property (IP) Cores in Airborne Electronic Hardware".
The ROI of Concurrent Design with CFD
Research from Aberdeen's Q1 2011 business review has found that the top strategy for manufacturers, reported by 46%, is to improve business execution. What does this mean for new product development? A look at Aberdeen's October 2010 "NPD - the 2011 Growth Imperative: Optimizing Speed and Cost in New Product Development" report reveals the top challenges that must be addressed to accomplish this.
What They Didn’t Teach You in Engineering School About 3D Pressure Drop Analysis
Computational Fluid Dynamics (CFD) analysis is no longer a discipline reserved only for highly trained practitioners. A new class of CFD analysis software known as “Concurrent CFD” is proving to be greatly effective at performing pressure drop analysis, enabling mechanical engineers to accelerate key decisions at their workstations, without the need for CFD specialists. Embedded into the MCAD environment, this intuitive process allows designers to optimize a product during the design stages, reducing manufacturing costs across a wide range of mechanical designs and systems.
Beer Fridge: A Personal Journey
Mini-fridges, commonly filled with beer and the occasional moldering sandwich, have become a ubiquitous fixture in college dorm rooms and office break areas. But for some reason they never seem to cool their contents as well as their full-size cousins in the kitchen. This paper, based on a series of blog entries, presents a light-hearted look at the problem and offers a solution. In doing so, it demonstrates some practical thermal analysis methods using Mentor Graphics FloTHERM and proves that thermal simulation can help engineers design better products for consumers.
Enhanced Turbulence Modeling in FloEFD
FloEFD is a unique CAD-embedded general purpose concurrent CFD software package largely automated to minimize the specialist expertise required to operate traditional CFD software. CAD-embedded CFD must simulate complex industrial turbulent flows with heat and mass transfer without simplifying the highly complex geometries. FloEFD is a mature code with over 10 years of commercial presence and a thousand man-years of development effort behind it. It's turbulence capabilities have been validated against some classic industrial CFD cases. It utilizes a modified k-ε two-equation turbulence model designed to simulate accurately a wide range of turbulence scenarios in association with its pioneering immersed boundary Cartesian meshing techniques that allow accurate flow field resolution with low cell mesh densities.
The classical two-equation k-ε empirical model for simulating turbulence effects in fluid flow CFD simulation is widely used and considered reliable for most industrial CFD simulations and it requires the minimum amount of additional information to calculate the flow field. In FloEFD the k-ε model is used with a range of additional empirical enhancements added to cover a wide range of industrial turbulent flow scenarios (such as shear flows, rotational flows etc.). For instance, damping functions proposed by Lam and Bremhorst for better boundary layer profile fit when resolving boundary layers with computational meshes have been added. This is coupled to a unique Two-Scale Wall Function (2SWF) treatment. This two-scale approach allows FloEFD to overcome the traditional CFD code restriction of having to employ a very fine mesh density near the walls in the calculation domain.
Advanced Immersed Boundary Cartesian Meshing Technology in FloEFD
For the numerical simulation of Navier-Stokes equations, the choice of the mesh type plays a significant role. Comparative calculations on different mesh types illustrates that the best simulation precision, characterized by minimum Local Truncation Error (LTE), is obtained on Cartesian meshes. For the boundary representation the Immersed Boundary (IB) approach, which does not require a boundary-conforming mesh, is used. Use of Cartesian meshes together with Immersed Boundary approach makes it possible to efficiently: minimize approximation errors; build operators with good spectral properties, so that robustness of method is guaranteed; speed up the process of grid generation; and make grid generation robust and flexible. Many other CFD methods require a mesh that fits the boundaries of the computational domain and often complex internal geometries. The body-fitted grid generation used is time-consuming, often requiring manual intervention to modify and cleaning-up the CAD geometry as a pre-requisite.
To implement the IB approach efficiently in FloEFD, a number of issues needed to be resolved: approximation of the governing equations in cut-cells that contain the solid-fluid interface; capture of boundary layers effects irrespective of boundary layer thickness using a Two-Scale Wall Functions (2SWF) approach (see Mentor Graphics Corp., 2011); automatic mesh generation with automatic detection of initial mesh settings (octree-based mesh structure); and Solution Adaptive Refinement (SAR).
Test cases given in this paper represent a small selection of our validation examples that illustrate the IB approach precision and flexibility of FloEFD meshing technology in the wide range of industrial examples of geometry and physical formulations.