Automotive & Electric Vehicles (EV)

Lithium ion batteries for commercial use pose barriers due to safety, cost related to cycle life, low-temperature performance, and thermal effects in the battery (overcharging can result in explosion).  Better battery thermal management systems (BTMS) are being explored, with both active cooling (fans and liquid) and passive cooling (Phase Change Materials (PCMs)).  Thermal conductivity enhancement of these PCMs with carbon based nanoparticles was investigated.​

Experimental

Investigating the thermal conductivity enhancement of PCMs for batteries was performed with a Modified Transient Plane Source sensor from C-Therm.  Testing was done before and after phase change (in solid and liquid state) of pure wax, 5% loaded and 10% loaded samples.

Thermal conductivity of PCM samples as a function of mass fraction of nanoparticles and temperature

Results and Conclusion

Significant increases in thermal conductivity were observed, going from 0.25 W/mK to as high as 2.75 W/mK.  Using 2mm layer of 5% and 10% weight loading, the PCM can maintain battery temperature 1.2 and 1.9℃ lower, compared to pure paraffin.

Temperature distribution in the module with 3 mm thick pure wax (left) and 1 mm wt% NePCM (right) at the end of driving cycle

This experiment was carried out using C-Therm’s Modified Transient Plane Source sensor.

The undeniable importance of braking power to the safe operation of an automobile has led to on-going research into the optimal properties of materials for modern braking systems. This note shows how the C-Therm Trident Thermal Conductivity Analyzer system is employed to effectively measure the thermal conductivity (k) of a wide range of sample types using its multi-sensor options.

In its simplest form, brakes work by first converting the kinetic energy of your vehicles motion to heat and then dissipating that heat to the atmosphere. The major component of importance in modern braking systems are the brake pads. Brake pads were traditionally made from pure metals due to their high thermal conductivities resulting in their uncanny ability to resist thermal stress and dissipate generated heat. Unfortunately, metal-based components can carry a significant weight and in-turn lower overall efficiency. Today, most brake pads have since been replaced by semi-metallic, ceramic or organic based composites to overcome the drawbacks of pure metals. A brief overview of the various brake pad types can be seen in Table 1, below.

Table 1: Brake Pad Types and Considerations

While there are many considerations to take into account (see above), ultimately stopping power can be most strongly related to thermal conductivity. To illustrate it’s ability to accurately and precisely test various brake pad materials, a C-Therm Trident Thermal Conductivity Analyzer was utilized with the Transient Plane Source  (TPS)  configuration operating in accordance to ISO 22007-2 to compare semi-metallic to ceramic brake pads (see Figure 1 & 2). Both sets of pads are base level units (<100$), however it should be noted the ceramic pads were ~20% more expensive. For testing of these samples the reported results are the average of five tests.

Figure 1: Semi-Metallic Brake Pad

Figure 2: Ceramic Brake Pad

Figure 3: Thermal Conductivity of Semi-Metallic and Ceramic Brake Pads

As can be seen from figure 3 above, the semi-metallic pads resulted in thermal conductivity of 4.36 W/mK, whereas the ceramic pads were only about 2.79 W/mK (44% difference). Trident’s TPS configuration was the optimal way to test these brake pads due to the hard and rigid nature of the samples. While not reported herein, it should be noted that C-Therm’s TPS module also simultaneously collects and displays diffusivity data for applications where both are required. All testing had a precision of better then 1.7%. The above results clearly demonstrate the superior thermal properties of semi-metallics over ceramics as well as coming in at a lower price point. Ultimately the higher thermal conductivity will result in an improved stopping performance as it can better dissipate the generate heat and lower the net thermal stress on the braking system.

Today’s need for conductive potting compounds is building the future of electric vehicle and battery performance.

Filled polymers are attractive because their properties are highly customizable, allowing engineers to design a material with the right combination of thermal and mechanical properties for the target applications. Additionally, they are lightweight in comparison to other composite materials. A filled polymer aircraft part may have a fraction of the mass a steel part would have, while retaining similar strength.

[Spanish] Vea acá el seminario web grabado con CoolMag28 y C-Therm

In thermal management, filled polymers are often used as potting compounds in electronics, to reduce thermal contact resistance and secure electrical components. Potting compounds are designed to be solid or gelatinous materials which provide structural support and physical protection of electronic components while also displacing heat and gas to prevent gas phenomena such as corona discharge. Increasingly, there is demand for potting compounds with improved thermal conductivity for better heat dissipation in high performance electronic devices. Accurate and repeatable measurement of thermal conductivity at a wide range of temperatures is a critical performance check – easily completed in the lab with
C-Therm’s Trident Thermal Conductivity Instrument.

