Ideal work

We will start with establishing the standard of excellence for efficient energy utilization the concept of ideal work. When this is reached, no further energy conservation is possible. 

We continue with a discussion of the usefulness of the various forms of energy and the method for determining it through the use of a relatively new concept, exergy. 

We proceed with a presentation of the quantitative criteria used to determine the degree of efficient energy utilization in a given process first and second law efficiencies, followed by a brief description of one of the methods used to obtain increased such efficiencies in the use of thermal energy. Cogeneration. We demonstrate the energy savings achieved and discuss the limitations involved and the ways around them. 

We continue with Kenney s commentary on the favorable economics of energy conservation, but also on the Institutional barriers that limit its wider applicability, and close the Chapter with some concluding remarks. 

For a given process, involving a specified change, there is an amount of work associated with it, referred to as Ideal Work W(id), which is  

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The turbine isentropic efficiency tjt measures the ratio of the actual to ideal work obtained ... 

A completely reversible processes is hypothetical, devised solely to find the ideal work associated with a given change of state. Its onlv con-neclion with an actual process is that it brings about the same change of state as the actual process, allowing comparison of the actual work of a process with the work of the hypothetical reversible process. 

Subtracting the ideal work rate as given by Eq. (4-359) yields... 

Calculation of Ideal Work If changes in kinetic and potential energies are neglected, Eq. (4-360) is apphcable. From the tabulated data,... 

Adiabatic efficiency is given by the following relationship Ideal work... 

If the expander effieieney is aeross the expander, the ideal work would be... 

In a turbine, not all energy supplied ean be eonverted into useful work— even with an ideal fluid. There must be some kinetie energy at the exit that is diseharged due to the exit veloeity. Thus, the utilization faetor is defined as the ratio of ideal work to the energy supplied... 

The actual work input coefficient, is written by taking the ideal work input coefficient, Equation 5.1, and modifying by the addition of the slip factor, SF. The geometric relationship of the Stodola slip function is shown in Figure 5-23. 

By replacing the ideal work input coefficient with actual work input coefficient, the actual head input can be written as... 

It should be noted that although optimum operating conditions for the Aaberg exhaust system might be accurately found under ideal working conditions, the following points should be considered ... 

If no Mollier diagram is available, it is more difficult to estimate the ideal work in compression or expansion processes. Schultz (1962) gives a method for the calculation of the polytropic work, based on two generalised compressibility functions, X and Y which supplement the familiar compressibility factor Z. 

Diesel cycle a repeated succession of operations representing the idealized working behavior of the fluids in a diesel engine. 

From this equation we established the earlier minimum for the amount of work, the ideal work, required to change the system s conditions from state 1 to 2 with AP = P2 - P, and AT = T2 - and thereby its thermodynamic properties AH = H2-H1 and AS = S2 - Sp... 

Use ratio to calculate ideal work of steam per Ibmol of gas... 

The maximum work results when the 1 kg of steam is reduced in a completely reversible process to the conditions of the surroundings, where it is liquid at 300 K (26.85 degC). This is the ideal work. 

Obviously the TOTAL rate of entropy generation is zero. This is because the ideal work is for a completely reversible process. 

This is a variation on Example 5.6., pp. 175-177, where all property values are given. We approach it here from the point of view that if the process is completely reversible then the ideal work is zero. We use the notation of Example 5.6 ... 

The system consists of two parts the apparatus and the heat reservoir at elevated temperature, and in the equation for ideal work, terms must be included for each part. 

The percent values above express each quantity as a percentage of the absolute value of the ideal work, to which the quantities sum. 

The ideal work of the process is that of a Carnot engine operating between the temperature of the refrigerated space and the temperature of the surroundings. 

In each case the ideal work and the lost work terms sum to give the actual work, and each term may be expressed as a percentage of the actual work. 

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