Heat Transfer|L1_Introduction on Heat Transfer

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本文深入探讨了热传递的三种基本方式：热传导、热对流和热辐射。详细解析了能量如何从高能粒子传递到低能粒子，以及温度不同的物体通过分子运动进行热量交换的过程。介绍了牛顿冷却定律及其在不同场景下的应用，以及斯特藩-玻尔兹曼定律在热辐射中的作用。

Introduction

usuallywe ues below coordinate in this class

在这里插入图片描述

you should remember the name of the three mode of heat transfer

Energy , from more energetic to the less energetic particles , due to interaction between the particles.
Contact between bodies at different temperatures by molecular motion.
Slid bodies is by conduction alone. The heat may transfer from a solid surface to a fluid partly by conduction and partly by convection.

convection is the process by movement of fluids.
Convection heat transfer includes both forced convection and natural convection
Heat transfer processes that involve change of phase of a fluid are also being considered to be convection.
Forced and natural convection: an example
Newton’s Law of cooling
$q=h\left(T_{w}-T_{f}\right)$ the fluid will heat up. h is the convection coefficient.
$q=h\left(T_{f}-T_{w}\right)$ the fluid will cold down. h is the convection coefficient.

Thermal radiation can occur through matter or through a
region of space that is void of matter
Stefan-Boltzmann Law
黑体表面的热辐射
$E_{b}=\sigma T^{4}$
Eb is the emissive power
σ is the Stefan- Boltzmann constant (5.67×10-8 Wm-2K-4)
T is the absolute temperature
Heat transfer rate:
$\Phi=\varepsilon_{1} A_{1} \sigma\left(T_{1}^{4}-T_{2}^{4}\right)$

ε is emissivity of the surface

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$q=\frac{T_{\infty 1}-T_{\infty 2}}{\frac{1}{h_{1}}+\frac{\delta}{\lambda}+\frac{1}{h_{2}}}$

where

$k=\frac{1}{\frac{1}{h_{1}}+\frac{\delta}{\lambda}+\frac{1}{h_{2}}}$

Heat convection two equation:

Stefan-Boltzmann Law
黑体表面的热辐射
$E_{b}=\sigma T^{4}$
Newton’s Law of cooling
$q=h\left(T_{w}-T_{f}\right)$ the fluid will heat up. h is the convection coefficient.
$q=h\left(T_{f}-T_{w}\right)$ the fluid will cold down. h is the convection coefficient.