Science & Technology, India (Commonwealth Union) – Designing a heat engine that can achieve peak power output while maintaining maximum efficiency is a formidable challenge. Practical heat engines are bound by the Carnot limit, a theoretical efficiency threshold that restricts the conversion of heat into useful work. However, in a groundbreaking development, scientists from the Indian Institute of Science (IISc) and the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) have pioneered a novel “micro heat engine” that transcends this limitation on a laboratory scale. Their remarkable achievement has appeared in the Nature Communications journal.
Corresponding author Ajay K Sood, who serves as the National Science Chair Professor at the Department of Physics, IISc, and holds the position of Principal Scientific Adviser to the Government of India indicated that they have accomplished what was previously deemed impossible: the simultaneous attainment of both high efficiency and high power.
Heat engines are devices designed to convert heat into work, such as moving a piston in a specific direction. To achieve 100% efficiency in an engine, wherein the process can be perfectly reversed, resulting in no heat wastage, French physicist Sadi Carnot proposed this concept in 1824. However, this ideal state can only be achieved if the process occurs at an exceptionally slow pace, which, in turn, results in zero power output, rendering the engine virtually useless. This inherent tradeoff between power and efficiency is a longstanding challenge in the field.
Sudeesh Krishnamurthy, a former PhD student at the Department of Physics, IISc, and the first author of this groundbreaking study pointed out that since the 1970s, efforts have been made to address the power-efficiency trade-off. He further indicated that in the early 2000s, researchers began exploring microscopic systems to tackle this conundrum. Interestingly, in 2017, a paper asserted that solving this thermodynamic puzzle was impossible.
In their recent research, the team emulated the operation of a traditional heat engine on a microscopic scale. Instead of employing a mixture of gas and fuel, they utilized a minuscule, gel-like colloidal bead and harnessed a laser beam to control its motion, much like the piston in a macroscopic engine.
“Our unique micro-scale engine operates with just one particle,” said Rajesh Ganapathy, Professor at JNCASR as well as another author. The size of the engine is very small, about 1/100th the width of a single human hair, he further stated.
Additionally, the team employed a rapidly fluctuating electric field to transition the engine between two distinct states. In this configuration, they observed a significant reduction in waste heat dissipation, resulting in an efficiency that approached 95% of the Carnot limit.
“What we have achieved is a reduction in heat distribution time through the introduction of the electric field. This reduction in heat distribution time allows the engine to operate at high efficiency and simultaneously yield a large power output even while operating at high speeds,” explained Krishnamurthy.
In their previous endeavor, the team engineered a high-power engine that harnessed a live bacterium to propel the particle and drive the system. In this latest undertaking, the researchers opted for a more efficient and durable approach by substituting the bacterium with an electric field to manipulate the particle within the colloidal medium.
Researchers of the study pointed out that the experimental outcomes demonstrate that, under specific conditions, it is possible to attain both high power and high efficiency. This breakthrough could serve as a stepping stone toward the development of more energy-efficient devices in the future.
“If one can draw a message from here and try to see how to make a practical interpretation of this micro engine, that is the next part of the story,” said Sood. “We have opened doors that scientists almost gave up opening due to the thermodynamic constraints set by Carnot in previous studies.”
