On this page you will find short articles that I will write on thermodynamics. There are four basic principles of thermodynamics, which are called laws of nature. These are named zeroth, first, second and third laws respectively. The reason for describing these laws as natural laws is because all observations made in nature up to date has conformed to these laws, in other words no contradictory observation has been made so far. Zeroth law is related to the definition of temperature.

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On this page you will find short articles that I will write on thermodynamics. If you ask someone walking on the street, what he understands from efficiency, he will probably answer this question by saying that efficiency is producing more, using time and other sources more effectively or something similar.

Efficiency may roughly be defined as the ratio of the desired product divided by the source that is expended to produce it. Some examples are the time spent to learn a certain subject or the amount of gasoline burned to go a certain distance.

No matter which measure we use, we always want efficiency to be high. Thermodynamics is the science that deals with energy transformations. For this reason efficiency is defined as the percentage of one form of energy transformed into another. Let us give two examples. The ratio of the thermal energy obtained in a boiler to the chemical energy spent is called the combustion efficiency or the thermal effiency of the boiler.

Here thermal energy is the energy of hot water or steam expressed in kJ, chemical energy is the energy of the fuel spent coal, natural gas,… in kJ. Let us next consider a car engine as an example. The thermal efficiency of the engine is defined as the work produced by the engine kJ divided by the thermal energy obtained from the burning of the fuel kJ. The concept of efficiency and related definitions have been given above verbally. Engineers and students that use thermodynamics, treat this subject in much more detail by using equations and numerical calculations.

Conversion of thermal energy to work in engines is realized in thermodynamic cycles. Otto cycle is associated with tha gasoline engine, the Diesel cycle with the Diesel engine and the Brayton cycle with the gas turbine. The upper limit of efficiency of these cycles is the Carnot efficiency. Carnot efficiency is the efficiency of a reversible ideal with no losses cycle.

A more realistic effiency definition for the Otto, Diesel and Brayton cycles is the Curzon —Ahlborn some call it Novikov-Chambadal efficiency. Both of the efficiency definitions are functions only of the maximum and minimum temperatures of the cycle. Explanations in this paragraph relate only to the conversion of thermal energy to work.

For devices where chemical energy is directly converted to work electricity such as the fuel cell, efficiency must be considered in a different context. In thermodynamics, the term sytem roughly means a certain mass or a mass passing through a control volume. System may undergo a change of state or process, where it may exchange heat and work with the surroundings.

An efficiency may also be defined for a change of state or a process of the system. However such a definition is usually related to the concept of entropy. Entropy will be the subject of a series of articles starting next month. Efficiency within the context of entropy will be discussed then. August 8,


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