Turbines temperature change

Since aerothermal performance of compressors and turbines is very sensitive to inlet temperature and pressure variations, it is essential to normalize the aerothermal performance parameters such as flow, speed, horsepower, etc., to standard-day conditions. When these corrections to standard conditions are not applied, a performance degradation may appear to occur when in fact it was a performance change resulting merely from ambient pressure and temperature changes. Some of the equations for obtaining correction to standard-day conditions are given in Table 19-3. 

Turbine fouling. This is indieated by an inerease in turbine exhaust temperature. Change in vibration amplitude will oeeur when fouling is exeessive and eauses rotor imbalanee. 

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. 

But another approach to multi-step cooling [8, 9] involves dealing with the turbine expansion in a manner similar to that of analysing a polytropic expansion. Fig. 4.4 shows gas flow (1 + ijj) at (p,T) entering an elementary process made up of a mixing process at constant pressure p, in which the specific temperature drops from temperature T to temperature T, followed by an isentropic expansion in which the pressure changes to (p dp) and the temperature changes from T to (7 - - dT). 

The catalyst should also be resistant to thermal shock, that is, a sudden increase or decrease in temperature. Rapid temperature changes occur during start-up or shut-down of the turbine. The most serious thermal shocks occur upon sudden loss of the turbine load. If the turbine load is lost (by opening a circuit breaker, for example) the fuel must be shut off immediately to prevent overspeeding and destruction of the turbine. The air continues to flow, however, so the temperatme of the catalyst drops very rapidly. Under these conditions the catalyst temperature can fall 1000°C in 100ms, which poses severe problems for ceramic materials. Most... 

The minus sign indicates that the power is given out. This 12kW of power would make a useful contribution to the 57 kW needed. However, if we look at the temperature change, we see that it might not be possible to harness all this power. From equation 9.9, we see that die temperature change through the turbine would be... 

Figure 13. Reactor Hot Pin Hot Spot Temperature Change during Loss of One of Two Turbines... 

A positive reactivity of 0.1 is inserted stepwise as a reactivity perturbation. The feedwater flow rate and the turbine control valve opening are kept constant. The results are shown in Figs. 4.9 and 4.10. The power quickly increases to 111% of the initial value. It is consistent with the analytical solution of prompt jump. Then, the power decreases due to reactivity feedbacks from Doppler and coolant density. The main steam temperature changes by following the power. The main steam pressure and the core pressure increase due to increases in the temperature and hence the volume flow rate of the main steam. The fuel channel inlet flow rate changes with the core pressure due to the relation between the feedwater flow rate and the core pressure shown in Fig. 4.4. The plant almost reaches a new steady state in 40 s. 

Sensors that are encased in robust EEx d housings operate more reliably when used for constant measurement of the rpm and valve positions in compressors and gas and steam turbines. This type of housing protects them from adverse environmental factors (EMV, temperature changes, humidity, and oscillations). 

Because oxides are usually quite brittle at the temperatures encountered on a turbine blade surface, they can crack, especially when the temperature of the blade changes and differential thermal contraction and expansion stresses are set up between alloy and oxide. These can act as ideal nucleation centres for thermal fatigue cracks and, because oxide layers in nickel alloys are stuck well to the underlying alloy (they would be useless if they were not), the crack can spread into the alloy itself (Fig. 22.3). The properties of the oxide film are thus very important in affecting the fatigue properties of the whole component. 

The reheat cycle increases the turbine work, and consequently the net work of the cycle, can be increased without changing the compressor work or the turbine inlet temperature by dividing the turbine expansion into two... 

The losses that are encountered in a plant can be divided into two groups, uncontrollable losses, and controllable losses. The uncontrollable losses are usually environmental conditions, such as temperature, pressure, humidity, and the turbine aging. Table 20-3 shows the approximate changes that would occur for these changes. It must be remembered that these are just approximations and will vary for individual power plants. 

In practical open circuit gas turbine plants with combustion, real gas effects are present (in particular the changes in specific heats, and their ratio, with temperature), together with combustion and duct pressure losses. We now develop some modifications of the a/s analyses and their graphical presentations for such open gas turbine plants, with and without heat exchangers, as an introduction to more complex computational approaches. 

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