Cooling air flow

The second half of the cooling air flow is directed to the front end of the rotor and from there through an aerodynamically shaped annular gap to the rotor surface, forming a film of cooling air down to the second stage. A small portion of this latter air flow is diverted to the labyrinths for sealing and cooling purposes. 

This design has a strut-supported porous shell (Figure 9-19). The shell attached to the strut is of wire from porous material. Cooling air flows up the central plenum of the strut, which is hollow with various-size metered holes on the strut surface. The metered air then passes through the porous shell. The shell material is cooled by a combination of convection and film cooling. This process is effective due to the infinite number of pores on the blade surface. The temperature distribution is shown in Figure 9-20. 

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 a particular blade row, for a given gas entry temperature Tgj, a cooling air entry temperature and an assumed allowable blade metal temperature Tbi, the blade cooling effectiveness eq is obtained. With ep = 0.4 and Pcooi = 0-7, then follows from Eq. (5.10). With C = 0.045 the cooling air flow fraction ip is obtained from Eq. (5.13). 

The results of calculations for the cooling air flow fractions in the first (nozzle guide vane) row of the turbine, ba.sed on the assumptions outlined in Section 5.2 for film cooled blading, are illustrated in Fig. 5.1. The entry gas temperature Tgi was taken as the combustion temperature Tcoi = Ty and the cooling air temperature as the compressor delivery temperature T2. The cooling air required is. shown here as a fraction of the exhaust gas flow, i.e. as ip/( 1 + ip), plotted against compressor pressure ratio and combustion temperature for an allowable blade metal temperature, Tpi = 800°C. Also shown are... 

We also give calculations of the performance of some of these various gas turbine plants. Comparison between such calculations is often difficult, even spot calculations at a single condition with state points specified in the cycle, because of the thermodynamic assumptions that have to be made (e.g. how closely conditions in a chemical reformer approach equilibrium). Performance calculations by different inventors/authors are also dependent upon assumed levels of component performance such as turbomachinery polytropic efficiency, required turbine cooling air flows and heat exchanger effectiveness if these are not identical in the cases compared then such comparisons of overall performance become invalid. However, we attempt to provide some performance calculations where appropriate in the rest of the chapter. 

Cooling air flow can he restricted hy blanking flaps, baffles or winter enclosures, providing that, if not automatic, the operating staff are aware of their presence and will restore the air flow when the weather turns warm again. 

The capillary cassette was placed directly on the heating surface of the thin-film resistive heater to minimize thermal capacitance. A Plexiglas frame was used to hold the assembly and allow access of the cooling air flow from the fans to the capillary cassette. 

A cascade cooler operates in a countercurrent manner in which the cooling air flows in direct contact with the hot material. Lifter flights on the interior wall of the cylinder lift distribute and transport the hot material. 

The principal controls for a blown film line are barrel (cylinder) and die temperatures, die gap, extrusion rate, internal air pressure, bubble diameter, cooling air flow or cooling rate, and line speed (take-off speed). These controls influence the film dimensions and properties. The frost (freeze) line height, which is a ring-shaped zone where the bubble frequently begins to appear frost because the film temperature falls below the softening range of the resin and crystallization occurs, is an indicator for many of these variables. The frost line may not be visible at times. When it is not, the zone where the bubble reaches its final diameter is considered to be the frost line. 

In the Walther-Beratherm shaft cooler the upper part of the shaft is of reduced diameter in order to increase the cooling air flow velocity in this part and thus produce a fluidized bed effect with the object of distributing the incoming clinker (discharged from the kiln) over the whole shaft cross-section and improving the heat transfer. 

The hood pressure control system functions as follows When the pressure in the hood rises, which may occur for example as a result of a decrease in the exit gas flow or an increase in the cooling air flow, the controller increases the volume of air delivered by the exhaust air fan. It does this by adjustment of a damper or an inlet vane control unit or by varying the fan drive motor speed. Conversely, when the pressure in the hood goes down, the air delivery rate of this fan is reduced by the control system. Thus, with the aid of the hood pressure controller, the exhaust air fan performs the function of a pressure relief valve. 

What all types of cooler have in common is that the cooling air flows directly — in counter-current or cross-current — through the clinker and that some or all of the... 

The operation of planetary and rotary coolers requires no special attendant personnel for control. The cooling air flow rate, the clinker discharge rate and the secondary air temperature automatically adjust themselves in relation to the clinker output of the kiln, the heat consumption and the temperature of the clinker on entering the cooler. Fluctuations in the discharge rate or temperature of the clinker on leaving the kiln which are caused by, for example, dislodgment of coating cannot be compensated in the cooler... 

A high motor temperature can indicate obstruction of cooling air flow or, if accompanied by high amperage, an increase in the gas load. Hig h bearing temperatures can indicate misalignment or improper lubrication. 

An air baffle, located between the steel containment vessel and the concrete shield building, which defines the cooling air flow path... 

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