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Mechanisms of Heat Transfer I
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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.
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Mechanisms of Heat Transfer II
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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...
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P-N junction
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A p-n junction is formed when p-type and n-type semiconductor materials are joined together. At the interface of the p-n junction, holes from the p-side and electrons from the n-side begin to diffuse into the opposite sides due to the concentration gradient. This diffusion of carriers leads to a region around the junction where there are no free charge carriers, known as the depletion region. The charge density within the depletion region for the n-side and p-side can be described by the...
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Metal-Semiconductor Junctions
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The contact of metal and semiconductor can lead to the formation of a junction with either Schottky or Ohmic behavior.
Schottky Barriers
Schottky barriers arise when a metal with a work function (Φm) contacts a semiconductor with a different work function (Φs). Initially, electrons transfer until the Fermi levels of the metal and semiconductor align at equilibrium. For instance, if Φm > Φs, the semiconductor Fermi level is higher than the metal's before contact. The...
Schottky Barriers
Schottky barriers arise when a metal with a work function (Φm) contacts a semiconductor with a different work function (Φs). Initially, electrons transfer until the Fermi levels of the metal and semiconductor align at equilibrium. For instance, if Φm > Φs, the semiconductor Fermi level is higher than the metal's before contact. The...
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Biasing of Metal-Semiconductor Junctions
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Biasing metal-semiconductor junctions involves applying a voltage across the junction. Specifically, the metal is connected to a voltage source, while the semiconductor is grounded. This technique is essential for controlling the direction and magnitude of current flow in electronic devices, including diodes, transistors, and photovoltaic cells.
In Schottky junctions, where the semiconductor is n-type, applying a positive voltage to the metal relative to the semiconductor reduces its Fermi...
In Schottky junctions, where the semiconductor is n-type, applying a positive voltage to the metal relative to the semiconductor reduces its Fermi...
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Mechanisms of Heat Transfer
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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...
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...
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在原子尺度的连接处散热.
Woochul Lee1, Kyeongtae Kim, Wonho Jeong
1Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
Nature
|June 15, 2013
概括
研究人员研究了原子和分子连接处的热散散. 他们发现,依赖能源的电子传输会导致不对称的热流,进步对纳米级热传输的理解.
科学领域:
- 凝聚物质物理学 凝聚物质物理学
- 纳米技术 纳米技术
- 量子运输是一种量子运输.
背景情况:
- 原子和单分子结合推动了电路微型化的极限.
- 它们作为测试纳米设备中的量子运输理论的平台.
- 虽然研究了电气和热电现象,但热散散仍然具有挑战性.
研究的目的:
- 为了研究单分子结节的电极中的散热.
- 了解电子传输特性与散热之间的关系.
- 为了建立一个框架,以弹性传输的介质层系统的散热.
主要方法:
- 使用定制制造的扫描探头与集成的纳米级热电偶.
- 在单分子 ("分子") 和少数原子 ("原子") 黄金连接处研究了散热.
- 分析了基于偏差极性和电荷载体类型 (电子与孔) 的散热不对称性.
主要成果:
- 发现能量依赖的传输特征导致分子连接处的不对称散热.
- 观察到这种不对称性取决于偏差极性和电荷载体 (电子/孔).
- 能量依赖性较弱的原子连接没有显著的不对称性.
结论:
- 电子传输特性与原子尺度连接处的散热特性直接相关.
- 建立了一个框架,以了解带有弹性传输的中视系统中的热散射.
- 铺平了对原子尺度佩尔蒂埃效应和热传输的实验研究的道路.


