The efficiency of heat engines

This equation was originally arrived at by the French Engineer Sadi Carnot in 1824 during his investigation on the efficiency of heat engines. In terms of the heat and the entropy changes in the system, the second law may be expressed as follows ... 

From the discussion of heat engines, the second law of thermodynamics states that it is impossible to achieve heat, taken from a reservoir, and convert it into work without simultaneous delivery of heat from the higher temperature to the lower temperature (Lord Kelvin). It also states that some work should be converted to heat in order to make heat flow from a lower to a higher temperature (Principle of Clausius). These statements acknowledge that the efficiency of heat engines could never be 100% and that heat flow from high temperatures to low temperatures is not totally spontaneous. Simply, the second law states that natural processes occur spontaneously toward the direction in which less available work can be used. 

Note that the enthalpy of combustion is 283.0kjmol an unrelated fact. The product of a Carnot efficiency of, say, 50% and the combustion enthalpy is 143.5 kW smol (cf 534.5). The potential superiority of the fuel cell is evident. Referring the efficiency of heat engines to the fuel... 

We may stress at this point that the conception of the role played by irreversible processes developed here is quite different from that in classical thermodynamics. In the latter, irreversible changes appear only as undesirable effects which reduce the efficiency of heat engines and which one must attempt to eliminate. On the other hand thermodynamic coupling, enables us to predict results such as separations and syntheses, which would be quite impossible to derive in the absence of a consideration of irreversible changes. 

Stated as an abstraction and generalization of engineering observations on the efficiency of heat engines. We start the discussion by presenting a nonmathematical qualitative summary of the arguments on efficiency. Then we define entropy and state the second law. Section 13.5 applies the definition to calculate entropy changes and to predict spontaneity of processes. 

We have said that entropy is a state function but we must justify this statement before proceeding. Traditionally this was done from a consideration of the efficiency of heat engines—a consideration which was a major preoccupation with the pioneers of thermodynamics. As chemists, we shall allow ourselves a short cut by considering only a perfect gas. 

A unique feature of heat engines is that some heat must be given off to the surroundings when they do work. With the piston in the up position, no further work can be done if we do not cool the cylinder back to T]. The cooling process removes some of the thermal energy that could otherwise be converted to work and thereby places a limit on the efficiency of heat engines. 

Using the equation in the Chemistiy in Action entitled The Efficiency of Heat Engines in Chapter 18 ... 

The efficiency of an OTEC system in corrverting heat stored in the warm surface water of the tropical oceans into mechanical work has a theoretical limif called the Carnot efficiency (named after Sadi Camof a French engineer who first defined the thermodyrrarrric restrictions on the efficiency of heat engines), where... 

French physicist, who first worked as a miiitary engineer. He then turned to scientific research and in 1824 published his analysis of the efficiency of heat engines. The key to this analysis is the thermodynamic Carnot cycle. He died at an early age of cholera. 

In 1865, building on the work of Kelvin, Sadi Carnot, and others who studied the efficiency of heat engines, Rudolf Clausius postulated that the entropy change of a system undergoing an infinitesimal reversible process was the heat absorbed (absolute temperature T (in kelvins) of the system ... 

We can use the second law of thermodynamics to establish precise theoretical limits on the efficiency of heat engines. 

According to published literature [2], various scientists initially designed, developed, and tested 10 aqueous electrolyte cell systems, six molten electrolyte cell systems, and only three solid electrolyte cell systems. As mentioned previously, the duel cell is an energy conversion device in which the chemical energy is isother-mally converted into direct current (DC) electricity. In addition, it can convert the chemical energy into the electricity without involving the thermodynamic relation demonstrated by the Carnot cycle to limit the efficiency of heat engines. 

Carnot, Nicolas Leonard Sadi (1796-1832)AFrenchphysicistwhobeganhlscareer as a military engineer before turning to scientific research. In 1824 he published a book Reflections on the Motive Power of Fire, which provided for the first lime a general theoretical approach to understanding the conditions under which the efficiency of heat engines could be maximized. The thermodynamic Carnot cycle eventoally led to the concept of entropy. He died aged 36 from cholera. 

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