Testing Thermal Conductivity

A great example of a filled polymer potting material is CoolMag™, designed to offer improved thermal performance relative to neat silicone potting materials. 

It is known that Conducted Heat Transfer happen as the transmission of phonons, the metal conductivity is very high thanks to its high amount of free electrons, using the right material structures with enough capacity for vibration and right lattice allow phonon transmission without electrons movements.

This is the foundation of CoolMag™28, a package of micro and nano particles with size ratios R, R/2, R/4, … R/2n increase diffusivity by using high density, high specific heat and high thermal conductivity crystals bonded by a minimum layer of a high inorganic content polymer based in SiO2 like PDMS, resulting in a solid isotropic structure.

The advantage? an isotropic structure makes the 1D problem of heat transfer from a hot point to a colder one a new 3D challenge as the hot point is now surrounded by a 3Dimensinal matrix of micro and nanoparticles transferring heat through closed surfaces (Isotherm surfaces):

Electric Vehicle Correction Choke with Potting Compound

Above: 3 Phase 7 KW, Power Factor Correction Choke set for an Electric Vehicle. The open-air part reaches 180ºC at full power with a liquid cooled plate, the part injected at low pressure with Coolmag™28 nano composite reaches 105ºC at the same conditions. 

CoolMag™ is a thermally conductive composite PDMS based elastomeric compound of encapsulant two component system, designed for Power Electronics in Automotive, especially in Electrified Vehicles with multiple functionalities:

• Heat Transfer, reduction of hot spots and minimizing average temperature of systems.
• Electric Isolation
• Mechanical protection.

Flame and fire protection (Retardant and Extinction). CoolMag™ is designed to provide thermal conductivity, electrical safety, hazard protection, mechanical and fire protection for electronic encapsulating applications.

The following graph below shows how high current Chokes with Coolmag™28 is stable at 65ºC at full load and how without CoolMag™28 reach Curie Temperature in just 300 seconds.

Inductance with and without CoolMag28 Resin

Heat transfer data was collected for thermal conductivity analysis using a C-Therm Trident Instrument with the Flex TPS (double-sided) test method, to better understand thermal performance of a sample of CoolMag™ 28. The sample specimen offers nearly tenfold improvement over the expected thermal conductivity of a neat silicone resin.

Premo Thermal Potting Compound Samples for Thermal Conductivity Testing

Properties of Thermally Conductive Potting Compound CoolMag 28

To learn more about C-Therm and the Trident Thermal Conductivity Instrument, visit www.ctherm.com or contact sales@ctherm.com

To learn more about CoolMag™ visit www.coolmag.net or contact x.mirabet@kadion.com

With much of the focus on the structural and mechanical aspects in automotive manufacturing, one can’t forget the measure of a quality vehicle also encompasses the individual’s comfortability. Simple aspects such as the “touch” sensation of the interior fabrics or panelling can all add or takeaway from the customers experience. This note shows how the C-Therm Trident system can be used to not only obtain important thermal conductivity (k), but also simultaneously obtain thermal effusivity data in the range of 5 to 40,000 Ws^1/2/m²K using the Modified Transient Plane Source (MTPS)  sensor.

Thermal effusivity plays a huge role in an individual’s perception of touch sensation and is most commonly associated with textiles (see Figure 1). While textiles have massive applications in the fashion and apparel sector, automotive interiors are also very demanding with regards to textile R&D. Aspects such as upholstery fabric, interior panelling and more are all textile heavy areas with the need for robust and precise testing of thermal effusivity properties. The ability to compare the quality perception of synthetic vs. natural materials is also of great importance to product development and is yet another area where C-Therm’s line of Thermal Analyzers can provide fast and precise testing results on a wide range of material types.

Figure 1: Honeycomb Paneling

The following is a study of various automotive companies’ overhead paneling which help to not only insulate heat, but also sound. Tests were performed on both the front (interior) and back (exterior) side using C-Therm’s Thermal Analyzer in MTPS configuration. For the testing of these samples, the panel layers consisted of at minimum an interior facing fabric, board or foam core and a backing material facing the exterior. The reported test values are the average of 3 tests per side. The effusivity test results can be seen below in Figure 2.

