Exploring High-Performance Applications for Distributed Transport Property Thermoelectrics

Exploring high-performance applications for distributed transport property thermoelectrics.

Thermoelectric devices are already used widely in thermal management applications in the aerospace and defense industries. While state-of-the-art electronics — such as night vision equipment, infrared detectors and avionics — utilize these devices for thermal regulation, efficiency limitations have curbed their use in other advanced applications.

A recent breakthrough in material technology has unlocked the potential of thermoelectrics (TE), opening up new doors for TE systems by delivering dramatic increases in heating and cooling efficiency and capacity.

This overview shows how the use of distributed transport property (DTP) technology can enable an adequate temperature difference between ambient and cold surfaces. (Image: DTP Thermoelectrics)

This new, patented distributed transport property (DTP) technology describes functionally graded materials with spatially varied transport properties. These properties, which include the Seebeck coefficient (S), electrical resistivity (ρ) and thermal conductivity (λ), are key metrics that define the overall performance of a TE material. DTP technology improves the maximum temperature difference (ΔT), coefficient of performance (COP) and total heat pumping capacity (Qc), providing better cooling and heating performance in TE systems and expanding their potential applications.

Fine-Tuning Thermoelectric Properties

Within a DTP material, the transport properties are spatially optimized, unlocking substantial performance gains; Seebeck coefficient, electrical resistivity and thermal conductivity vary throughout the DTP material.

The magnitude of each transport property progressively becomes larger toward the hot end of the material. By varying the Seebeck coefficient, electrical resistivity and thermal conductivity throughout the length of the legs, the DTP material structure changes the temperature profile to closely match the shape that creates optimum performance.

This figure illustrates Seebeck coefficient (S) varying with position in a thermoelectric (TE) cooling couple consisting of N and P type elements. Toward the hot end, the spatially varying Seebeck coefficient in the N type TE material is progressively more negative, while the coefficient in the P type material is progressively more positive. (Image: DTP Thermoelectrics)

Adjusting these transport properties to achieve ideal cooling, heating and temperature control, unlocks new applications that were not previously possible in solid state.

With the emergence of advanced manufacturing processes like spark plasma sintering, ion implantation and additive manufacturing, production of DTP thermoelectric materials has now been enabled at a cost-effective price point to solve real-world challenges.

Thermal Benefits

The maximum achievable ΔT of a standard TE module in cooling mode is 73 °C when based on a hot-side temperature of 27 °C. To increase the ΔT, additional stages must be added to the device, driving up costs and design complexity, as well as reducing cooling capacity due to the additional interfacial resistances. A DTP module can reach beyond standard ΔT markers without the need for these multiple stages.

By varying the Seebeck coefficient, electrical resistivity and thermal conductivity throughout the length of the couple, the DTP material structure changes to closely match the shape that creates optimum performance, as shown in this figure. (Image: DTP Thermoelectrics)

Based on numerical modeling, a single-stage DTP thermoelectric device operating in cooling mode can achieve a maximum ΔT of more than 85 °C, with the potential to reach 100 °C, based on a hot-side temperature of 27 °C. This is a major performance boost compared to a standard single-stage conventional thermoelectric (CTE) module with a ΔT of 73 °C. While cascaded CTEs can also reach these high temperature differences, DTP systems can outperform multi-stage CTEs with just one stage.

DTP modules deliver 140 percent higher efficiency and 200 percent more cooling power compared to standard thermoelectric systems at high ΔT.

Aerospace and Defense Applications

Pipe heating in induction oven for polymer coating. (Image: Vladimir Mulder/Shutterstock.com)

DTP thermoelectric materials open up new possibilities for solid-state cooling and temperature control applications. They also provide important competitive advantages for current applications and enable new solid-state cooling and temperature control system designs.

For example, aerospace and defense applications require precision-engineered systems that can operate in non-optimal, even extreme conditions. The higher cooling capacity of DTP systems make them ideal for battery thermal management or occupant cooling for any vehicle that uses electric propulsion — such as unmanned aircraft, underwater remote operated vehicles (ROV) and electric vehicles (EV).

Sometimes, these vehicles must feature a compact design, as is the case with drones. DTP’s thermal advantages can improve payload cooling systems. For example, a drone delivering temperature-sensitive medication to inaccessible areas can keep the medical payload cooler and for a longer time, increasing the maximum range of the drone’s aid. The better cooling efficiency can also extend the mission length for drones.

Advanced optics and sensor technology draw significant power and need optimal cooling to ensure proper function. For example, some infrared imaging sensors operate at -80 °C, which is close to the ΔT potential for a single-stage DTP system. A two-stage DTP system could easily cool the electronics of such an infrared imaging sensor and — as the technology matures — single-stage DTP will most likely be capable of handling such a temperature difference.

Spatially optimized transport properties provide unprecedented levels of cooling in solid-state systems and can deliver major improvements in maximum temperature difference, efficiency and cooling power. This innovative technology opens the door to new solid-state cooling and temperature control applications and offers attractive advantages to current TE applications. Although this technology is relatively new, sizable performance benefits continue to appear on the horizon as the technology matures.

This article was written by Doug Crane, Chief Technology Officer, DTP Thermoelectrics. For more information, visit here .