Camot engine

Comprehensive discussions of fuel cells and Camot engines Nemst law analytical fuel cell modeling reversible losses and Nemst loss and irreversible losses, multistage oxidation, and equipartition of driving forces. Includes new developments and applications of fuel cells in trigeneration systems coal/biomass fuel cell systems indirect carbon fuel cells and direct carbon fuel cells. 

The Camot engine is a device by which a working substance can exchange mechanical work with its surroundings and can exchange heat with two heat reservoirs. 

Carnot stated that the efficiency of a reversible Camot engine depends only on the temperatures of the heat reservoirs and is independent of the nature of the working substance. This theorem can be proved by showing that the assumption of a reversible engine with any but the known efficiency of a reversible Camot engine leads to a contradiction of the Clausius statement of the second law. 

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

As the efficiency of a Camot engine is independent of the working substance, the efficiency given in Equation (6.42) for an ideal gas must be equal to that given in Equation (6.29) for any reversible Camot engine operating between the same heat reservoirs. Thus,... 

Curzon, F.L. Ahlborn, B. Efficiency of a Camot engine at maximum power output. Am.. Phys. 1975, 43, 22. 

A Camot engine operates between two heat reservoirs in such a way that all heat absorbed is absorbed at the constant temperature of the hot reservoir and all heat rejected is rejected at the constant temperature of the cold reservoir. Any reversible engine operating between two heat reservoirs is a Camot engine an engine operating on a different cycle must necessarily transfer heat across finite temperature differences and therefore cannot be reversible. 

Since a Camot engine is reversible, it may be operated in reverse the Camot cycle is then traversed in the opposite direction, and it becomes a reversible... 

Imagine that a stream of fluid in steady-state flow serves as a heat source for an infinite set of Camot engines, each of which absorbs a differential amount of heat from the fluid, causing its temperature to decrease by a differential amount, and each of which rejects a differential amount of heat to a heat reservoir at temperature Tf). As a result of the operation of the Camot engines, the temperature T of the fluid decreases from T, to T>. Equation (5.8) applies here in differential form, wherein tj is defined as... 

The minus sign is included because Q is heat transfer with respect to the flowing fluid. Show that the total work of the Camot engines is given by... 

The Camot-engine cycle, described in Chap. 5, operates reversibly and consi of two isothermal steps connected by two adiabatic steps. In the isothermal stc at higher temperature TH, heat < H is absorbed by the working fluid of engine, and in the isothermal step at lower temperature Tc, heat QC is discard... 

Consider the direct transfer of heat from a heat reservoir at T, to another heat reservoir at temperature T2, where T, > T2> T0. It is not obvious why the lost work of this process should depend on T0, the temperature of the surroundings, because the surroundings are not involved in the actual heat-transfer process. Through appropriate use of the Camot-engine formula, show for the transfer of an amount of heat equal to Q that... 

Fignie 5.2 Camot engines 1 and 2 together constitute a third Camot engine. 

A particular power plant operates with a heat-source reservoir at 300°C and a heat-sink reservoir at 25°C. It has a thermal efficiency equal to 60 percent of the Camot-engine thermal efficiency for the same temperatures. 

To what temperature must the heat-source reservoir be raised to increase the thermal efficiency of the plant to 40 percent Again 17 is 60 percent of the Camot-engine value. 

In the preceding discussion we identified temperature levelsby the kelvin scale, established with ideal-gas thermometry. This does not preclude taking advantage of the opportunity provided by the Camot engine to establish a thermodynamic tempQxaXnxe scale that is traly independent... 

The cycle traversed by an ideal gas serving as the working fluid in a Camot engine is shown by a PV diagram in Fig. 5.3. It consists of four reversible steps ... 

A Camot engine receives 250 kW of heat from a heat-source reservoir at 798.15 K (525°C)and rejects heat to a heat-sink reservoir at 323.15 K (50°C). What are the power developed and the heat rejected ... 

A Camot engine operates between two finite heat reservoirs of total heat capacity and C. ... 

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 ... 

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