Arbitrary overall efficiency

Many preliminary analyses of gas turbines are based on the assumption of a closed air standard cyclic plant, and for such analyses the use of tj as a thermal efficiency is entirely correct (as discussed in the early part of Chapter 3 of this book). But most practical gas turbines are of the open type and the rational efficiency should strictly be used, or at least its approximate form, the arbitrary overall efficiency tjq. We have followed this practice in the latter part of Chapter 3 and subsequent chapters even though some engineers consider this differentiation to be a somewhat pedantic point and many authors refer to tjo as a thermal efficiency (or sometimes the lower heating value thermal efficiency ). 

Calculation of the specific work and the arbitrary overall efficiency may now be made parallel to the method used for the a/s cycle. The maximum and minimum temperatures are specified, together with compressor and turbine efficiencies. A compressor pressure ratio (r) is selected, and with the pressure loss coefficients specified, the corresponding turbine pressure ratio is obtained. With the compressor exit temperature T2 known and Tt, specified, the temperature change in combustion is also known, and the fuel-air ratio / may then be obtained. Approximate mean values of specific heats are then obtained from Fig. 3.12. Either they may be employed directly, or n and n may be obtained and used. 

With turbine and compressor work determined, together with the heat supplied , the arbitrary overall efficiency is obtained. 

Fig. 4.9 shows the results of calculations based on these assumptions in comparison with the uncooled calculations (the other assumptions were those listed for the earlier uncooled calculations in Section 3.4.1). The (arbitrary) overall efficiency is shown plotted... 

The (arbitrary) overall efficiency and specific work quantities obtained from these calculations are illustrated as carpet plots in Fig. 4.11. It is seen that the specific work is reduced by the turbine cooling, which leads to a drop in the rotor inlet temperature and the turbine work output. Again this conclusion is consistent with the preliminary analysis and calculations made earlier in this chapter. 

Fig. 5.6 shows the results of a set of computer calculations for the [CBTJics plant in the form of (arbitrary) overall efficiency (tjq) against pressure ratio (r) with the combustion temperature T ox as a parameter. Fig. 5.7 shows tjq plotted against T x with r as a parameter and Fig. 5.8 shows a contour plot of tjq against T ox and r. There is a flat efficiency plateau around T ox 1750°C, less than the maximum value used in these calculations, which approaches the stoichiometric limit. 

Thus, the (arbitrary) overall efficiency of the whole plant is... 

The arbitrary overall efficiency of the combined plant (Eq. (7.12)) may then be written... 

For an open circuit power plant, an (arbitrary) overall efficiency has been defined as W... 

Figure 3 shows a comparison of the model prediction of the overall collection efficiency as a function of superficial gas velocity versus the experimental data of Tardos et al (12). Since the charge acquired on the collectors was not reported, assumed values shown in Figure 3 were employed. It should be noted that this assumed functional dependency between and was not entirely arbitrary, but qualitatively suggested by experimental measurements of the electric potential in the fluidized bed (12). An important aspect of Figure 3 is both the model prediction and experimental... 

The overall tray efficiency E fy (often called Murphree efficiency ) takes into account concentration gradients on the tray. It has an arbitrary definition based on the average total vapor composition leaving the froth and the specific liquid composition leaving the tray [not the average composition on the tray (see Figure 12.58)]. Because of this arbitrariness, the overall tray efficiency valne can exceed 1.0. When there are no composition gradients on the tray, = Ey,y... 

Using a generating function similar to the one introduced by Malkin et al. [99], Jankowiak et al. obtained several analytic sum rules. From these sum rules, it is then possible to estimate the contribution of any overlap integral or an entire group of them to the total intensity. Several scenarios were defined to maximize the efficiency of the overall procedure. Due to its analytic definition, the method relies on very little arbitrary parameters to work, so it can be safely used in a blackbox procedure. 

The choice between trays and packing is somewhat arbitrary because eitho- can usually be designed to do an adequate job, and the overall economics ate seldom decisively in favor of one or the other. At tUs time, sieve tray columns ate probably the most popular for both absorbs and strippers in conventional, large commercial amine plants while packed columns are often used for revamps to increase edacity or efficiency and for special applications. 

Fig. 6.5.1 is presented to help visualize the mass loading ( saltation ) and classification phenomenon that exists in the general case when the incoming mass loading exceeds the limit-loading. This illustration, which is a simple material balance, was created for a unit mass entering the cyclone over some arbitrary time interval. Note that the underflow solids quantity, divided by the feed solids quantity (unity), gives the overall collection efficiency as presented by Eq. (6.5.1). 

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