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Heat Engines

Heat Engines

A heat engine is a device used to extract heat from a source and then convert it into mechanical work used for various applications. For example, a steam engine on an old-style train can produce the work needed for driving the train.
Whenever we consider heat engines (and associated devices such as refrigerators and heat pumps), we do not use the standard sign convention for heat and work. For convenience, we assume that the symbols Qh, Qc, and W represent only the amounts of heat transferred...

The Carnot Cycle

The Carnot Cycle

Converting work to heat is an irreversible process, and the purpose of a heat engine is to reverse the effect partially. Heat engines aim to increase the efficiency of the reversal, that is, maximize the work retrieved from heat. If the efficiency of a heat engine were 100%, it would imply reversing the process completely without introducing any other effect. Thus, it would violate the second law of thermodynamics.
What could be the theoretical limit to the efficiency of a heat engine? The...

Mechanisms of Heat Transfer II

Mechanisms of Heat Transfer II

In convection, thermal energy is carried by the large-scale flow of matter. Ocean currents and large-scale atmospheric circulation, which result from the buoyancy of warm air and water, transfer hot air from the tropics toward the poles and cold air from the poles toward the tropics. The Earth’s rotation interacts with those flows, causing the observed eastward flow of air in the temperate zones. Convection dominates heat transfer by air, and the amount of available space for the airflow...

Mechanisms of Heat Transfer

Mechanisms of Heat Transfer

Heat transfer between the human body and its environment occurs through four main mechanisms: conduction, convection, radiation, and evaporation.
Conduction, accounting for approximately 3% of body heat loss at rest, is the process of exchanging heat between molecules of two materials in direct contact. This can result in both heat loss and gain. For instance, when the body is submerged in water, which conducts heat 20 times more effectively than air, it can either lose or gain significant...

Mechanisms of Heat Transfer I

Mechanisms of Heat Transfer I

Just as interesting as the effects of heat transfer on a system are the methods by which the heat transfer occur. Whenever there is a temperature difference, heat transfer occurs. It may occur rapidly, such as through a cooking pan, or slowly, such as through the walls of a picnic ice box. So many processes involve heat transfer that it is hard to imagine a situation where no heat transfer occurs. Yet, every heat transfer takes place by only three methods: conduction, convection, and radiation.

Mechanism of heat transfer

Mechanism of heat transfer

Understanding heat transfer mechanisms is essential for understanding how our bodies maintain balance in different environmental conditions. When the environment is thermoneutral, the body is in a state of balance, neither using nor releasing energy to maintain its core temperature. However, when the environment is not thermoneutral, the body employs four heat transfer mechanisms to maintain homeostasis: conduction, convection, evaporation, and radiation. These mechanisms facilitate heat...

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Author Spotlight: Optimization of Airflow Velocities in Battery Cooling Systems for Enhanced Thermal Performance and Reduced Energy Consumption

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Overcoming power-efficiency tradeoff in a micro heat engine by engineered system-bath interactions.

Sudeesh Krishnamurthy¹, Rajesh Ganapathy^2,3, A K Sood^4,5

¹Department of Physics, Indian Institute of Science, Bangalore, 560012, India.

Nature Communications

|October 27, 2023

Summary

Researchers experimentally reversed the power-efficiency tradeoff in colloidal Stirling engines. This breakthrough in finite-time thermodynamics allows engines to exceed quasistatic efficiency, overcoming fundamental limitations in engine design.

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Area of Science:

Thermodynamics
Colloidal Science
Nanotechnology

Background:

Real heat engines face an inherent tradeoff between efficiency and power output, a fundamental limitation in thermodynamics for over two centuries.
Existing optimal protocols can only minimize, not eliminate, this power-efficiency tradeoff in both macro and micro engines.
Theoretical studies suggest this tradeoff is universal for passive and active engines, limiting engine design.

Purpose of the Study:

To experimentally overcome the power-efficiency tradeoff in a colloidal Stirling engine.
To explore strategies for enhancing engine performance beyond traditional thermodynamic limitations.
To enable the development of more efficient and powerful engines and devices.

Main Methods:

Utilized a colloidal Stirling engine for experimental investigation.
Selectively reduced relaxation times during isochoric processes.
Engineered system-bath interactions using electrophoretic noise.

Main Results:

Successfully reversed the power-efficiency tradeoff in the colloidal Stirling engine.
Identified a specific window of cycle times where this reversal occurs.
Demonstrated engine performance surpassing quasistatic efficiency.

Conclusions:

The study presents a novel strategy to overcome the fundamental power-efficiency tradeoff in heat engines.
This approach liberates engine design from historical restrictions, paving the way for advanced engine technologies.
The findings have significant implications for the development of highly efficient and powerful micro and macro engines.