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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...
01:30The 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...
What could be the theoretical limit to the efficiency of a heat engine? The...
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...
01:14Mechanisms 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.
01:14Mechanisms 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.
01:19Mechanism 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...
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Updated: Jul 15, 2026
04:58
A Rapid Method for Modeling a Variable Cycle Engine
Published on: August 13, 2019
Collective working regimes for coupled heat engines.
B Jiménez de Cisneros1, A Calvo Hernández
1Departamento de Física Aplicada, Universidad de Salamanca, 37008 Salamanca, Spain.
Physical Review Letters
|May 16, 2007
Summary
This study models coupled heat engines to explore individual versus collective behavior. A control parameter reveals distinct operating regimes, including maximum efficiency and power, with surprising findings for the latter.
Area of Science:
- Thermodynamics
- Statistical Mechanics
- Non-equilibrium Systems
Background:
- Understanding the behavior of coupled systems is crucial in thermodynamics.
- Linear irreversible thermodynamics often simplifies complex systems for analysis.
- The trade-off between efficiency and power is a fundamental concept in heat engine design.
Purpose of the Study:
- To investigate the interplay between individual and collective behaviors in arrays of coupled heat engines.
- To identify control parameters governing the operation regimes of such arrays.
- To analyze the conditions for maximum efficiency and maximum power in these systems.
Main Methods:
- Development of a theoretical model for arrays of coupled heat engines.
- Analysis within the framework of linear irreversible thermodynamics.
Main Results:
- Identification of a control parameter that dictates the array's operational regime.
- Analysis of regimes for maximum efficiency and maximum power.
- A general derivation of the Curzon-Ahlborn efficiency for maximum power, independent of individual engine operation.
Conclusions:
- Coupled heat engine arrays exhibit distinct operational regimes controlled by a specific parameter.
- The efficiency at maximum power for the array is surprisingly robust, not depending on individual engine optimization.
- This model provides insights into collective phenomena in linear irreversible thermodynamics.