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Sustainable and the environment > R.K.Al-Dadah > Flashcards

R.K.Al-Dadah Flashcards

1
Q

What are the relative merits of gas turbines and stream turbines?

A
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2
Q

What is combinded heat and power?

A

Schemes which combine electrical generation with heat for space heating and / or specific industrial processes are referred to as Combined Heat and Power (CHP) .

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3
Q

What are the advantages of CHP?

A
  • Efficient use of fuel resources by recovering about two thirds of the wasted heat.
  • Improved national energy efficiency and the preservation of non-renewable energy resources.
  • Reduction in environmental pollution - more efficient conversion of less fuel.
  • Local generation of electricity and the reduction of the cost of transportation of electricity.
  • Investment in industry - investing in city based CHP schemes increases jobs availability in the city and the country on overall.
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4
Q

What is the heat to power ratio?

A

The ratio of heat energy to electrical energy produced.

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5
Q

What is the back pressure arrangement for the steam turbine CHP system?

A

For the back-pressure type, the condenser pressure is controlled according to the heat / power ratio. The higher the heat demand, the higher the condenser pressure required to supply the heat needed. But this will be on the account of the power generated.

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6
Q

What is the ideal heat to power ratio of the back pressure CHP system?

A

9:1

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7
Q

What is a prime mover?

A

Prime mover” is a technical term of art in science and engineering meaning any machine (or component of a machine) that converts energy from a source energy into mechanical energy (shaft power)

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8
Q

How does the pass out arrangment work for CHP steam turbine systems?

A

For passout type arrangement, the heat is supplied by a proportion of steam bled out of the turbine at intermediate stage through the expansion process

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9
Q

What is the ideal heat to power ratio of the passout arrangment of a CHP steam turbine system?

A

3:1

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10
Q

What is the ideal heat to power ratio for a gas turbine CHP system?

A

3:1

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11
Q

What is the ideal heat to power ratio for a large diesel engine?

A

1:1

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12
Q

What is the ideal heat to power ratio of a small IC engine CHP system?

A

2:1

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13
Q

What is a tri generation system?

A
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14
Q

How does absorption cooling work?

A
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15
Q

How should wind turbines be spaced?

A
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16
Q

What is a vertical axis wind turbine?

A
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17
Q

What is the velocity distribution of air as it goes through a wind turbine?

A

Velocity of air at outlet from the slipstream is smaller than velocity at inlet, but velocities immediately upstream and immediately downstream of the turbine rotor are the same.

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18
Q

What is the pressure distribution of air as it goes through a wind turbine?

A
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19
Q

What is Betzs law?

A

• As the wind turbine extracts energy from the air flow, the air is slowed down, which causes it to spread out and diverts it around the wind turbine to some extent. Albert Betz, a German physicist, determined in 1919 (see Betz’ law) that a wind turbine can extract at most 59% of the energy that would otherwise flow through the turbine’s cross section. The Betz limit applies regardless of the design of the turbine

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20
Q

What is the interferance factor?

A

a=(v1-v2)/v1

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21
Q

What is the maximum power in the air that goes through a wind turbine?

A

Pmax=0.5*mflow rate*V2

Pmax=0.5*ρ*A*V3

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22
Q

How do you find the energy extracted by a wind turbine?

A

Pextracted=KEin-KEout

=0.5*mflow rate*V12-0.5*mflow rate*V42

=ρA2V2*0.5*(V12-V42)

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23
Q

What is the efficiency of a wind turbine in terms of the interferance factor?

A

η=4a(1-a)2

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24
Q

What interferance factor gives the greatest wind turbine efficiency?

A

1/3

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25
Q

What are some of the advantages of nuclear power?

A
  • Nuclear power costs about the same as coal, so it’s not expensive to make.
  • Does not produce smoke or carbon dioxide
  • Produces huge amounts of energy from small amounts of fuel.
  • Produces small amounts of waste.
  • Nuclear power is reliable.
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26
Q

What can cause a nucleus to be unstable?

A

Having too many or too few neutrons and having too much energy.

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27
Q

what are the units of the decay constant?

A

s^-1

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28
Q

what is the decay constant a measure of?

A

The probability that an individual nucleus will decay in one second.

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29
Q

What is the half life?

