Energy consumption and lost work

In this chapter, we show that it is not so much energy that is consumed but its quality, that is, the extent to which it is available for work. The quality of heat is the well-known thermal efficiency, the Carnot factor. If quality is lost, work has been consumed and lost. Lost work can be expressed in the products of flow rates and driving forces of a process. Its relation to entropy generation is established, which will allow us later to arrive at a universal relation between lost work and the driving forces in a process. 

In a way the situation can be compared with consuming food. If we made a thorough analysis of food consumption, we would conclude that it is not its mass that we have consumed, as the mass balance is not affected. Nor is it the energy that we have consumed as a properly performed energy balance will show. This led Schrodinger [1] to his somewhat desperate question If it is mass nor energy that we extract from food then what is it...  

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In Chapter 2, we pay a renewed visit to thermodynamics. We review its essentials and the common structure of its applications. In Chapter 3, we focus on so-called energy consumption and identify the concepts of work available and work lost. The last concept can be related to entropy production, which is the subject of Chapter 4. This chapter shows how some of the findings of nonequilibrium thermodynamics are invaluable for process analysis. Chapter 5 is devoted to finite-time finite-size thermodynamics, the application of which allows us to establish optimal conditions for operating a process with minimum losses in available work. 

An example of reducing energy consumption in use is found in 4-stroke automobile lubricants.Only about 20-35% of the energy released by the combustion of fuel is turned into useful mechanical work. The rest is lost as heat and friction. Lubricants play an important role in the overall efficiency of the vehicle. 

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