Unit 6 Chemical and Process Thermodynamics-1_化学工程与工艺专业英语音频资料_免费在线阅读收听下载

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Unit 6 Chemical and Process Thermodynamics

Before committing a great deal of time and effort to the study of a subject, it is reasonable to ask the following two questions: what is it? What is it good for? Regarding thermodynamics, the second question is more easily answered, but an answer to the first is essential to an understanding of the subject. Although it is doubtful that many experts or scholars would agree on a simple and precise definition of thermodynamics, necessity demands that a definition be attempted. However, this is best accomplished after the applications of thermodynamics have been discussed.

1．Applications of Thermodynamics
There are two major applications of thermodynamics, both of which are important to chemical engineers:
(ⅰ)The calculation of heat and work effects associated with processes as well as the calculation of the maximum work obtainable from a process or the minimum work required to drive a process.
(ⅱ)The establishment of relationships among the variables describing systems at equilibrium.

The first application is suggested by the name thermodynamics, which implies heat in motion. Most of these calculating can be made by the direct implementation of the first and second laws. Examples are calculating the work of compressing a gas, performing an energy balance on an entire process or a process unit, determining the minimum work of separating a mixture of ethanol and water or evaluating the efficiency of an ammonia synthesis plant.

The application of thermodynamics to a particular system results in the definition of useful properties and the establishment of a network of relationships among the properties and other variables such as pressure, temperature, volume, and mol fraction. Actually, application 1 would not be possible unless a means exists for evaluating the necessary thermodynamic property changes required in implementing the first and second laws. The property changes are calculated from experimentally determined data via the established network of relationships. Additionally, the network of relationships among the variables of a system allows the calculation of values of variables which are either unknown or difficult to determine experimentally from variables which are either available or easier to measure. For example, the heat of vaporizing a liquid can be calculated from measurements of the vapor pressure at several temperatures and densities of the liquid and vapor phases at several temperatures, and the maximum conversion obtainable in a chemical reaction at any temperature can be calculated from calorimetric measurements performed on the individual substances participating in the reaction.

Unit 6 Chemical and Process Thermodynamics-1

Unit 6 Chemical and Process Thermodynamics-1

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