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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...

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.

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...

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...

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...

Quantifying Heat

Quantifying Heat

Thermal Energy Microscopically, thermal energy is the kinetic energy associated with the random motion of atoms and molecules. Temperature is a quantitative measure of “hot” or “cold”, which depends on the amount of thermal energy. When the atoms and molecules in an object are moving or vibrating quickly, they have a higher average kinetic energy (KE) (or higher thermal energy), and the object is perceived as “hot”, or it is described as being at a higher temperature. When the...

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Related Experiment Video

Updated: Jan 27, 2026

Fabrication of Three-Dimensional Graphene-Based Polyhedrons via Origami-Like Self-Folding

Fabrication of Three-Dimensional Graphene-Based Polyhedrons via Origami-Like Self-Folding

Published on: September 23, 2018

Graphene-based bidirectional radiative thermal transfer method for heat engines.

Alireza Nojeh, George A Sawatzky, Lorne A Whitehead

|March 16, 2019

Summary

This summary is machine-generated.

This study introduces a novel hybrid working fluid for heat engines, utilizing graphene layers for rapid radiative heat transfer. This innovation significantly boosts cycle frequency and specific power compared to traditional methods.

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Area of Science:

Thermodynamics
Materials Science
Nanotechnology

Background:

Conventional heat engines are limited by slow heat transfer rates.
Non-radiative thermal transfer restricts the operational frequency of closed-cycle engines.
Developing advanced working fluids is crucial for improving engine efficiency.

Purpose of the Study:

To enhance heat transfer rates in heat engines.
To develop a novel hybrid working fluid with superior thermal properties.
To increase the specific power output of heat engines.

Main Methods:

Dispersing individual graphene layers in an inert gas to create a hybrid working fluid.
Utilizing bidirectional thermal radiation exchange for heat transfer.
Characterizing the composite properties of high optical absorption/emission and low specific heat.

Main Results:

Achieved substantially enhanced heat transfer rates.
Demonstrated rapid heating and cooling of the working fluid.
Enabled significantly greater cycle frequencies and increased specific power.

Conclusions:

The proposed hybrid working fluid offers a pathway to overcome limitations in conventional heat engines.
Radiative heat transfer using graphene-based fluids presents a promising approach for high-performance thermal systems.
This method has the potential to revolutionize heat engine design and efficiency.