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CIVE40010 - Energy and environmental engineering > 3 Technical Concepts and Overview > Flashcards

3 Technical Concepts and Overview Flashcards

1
Q

When is an object said to have done work?

A

When it has been displaced against physical resistance

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2
Q

What it the formula to find work in terms of integrals?

A

W = ∫ F*dl

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3
Q

What is a Joule?

A

Work done moving 1 meter against a force of 1 newton

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4
Q

What is energy?

A

Capacity to perform work

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5
Q

What are the 3 forms of energy?

A
  • Kinetic
  • Potential
  • Chemical
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6
Q

What is power?

A

Power is the rate of doing work

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7
Q

What is a Watt defined as?

A

Watt, defined as 1 Joule per second

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8
Q

What two quantities does ohms low relate?

A

Ohms law relates the voltage difference and the electrical current flowing through the resistance

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9
Q

How does heating a wire affect the current?

A

Heating in wire increases with the square of the current

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10
Q

Whats the maximum solar power at the Earths surface?

A

1π‘˜π‘Š/π‘š^2

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11
Q

Whats the rating of an open cycle gas turbine?

A

300 π‘€π‘Š

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12
Q

How much is 1 barrel of oil equivalent?

A

6GJ

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13
Q

How much is 1 cubic meter of gas?

A

40 MJ

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14
Q

What is the fossil fuel equivalent conversion?

A
  • Is approximate and depends on the reference fuel
  • Depends on where the fossil fuel equivalent has come from
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15
Q

Which laws of thermodynamics need to applied?

A
  1. The First Law of Thermodynamics
  2. The Second Law of Thermodynamics
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16
Q

What is the first law of thermodynamics?

A

Energy is neither created nor destroyed but converted from one from to another

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17
Q

How is energy in a frictionless environment?

A

𝑄 = π‘ž + π‘Šπ‘œπ‘Ÿπ‘˜

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18
Q

What is the second law of thermodynamics?

A

A device operating continuously cannot export only work from an isolated source of heat

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19
Q

What is a device doing work paired with?

A

Energy from a higher temperature

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20
Q

What are energy flows associated with in society?

A
  • Static engines
  • Chemical process plant
  • Keeping warm and cool
  • Transport of people and goods
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21
Q

What is an example or the second law of thermodynamics?

A

Heat engine that extracts mechanical work from a heat source

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22
Q

What does the 2nd law state in terms of q?

A

q β‰  0

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23
Q

What happens as energy flows through a process?

A

Grade deteriorates

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24
Q

What is the theoretical maximum extractable work called?

A

Exergy

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25
Q

What is a heat source exergy like and what does it depend on?

A

<100%
- Hot source temperature
- ambient temperature

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26
Q

What happens if heat source tends to infinity?

A

The source tends to pure exergy and is said to be very high grade

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27
Q

What happens if heat source is close to ambient?

A

There is little content left and the heat source is very low grade

28
Q

How do you calculate efficiency?

A

πœ‚ = Output/input

29
Q

What is first law efficiency?

A

Uses energy arriving at the process ignoring grade or upstream energy system losses

30
Q

What is primary energy efficiency?

A

Replaces the delivered energy* input by the primary energy* required to produce it

31
Q

What is exergy efficiency?

A

Compares the actual consumption against that required by a thermodynamically ideal process

32
Q

How do you calculate exergy efficiency?

A

πœ‚ = required exergy/total exergy input

33
Q

What is an energy system?

A

Accepts one or more energy flows and transforms them to produce one or more energy flows of different grade

34
Q

Where is there a large amount of exergy lost in a conventional power station?

A

Between the combustion flame and the steam entering the turbine

35
Q

What a Combined Cycle Power Plant?

A

Use a gas turbine to take exergy from the gas flame and pass the cooled down gases (if 500C is cool!) to a steam
plant driving a steam turbine.

36
Q

What is an ideal heat engine called?

A

Carnot Engine

37
Q

What two energy systems are exergetically more efficient?

A
  • Heat Pump
  • Combined Heat and Power
38
Q

How does heat pump work?

A

Energy is taken from a cool (low grade source) and power is supplied (100% exergy) to raise its grade to discharge as heat at a higher temperature

39
Q

How does the Carnot engine work?

A

Takes energy at a rate 𝑄̇ from a heat source at 𝑇_h and discharges waste heat at a rate π‘žΜ‡ to a heat sink at 𝑇_c. while producing power π‘ŠΜ‡ , without loss of exergy in the process

40
Q

What does a refrigerator do in a heat pump system?

A

Extracts energy from a cold volume and discharges it at above kitchen temp at the back of the fridge.

41
Q

what is the function of an air
conditioning mit?

A

Removes heat from a room and discharges at a higher temp in a β€œcondenser” usually located on the roof

42
Q

How is power supplied in refrigerant circuit?

A

Compressor

43
Q

How does an air-to-air heat pump work?

A

Takes heat from ambient and ups its grade by adding exergy of its shaft power to the flow of energy into building

44
Q

How much work supplied to heat pump?

A

13% of the heat requirement

45
Q

What is the temp of the heat flow of an air-to-air heat pump?

A

30 - 40˚C

46
Q

What is the equation for COP?

A

𝑄̇ = 3 βˆ’ 4 π‘ŠΜ‡

47
Q

How can performance of a2a improve?

A

Geothermal heat source rather
than air

48
Q

Why is condensing at 35˚C in a steam turbine not good?

A

Too low for use in central heating, and therefore it is genuinely waste heat

49
Q

What is CHP?

A

Use of a heat engine or power station to generate electricity and useful heat

50
Q

What is raw fuel entering the economy termed as?

A

Primary energy

51
Q

What are the examples of secondary energy?

A
  • Refined oil
  • Town gas
  • Electrical power
52
Q

What is useful energy?

A

Energy may need to be converted on site to provide the final service

53
Q

Why must energy supply match demand approximately?

A

To ensure stability of the energy grid and constant supply, despite the variability in consumption

54
Q

How is electricity stored in the UK, and what is its significance?

A

Limited to short durations, typically 1-2 minutes using batteries with around 1GW capacity

55
Q

What are the challenges in electricity supply and demand matching in the UK?

A
  • complex real-time system operations
  • spatially-distributed and time-varying demand
  • need for a variety of generators
56
Q

What mechanisms are used in the UK to ensure electricity supply meets demand?

A

regulated electricity market

57
Q

What happens if sufficient capacity is not provided in markets like housing and transport?

A
  • Housing price goes up
  • Impacts on time and GDP in the transport market
58
Q

How is the electricity market different from other markets when capacity is insufficient?

A

Insufficient capacity can lead to system failure

59
Q

What does the β€œday ahead market” in the electricity sector signify?

A

The day ahead market represents the wholesale price of electricity for the next day, reflecting anticipated demand and available supply.

60
Q

Why’s is capacity not always utilised?

A
  • Variability in renewable energy sources (like wind and solar)
  • Market demands
  • Maintenance cycles
  • System efficiency
61
Q

What is the capacity factor?

A

Ratio of average generation rate to installed capacity

62
Q

What is the LCoE?

A

Lowest price that consumers need to pay for the electricity generated to break even at the end of the project lifetime

63
Q

How do you calculate LCoE?

A

(OPEX + CAPEX)/E

64
Q

What is the learning rate?

A

Characteristic parameter that defines the cost reduction [%] for each doubling of cumulative capacity.

65
Q

What cost reductions due to?

A

Mainly due to technology innovation and to a reduction in perceived risk.

CIVE40010 - Energy and environmental engineering (21 decks)

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