Applications of Energy Transfer

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Applications of Energy Transfer

• Dr Neil J Hewitt
• Centre for Sustainable Technologies
• University of Ulster

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Consider the Energy Transfers.

• Power plants and homes.

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Power Stations

• Coal
• Steam Cycle efficiency
• Nuclear
• Steam Cycle efficiency
• Gas
• Joule/Brayton Cycle efficiency
• Wind
• Turbine efficiency
• Hydro
• Turbine efficiency

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Nuclear Power Plant
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4 5
Super heater
Boiler
Reheat
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6 7
Q24
Q45
W12
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Condenser
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T
Q81
5
7
3 4
6
2
8
1
s
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Steam Based Technologies

• Chief limit on efficiency
• Rankine Cycle
• Carnot is the best
• Steam Turbine
• Metallurgical limit
• 540C

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Gas Based Technologies
Fuel
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3 1100C
COMBUSTIONCHAMBER
TURBINE
W
COMPRESSOR
1 Air Inlet
Exhaust products 4
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Combined Cycle Gas Turbine
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Large Scale Hydro Power
Large-scale hydro dam at Sloy, Scotland
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Estimating the Power
Itaipu Dam, Brazil
Potential Energy Mass flow x gravity x
height Itaipu uses on average 9000 tonnes water
per second which falls about 120m.
Therefore 9,000,000 kg/s x 9.81 ms-2 x 120 m
10.6 GW
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Issues
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Wind Power

• Most common
• Horizontal axis wind turbine
• Battery charger to 2MW
• Onshore sites limited
• Visual intrusion
• Offshore

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Power from the Wind

• Power from the wind is given by

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Power from the Wind
Area, A 100m2 (Rotor Ø 11m)
Power contained in the wind 1/2 ?AV3 Where ?
1.2 kg/m3 0.5x1.2x100x103 60,000W
Air Velocity, V 10m/s
N.B The power contained in the wind is not the
power that can be extracted by a wind turbine
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The Betz Limit

• Maximum power extraction possible

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Resources - Onshore

• Hill _at_ 50m
• Blue 11.5 m/s
• Red 10-11.5 m/s
• Yellow 8.5-10 m/s
• Green 7-8.5 m/s

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Offshore Wind Resource

• 50m hub
• gt10km off-shore
• Blue gt9m/s
• Red 8-9 m/s
• Green 7-8 m/s
• Yellow 4.5-6 m/s

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The Environmental Issues
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The Environmental Issues
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The Environmental Issues
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The Environmental Issues
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The Worlds climate in danger
Executive summary Monday January 22, 2001

• There is new and stronger evidence that most of
  the warming observed over the last 50 years is
  attributable to human activities
• Human influences will continue to change
  atmospheric composition throughout the 21st
  century
• The globally averaged surface temperature is
  projected to increase by 1.4 to 5.8 C by 2100
• The projected warming is very likely to be
  without precedent during at least the last 10,
  000 years

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Effect on UK?
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What might be done?

• Renewable Energy
• Energy Efficiency
• Enhanced Oil Recovery
• CO2 capture and the clean combustion of fossil
  fuels
• Nuclear Energy

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Pathways to a low carbon economy UK Emissions
(MtC)
Current forecasts
more energy efficiency
more renewables
CO2 sequestration
RCEP target
impact of hydrogen
60 reduction from 1997
"Low Carbon Economy"
1995
2000
2005
2010
2015
2020
2025
2030
2035
2040
2045
2050
Year
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Are we on track?
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Renewable Energy

• Energy that flows naturally and repeatedly in
  the environment
• Direct from the sun
• Solar power, solar panels, PV cells, passive
  solar design
• Indirectly from the sun
• Wind, waves, running water, biomass

• Energy indirectly from the Moon
• Wave Tidal
• Energy from within the Earth
• Geothermal
• Energy from our lifestyle
• Energy from waste
• MSW sewage sludge

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How Solar Radiation is transformed into various
forms of renewable power on earth
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Domestic PV Electricity Generation.
Distribution circuit breakers
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Domestic PV Application
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Passive Solar Design for Heating
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Example of Direct Gain South facing Glazing.
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Integrated Storage Solar Water Heaters
Poor heat removal over the day
Section of solar water heater combining collector
storage
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Typical Flat Plate Solar Water Heating
Installation
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Wind Power

• Small Scale
• Village Scale
• Town Scale
• Building Integrated
• Engineering Structures

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Small Scale

• Stand alone.off-grid

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Village Scale

• Hockerton.

