Energy 4 Flashcards
What would be a typical maximum temperature and pressure of steam in a steam turbine?
Typical highest inlet steam temperatures are 566°C - 620°C
Typical highest pressure in a steam turbine are 250-290 bar
In the combined cycle gas turbine, the steam temperature reaches a peak at 565 degrees Celsius and 138 Bar
How is the steam produced in a combined cycle gas turbine (CCGT)?
In a Combined Cycle Gas Turbine (CCGT), steam is produced by capturing and utilizing the waste heat from the gas turbine. The hot exhaust gases from the gas turbine are passed through a heat recovery steam generator (HRSG), where water is converted into steam. This steam then drives a steam turbine, contributing to the overall power generation efficiency of the system.
Write down an expression for the fluid power available to a turbine based on the velocity of the
flow.
P = 1/2 pAV^3
where,
P is the fluid power,
ρ is the density of the fluid,
A is the cross-sectional area of the flow
V is the velocity of the fluid flow.
What is the value of the Betz limit for a turbine and explain the significance of it.
0.593
Betz limit: Max efficiency for a wind turbine is 59.3%, determined by airflow laws. Real turbines operate under due to air resistance, mechanical losses, and wake effects. It’s a fundamental cap on wind energy extraction efficiency.
- Define the efficiency of a turbine
Efficiency = Shaft power extracted / Fluid power available
n = Wshaft/(pght)Q
work rate on shaft
pressure available
volumetric airflow
For a hydropower turbine, what is a typical turbine efficiency?
Typical hydropower turbine efficiency ranges from 80% to 90%, converting water’s kinetic energy into electricity.
What are the operational characteristics of a turbine for power generation?
Narrow optimal operating range.
Max. efficiency strongly determined by blade geometry.
Operational point defined by ratio of rotational speed and flow velocity
Torque is maximum when wheel is stationary, but power is zero
In 2019, approximately what was the installed capacity of all onshore wind turbines in Ireland?
Approximately 3000MW
Source: SEAI
Define the term “capacity factor”.
Capacity factor: ratio of the actual output of a power plant to its maximum potential output if it operated at full capacity continuously, expressed as a percentage.
CF = Annual energy generated (MWh) / Rated Capacity(MW) x 8760(hours)
What is approximate average capacity factor of onshore wind power in Ireland?
SEAI reports 743 ktoe from wind in 2018
CF = 743(ktoe) x 11,630 / 4235(MW) 8760(hours) = 23%
Source: Lecture Notes
What are the disadvantages of Darrieus type vertical axis wind turbines?
Poor starting torque
Performance can be
sensitive to gusts
Tip speed cannot exceed
wind speed by much
hence efficiency limited
Source: Lecture Notes
What are the disadvantages of Savonius type vertical axis wind turbines?
Low speed, high torque
Performance not too
sensitive to gusts
Tip speed cannot exceed
wind speed hence efficiency
limited.
What are the technical reasons to build commercial horizontal axis wind turbines higher?
Building commercial horizontal axis wind turbines higher:
increases energy capture due to higher and more consistent wind speeds
reduces turbulence and improves efficiency
and allows for larger rotor diameters, enhancing overall power generation.
Write down an expression that approximates the variation of wind speed with altitude in the
atmospheric boundary layer. Give approximate values for any constants.
Approximate as:
V1/V2 = (Z1/Z2)^a
a depends on terrain:
a approx=1/7 for flat sea or land.
a approx= 1/5 for countyside.
but has complex relationship due to weather.
What is the power coefficient for a wind turbine?
c_p = shaft power / wind power available = Wshaft / 1/2 pAV^3
