Control-surface

Surface science has tlirived in recent years primarily because of its success at providing answers to frmdamental questions. One objective of such studies is to elucidate the basic mechanisms that control surface reactions. For example, a goal could be to detennine if CO dissociation occurs prior to oxidation over Pt catalysts. A second objective is then to extrapolate this microscopic view of surface reactions to the... 

Fig. 21. Control volumes for appHcation of the integral equations of motion where 1, 2, and 3 are the location of control surfaces and Sy (a) general,...

Averaging the velocity using equation 50 yields the weU-known Hagen-Poiseuille equation (see eq. 32) for laminar flow of Newtonian fluids in tubes. The momentum balance can also be used to describe the pressure changes at a sudden expansion in turbulent flow (Fig. 21b). The control surface 2 is taken to be sufficiently far downstream that the flow is uniform but sufficiently close to surface 3 that wall shear is negligible. The additional important assumption is made that the pressure is uniform on surface 3. The conservation equations are then applied as follows ... 

Experimental techniques to visualize flows have been extensively used to define fluid flow in pipes and air flow over lift and control surface of airplanes. More recently this technology has been appHed to the coating process and it is now possible to visualize the flow patterns (16,17). The dimensions of the flow field are small, and the flow patterns both along the flow and inside the flow are important. Specialized techniques such as utilizing small hydrogen bubbles, dye injection, and optional sectioning, are required to visualize these flows. 

With control surfaces at 1 and 2 as shown in the figure, Eq. (6-17) in the absence of losses and shaft work gives... 

The top pressure controller varies the level of liquid in the condenser, so it, like the reboiler, must have extra surface for the derating required for control. Many other control methods also require some control surface. If noncondensibles are present, a vent should be provided. Otherwise, they collect at the liquid seal. With large amounts of noncondensibles, another type of system should be considered. 

Equation set (9.104) approximates to an inverse square law, and increases the controller gains at low speeds, where the control surfaces are at their most insensitive. 

MATLAB Fuzzy Inference System (FIS) editor can be found in Appendix 1. Figure 10.16 shows the control surface for the 11 set rulebase fuzzy logic controller. 

Fig. 10.16 Control surface for 11 set rulebase fuzzy logic controller.

Environmental factors such as severe hailstorms and human errors such as impact by aircraft service equipment also cause in-service damage to bonded assemblies. Bonded honeycomb sandwich assemblies are particularly prone to such damage because of their customary use as lightly loaded fairings and flight control surfaces and subsequent thin facesheets and relative fragility. 

Fig. 34. Flight control surfaces with trailing edge wedges. Reproduced by permission of the Boeing Company.

Fig. 1.2 shows a gas turbine power plant operating on a closed circuit. The dotted chain control surface (F) surrounds a cyclic gas turbine power plant (or cyclic heat engine) through which air or gas circulates, and the combustion chamber is located within the second open control surface (Z). Heat (2b is transferred from Z to Y, and heat (2a is rejected from Y. The two control volumes form a complete power plant. 

Usually, a gas turbine plant operates on open circuit , with internal combustion (Fig. 1.3). Air and fuel pass across the single control surface into the compressor and combustion chamber, respectively, and the combustion products leave the control surface after expansion through the turbine. The open circuit plant cannot be said to operate on a thermodynamic cycle however, its performance is often assessed by treating it as equivalent to a closed cyclic power plant, but care must be taken in such an approach. 

For a cyclic gas turbine plant in which fluid is circulated continuously within the plant (e.g. the plant enclosed within the control surface Y in Fig. 1.2), one criterion of performance... 

The heat supply to the cyclic gas turbine power plant of Fig. 1.2 comes from the control surface Z. Within this second control surface, a steady-flow heating device is supplied with reactants (fuel and air) and it discharges the products of combustion. We may define a second efficiency for the heating device (or boiler) efficiency. 

B is the heat transfer from Z to the closed cycle within control surface Y, which occurs during the time interval that A/f, the mass of fuel, is supplied and [CV]q is its calorific value per unit mass of fuel for the ambient temperature (Tq) at which the reactants enter. F = A/f[CV]o is equal to the heat (0o) that would be transferred from Z if the products were to leave the control surface at the entry temperature of the reactants, taken as the temperature of the environment, Tq. Fig. 1.7 illustrates the definition of calorific value. 

Fig. 4.8 shows the open cooling process in a blade row diagrammatically. The heat transfer Q, between the hot mainstream (g) and the cooling air (c) inside the blades, takes place from control surface A to control surface B, i.e. from the mainstream (between combustion outlet state 3g and state Xg), to the coolant (between compressor outlet state 2c and state Xc). The injection and mixing processes occur within control surface C (between states Xg and Xc and a common fully mixed state 5m, the rotor inlet state). The flows through A plus B and C are adiabatic in the sense that no heat is lost to the environment outside these control surfaces thus the entire process (A + B + C) is adiabatic. We wish to determine the mixed out conditions downstream at station 5m. 

The total enthalpy change across the whole (stationary) cooled blade row is straightforward and is obtained for the overall process (i.e. the complete adiabatic flow through control surfaces (A + B) plus (C)). Even though there is a heat transfer Q internally between the unit mainstream flow and the cooling air flow i//, from A to B, the overall process is adiabatic. 

In the simplified a/s analysis of Section 4.2 we assumed identical and constant specific heats for the two streams. Now we assume semi-perfect gases with specific heats as functions of temperature but we must also allow for the difference in gas properties between the cooling air and the mainstream gas (combustion products). Between entry states (mainstream gas 3g, and cooling air, 2c) and exit state 5m (mixed out), the steady flow energy equation, for the flow through control surfaces (A + B) and C, yields, for a stationary blade row,... 

To determine the overall change in total pressure we must now consider the three control surfaces A, B and C of Fig. 4.8 separately. 

Thus, Po and To at exit from the control surfaces A and B are given by A (mainstream gas)... 

A more sophisticated approach would not only take account of Eqs. (4.45) and (4.46) to give the two stagnation temperatures at exit from control surfaces A and B, but it would also not assume the total pressures of coolant and mainstream to be the same. Eor the first nozzle guide vane row these can be derived by accounting for losses as follows ... 

Here A5inicrn.ii is the entropy increase of the cooling fluid in control surface B due to friction and the heat transfer (Q, in), A5,nu,iii is the entropy created in the metal between the mainstream and the coolant (or metal plus thermal barrier coating if present) due to temperature difference across it, A uxiemai is the entropy increase in the mainstream flow within control surface A before mixing due to heat transfer (Q, out), plus the various entropy increases due to the mixing process itself in control surface C. 

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