1. Thermal Expansion Conduction, Convection, Radiation
Plumbing Science
Thermal Expansion
Conduction, Convection, Radiation
Barry Spick

2. Thermal Expansion Most materials expand when heated
Why do they expand?
Because they are made up of molecules which move about more vigorously when heated.
What do the molecules do when they do this?
They move further apart and consequently take up more room or as we say ‘expand’
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3. Thermal Expansion
What do you think happens when a material cools down?
Yes they do the reverse of when they expand. The material gets smaller and contracts
How do we measure this
By using the formula
length x temperature rise x coefficient
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4. Coefficient Table Material Coefficient 0C Plastic 0.00018 Zinc
lead
Aluminium
Tin
Copper
Cast Iron
Mild Steel
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5. Example
Find the amount a 6m long plastic discharge stack will expand due to a temperature rise of 190C.
Length x temp rise x coefficient
=6 x 19 x
= m or 20.52mm
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6. Thermal Expansion What does this prove to us?
That we need to take into account the amount that materials expand and contract.
When do we need to take this into account?
When designing or installing systems
What could be the result of not allowing for this?
A breakdown of the systems or materials.
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7. Heat Transfer
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8. Heat Transfer How many methods of heat transfer are used in plumbing?
Three
What are they called?
Conduction
Convection
Radiation
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9. Conduction What is Conduction?
It is the transfer of energy through a material
What causes conduction to occur?
It is the result of increased vibration of molecules as the material is heated.
Which materials are good conductors of heat?
Metals. Wood is a poor conductor of heat
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10. Conduction Do gas and liquids conduct heat? Yes but poorly
Which material that plumbers use has a high conductivity compared to steel?
Copper
Other materials that are poor conductors :
Wood
Ceramic
Plastics
What are these materials better known as?
Thermal insulators
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11. Convection What is convection?
Is the transfer of heat by means of the movement of a locally heated fluid substance (usually air or water).
What causes convection?
When heat is applied it causes expansion and which in turn causes lowering of the density.
What happens to the fluid now?
It will rise as in the following example
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12. Convection
An example of gravity circulation using the effects of convection
Where else would convection be used?
Radiators
Gas fires
Convector Heaters
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13. Radiation What is Radiation?
It is the transfer of heat from a hot body to a cooler one without the presence of a material (other than air)
From what would we feel heat radiation?
The sun
Gas fire radiant’s
Radiators
Dull matt surfaces absorb heat more efficiently than shiny polished surfaces
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14. Radiation What would have a dull matt surface? Solar panel
Where could these be used?
As in the photo on a house.
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15. Lesson Complete
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16. Principles of Electricity
JTL Chapter 4
Pages 109 to 127
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17. What is Electricity It is a flow of electrons
For electric current to flow two requirements are necessary:
A source of chemical energy e.g. Battery
A continuous loop of conducting material
copper
A chemical reaction takes place in the battery produces an excess
Of electrons at one pole of the battery
Electrons have a negative electrical charge
This pole is the negative terminal or cathode
The opposite end is the Anode
If the two terminals are connected in a continuous loop
A circuit of electrons
An electric circuit!
Duracell +
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18. Electricity in Simple Circuits
Three important variables relating to electrical circuits:
Current
Voltage
And resistance
Electric current is the flow of electric charge q (Coulombs)
It is the amount of charge q that passes a given point in a wire in a time t, I = q ÷ t
Current is measured in AMPERES
1 ampere (A) = 1 C / 1 s q
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19. Potential difference or Voltage (symbol V)
Voltage is what causes charge to move in a conductor
It plays a role similar to pressure in a pipe; to get water to flow there must be a pressure difference between the ends, this pressure difference is produced by a pump
A battery or a generator is like a pump for the charge, it provides the energy for pushing the charges around a circuit
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20. Comparisons with water
If you represent the rate of flow of water in a pipe then voltage would correspond to the water pressure.
In a closed circuit such as central heating system, would be governed by the size and power of the pump
In an electric circuit by the battery
copper
Duracell +
Duracell +
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21. Ohm’s Law
Flow of electrons (the current ‘I’) in an electrical circuit is related to the potential difference (the Voltage ’V’) and the resistance ‘R’ of the circuit materials.
Just as the flow of water through pipes is related to the water pressure and the diameter of the pipes in the system.
These have been summarised in the form of a law known as Ohm’s Law.
This states that the current flowing in a circuit is proportional to the potential difference (the Voltage), providing that the temperature of the conductor remains constant.
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22. Ohm’s Law
Can be written in three different ways in order to isolate the variables in turn
Current (I) = Voltage (V)
Resistance (R)
Voltage = I X R
Resistance = V I Or
Volts (V) = Watts (W)
Amps (A)
Watts = A X V
Amps = W V
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23. Fuses (Circuit breakers)
Why do we need fuses?
They are a safety device which aims to prevent high electrical current passing through wires that are not designed to carry such large charges.
Is this important?
Yes, because by preventing to high a current passing through the wire, you prevent it from overheating and thus catching fire.
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24. How do fuses work Some types of fuses that exist contain fuse wire
they melt when an excessive current is passed across it
MCB’s are devices which will trip a switch to break the electrical current if excessively high current is detected
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25. RCD’s Now days you will also come across the:
Residual Current Device (RCD)
This is a highly sensitive device
Provides a higher degree of protection to high risk parts of the electrical system.
Used mainly to protect plug socket outlet ring mains, electric showers, pumps on whirlpool baths.
The RCD works by measuring the potential difference between the different electrical conductors in the system e.g. live and neutral.