A

The average time it takes for the number of undecayed atoms is halve.

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30
Q

What is mass defect?

A

The difference between the total mass of a particle and the sum of the masses of the constituent parts.
The mass gets lossed as energy emitted when they bond.

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31
Q

What is the binding energy?

A

The energy needed to separate all of the nucleons in a nucleus.

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32
Q

How large is the Mev?

A

1.6 X 10^-13 joules.

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33
Q

Why does nuclear fusion release energy?

A

Combining small nuclei increases the binding energy per nucleon meaning energy is released.

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34
Q

In terms of binding energy per nucleon, how does nuclear fission give energy?

A

A large nucleus is split in two, meaning an increase in the binding energy per nucleon so energy is given out.

35
Q

What is critical mass?

A

The smallest amount of fissile material needed to sustain a nuclear reaction.

36
Q

How is nuclear fission like a chain reaction?

A

Because when it happens, neutrons are released and these can take induce more reactions to happen.

37
Q

What is the purpose of a moderator?

A

To slow down the neutrons so that they can be captured by other nucleolus.
Choosing a moderator that will absorb more as temperature increases will reduce the chance of meltdown.

38
Q

What is a super critical mass?

A

One where each reaction will induce several more reactions. Super critical mass is used in nuclear reactors and control rods are used to control it.

39
Q

What are control rods?

A

Rods that absorb neutrons (boron) and can be inserted by varying degrees to affect the number of reactions. In an emergency they are inserted all the way to stop the reaction.

40
Q

What does the coolant in a nuclear reactor do?

A

It absorbs the heat from a nuclear reaction meaning it can be latter turned into steam to give energy.

41
Q

Why is a nuclear reactor in a concrete case?

A

to stop radiation coming out

42
Q

Why are the waste products of a nuclear reactor unstable

A

They usually have a larger proportion of neutrons than nuclei of a similar atomic number, making them unstable.

43
Q

what is one of the practical uses of radioactive waste?

A

Used as tracers in medical diagnosis.

44
Q

What is done with radioactive waste?

A

They have to be handled with care(remote control, impact proof flasks). When removed from a reactor, they are originally very hot and they are put in cooling ponds until the temperture falls.(several months)
It is them stored underground in sealed containers until the activity has fallen.
uranium removed from active waste.
vitrification

45
Q

Why is nuclear fusion hard to achieve?

A

All nuclei are positively charged meaning that the electrostatic force will repel them and they need to get close enough so that the strong nuclear force will pull them together. They need about 1 Mev of KE to achieve this which is a lot.

46
Q

why does fission in uranium fuel rods cause them to get very hot?

A

fission fragments and neutrons collide with each other and other things and transfer ke. They vibrate more and this causes heat.

47
Q

what is enriched uranium?

A

It has a higher proportion of 235 than natural uranium(238)

48
Q

why is it that after time fuel rods become more dangerous?

A

They will contain unstable fragments that emit beta and gamma radiation. They have a short half life and will damage people

49
Q

what is a self sustaining chain reaction?

A

fission reactions give out neutrons
neutrons cause further fission
self sustaining when one fission leads to at least one further fission

50
Q

what is involved in the process of moderation?

A

There is a large no. of collisions
there are elastic, ke is given to the moderator atoms
they don’t absorb neutrons
they should have a relatively low mass.

51
Q

Why might carbon dating be inaccurate ?

A

The item may have not been made immediately after the wood was killed.
Can’t be sure of carbon 12 to 14 ratio many years ago.
Contamination
Small count rates are susceptible to statistical variation.

52
Q

What can a chain reaction only happen when the uranium has a certain mass?

A

The number of escaping neutrons ∝ surface area
As mass increases surface/volume ratio falls
So less neutrons escape.
Fraction producing fission increases as mass increases

53
Q

what is an equation that uses the number of half lives to find the amount of mass of a radioactive sample.

A

remaining mass=(0.5)^n*mₒ
mₒ was the starting mass.
n is the number of half lives. This equation also works for activity and concentration.

54
Q

How do you find the energy emmited by a black body?

A
55
Q

How does the energy emitted by a blackbody at a given wavelength change?

A
56
Q

How do you find the engery emitted by a real body?

A
57
Q

What does ε depend on?

