Lost-work functions

Clearly, the lower the ionization energy with respect to the work function, the greater is the proportion of ions to neutrals produced and the more sensitive the method. For this reason, the filaments used in analyses are those whose work functions provide the best yields of ions. The evaporated neutrals are lost to the vacuum system. With continued evaporation of ions and neutrals, eventually no more material remains on the filament and the ion current falls to zero. 

The rate of lost work as a function of the chemical affinity (in dimensionless units see text). The solid line is Equation 4.37, whereas the dashed-dotted line is the parabolic asymptote for small A/RT0 and the dotted line is the linear asymptote for large A/RT0. 

The rate of lost work as a function of the chemical affinity (in dimensionless units see text). 

A is sometimes called the work function because the decrease in A is the maximum work that the system can perform in any isothermal process. To see this, we calculate — 8vt rev, which is the maximum work done by the system, because no energy is lost by friction in a reversible process ... 

The Survivor function, F(t), is the number of elements of the statistical sample which have not failed or lost their function at time t and are still working. In the case of a Weibull statistic model, the survivor function is given by the relation ... 

It is easy to apply equation (3) to all the system or to a subsystem. However, it is also desirable to evaluate the lost work which accompanies the discharge of a stream into a reference environment or alternatively the maximum work which can be obtained if the stream is brought reversibly to the state of the reference environment. The function "Essergy" equation (4), derived and named by Evans (4) leads to such evaluations... 

This formula predicts that the surface charge density imparted by metal contact to the insulator surface is directly proportional to the work function of the metal. Also, the charge is not sensitive to any critical separation at which electrical contact is lost this is a consequence of the effective capacity of a surface with a... 

B is generally referred to as the availability function, and the T ASi term is generally referred to a the lost work LW. Thus... 

Alter the design of the cyclohexane process in Example 9,5 to reduce the lost work and increase the thermodynamic efficiency. Use a simulation program to complete the material and energy balances, and compute the entropies and availability functions for all of the streams, as well as the lost work for each piece of equipment. 

The optimal minimum approach temperature is a function maiidy of the temperature levels of the two streams as indicated in Heuristic 25 of Chapter 5, and the lost work analysis in... 

If the process decreases the availability function for the flowing streams, then the right-hand side of Eg, (9,28) will be a positive quantity. That decrease will be converted to useful work done on the surroundings and/or lost work. However, if the lost work is greater than the decrease in availability, work will have to be transferred from the surroundings to the processing system. If the process is also reversible, then JV. is the maximum work that can be extracted from the decrease... 

The results in Figure 921 and Table 9 5 are used to perform a second-law analysis. The dead-state temperature is taken as 100°F. The calculation of lost work for the entire process and the corresponding second-law efficiency is carried out conveniently on a spreadsheet by transferring results from ASPEN PLUS, as shown in Figure 9 28. Note that the availability function for each stream can be computed and printed by ASPEN PLUS. The overall efficiency is only 25.7%. Similar analyses are carried out readily for the separate operations in the process. The fraction of the total lost work for each operation is as follows ... 

---