Beat the Heat

By Dipankar Choudhury, Vice President, Program Management, ANSYS

All products and processes have a thermal comfort zone — a range of temperatures in which they work most efficiently. Whether this temperature is in the arctic range (for instance, an instrument cooled by liquid nitrogen) or closer to an inferno (like the inside of a gas turbine combustor), understanding your product's thermal sweet spot is important to your design efforts. Engineering simulation can provide the knowledge you need for the most efficient design and operation of your thermally sensitive devices.

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Beat the Heat

Heat is generated during the normal operation of many products. Sometimes, this heat needs to be removed to prevent damage, and sometimes equipment needs to be kept warm enough to work correctly. Thermal management is the science of handling heat in the most efficient manner for a specific application.

Controlling the temperature of equipment and devices is important in many industries, including aerospace (satellites, anti-icing systems, turbines); automotive (exhaust systems, drivetrain, disc brakes); consumer products (appliances, mobile and wearable devices); electronics (graphics cards, welds, computers); and process equipment (pipes, boilers, condensers). There are too many examples to list.

Failure to properly manage heat can be costly because it can lead to inefficiency in energy use, sub-optimal performance, and even equipment failure, with potential safety and health implications for workers nearby. Optimal performance may depend on maintaining temperature to sustain a chemical reaction, or avoiding temperatures at which materials become brittle. Turbine blades that deform due to thermal effects do not operate as efficiently as those that retain their intended shape. Repeated thermal deformations due to temperature cycling can cause cracks, leaks or total failure in pipes, tanks and other containment vessels. Predicting thermal effects and deformations is key to ensuring the safe and efficient performance of this equipment.

This issue of ANSYS Advantage contains an interview with Alan Wong, president and chief executive officer of Aavid Thermalloy, which designs thermal management solutions for a wide range of consumer products. Their solutions are commonly found in personal computing products, such as desktops, laptops, printers and video game consoles, as well as in servers, network devices, instrumentation and consumer electronics. See Cooling Trend for Alan Wong's high-level overview and insights into the thermal management field.

THE SIMULATION SOLUTION

Engineering simulation is essential to predict thermal effects in many types of products and processes. For less-complex systems, single physics models suffice. For example, engineers at Nebia used ANSYS fluid dynamics software to simulate the mist of small water droplets flowing from their revolutionary water-saving showerhead. Tiny droplets release their heat too quickly, but Nebia engineers found a way to provide customers with a hot shower using ANSYS thermal modeling. See Full Steam Ahead for their story.

Similarly, Mechanical Solutions, Inc. and Purdue University researchers used ANSYS CFD simulation to evaluate novel turbine-blade cooling channel geometries, resulting in development of an innovative geometry that outperforms existing designs. See Weaving In and Out.

And DuPont engineers were able to determine the junction temperature of an LED — which can't be measured physically because the junction is located deep inside the chip — using ANSYS simulation. This enabled them to produce guidelines for developing reliable LED substrates for lighting manufacturers that require a broad range of configurations. Read more about their work on Lighting the Way.

So single physics solutions are viable for some thermal management challenges. However, most thermal management problems do not occur in isolation or align themselves neatly in a single discipline, and multiphysics solutions are often needed.

Exhaust gas recirculation cooler simulation

Exhaust gas recirculation (EGR) coolers reduce emissions from engines by helping to decrease in-cylinder temperatures. EGRs are subject to thermo-mechanical fatigue from cyclic thermal and mechanical loading, resulting from complex physical interactions. By using multiphysics simulation within an integrated platform, engineers can reliably design this important engine component early in the development cycle.

START WITH TRUSTED SINGLE PHYSICS SOLVERS

Fortunately, extending single physics simulations to multiphysics capabilities to provide deep insight into thermal management is straightforward, even if you have never worked with multiphysics before. Strong single physics solvers are the key. Just as a chain is only as strong as its weakest link, a multiphysics simulation is only as strong as its weakest solver. So why not just use the strongest solver available for each step of your simulation? ANSYS has best-in-class physics solvers for fluids, thermal, structures and electronics, as demonstrated by a history of simulating complex applications requiring deep physics across many industries. Additional capabilities, like HPC scalability and accuracy, allow you to choose the method that provides the level of fidelity you need, taking your internal processes, available resources and project timelines into account.

Most thermal management problems do not occur in isolation or align themselves neatly in a single discipline, so multiphysics solutions are often needed.