A

ε is the emissivity and in general it depends on the wavelength, the temperature and the direction of emission.

A surface is said to be diffuse if its properties are independent of direction and Gray if its properties are independent of wavelength.

58
Q

What are absorbtivity, reflectivity and transmissivity?

A

α+ρ+Τ = 1

For a thick, opaque object,

α+ρ=1 as τ=0

59
Q

What is specular reflection of radioation?

A

angle of incidence = angle of reflection

60
Q

What is diffuse emission of radiation?

A

reflected energy leaves in all directions

61
Q

What is Kirchoff’s thermal law?

A

For an arbitrary body emitting and absorbing thermal radiation in thermodynamic equilibrium, the emissivity is equal to the absorptivity.

α=ε

62
Q

What is the view factor?

A

The view factor is used to account for the effect of orientation on radiation heat transfer between surfaces. The view factor from a surface i to a surface j is defined as Fij and is equal to the fraction of radiation leaving surface i that strikes surface j directly.

63
Q

What are the different ranges for the view factor?

A

The view factor ranges between 0 and 1 Fij=0 indicates that the two surfaces do no have a direct view of each other and thus radiation leaving surface i cannot strike surface j. Fij=1 indicates that surface j completely surrounds surface i so that the entire radiation leaving surface i is intercepted by surface j e.g. two concentric spheres. Also Fii = 0 for plane and convex surfaces.

64
Q

How do you find the energy emitted by a grey body?

A

E=εσT4

ε is the emissivity and depends on wavelength, temperature and the direction of emission. A surface is said to be diffuse if its properties are independent of direction and Gray if its properties are independent of wavelength

65
Q

What is the equation for heat transfer in terms of thermal resistance?

A

Q=E/R

66
Q

What is the equation for surface resistance to radiation?

A

R=(1-ε)/Aε

67
Q

What is the equation for space reistance to radiation?

A

R=1/AF

68
Q

What is the reciportary rule of view factors?

A

A1F12=A2F21

69
Q

What is the mole?

A

6.023*1023 particles in a mole

Number of atoms in 12 grams of cardon 12.

70
Q

What is the atomic mass unit?

A

The weight of one proton or neutron. We know 1 mole weighs 1 gram so it is 0.001/6.023*1023

=1.66*10-27 kg

71
Q

What are some good moderator materials?

A
72
Q

How do you find the density of air?

A

ρ=P/RT

R=287

73
Q

How do you find the thrust acting on a wind trubine due to engery extraction?

A

Thrust=energy extracted / V2

V2 is the velocity right at the turbine blades.

74
Q

How do you find V2 in a wind turbine?

A

V2=(V1+V4)/0.5

75
Q

How can you find the temperture of a planet from the temperture of the sun?

A

Assuming the planet to be a black body, the energy gained from the sun is the same as the engery emmited.

f =Rsun2/Rplanet around the sun2

76
Q

What must be done to find the temperture of a planet assuming it is not a black body?

A

Remember it will not absorbe all of the suns short wavelengths and will not emit all of its longwave lengths.

Sun energy absorbed*(1-ρ)=Earth engergy emmitted*(1-υ)

υ=reflectivity of long waves

ρ= reflectivity of long waves.

77
Q

What is the equation pressure and temperture in an iscentropic process?

A
78
Q

What is the equation for the isentropic efficiency of a turbine?

A
79
Q

What is the equation for the isentropic efficiency of a pump?

A
80
Q

What are the rules for the positioning of external heating and cooling in relation to the pinch point?

A

No external heating below the pinch point.

No external cooling above the pinch point

81
Q

How do you know when you can connect hot and cold streams together?

A

Above the pinch point, the specific heat capacity of the cold streams must be greater than that of the hot streams they are connected to.

Below the pinch point, the specific heat capacity of the hot streams must be greater than that of the cold streams they are connected to.

82
Q

Upon having found the pinch point and you are calculating the heat transfers for the streams. Which pinch tempertures are used for which streams?

A

Higher pinch temp for hot streams. Lower pinch temp for cold streams.

83
Q

What is the significance of the temperture difference with pinch technology?

A

The smaller the temperture difference, the more expensive the heat exchangers

84
Q

What is the equation for the surface area of a sphere?

A

4πr2

Sustainable and the environment (2 decks)

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