华中科技大学工程热力学课件 绪论

Science was a hobby but he soon started to investigate the feasibility of replacing the brewery's steam engines with the newly invented electric motor. In 1838, his first scientific papers on electricity were contributed to Annals of Electricity, the scientific journal founded and operated by Davies's colleague, William Sturgeon He formulated Joule's laws in 1840 and hoped to impress the Royal Society but found, not for the last time, that he was perceived as a mere provincial dilettante
工程热力学
Thermodynamics
主讲老师：方海生
问题一：关于能量你知道多少？
能量的来源？
能量的形式？
能量的来源与形式
常规能源：
化石燃料
生物质能 水能
新能源：
海洋能 地热能 太阳能 核能 风能
•人们由自然界获得能量的主要形式是： 热能！ 据统计，经过热能形式而被利用的能量在 我国占90％以上，世界上其它国家也超过 85％。
When Sturgeon moved to Manchester in 1840, Joule and he became the nucleus of a circle of the city's intellectuals. The pair shared similar sympathies that science and theology could and should be integrated. However, Joule's interest diverted from the narrow financial question to that of how much work could be extracted from a given source, leading him to speculate about the convertibility of energy. In 1845, Joule read his paper On the mechanical equivalent of heat to the British Association meeting in Cambridge. In this work, he reported his best-known experiment, involving the use of a falling weight to spin a paddle-wheel in an insulated barrel of water, whose increased temperature he measured. He now estimated a mechanical equivalent of 819 ft· lbf/Btu (4.41 J/cal).
蒸汽动力装置
T
1 BOILER 4 TURBINE
qin
2 CONDENSER
wout
qin
1
4
wout
3
qout
win
win
3 PUMP
qout
2
s
三要素:热源、工质、来源 h1 h2 h1 h2 提高循环效率的 t h1 h3 h1 h2 途径在哪里？
内燃动力装置
动力的产生——发动机，电厂等。 Propulsion systems — aircraft, rockets, etc.
驱动系统——航行器，火箭等。 Alternative energy systems — fuel cells, solar heating, geothermal, wind energy, ocean thermal, etc. 可再生能源的利用——燃料电池，太阳能加热系统， 地热系统，风能，海洋能
The son of Benjamin Joule (1784–1858), a wealthy brewer, and Alice Prescott Joule, James Prescott Joule was born in the house adjoining the Joule Brewery in New Bailey Street, Salford, 24 December 1818 He received two years' education in arithmetic and geometry before Dalton was forced to retire. Joule was subsequently tutored by John Davies. Joule became a manager of the brewery and took an active role until the sale of the business in 1854.
Aviation
Piston, Gas Turbine & Rocket Engines
Jet Engines
Power Plants
Air Conditioning
Global Climate
Water Vapor System
Biological Systems
问题五：热力学研究方法及特点？
热力学第二定律的实质就是能量贬值原理。 热力学第二定律深刻地指明了能量转换过程 的方向、条件及限度。
水总是从高处向低处流动 气体总是从高压向低压膨胀
热量总是从高温物体向低 温物体传递
会引起可用能损失的几种情况
热量从高温传向低温，直至接近环境温度 流体从压力高处流向压力低处，直至接近与环 境相平衡的压力。 物质从浓度高处流向压力低处直至接近与环境 相平衡的浓度 物体从高的位置降落到稳定的位置。
combustion 88%
Thermal energy in steam
Steam turbine
46%
electricity
98%
Mechanical energy In turbine
Overall efficiency: 88% ×46% × 98% = 40%
问题四：热力学的任务是什么？？
Steam Power: 1800
Transportation- Rail Road
Transportation- Automobiles
The first car that ever mastered a drive was built by the German engineer and inventor Carl Benz in 1885
热力学重要内容
研究能量转换规律（其实质就是热能向其它有序 能的转换），以及如何提高能量转换效率的学科 。 基本内容：
基本概念和定律； 工质的性质和过程； 工程应用（各种循环）。
热力学涉及应用领域
Combustion systems 燃烧系统 Power production — engines, power plants, etc.
问题二：热能与机械能、电能的区别在哪里？
本质？ 利用方式？
机械能
机械能是与物体宏观机械运动或空间状态相关的能量 ，前者称为动能，后者称为势能。
电能
电能是和电子流动与积累有关的一种能量，通常由电 池中的化学能转换而来，或是通过发电机由机械能转 换得到；反之，电能也可以通过电动机转换为机械能 ，从而显示出电做功的本领。
Transportation- Automobiles
Ford Model T 1910
Aviation: 1900
The world's first power-driven, controlled and sustained flight invented and built by Wilbur and Orville Wright flown by them at Kitty Hawk, North Carolina December 17, 1903 by original scientific research the Wright Brothers discovered the principles of human flight as inventors, builders, and flyers they further developed the aeroplane, taught man to fly, and opened the era of aviation."
热能
构成物质的微观分子运动的动能和势能总和称为热 能。这种能量的宏观表现是温度的高低，它反映了 分子运动的激烈程度。
机械能 有序能 电能 热能 无序能
热能的利用
两种基本方式
直接利用：即将热能直接用于加热物体 如：烘干、蒸煮、采暖、熔化等等； 间接利用：将热能转变为其它形式的能量 如：热能向机械能的转换 热能向机械能转换后再由机械能转换为电能 热能向电能直接转换
Died：11 October 1889 (aged 70) Sale, Cheshire, England, UK
Citizenship：British Fields：Physics, Known for First Law of Thermodynamics
Influences: John Dalton John Davies
A statue of Joule in the Manchester Town Hall Joule's gravestone in Brooklands cemetery
问题四：既然能量守恒，何来能源消耗、能 源危机？
能量wk.baidu.com值原理
能量不仅有量的 多少，还有质的 高低。热力学第 一定律只说明了 能量在量上要守 恒，并没有说明 能量在“质”方 面的高低。
电荷从高电位迁移到接近于环境的电位。
• 自然界当中，任何实际过程都会引起能量损失
• 能量使用的过程就是能量被贬值、被消耗的过程
Energy efficiency of some common energy conversion device
火电站的能量转换效率是多少？
Chemical energy In coal
热力学涉及领域（二）
Fluid compression and movement — fans, pumps, compressors, etc.
流体压缩和运动——风机，泵，压缩机等。 HVAC — refrigeration systems, heat pumps, etc.
供热通风与空调工程——制冷系统，热泵等。 Cryogenics — gas separation and liquefaction 低温——气体分离及液化 Biomedical applications 生物医学应用
关键问题：能量转换！
问题三：能量在使用过程中会消失吗？
James Joule (1818~1889)
热力学第一定律：能量守恒
系统的内能=系统吸收的热量+对系统做功
能量相互转换
James Joule – Physicist
Born：24 December 1818，Salford, Lancashire, England, UK
燃气 进口
T 3
4
排入大 气
2
1 0 三要素:热源、工质、来源 提高循环效率的 循环热效率公式 途径在哪里？
5
s
问题六：热力学和传热学有什么关系？
James Joule (1818~1889)
热力学第一定律：能量守恒
系统的内能=系统吸收的热量+对系统做功