If small changes occur in the electrical current the system is isolated
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26. Fuse Rating How do we rate a fuse? Remember Ohm’s Law?
Amps = watts / volts
In domestic situations fuses are overrated
A fuse with too high rating is used for example
If a lamp contains a 100 w light bulb the fuse rating would be as follows
100/240 (domestic voltage) = amps
Therefore a 1 amp fuse would be sufficient for use. Usually a 3 amp fuse would be fitted and sometimes a 13 amp
This would not be deemed as safe and there would be insufficient protection for the user
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27. Fuses Cont’d This is where there is confusion
1 amp of current is more than sufficient to kill at 240 volts.
REMEMBER
The purpose of the fuse is to protect the wiring, the earth is to protect you - the user
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28. Circuits Series circuit There are two basic circuits: Series circuit
Parallel circuit
A series circuit is where a current is made to pass through each component in a circuit
The current should be the same in any part of the circuit. But the voltage will vary depending upon resistance of each component
The total voltage of all components must not exceed the total voltage, otherwise the bulbs won’t glow sufficiently
Series circuit
Lamp (Bulb)
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29. Parallel Circuit
In a parallel circuit there are alternative routes open to the flow of electrons, and the current will flow along both.
If a bulb blows in this then the others will stay lit
For example house lighting is wired in parallel, xmas tree lights are wired in series
Lamp (Bulb)
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30. Direct and Alternating Current
In a D.C. circuit the electron flow is in the same direction all the time.
One example would be from the anode to the cathode of a battery
Exercise: given a battery, some wire and a
light bulb, connect them so that the bulb is on.
1.5 V
The battery polarity
+/- does not matter,
Either way the bulb
Will be on.
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31. A.C.Current Is found in the majority of domestic properties
Usual voltage level is V a.c.
In 1831 Michael Faraday found that moving a bar magnet through a wire coil generated electricity.
It is produced by Electromagnetism:
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32. A.C. Current Cont’d
When A.C. electricity is used it’s essential that appliances be ‘earthed’ as this completes the formation of a circuit necessary for current flow.
The way it works:
Current flows to the appliance from the Phase (live)
Then from the neutral wire (which is in effect connected to earth) the current flows continuously back and forth in the UK
The rate is 50 times a second or 50 Hertz
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33. Generating Electricity
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34. Generation of Electricity
Electricity is generated in power stations using electromagnetic generation
Most electricity in the UK is produced by steam driving an alternator
How does it do this ?
Water is heated until it becomes high pressure steam;
The steam is forced onto the vanes of a steam turbine
This in turn rotates the alternator (Generator)
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35. Example of Electricity Generation
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36. Supplying Electricity
After the electric is produced it is fed onto the national grid system
It is a network of over 5000 mls of overhead and underground power lines
They link power stations throughout the country
The voltages are between 130 – 400 KV
It is taken from the grid into sub-stations transformed down to 11KV and then distributed to local sub-stations.
The supply is then transformed down to 400V
Distributed in underground radial circuits to customers
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37. The final part of the journey
The electricity arrives at the customers main intake point. Here you will find
A sealed overcurrent device (Main Fuse)
A meter
Consumers installation must be controlled by a main switch.
Located as close as possible to supply co equipment
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38. Regulations and standards
Which regulations and standards cover electricity?
IEE wiring regulations 17th edition
BS7671
Electricity at work regulations
Part P building regulations
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39. Basic Domestic Circuits
Three basic circuits:
Lighting circuit
Ring main circuit – 13 amp socket outlets
Spur outlets
Lighting Circuit
It is a radial circuit
To prevent the light being on continuously live or phase the wire is passed through a switch. These switches can be two way (usually on a stairways) and require special switch controls.
Cable is usually 1.5mm2 twin and earth PVC insulated cable
Protected by a 6 amp MCB fuse at the consumer unit
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40. Wiring Colours Earth Live or Phase Neutral
From 1st of April the new European harmonised wiring colours for electrical installations commencing on site have to be used.
Part P of the Building Regulations cover this and the following are the new colours;
Earth
Live or Phase
Neutral
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41. One Way Lighting Circuit
Off On
S/L
Light Switch
Earth
Brown sleeve to indicate live/phase
Live or Phase
Neutral
4 Way Junction Box
Light
When switch is in ON position electricity begins to flow
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42. Kitchen normally has its own ring main
Ring main Circuit
Sockets in domestic properties which feed televisions stereos are normally 13amp sockets fed from a continuous ring circuit
The ring main is fed using 2.5mm2 twin and earthed PVC cable
Protected at the consumer unit with a 32amp MCB or fuse
Kitchen
Kitchen normally has its own ring main
Consumer unit
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43. Spur Outlets
Used to connect into a ring main circuit on an existing system.
On new installations you would not normally come across these
Connects to the ring main through junction box
Spur Cable
Ring Main
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44. Full wiring diagram
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45. Earth Continuity, bonding and temporary bonding
All exposed metalwork in buildings must be bonded together
Gas and water pipes can provide a path for stray electrical current
The bonding of all exposed metal components in a dwelling that are not part of the electrical installation is known as the equipotential bonding
The E.B. conductor is found in the consumer unit
Where is Supplementary Bonding fitted?
to link sections of central heating, cold water, hot water where metal pipe work have been separated by plastic fitting’s or length’s of plastic pipe.
Ensures earth continuity throughout the property
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46. Earth Bonding Example
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47. Temporary Bonding
During maintenance when removing a section of pipe work
Earth continuity needs to be maintained
Achieved by bridging the gap
Use a temporary bonding wire
Secure in place before pipe is removed
Earth clips to be used when bonding earth wire to pipework
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48. Lesson Complete
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