MOTOR Magazine

A MOTOR Magazine Newsletter
August 29, 2019

Contributed by Bob Chabot
Simulation Drives Thermal Management

It verifies the reliability of modern electronic systems

Simply stated, simulation enables the quicker development and safer thermal management in the design of diverse automotive electronic devices and currents. It’s also enabling quicker introduction of these designs into the vehicles you service and repair. In particular, simulation spans the achievement of design goals associated with reliability, energy and cost efficiency, safety, and user experience.

These concurrent investigations of the capabilities and features of heat transfer mechanisms and factors within a system that cause temperature variations lead to a better understanding of the impact of design changes on a product’s performance. In addition to physics modeling capabilities, they provide the ability to turn multiphysics models into simulation applications, allowing for greater access to numerical simulation.

It’s a trend that is helping drive new and safer technologies into the vehicles you service and repair. With simulation taking an increasing role, isn’t it time to learn more about how simulation affects you?

The three modes of heat transfer — conduction, convection and radiation — can coexist and should be considered in most thermal management applications because each type of heat transfer mechanism contributes to the total heat flux in a numerical model. Simulation applications enable engineers and specialists to deploy earlier tests of designs that are more effective than past design methods. As shown in this image, simulation results can show the contributions of conductive heat flux (top left), convective heat flux (top right), and surface radiosity (bottom left) to the total heat flux (bottom right) of a heat sink. (All images — ConSol Software GmbH)

Expect Simulation to Impact Your Service and Repair
Previously, the design of electronic devices depended largely on the experience accumulated through expensive and time-consuming experimental campaigns. Today, modern electronic systems and devices rely more heavily on simulation, earlier in the design process. Technical information has not only grown in scope, increasingly it needs to be known and acted upon sooner.

Timing matters. It’s driving the use, pace and value of simulation — from general thermal management of automotive devices to engineering objectives primarily involving efficiency, safety, reliability, user experience and cost reduction. The modern design of all types of electronic devices must also consider material properties, maintaining proper current levels and avoiding thermal fatigue.

Simulations enable the accurate representation of multiphysics phenomena by properly coupling cooling and thermal behavior, such as fluid flow, heat transfer and mechanical behavior. For example, a modern heat transfer module (HTM) can be used alone or with an AC/DC module, where the effect of electric current levels can also be evaluated. It also provides a dedicated physics interface for defining the monitoring, analyze and control of models of the heat transfer and flow in fluid and solid domains. Plus it’s less expensive, quicker-to-market and more effective than past design processes.

The thermal loading in an electrical control unit (ECU) for a wiring harness can have significant impact on the performance of the entire vehicle. In this image, simulation is used to characterize thermal profiling — the heat transfer through the ECU — either to avoid overheating by confirming the feasibility of a design and part choice, or to suggest any necessary changes. This thermal profiling simulation image shows the temperature distribution throughout the rotor assembly (left) as well as the stator and rotor assembly (right). It helps optimize the wiring harness before installation with the power steering unit’s ECU. This model is also used to predict a system's thermal performance when the ECU is installed on a vehicle.

Simulations Put More Dimensions in Play
Heat transfer applications often appear together with, or as a result of, other physical phenomena. To accurately simulate such cases, the simulation model needs to account for coupled effects as well as the thermal dependence of material properties.

The geometry and material properties of a design can provide insight into heat dissipation rates and the maximum temperature tolerated by individual components. This information allows engineers and technicians to decide, from design through use once installed, whether parts are withstanding the heat load for their projected service life, or if cooling methods must be implemented or adjusted.

Consider these two applications:

  • Cooling can be achieved using strategies such as adding an airflow over a surface, embedding cooling or heating channels into a surface, or introducing a heat pipe. Heat sinks and fans are frequently used in consumer devices, while heat pumps or thermoelectric coolers are more commonly used in larger electronic and electromechanical systems.
  • For structural mechanic simulations where temperature variations induce relevant deformations that must include thermal stress. These deformations can result in the warping or breaking of small, crucial parts such as wires, bonds, and connectors. Other thermal applications include a range of part designs, temperature control methods, and manufacturing processes, such as weighing thermal loading when considering heat dissipation in small products, controlling thermal calibration for sensitive machinery or increasing the conversion efficiency of a photovoltaic cell.

Numerical simulation is also used in the development of manufacturing processes for high-end automotive battery systems. This image shows the hottest points within a lithium-ion battery cell (top) and the propagation of temperature to the cell interior over time (bottom). For example, lithium-ion batteries have shown a tendency to degrade at high temperatures, they must adhere to stringent regulations guaranteeing their ability to withstand operating temperature fluctuations. Heat transfer modeling helps determine whether high welding temperatures can create enough temperature propagation within cells to cause irreversible damage, electrolyte decomposition and capacity loss. These simulations discovered that laser welding is significantly less detrimental than tab welding.

Thermal Mechanisms for Mechanics
The design of electronic and electromagnetic systems and devices — which are increasingly present in vehicles — often requires consideration of multiple heat transfer processes and how each affects performance. Simulation is ideal for this. For example, heat generation due to Joule heating can create a rise in temperature that must be monitored and carefully controlled to avoid part failure. But it’s the mechanisms of heat transfer that form the foundation behind the modeling and simulation of thermal problems.

Conduction and convection are the primary mechanisms that govern heat transfer throughout a process or device. Conduction occurs through solid components, such as motors and wires. It can also result from the transfer of energy due to electron movements and molecular vibration and occurs in a stationary solid or fluid medium when a temperature gradient exists.

Convection occurs through fluid channels, such as open space for air flow around a heat source. For example, convective cooling at a surface can be induced by fluid motion and results from the transfer of energy by bulk or macroscopic motion of the fluid. In addition, forced or free (i.e. natural) convection is considered when the fluid flow is caused by either external means or buoyancy forces.

But in addition, radiation can also contribute to the heat transfer of a device, such as between opaque surfaces at different temperatures with or without a participating media. The net rate of radiative heat transfer from a surface is obtained by taking the difference between its emissive power and the irradiation it receives.

Show You the Money
Numerical simulation has become a widely used tool for the design of electric and electromagnetic devices. By developing realistic multiphysics models, the need for expensive and time-consuming physical prototyping can be significantly reduced — which greatly benefits the time to market and production costs of today's high-tech products.

For example, consider lithium-ion batteries, which have a tendency to degrade at high temperatures, and must be designed to adhere to stringent regulations guaranteeing their resistance to expected temperature fluctuations. While it is well known that manufacturing processes, such as welding, would greatly increase the temperature within a battery, the extent to which such elevated temperatures could propagate within and compromise a cell was not known.

Of note, it was a heat transfer simulation modeling study by researchers at NEXT ENERGY that determined high welding temperatures using some methods could create enough temperature propagation within lithium-ion cells to cause irreversible damage. When they used simulations to analyze heat transfer by conduction, they made an amazing discovery that ensures whether lithium ion cells are safe or not.

Specifically, they discovered that the temperature propagation from tab welding reached temperatures of 1100°C — enough to induce irreversible damage and create an explosion and fire. In contrast, the researchers showed that laser welding was significantly less detrimental than tab welding because it reached much lower temperatures and with care can avoid irreversible damage. That use of simulation has helped make these batteries safer.

In its relatively short history, simulation has come a long way. The use of simulation results is increasingly necessary in order to understand the underlying physical processes of any system. Simulation is also on the cusp of going beyond use by engineers, researchers and scientists. Expect shops to soon be able to use simulation to assess the state, safety and future reliability of systems on the vehicles your customers drive. So don’t be surprised when simulation enters the practices you rely on to provide vehicle service and repair.

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