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

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’ Barry Spick

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 Barry Spick

Coefficient Table Material Coefficient 0C Plastic 0.00018 Zinc 0.000029 lead 0.000029 Aluminium 0.000026 Tin 0.000021 Copper 0.000016 Cast Iron 0.000011 Mild Steel 0.000011 Barry Spick

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 0.00018 = 0.02052m or 20.52mm Barry Spick

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. Barry Spick

Heat Transfer Barry Spick

Heat Transfer How many methods of heat transfer are used in plumbing? Three What are they called? Conduction Convection Radiation Barry Spick

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 Barry Spick

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 Barry Spick

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 Barry Spick

Convection An example of gravity circulation using the effects of convection Where else would convection be used? Radiators Gas fires Convector Heaters Barry Spick

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 Barry Spick

Radiation What would have a dull matt surface? Solar panel Where could these be used? As in the photo on a house. Barry Spick

Lesson Complete Barry Spick

Principles of Electricity JTL Chapter 4 Pages 109 to 127 Barry Spick

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 + Barry Spick

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 Barry Spick

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 Barry Spick

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 + Barry Spick

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. Barry Spick

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 Barry Spick

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. Barry Spick

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 Barry Spick

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 Barry Spick

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) = 0.416 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 Barry Spick

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 Barry Spick

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) Barry Spick

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) Barry Spick

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. Barry Spick

A.C.Current Is found in the majority of domestic properties Usual voltage level is 230-240V a.c. In 1831 Michael Faraday found that moving a bar magnet through a wire coil generated electricity. It is produced by Electromagnetism: Barry Spick

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 Barry Spick

Generating Electricity Barry Spick

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) Barry Spick

Example of Electricity Generation Barry Spick

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 Barry Spick

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 Barry Spick

Regulations and standards Which regulations and standards cover electricity? IEE wiring regulations 17th edition BS7671 Electricity at work regulations Part P building regulations Barry Spick

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 Barry Spick

Wiring Colours Earth Live or Phase Neutral From 1st of April 2006 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 Barry Spick

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 Barry Spick

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 Barry Spick

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 Barry Spick

Full wiring diagram Barry Spick

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 Barry Spick

Earth Bonding Example Barry Spick

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 Barry Spick

Lesson Complete Barry Spick