6 kW Unit
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Town Scale

• Building Integration?

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Town Scale

• Building Integration?

Good speed Enhanced areas
Bad wind Shear areas
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Urban electricity generation

• Issues
• Grid control
• Demand-side
• Supply-side
• Safety
• Net-metering
• Virtual Power Station

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Improved Building Skin

• Fabric
• Glazing
• Insulation
• Air-tightness
• Heavyweight versus Lightweight Construction

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Heat Transfer

• Heat transfer
• Rate of Energy Transfer
• Promotion of heat transfer
• Boilers, heaters, heat exchangers
• Prevention of heat transfer
• Insulation etc
• Three types of Heat Transfer
• Conduction, Convection Radiation

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Conduction

• Why do substancesconduct?
• Solids
• Heat gives molecules energy
• Increased vibration about theirmean positions
• Insulators
• Molecules tightly held -little movement
• Conductors
• Electrons free to move - heat, electricity etc.

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Conduction

• Why do substances conduct?
• Liquids
• Single molecules are able to move long distances
• Many collisions transferring energy
• Gases
• Single molecules are free to move long distances
• Conductivity is lower than liquids or solids
• Very long MEAN FREE PATH

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Conduction

• Fouriers Law of Heat Conduction
• Assume a steady flow of heat
• Independent of wall thickness in one dimension
• Heat flow is proportional to
• Area of the flow
• Temperature difference
• Heat is inversely proportional to
• Wall thickness

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Conduction

• Fouriers Law of Heat Conductionwhere Q
  heat (J), t time (s), A area (m2), T
  temperature (K) and k thermal conductivity (W/m
  K)

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Conduction

• ExampleA steel bar is heatedat one endk 14
  W/mKHow much energyis conducted in40
  seconds?Q/t 14 x 2 x (500-25)/10Q/t 1330
  watts (J/s)Q 1330 x 40 53200 J

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Conduction

• Typical values of Thermal Conductivity
• Foam 0.010 W/mK
• Air 0.026 W/mK
• Wood 0.150 W/mK
• Water 0.600 W/mK
• Glass 0.800 W/mK
• Concrete 1.100 W/mK
• Aluminium 240.000 W/mK

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Convection

• Bulk movement of thermal energy in fluids

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Convection

• Forced convection
• Caused by pump or fan etc
• Natural convection
• Thermally induced temperature gradient
• Fluid is in motion and affected by
• Type of flow
• Turbulent or laminar ie velocity
• Viscosity and density

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Convection

• Fluid is in motion
• Velocity distribution
• Velocity increases withdistance from the wall
• This leads to a temperature distribution
• Thermal boundary layer

Wall
Tf
Tw
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Radiation

• Conduction and convection require a medium to
  transfer heat
• Radiation passes throughvacuum of space
• Electromagnetic radiation
• X-rays
• light
• radiowaves etc

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Radiation

• Stefan-Boltzmann Law of Radiationwhere
  emissivity E lt 1A area (m2)T temperature
  (K)and o 5.67 x 10-8 W/m2K4

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Radiation
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Heat Transfer

• Layered systems e.g. buildings
• Need to calculate
• THERMALTRANSMITTANCE (U)
• U VALUES
• Units W/m2K
• Overall coefficient ofheat transfer

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Heat Transfer

• Heat transfer calculated by Resistance Method
• Sum of thermal resistances of wall components
• In series
• RTR1R2R3RN

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Heat Transfer

• For a wall of a single material of thermal
  conductivity k and thickness Landwhere h
  is the film/surface conductance

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Heat Transfer

• Film/surface conductance
• Why does glass feel cold?
• For a wall with an air space made of two
  materials (k1 and k2) and thicknesses (L1 and L2)
  separated by an air space of conductance C

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Control of Temperature
Toast
Press the lever down
FOOD!

Preset the temperature/ scale
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Control of Temperature
Space Heating
Boiler
Fuel
Heat Losses
Room Thermostat
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Control of heat transfer and airflow
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Ventilated Glazing
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Pump-out vacuum glazing technology
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Infra-red images of vacuum glazing

• Increased heat conduction visible through support
  pillar array

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Insulation
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Air-Tightness
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Heavyweight v. Lightweight?
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Conclusions

• We can improve our power generation efficiencies
  and diversify sources
• We need to improve our buildings heat loss in
  winter and reduce heat gains in summer through
• Better controls
• Better building standards