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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...
01:12Heat Flow and Specific Heat
Heat is a type of energy transfer that is caused by a temperature difference, and it can change the temperature of an object. Since heat is a form of energy, its SI unit is the joule (J). Another common unit of energy often used for heat is the calorie (cal), which is defined as the energy needed to change the temperature of 1 g of water by 1 °C, specifically between 14.5 °C and 15.5 °C, since the energy needed shows a slight temperature dependence. Another commonly used unit is the kilocalorie...
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...
01:21Path Between Thermodynamics States
Consider the two thermodynamic processes involving an ideal gas that are represented by paths AC and ABC in Figure 1:
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05:20
Characterization of Thermal Transport in One-dimensional Solid Materials
Published on: January 26, 2014
Modeling heat transport through completely positive maps.
Hannu Wichterich1, Markus J Henrich, Heinz-Peter Breuer
1Fachbereich Physik, Universität Osnabrück, Barbarastrasse 7, D-49069 Osnabrück, Germany. hwichter@uni-osnabrueck.de
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|October 13, 2007
Summary
Researchers explored heat transport in quantum spin chains using open quantum systems. They developed a new quantum master equation to accurately model energy currents in systems with varying temperatures.
Area of Science:
- Quantum physics
- Condensed matter physics
- Statistical mechanics
Background:
- Understanding heat transport in quantum systems is crucial for developing quantum technologies.
- Previous models, like the Lindblad equation, struggle with non-equilibrium steady states.
Purpose of the Study:
- To investigate heat transport in a spin-1/2 Heisenberg chain coupled to thermal baths.
- To develop an accurate quantum master equation for describing stationary energy currents.
Main Methods:
- Analysis within the theory of open quantum systems.
- Microscopic derivation of quantum master equations.
- Comparison of standard Lindblad equation with a newly derived master equation.
Main Results:
- The standard Lindblad equation is inadequate for describing non-vanishing energy currents.
- A novel master equation accurately describes stationary energy currents.
- The new equation ensures a completely positive dynamical map.
Conclusions:
- A new quantum master equation provides a more accurate framework for studying heat transport.
- This work enables efficient numerical simulations of heat transport in larger quantum systems.