Efficiency Carnot cycle

In the conversion of fossil and nuclear energy to electricity, the value of high temperature solution phase thermodynamics in improving plant reliability has been far less obvious than that of classical thermodynamics in predicting Carnot cycle efficiency. Experimental studies under conditions appropriate to modern boiler plant are difficult and with little pressure from designers for such studies this area of thermodynamic study has been seriously neglected until the last decade or two. 

The simple Rankine cycle is inherently efficient. Heat is added and rejected isothermally and, therefore, the ideal Rankine cycle can achieve a high percentage of Carnot cycle efficiency between the same temperatures. Pressure rise in the cycle is accomplished by pumping a liquid, which is an efficient process requiring small work input. The back-work ratio is large. 

Suppose an ideal regenerator is added to an Ericsson cycle. The regenerator would absorb heat from the system during part of the cycle and return exactly the same amount of heat to the system during another part of the cycle. What would be the difference between the Ericsson cycle efficiency and the Carnot cycle efficiency ... 

Why cannot the Carnot cycle efficiency be approached in the real world ... 

The reaction that gives chemical energy to heat engines in cars (hydrocarbon oxidation) has to obey the Carnot cycle efficiency limitation (I - 7 , y7),igh).With around body temperature (37 °C), the metabolic would have to be 337 °C to explain this metabolic efficiency in terms of a heat engine. Thus, the body energy conversion mechanism cannot use this means to get the energy by which it works. 

Estimate the annual cost of providing refrigeration to a condenser with duty 1.2 MW operating at —5°C. The refrigeration cycle rejects heat to cooling water that is available at 40 °C and has an efficiency of 80% of the Carnot cycle efficiency. The plant operates for 8,000 hours per year and electricity costs 0.06/kWh. 

For this temperature range, the Carnot cycle efficiency is... 

A DEEPER LOOK. .. Carnot Cycles, Efficiency, and Entropy... 

The existence of a finite heat transfer in the isothermal processes is affected with the assumption of a non-endoreversible cycle with ideal gas as working substance. Power output and ecological function have also an issue that shows direct dependence on the temperature of the working substance. Expressions obtained with the changes of variables have the virtue of leading directly to the shape of the efficiency through Z, function. Thus, in classical equilibrium thermodynamics, the Stirling cycle has its efficiency like the Carnot cycle efficiency in finite time thermodynamics, this cycle has an efficiency in their limit cases as the Curzon-Ahlborn cycle efficiency. 

Thus, Sadi Carnot s analysis of Carnot cycle provided the theory for the formulation of the first and the second law of thermodynamics. His concept is that for a system undergoing a cycle, the net heat transfer is equal to the net work done, which led to the first law of thermodynamics. Similarly, the concept that a heat engine cannot convert all the heat absorbed from a heat source at a single temperature into work even under ideal condition led to the second law of thermodynamics. Carnot cycle efficiency gives the idea about the maximmn theoretical efficiency of an engine. Sadi Carnot was rightly honored with the title Father of Thermodynamics for his invaluable contribution to thermodynamics. 

Figure 3.11 Comparison between the thermodynamic efficiency of a heat engine (Carnot cycle efficiency) and the ideal efficiency of an H2-O2 fuel cell.

Substituting Equation 3.40 into Equation 3.39, the Carnot cycle efficiency... 

The amount of heat addition (Qh), heat rejection (QJ, and turbine work output (Wnet) in a heat engine cycle is estimated by applying the first law of thermodynamics. The thermal efficiency of a real heat engine cycle is less than the reversible Carnot cycle efficiency given by Equation 4.3. 

Variation of fuel cell and Carnot cycle efficiencies with temperature. 

Figure 4.1 P-V diagram for the development of the Carnot cycle efficiency by Clapeyron.

In other words, the same way that these imperfections prevent the continuous motion of a body or the conversion of its kinetic energy completely into work, the generation of entropy - resulting also from such physical imperfections - prevents the realization of the Carnot cycle efficiency. 

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