The Carnot Cycle for Elastomers

In elementary thermodynamics, the Carnot cycle illustrates the production of useful work by a gas in a heat engine. This section outhnes the corresponding thermodynamic concepts for an elastomer and illustrates a demonstration experiment. 

By carrying a gas, elastomer, or any material through the appropriate closed loop with a high- and low-temperature portion, they may be made to perform work proportional to the area enclosed by the loop. A system undergoing such a cycle is called a heat engine. 

Next the gas undergoes a reversible isothermal expansion from state 2 to state 3. While expanding, the gas does work l 23l on the surroundings while absorbing heat q2. Then there follows a reversible adiabatic expansion of the gas from state 3 to state 4, the temperature dropping from T2 to T. During this step, the gas does work l ()34l on the surroundings. 

there is an isothermal compression of the gas from state 4 to state 1 at Ti. Work Irotil is performed on the gas, and heat l il flows from the gas to the surroundings. 

An increase in the volume of the gas, however, corresponds to a decrease in the length of a stretched elastomer. It is important to note that at no time does the elastomer come to its rest length, Lq. Interestingly the corresponding rest volume of a gas is infinitely large. 

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