ADD AN AUTOMATED MULTIPHYSICS SIMULATION PLATFORM

With ANSYS Workbench, automated setup and workflows for multiphysics empower you to perform multiphysics simulations quickly and easily. Workbench enables you to graphically connect single physics solvers to perform multiphysics simulations with simple drag-and-drop functionality. Being able to visualize your workflow lets you confirm that your process is viable before you start the simulation. Once linked together in Workbench, all simulations share common tools, like geometry, meshing, parameterization and post-processing.

But, by far, the real power of ANSYS Multiphysics lies in the automated data exchange and solver coordination that streamline multiphysics simulations. Workbench performs fast, accurate, automated data exchange between meshes created for different physics using the connections you have established, and coordinates solvers for smooth coupled simulations. Eliminating the need to run a single physics simulation and manually transfer data to the next solver saves time and money, and reduces the chance of operator-induced error.

Fin and tube compact heat exchanger simulation
Fin and tube compact heat exchangers (FTCHEs) are commonly used in air-conditioning systems, automotive cooling systems and other thermal engineering applications. To increase efficiency, ANSYS Fluent was employed to increase heat transfer with moderate pressure loss compared to previous techniques.

By far, the real power of ANSYS Multiphysics lies in the automated data exchange and solver coordination that streamline multiphysics simulations.

CHOOSE ONE-WAY OR TWO-WAY MULTIPHYSICS SIMULATION

Multiphysics connections come in two varieties, with your choice depending on the complexity of the problem you are trying to solve: one-way data transfer and two-way co-simulation. One-way, sequential simulations allow temperature and heat transfer coefficient data to be transferred from one simulation to another, say from fluid to structural. They are useful in situations where the fluid flow has some effect on the structure, but not vice versa. In this case, the CFD simulation would be run first, and the results would automatically be transferred to the structural simulation solver. The multiphysics simulation would end after the structural solver completed its calculations, and the results would be used to inform the design of the equipment in question.

Two-way coupled analyses are more complex and resource-intensive. They involve the passing back and forth of calculated results between two solvers, and are used in situations in which flow affects structure, and the structural change then affects flow. Like one-way simulations, they benefit from automated data transfer of temperature and heat transfer coefficient data, as well as information about mesh deformations. They also benefit from advanced solver coordination.

Engineering simulation using single physics or multiphysics solutions is essential in overcoming thermal design challenges.

ONE-WAY MULTIPHYSICS SOLUTIONS

For thermal management, many engineers start with extended single-solver capabilities. They gain more insight using one-way couplings between products and save two-way coupled simulations for when tightly-coupled complex analysis is truly required.

Kyungshin, a manufacturer of automotive electronics systems, improved the thermal management of its smart PCB junction using one-way ANSYS multiphysics simulation. They started with ANSYS SIwave to predict where high temperatures could arise based on current density and power dissipation. These results were automatically fed into ANSYS Icepak to identify where the PCB was overheating. For more details, see the article on Keeping the Block Cool.

Similarly, researchers at Tianjin University and Purdue University coupled PID controller simulations of ANSYS Simplorer with the thermal solver of ANSYS Fluent to develop a more efficient environmental control system (ECS) for passenger comfort in aircraft. See Climate Control Gets Elevated.

TWO-WAY MULTIPHYSICS SOLUTIONS

In two-way thermal management simulations, data is transferred from one solver to the other multiple times during the simulation. The flow field thermal characteristics may be evolving, and the impact of this evolution on the temperature of adjacent structures is of interest. Or perhaps heat is being generated in the solid object, and you are interested in how fast the surrounding fluid can remove the heat.

This issue includes a study we did at ANSYS to predict warping and dynamics of PCBs under thermal loading. The focus of this work was a bidirectional multiphysics workflow between ANSYS SIwave and ANSYS Icepak. The details start on Taking the Heat.

ANSYS simulation of CNG vehicle regulator
Image courtesy Parker Aerospace.
Comprehensive conjugate heat transfer analysis of natural gas expansion in a CNG vehicle regulator using ANSYS CFD
Rotary engine cooling
Image courtesy PFman.
Simulation of a pair of coolant water jackets to replace the original air-cooling system in a new multipurpose rotary engine
 

CONCLUSION

Thermal management is a challenge for most products and processes being developed today. As this issue shows, engineering simulation using single physics or multiphysics solutions is essential in overcoming these design challenges, and ANSYS can help you every step of the way.

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