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01:14Mechanisms 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.
01:14Mechanisms 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 heat.
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 heat.
01:20Mechanisms 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...
01:10Heat 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...
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...
01:19Mechanism 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...
02:46Quantifying 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 atoms and...
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Updated: May 8, 2026
11:03
An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
Published on: December 4, 2017
Quantum dynamical framework for Brownian heat engines.
1Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078-3072, USA.
Summary
We developed a new theory for microscopic heat engines based on quantum Brownian motion. This formalism accurately predicts engine performance and reveals how dissipation and finite operation times affect efficiency.
Area of Science:
- Thermodynamics
- Quantum Mechanics
- Statistical Mechanics
Background:
- Microscopic heat engines are crucial for nanotechnology.
- Understanding their performance under realistic conditions, including dissipation and finite operation times, is essential.
- Existing theories often struggle to capture these non-ideal effects.
Purpose of the Study:
- To present a self-contained formalism for analyzing microscopic Brownian heat engines.
- To investigate the impact of dissipation and finite operation times on engine performance.
- To derive exact analytical results for engine efficiency and thermodynamic relations.
Main Methods:
- Modeling heat engines using the Brownian motion of a quantum harmonic oscillator.
- Analyzing the dynamics of decoupling and recoupling systems between thermal baths.
- Developing a technique to compute corrections for finite operation times.
Main Results:
- The theory reproduces standard steady-state thermodynamics results.
- Exact analytical results were obtained for engine efficiency, particularly for steps involving bath changes.
- Thermodynamic complementarity relations and efficiencies at maximum power were computed for Carnot, Stirling, and Otto engines.
Conclusions:
- The presented formalism provides a powerful tool for understanding microscopic heat engines.
- Dissipation and finite operation times significantly influence engine efficiency.
- The methods and models have potential applications beyond heat engines.