This summer has been full of new developments in thermal materials. In the thermal management industry, the term thermal materials typically refers to thermal interface materials or commercial high conductivity metals like aluminum and copper. However, in recent years researchers, engineers, and designers have been busy trying to expand the portfolio of materials that can be used for thermal management.
Let’s take a look at the interesting thermal materials that sprung up this summer and see how they fall into thermal applications.
Converting Acoustic Energy into Heat
When we consider acoustics in the thermal management industry, is usually regarding the concern over noise produced by fans and pumps within the cooling system. But chemical engineers from BASF have developed a new acoustic foam material that brings a whole new spin on the relationship between acoustics and thermal energy. The new melamine resin foam, named Basotect®, is an incredibly effective sound dampener with wide reaching applications for quieting loud areas and applications. It does this through the unique ability of absorbing acoustic energy into the foam and converting it into thermal energy, generating heat. The material also acts as a thermal insulator. Between generating heat and acting as a thermal insulator, the use of this foam carries additional thermal management implications and challenges.
Thermal Possibilities of Acoustic Foam
Implications of using such a foam may alter design decisions made by engineering teams. If Basotect® is exposed to large amounts of acoustic energy, it could produce large amounts of thermal energy, which may be easily overlooked during product development. As it acts as a thermal insulator, encasing any electronics or other heat sources in or near the foam should be done with caution. Basotect’s® ability to generate and insulate heat may inadvertently create thermal buildup and cause performance issues associated with too much heat.
With such thermal materials like Basotect®, there might be some unique applications where we can convert acoustic energy to thermal energy for heating or electric generation purposes. Large swaths of the foam could be installed by airports or highways where noise is generated on a consistent basis. Installations like these could kill two birds with one stone: reduce noise and find a way to make that energy useful. Either way, there’s plenty of cool potential applications for this acoustic foam as a thermal material down the road.
Almost Black Body Surfaces
Radiation is an important part of thermal management, especially for natural convection solutions. Emissivity is a rating from 0 to 1 on how much radiation a surface can absorb or emit. The theoretical surfaces with a perfect ability to absorb and emit radiation are considered black body surfaces, which have an emissivity of 1. Surfaces that are more able to transmit heat in the form of radiation are preferred for thermal management systems since it’s a passive way to get rid of a few more watts. This is why you’ll see heat sinks in natural convection solutions anodized or powder coated since those surfaces have a much better emissivity than unfinished aluminum or copper. Anodizing a surface might only get a surface to an emissivity of 0.65 to 0.8. While that’s better than nothing, there’s still room for improvement.
Vantablack®: The Closest Thing to a Dark Abyss
A couple years ago, Surrey NanoSystems came the closest to creating a true black body surface with their Vantablack® coating. VANTA actually comes from the description of the coating: Vertically Aligned Carbon Nanotube Arrays. These vertical nanotubes are grown on a subtrate that’s enclosed in a specialized environment. The neat thing about the nanotubes being oriented vertically is that it allows electromagnetic (EM) energy, which includes visible light, to enter in the end of the tube. While the energy may be able to bounce back and forth between the internal surfaces of the tube a few times, eventually that energy will be absorbed by the molecules of the nanotube. When the molecules absorb all this EM radiation, that energy becomes energy in the form of heat that conducts down to the substrate of the Vantablack surface. This process happens for EM radiation with all ranges of wavelength coming from every direction, which is what makes this coating so close to an ideal black body.
This video by Surrey NanoSystems shows just how absorbent Vantablack is to light:
“This video shows super bright LED lights being shone onto a Vantablack coated hex pattern on wrinkled aluminium foil, compared with the previously blackest commercially available coating in the Visible and IR spectrum.”
This summer, Surrey NanoSystems developed a newer and more easily applied version of Vantablack® called Vantablack® S-VIS. Instead of growing a forest of little nanotubes on the surface, the nanotubes can be spray painted on a surface at much lower temperatures. While its predecessor absorbs up to 99.965% of electromagnetic radiation, Vantablack® S-VIS absorbs a measly 99% of all EM waves. Either way, looking into either Vantablack® surface is just staring into a dark void, even if that surface is highly contoured.
Use of Vantablack® as a Thermal Material
Vantablack’s application can extend into being a thermal material. Coating a natural convection heat sink with Vantablack® could improve it’s performance when it comes to radiating it’s heat away. Emissivities close to 1 are ideal in natural convection applications and Vantablack® fits the bill. As with BASF’s acoustic foam, any material that absorbs one form of energy must release it in another, so Vantablack surfaces could also have the potential to heat buildings or generate electricity. This could be especially helpful in space applications where you have a near limitless supply of light from the sun. Unfortunately, Vantablack® is a delicate coating, so until we can find effective ways to protect its surface without severely diminishing its properties, these thermal applications are mostly theoretical.
Built in Thermal Management
3D printing is a hot topic these days. Not only are we seeing the pallet of printable materials expand, but the properties derived from 3D printed structures are creating new opportunities and areas of research. Students at Delft University of Technology and Eindhoven University of Technology in the Netherlands are creating a new structure that could change how homes are built and how they regulate heat. Their Spong3D project has generated a 3D printable structure that combines two separate systems into a single unit to both store thermal energy and help regulate the passage of heat through the wall.
Spong3D utilizes both a liquid and air within the same structure for a few purposes: the air acts as a natural insulator, especially when encapsulated and the liquid can be moved to transfer heat, but it can also be used as a thermal mass to help store heat. In this manner, heat captured by liquid in the summer months can be stored in the liquid and released on a particular side of the structure when needed. Without the key benefits of 3D printing, such an integrated and complex structure would not be feasible. Leak-tight, quick and economical production of structures like Spong3d are possible with the latest developments within the 3D printing industry.
Spong3D as a Thermal Management Solution in Cold Climes
Outdoor electronics may be able to benefit from a technology like Spong3d embedded in its enclosure. Subfreezing temperatures make electronic startup a delicate process, especially when heat pipes or vapor chambers are involved. Heat sources can heat up, melt local liquid in the heat pipe, and vaporize before the rest of the cooling solution has a chance to heat up. When the vapor travels away from the immediate area of the heat source, it comes in contact with freezing surfaces and condenses, like it typically would. But since the rest of the heat pipe is frozen, the condensed fluid freezes too and doesn’t return to the heat source to start the process again. So in a way, the heat pipe dries out and cannot cool the heat source effectively until the rest of the heat pipe thaws out. By storing some heat for those chilly days, a Spong3d enclosure may be able to release just enough heat to warm up the heat pipes above freezing where the potential of dry-out is averted.