Heat engine operation

Stirling engines also have the maximum theoretical possible efficiency because their power cycle (their theoretical pressure volume diagram) matches the Carnot cycle. The Carnot cycle, first described by the French physicist Sadi Carnot, determines the maximum theoretical efficiency of any heat engine operating between a hot and a cold reservoir. The Carnot efficiency formula is... 

The efficiency of the Carnot heat engine operating between a fixed high-temperature heat source thermal reservoir at Th and a fixed low-temperature heat sink thermal reservoir at Tl is irrespective of the working substance. 

Do Otto heat engines operate on a closed system or an open system Why ... 

The temperature scales that have been discussed earlier are quite arbitrary and depend upon the properties of a particular substance. Kelvin was the first to observe that the efficiency of a reversible heat engine operating between two temperatures is dependent only upon the two temperatures and not at all upon the working substance. Therefore, a temperature scale could be defined that is independent of the properties of any substance. 

We prove the identity of the Kelvin scale and the ideal gas scale by using an ideal gas as the fluid in a reversible heat engine operating in a Carnot cycle between the temperatures T2 and 7. An ideal gas has been defined by Equations (2.36) and (2.37). Then the energy of an ideal gas depends upon the temperature alone, and is independent of the volume. 

We now discuss the efficiency of a reversible heat engine operating in a Carnot cycle. The efficiency depends upon the difference between the two temperatures. The greater the difference for a fixed T2 is, the greater the... 

We continue with a reversible heat engine operating in a Carnot cycle, but center our attention on the working substance rather than on the entire system consisting of the heat engine, the work reservoir, and the two heat reservoirs. For such a cycle we can write... 

A heat engine operates between 130 and 30°C. How much heat must be taken from the high temperature to obtain 6 kcal of work Assume there is no frictional loss of energy. 

The conventional generation of electrical energy from a fuel requires the use of a heat engine which converts thermal energy to mechanical energy. All heat engines operate by the Carnot cycle, and their maximum efficiency is about 40-50% (for the modern gas-fired power stations, the efficiency is about 55%). 

Thus, the efficiency of reversible heat engine depends only on the temperatures between which the heat engine operates. The lower the temperature of sink where the lower quality of heat is discarded the higher is the efficiency of the heat engine. 

If a reversible heat engine operates between two constant temperature reservoirs, then the thermodynamic temperature is defined as being proportional to the quantity of heat transferred to and from it in a reversible cycle (Kelvin, 1848). 

We now ask how efficiently this energy conversion process can be carried out in a heat engine operating in cycles. The efficiency is measured by a quantity 77 defined as... 

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 ... 

Carnot s analysis of efficiency for a heat engine operating reversibly showed that in each cycle q/T at the high temperature reservoir and q/T at the low tem-peratnre environment snmmed to zero ... 

This result, called the Carnot efficiency or the thermodynamic efficiency, places a fundamental limit on the efficiency with which heat can be converted to mechanical work. Only if the high temperature, T, were infinite or the low temperature, T , were zero would it be possible to have a heat engine operate with 100% efficiency. To maximize efficiency, the greatest possible temperature difference should be used. Although we derived this result specifically for the ideal gas, we will show later in this section that it applies to any reversible engine operating between two temperatures. For a real engine, which must operate irreversibly, the actual efficiency must be lower than the thermodynamic efficiency. 

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