the Institute for Critical Technology and Applied Science , who led the study . “ There ’ s a lot of interest in capturing that heat , which now gets discarded .”
Converting some of the lost heat to electricity would lower
PRIYA overall fuel consumption , cutting costs and blunting environmental impacts . By siphoning off heat more quickly , it would also increase the performance of systems with electrical components , which operate more efficiently at lower temperatures .
The new thermal energy harvester , described in a study published in Scientific Reports , brokers the conversion of heat to electricity by taking advantage of materials called soft magnets , which are easily magnetized and demagnetized .
One such material is gadolinium , which is magnetic at around room temperature , but loses its magnetism as it warms up .
In Priya ’ s energy harvester , a gadolinium soft magnet is attached to a flexible plastic cantilever . A hard , or permanent , magnet rests against the heat source — for example , the hot surface of a computer ’ s CPU . Magnetic attraction pulls the two magnets together , allowing heat to flow from the hard magnet into the soft magnet . This heats the soft magnet above its transition temperature , and it becomes nonmagnetic .
Without magnetic attraction to bind it to the hard magnet , the soft magnet is pulled away by the cantilever . Separated from the heat source , the soft magnet cools down ; the drop in temperature reactivates its magnetic properties , starting the process over again .
Pulled in one direction by the hard magnet , and the other by the cantilever , the soft magnet cycles up and down as it gains and loses magnetism . Meanwhile , it absorbs heat from the hot surface via the hard magnet , cooling it and dispersing the thermal energy into the environment , which acts as a heat sink .
But the energy contained in the heat is recycled , MOMENTUMSPRING ' 17 because the piezoelectric cantilever converts the soft magnet ’ s up-and-down motion into electricity that can be used or stored .
One of the key advantages of the device is that it effectively harvests thermal energy from heat sources not dramatically hotter than the ambient air — the kind most common in homes and industrial plants .
“ If you look around , you see mostly low-temperature gradients ,” Priya said . “ But at low temperatures , there aren ’ t many promising solutions .”
In tests , the researchers used their device to harvest thermal energy from heat sources around 70 to 80 degrees Celsius . The device operating temperature is mainly governed by the heat required to demagnetize the soft magnet ; with currently available materials , it can be as low as 50 to 60 degrees Celsius .
The new energy harvester ’ s ability to operate at moderate temperatures — along with its compact size and mechanical simplicity — could make it practical for household use . Priya envisions that the heat emanating from everyday appliances could be used to power networks of sensors in data-driven “ smart ” homes .
“ There are a lot of places where even a watt of electricity is sufficient , if you want to run a sensor node ,” Priya said . “ Let ’ s say you want to monitor some process , like measure a temperature or a fluid flow or pressure change . All you need is a burst of thermal energy available to you in a periodic manner .”
The researchers are scaling up the thermal energy harvester to increase its electrical output , refining the materials and design , and adapting it for specific applications .
The study ’ s first author is Jinsung Chun , a postdoctoral researcher in the Department of Mechanical Engineering . First-year doctoral student Ravi Kilgore , who holds a Doctoral Scholars Fellowship from the Institute for Critical Technology and Applied Science , and other graduate students in the department of mechanical engineering also worked on the project .
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