SEM images of the material hot-pressed at a) 1123 K, b)1173 K, c) 1273 K, and d)1373 K. Credit: University of Houston
Material created with high heat yields record power output density. With energy conservation expected to play a growing role in managing global demand, materials and methods that make better use of existing sources of energy have become increasingly important. Researchers reported this week they have demonstrated a step forward in converting waste heat – from industrial smokestacks, power generating plants or even automobile tailpipes – into electricity.
The work, using a thermoelectric compound composed of niobium, titanium, iron and antimony, succeeded in raising the material’s power output density dramatically by using a very hot pressing temperature – up to 1373 Kelvin to create the material. “The majority of industrial energy input is lost as waste heat,” the researchers wrote. “Converting some of the waste heat into useful electrical power will lead to the reduction of fossil fuel consumption and CO2 emission.”
Thermoelectric materials produce electricity by exploiting the flow of heat current from a warmer area to a cooler area, and their efficiency is calculated as the measure of how well the material converts heat – often waste heat generated by power plants or other industrial processes – into power. For example, a material that takes in 100 watts of heat and produces 10 watts of electricity has an efficiency rate of 10 percent.
That’s the traditional way of considering thermoelectric materials. But having a relatively high conversion efficiency doesn’t guarantee a high power output, which measures the amount of power produced by the material rather than the rate of the conversion. Because waste heat is an abundant – and free – source of fuel, the conversion rate is less important than the total amount of power that can be produced.
“For most thermoelectric materials, a power factor of 40 is good,” Ren said. “Many have a power factor of 20 or 30.” The new material has a power factor of 106 at room temperature, and researchers were able to demonstrate an output power density of 22 watts/sq cm, far higher than the typical 5 to 6 watts. “This aspect of thermoelectrics needs to be emphasized,” he said. “You can’t just look at the efficiency. You have to look also at the power factor and power output.” http://www.uh.edu/news-events/stories/2016/November/11142016Ren-New-Thermoelectric-Material.php
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