Camot heat engine

Whenever energy is transformed from one form to another, an inefficiency of conversion occurs. Electrochemical reactions having efficiencies of 90% or greater are common. In contrast, Camot heat engine conversions operate at about 40% efficiency. The operation of practical cells always results in less than theoretical thermodynamic prediction for release of useful energy because of irreversible (polarization) losses of the electrode reactions. The overall electrochemical efficiency is, therefore, defined by ... 

Nicolas Leonard Sadi Carnot, the French engineer and physicist, was bom in Paris in 1796. His father, Lazare Nicolas Marguerite Carnot, was in the French military service. Sadi Camot is considered as the founder of modem thermodynamics. Famous for his invaluable contributions to science and thermodynamics, Sadi Camot was honored with the title Father of Thermodynamics. Some of his noteworthy contributions to thermodynamics are the concepts of Camot heat engine, Camot cycle, Carnot s theorem, Camot efficiency, and reversible cycle. 

To do this, we must consider an idealized model of a heat engine called a Camot heat engine, which operates between a high-temperature heat source at temperature Ti, and a colder heat sink at temperature Tc, as shown. 

A Camot heat engine operates according to the following four-step cycle ... 

Using an analysis similar to that used to determine the efficiency of a Camot heat engine, the maximum COP of a refrigerator or air conditioner is given by... 

FIGURE 1.3 Thermodynamic efficiencies of a fuel cell and a hypothetical Camot heat engine, plotted as a function of temperature. A fuel cell that forms water in a gaseous phase has a higher efficiency compared to a fuel cell that produces liquid water. The efficiency difference corresponds to the enthalpy of vaporization. 

Figure 6.4. Scheme of two Camot engines, one acting as a heat engine and the other as a... 

Schematic representation of (a) Carnot heat engine and (b) Camot refrigerator used as a heat pump. 

Just as the Carnot cycle C of Fig. 4.3 can be claimed to be the most efficient possible heat engine ( reai < camot = 1 — Itfc/tfhlX so t0° can reverse Carnot cycle C be claimed to be the most efficient possible refrigerator ... 

With the improved C in hand, we can now envision operating the old Camot cycle as a heat pump C, then coupling this to C as shown in (4.15), using the heat output qh from heat pump C, to drive the improved heat engine C (i.e., with qh = ) ... 

Statement of the Camot-Claiisitis principle for an open reversible transformation. Entropy.—These propositions suffice to give a clue to the importance of the principle of Carnot and Claufflus in the theory of heat-engines but the study of the motive power of heat is not our object so let us return to the principle itself and try to put it into such a form that it may be easily applied to the problems of chemical mechanics. 

A heat engine operating in outer space may be assumed equivalent to a Camot engine operating between reservoirs at temperatures Th and Tc- The only way heat can be discarded from the engine is by radiation, the rate of wliich is given (approxiniately)by ... 

In classical equilibrium thermodynamics, the simplest model of an engine that converts heat into work is the Camot cycle. The behavior of a heat engine working between two heat... 

Camot cycle - A sequence of reversible changes in a heat engine using a perfect gas as tbe working substance, which is used to demonstrate that entropy is a state function. The Camot cycle dso provides a means to calculate tbe efficiency of a beat engine. 

Fig. 4.2 (a) Ideal thermodynamic efficitaicy of polymer electrolyte membrane fuel cells (PEMFCs) compared to that obtained in the Camot process, (b) Comparison of processes in a cogenerated heat engine with fuel cell performance (From [2])... 

A heat engine, as mentioned in Sec. 4.2, is a closed system that converts heat to work and operates in a cycle. A Carnot engine is a particular kind of heat engine, one that performs Carnot cycles with a working substance. A Camot cycle has four reversible steps, alternating isothermal and adiabatic see the examples in Figs. 4.3 and 4.4 in which the working substances are an ideal gas and H2O, respectively. 

We can apply a similar line of reasoning to the heat engine that the Kelvin-Planck statement claims is impossible (a Kelvin-Planck engine ) by seeing what happens if we assume this engine is actually possible. We combine a Kelvin-Planck engine with a Camot heat pump, and make the work performed on the Camot heat pump in one cycle equal to the work performed by the Kelvin-Planck engine in one cycle, as shown in Fig. 4.6(c). One cycle of the combined system, shown in Fig. 4.6(d), shows the system to be a device that the Clausius statement says is impossible. We conclude that if the Clausius statement is correct, then the Kelvin-Planck statement must also be correct. 

The Camot efficiency is the theoretical maximum efficiency by which a heat engine can do work when operating between two temperatures. The greater the difference in temperatures, the greater is the efficiency by which heat can be converted into work. 

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