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十九世纪中叶,正当大工业机器生产得到进一步发展的时候,机械工业要求提高热机效率以适应当时生产的发展。实际上当时的热机效率很低,仅及燃料供给热量的1—2%,如果消除摩擦、辐射等所消耗的热量外,热机能否全部地把热能转化为有用的机械功?这是当时机械设计的一个极其重要的课题。早在1824年卡诺分析了吸热作功的关系,提出了卡诺循环。后来开尔芬根据卡诺循环指出了在热能转化为机械功的时候,需要一个高温(T_1)热能源和低温(T_2)的热能储,热功转化的效率在本质上需受这两个温度的差值(T_1-T_2)的限制,热机效率(η)服从下列关系式:η(?)(T_1-T_2)/T_1在这个原理里就已经预示了一个范围较广的、不限于热转化为机械功的客观规律的存在。这个规律就是热力学第二定律。到了十九世纪中叶,克劳胥斯(Clausius)(1850年)和开尔芬(Kelvin)(1851年)分别提出了他们各自关于热力学第二定律的说法。接着克劳胥斯在1854年引入了熵的概念并且在1865年给这个热力学状态函数命了名。自那以后,热力学发展很快。到了十九世纪末叶吉布斯(Gibbs)、波尔兹曼(Boltzmann)等人使用了经典力学的理论和数学统计
In the mid-nineteenth century, while the production of large-scale industrial machinery was further developed, the machinery industry demanded to increase the efficiency of heat engine to adapt to the development of production at that time. In fact, at that time, the heat engine efficiency was very low, only 1-2% of the heat supplied by the fuel. If the heat consumed by friction and radiation was eliminated, could the heat engine completely convert the heat into useful mechanical work? Design an extremely important issue. As early as 1824, Carnot analyzed the relationship between endothermic work, proposed Carnot cycle. Later, according to Carnot cycle, Kaelin pointed out that when heat is converted into mechanical work, a high temperature (T 1) heat source and a low temperature (T 2) heat storage are needed. The conversion efficiency of heat power is essentially affected by both temperatures (T 1 -T 2), the efficiency of heat engine (η) obeys the following relation: η (?) (T_1-T_2) / T_1 In this principle, a wider range is foreseen, not limited to thermal conversion The objective laws of mechanical work exist. This law is the second law of thermodynamics. By the mid-nineteenth century, Clausius (1850) and Kelvin (1851) proposed their respective claims about the second law of thermodynamics. Then Clausius introduced the concept of entropy in 1854 and named the thermodynamic state function in 1865. Since then, thermodynamics has developed rapidly. By the late nineteenth century Gibbs, Boltzmann, and others, used theorical and mathematical statistics of classical mechanics