Thermal Calculations as part of Finite Element Analysis

It is critical to consider all existing risks for the future device, as well as detrimental effects from the environment before launching it into series production. To prevent the product from outer and inner hazards, the dangers are commonly specified in the operating manual. If a user follows the instructions conscientiously, then the device will serve its best and perform the implemented functions diligently. A user may, in the meantime, anticipate some "strength margin" and be pleased to see that the selected product performs in challenging circumstances far more effectively than was expected. 

In the previous article, we highlighted how finite element analysis (FEA), in particular strength calculations for a smartphone, can enhance the user experience. The calculations were based on a gadget falling from a height of 1.5 meters. Dropping is an external factor that affects a gadget. 

This article focuses on exploring the internal factors that influence the router overheating, and their relevance within the framework of finite element analysis, in particular a finite element method (FEM).

Why carry out thermal calculations?

Is it really worth conducting thermal calculations?

The answer is yes. Thermal calculations are a guarantee of safe and comfortable use of any device, as they allow the manufacturer to foresee the areas of the device that will overheat. As a result, they may feel more confident that a user will be protected from short circuits and even fire, and won't experience deformation of the device's internal and external components.

Thermal calculations, as a finite element method, are a tremendous aid to the manufacturer, as they assist in finding the optimal correlation between heat input and output in the device. This enables choosing the most suitable device dimensions as well as the most appropriate and secure options for positioning the cooling system, heating elements, and other device components.

Thermal calculations: stages

As it was mentioned in the previous article, CAE and CAD systems are the basic tools for carrying out calculations. Real experiments on actual objects have significantly decreased since the invention of computer-aided design technologies, such as FEA analysis in ANSYS. These days, thermal calculations no longer necessitate creating numerous prototypes of the device and checking how adding one component or another will affect the actual device. 

Thermal calculations begin with an examination of modeling requirements. At this point, we must decide what input data we need and what results we wish to achieve. Then the model built in the CAD system has to be prepared for the calculation. The device’s geometry must be simplified while accounting for the impact of various elements’ characteristics on the outcome of calculations.  

A solution like this speeds up calculation processing and makes it easier to build the calculation grid. However, the simplifications must be carried out correctly to maintain a reasonable level of computation accuracy. 

The next stage is setting up the environment for the model. Both the calculating grid and the contact surfaces must be configured. After that we proceed to the parameters of convective and radiation heat transmission of the product’s components, contact surfaces of all components, body and ambient temperatures, and heaters. In the end, we determine the physical parameters needed for the calculation. 

After creating and configuring the model, one may run the CAE calculation! If the results do not satisfy the laws of physics, the model can be corrected, new parameters can be specified, and the materials from which the elements are constructed can be altered.

Ways to prevent overheating of the device with FEA

Before looking at potential solutions, it's important to note that overheating might be a reasonable response from the device to external factors. Any device is vulnerable to overheating if the outside temperature is higher than what is normal for that product. Its temperature might also be directly impacted by how effectively air flows from the product to the outside environment and back. Therefore, it is critical to set conditions that are close to reality while modeling in order for convective heat transfer to accurately reflect real-world use scenarios and occasionally even some extreme ones. So, for example, if you leave the phone in a case while programs are operating in the background and in a jeans pocket, the gadget will noticeably strongly and rapidly heat up. 

As was mentioned above, the issue of device overheating and its solution will be described using the example of a typical router. The router has 5 antennas, all of which produce a strong signal. In other words, the antennas consume much power that dissipates outside. The device also supports LTE Cat 4 signal. The module put on the board consumes a maximum power of 5.5W. The router uses 20W of power in its entirety. Electronics designers, who are familiar with the heat output of the components they use, usually supply this information before commencing finite element simulation. 

We need to simplify the device's geometry in order to do quick and precise calculations. It is advised to get rid of any parts that use less than 0.5W of power because doing so will speed up the machine's calculations while also ensuring that the results are highly accurate. Ventilation holes should be made beforehand, without taking into account the router’s design. Next, we set the board component’s heat output. The outside temperature is 30 degrees. The static pressure is 0.101325 MPa.

The first step in the calculations is building the device model in the CAD system. The router model is shown in figure 1 after all the aforementioned changes have been made.

You can trace the airflow in the router in figure 2. Hot air rushes upward.

Cold air flows into the holes on the front of the router (Pic. 3).

The holes through which hot air enters the environment are seen in figure 4. Remember that every ventilation hole will change the device’s appearance, thus it’s best to incorporate an industrial designer in the product’s CAD or CAE system proof stage. In this way, the device will be not only reliable, but also comfortable to use. 

According to the thermal calculations, the LTE module is the component that overheats the most. The datasheet below states that the operating temperature range for the LTE module is -40°C to +85°C. But during the simulation, its temperature was higher than what was allowed.

It is crucial to double-check the temperature measurements of each calculation component involved in the calculation. This will enable us to identify which of them poses a specific threat to the device's normal operation.

The parts that overheat the most demand a cooling system. In our situation, a radiator would make sense because the fan uses more energy and makes more noise.

The radiator's installation had no effect on the body’s height. However, it is frequently required to alter a product's look during design, such as changing the height to accommodate a new component, or altering the arrangement of existing ones. 

Thus, the element whose warming adversely impacts the router's performance might be identified using thermal calculations. The risk can be minimized and equipment damage can be prevented with the application of this knowledge and finite element analysis.

Remember that any significant changes to the electronics and enclosure's design should be accompanied by parallel thermal calculations. As a result, there will be less need for rework, the test cycle will be shortened, and there will be fewer production-related faults.