Figure 2: MTPS Thermal Effusivity Analysis of Automotive Composite Paneling

As can be seen from the figure above, in all cases the interior facing fabric was lower in thermal effusivity then the exterior facing backing material. This is a purposeful design as the lower thermal effusivity side, which is directly visible as the car interior, has a better ability to maintain the internal temperature. Conversely, the back-side material which has a larger thermal effusivity would be better at dissipating any external heat from the external environment. It should be noted that in this study the Hyundai panelling material resulted in the highest thermal effusivity for both the front and rear facing side.

Today’s tires aren’t made of pure rubber, but composite materials of elastomers, reinforcement fibers, plasticizers and much more which help improve performance and extend lifetime. Composite manufacturing can be complex in nature due to issues such as non-homogenous dispersion of additives which can lead to weak points. It is therefore crucial to be able to not only measure, but “map” results of interest. This note will help demonstrate the importance of thermal conductivity (k) in composite tire manufacturing and how C-Therm’s Trident system can be used to obtain that critical information using the Modified Transient Plane Source (MTPS)  sensor conforming to ASTM D7984. This proprietary, single-sided sensor is ideal for fast paced QA/QC and R&D environments with test times ranging from 0.8 to 3 seconds.

The frictional resistance between your tires and the road determine exactly how fast you can accelerate, take turns and most importantly how fast you can stop. On a very basic level, friction can be thought to come from the “surface roughness” between the two objects that are pressed in contact.  The frictional force is also proportional to the coefficient of friction (µ). As is with everything involving friction, generated heat plays a major role in overall performance. It is therefore vital to ensure a strong understanding of thermal conductivity characteristics.  For a closer look at the physics behind car tires and friction here is a detailed video from Michel Van Biezan, University of Los Angels.

C Therm’s MTPS method was employed by P. Vizureanu et al., Faculty of Material Science and Engineering at the Technical University of Iaşi (2015), with the goal of investigating the properties of reinforced rubber composites with different carbon nanotube (CNT) concentrations. The single-sided MTPS module was an excellent fit for analysis of these sample types as both thermal conductivity and effusivity are measured directly providing a detailed overview of the thermal characteristics of the samples. Various CNT loadings from 5-30% were investigated on two different substrate thicknesses (10 and 20mm). Results from this study can be seen in Figure 1, below. Data represents the average result of 10 runs per sample.

Figure 1. MTPS Thermal Conductivity Analysis of Rubber Composite Samples

Figure 2. SEM Imaging of Rubber Composite at Different CNT Concentrations¹

P. Vizureanu et al. (2015) found that an increase to CNT concentration lead to an overall increase in thermal conductivity (see Figure 1). Most notably the 30% CNT loading had the largest thermal conductivity increase of ~26% for both the 10 and 20mm samples. Further analysis found that the effective increase was not only dependant on CNT concentration, but also the geometry and distribution of the additives. It was concluded that the large increase to thermal conductivity represented a success for all applications with thermal input. Although done qualitatively (see Figure 2), this paper is an excellent example of how the non-destructive MTPS method would allow for high precision (better then 1%) thermal mapping of the samples to gain quantitative insight into the overall distribution of the CNTs.

Potting compounds are often necessary in electronics to protect finished products from vibration, corrosion, electrical discharge, and other impurities. The electric vehicle (EV) industry reflects this, as not only do they require electrically insulative potting compounds, but also materials with high thermal conductivity.

Electric Motor Component, Potting Compounds Are Necessary to Cool and Protect the Motor, and the Correct Thermal Conductivity Compound Must be Chosen

Having the right thermal conductivity is essential to ensure adequate cooling of all electrical components. Since all components will have a maximum temperature they must not exceed, thermal conductivity becomes a key parameter in the choice of potting compound. High thermal conductivity will be desired for these compounds to dissipate heat more efficiently. However, other physical properties like electrical conductivity, chemical resistance, and flexibility have to be balanced with the thermal requirement; this means that the thermal conductivity of many different compounds under many different conditions has to be known.

It is necessary to test these compounds under their expected conditions to get the most representative results, which requires adaptable and flexible testing instruments. For more information on how thermal conductivity can help you pick the optimal potting compound, contact us.