A Short Course in Energy Conversion Session 8

Jim Rauf

1OLLI Fall 2019

OLLI Fall 2019 2

• Telephone• Sound• Microphone• Speaker• Television• Radio• Microwave oven• Refrigeration/Air conditioning/Heat Pump• Review• Everyday energy conversion

Telephone

• The telephone makes use of a microphone and a speaker

• The microphone converts mechanical energy, sound, into electrical energy

• The speaker converts electrical energy, the signal, into mechanical energy, sound

• The telephone uses a combination of acoustics and electricity transmitted through wires from one point to another.

• Acoustic vibrations work a metallic substance and electrode separated by a plastic barrier.

• As we speak the metallic substance works back-and-forth, hence, closer to and farther away from the electrode causing variations in voltage.

• These variations in voltage are carried through the wire and are reconverted on the other hand into acoustics which we can hear

• Pure electrical signals, data, can also be transmitted by telephone

• Telephone signals can also be transmitted thru the air by radio waves

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Sound

• Sound is a wave that is created by vibrating objects and propagated through a medium from one location to another

• A wave can be described as a disturbance that travels through a medium, transporting energy from one location to another location.

• The medium is the material through which the disturbance is moving; it can be thought of as a series of interacting particles.

• This process continues in consecutivefashion, with each individual particleacting to displace the next particle

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Material M/s Ft/sAir, dry at 20°C 343 1125Hydrogen at 0°C 1 280 4200Water at 15 °C 1 500 4290Lead 2 160 7090Concrete 3 100 10200Wood 3 800 12500Glass 5 500 18500Steel 5 800 19000

Speed of Sound

Microphone

• A microphone is an acoustic-to-electric transducer that converts sound (mechanical) energy into electrical energy, an electrical signal

• Several type of microphones:– Dynamic microphone -

electromagnetic induction– Condenser microphone-

capacitance change– Crystal microphone-piezoelectric

effect • Dynamic microphones work via

electromagnetic induction • A small movable induction coil,

positioned in the magnetic field of a permanent magnet, is attached to the diaphragm

• Sound wave moves the diaphragm• When the diaphragm vibrates, the

coil moves in the magnetic field, producing a varying current in the coil

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Microphone• Condenser Microphones use a

capacitor to convert sound energy into electrical energy-audio signal

• A capacitor has two plates with a voltage between them

• The front plate is made of very light material and acts as the diaphragm

• Sound causes the diaphragm to vibrate, changing the distance between the two plates

– When the plates are closer together, capacitance increases and a charge current occurs

– When the plates are further apart, capacitance decreases and a discharge current occurs

• The small mass requires less sound energy to move the diaphragm

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Microphone

• Piezoelectric microphone or crystal microphone uses the ability of some materials (Quartz is a commenmaterial) to produce a voltage when subjected to pressure

– It convert vibrations into an electrical signal in microphones

• Crystal microphones were difficult to match to early transistor equipment, and were quickly supplanted by dynamic microphones and small condenser microphones

• Piezoelectric transducers are often used as contact microphones to amplify sound from acoustic musical instruments, and to record sound underwater under high pressure

• Automotive engine management systems use piezoelectric transducers to detect Engine knock (Knock Sensors)

• A piezoelectric transducer is also used in fuel injection systems to measure manifold absolute pressure (MAP sensor) to determine engine load, and ultimately the fuel injectors milliseconds of on time

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Speaker

• The loudspeakers in your radio, television or stereo system consists of a permanent magnet surrounding an electromagnet that is attached to the loudspeaker membrane or cone.

• By varying the electric current through the wires around the electromagnet, the electromagnet and the speaker cone can be made to move back and forth-creating sound waves

• Electrical energy to mechanical energy

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Radio

• Radio converts electrical energy of the radio wave - electromagnetic radiation signal - into mechanical energy, sound, thru the radio’s speaker

• The electrical energy come from the electromagnetic radiation “captured” by the radio’s antenna which is amplified by the radio’s electronic circuits sufficiently to “drive” a loud speaker by means of a magnet

• The motion of the speaker’s diaphragm creates the sound

• Electrical resonance of tuned circuits in radios allow individual stations-frequencies- to be selected

• A resonant circuit will respond strongly to a particular frequency, and much less so to differing frequencies

• This allows the radio receiver to discriminate between multiple signals differing in frequency

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Radio

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Microphone

Sound

Antenna “Tuned” circuitSpeaker Sound

Television

• Television is a three-part system: • TV camera that turns a picture and

sound into a signal • TV transmitter that sends the signal

through the air• TV receiver (the TV set in your home)

that captures the signal and turns it back into picture and sound

• TV creates moving pictures by repeatedly capturing still pictures and presenting these frames to your eyes so quickly that they seem to be moving

• The images are flickering on the screen so fast that they fuse together in your brain to make a moving picture

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TV Camera

• Modern TV cameras lenses focus the scene being filmed onto small, image-sensing microchips charge coupled devices (CCD) or complementary metal-oxide-semiconductor (CMOS) sensors), which convert the pattern of colors into digital, electrical signals-light to electrical energy

• The image sensing chips in today's HDTV (high-definition television) cameras generally have either 720 or 1080 lines

• Some cameras use three separate sensors, capturing separate red, blue, and green signals—the primary colors from which any color on your TV can be made

• 1) White light passes through the lens and Enters a beam splitter

• 2) The light enters a beam splitter, a two-part, prism that divides the light into separate red, green, and blue beams-Each of which is detected by a separate CCD or CMOS image sensor

• 3) A circuit synchronizes and combines the outputs from the red, green, and blue image sensors to make a single video signal based the brightness and color of each part of the image

• 4) Another part of the circuit recreates the image on a small screen in a viewfinder

• 5)Sound from a microphone is synchronized with the video signal to produce a signal ready for transmission

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LCD TV

• LCD televisions produce an image by selectively filtering a white light

• The light is typically provided by a series of cold cathode fluorescent lamps (CCFLs) at the back of the screen, although some displays use white or colored LEDs instead

• Millions of individual LCD shutters, arranged in a grid, open and close to allow a metered amount of the white light through

• Each shutter is paired with a colored filter to remove all but the red, green or blue (RGB) portion of the light from the original white source

• Each shutter–filter pair forms a single sub-pixel

• The sub-pixels are so small that when the display is viewed from even a short distance, the individual colors blend together to produce a single spot of color, a pixel

• The shade of color is controlled by changing the relative intensity of the light passing through the sub-pixels

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Microwave Oven

• Microwaves are radio waves with a frequency of 2,450 megahertz

• Microwaves are generated by a cavity magnetron, a high-powered vacuum tube that uses the interaction of a stream of electrons with a magnetic field to generate microwaves

• The microwaves are absorbed by water, fats and sugars where they are converted directly into molecular motion -- heat

– They are not absorbed by most plastics, glass or ceramics and are reflected by metal

• There is heat everywhere all at once because the molecules are all excited together

• Electrical energy is converted into microwaves (radio waves) which “excite” the molecules in food

• The ”excited” molecules (kinetic energy) are converted into heat (thermal energy) evenly within the food which cooks the food

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Refrigeration-A Reverse Heat Engine• The compressor –driven by an

electric motor- compresses the refrigerant gas-heating it

• The coils on the back of the refrigerator let the hot gas dissipate its heat-into room

• The gas condenses into liquid at high pressure

• High-pressure liquid flows through the expansion valve

– On one side is high-pressure liquid– On the other side is a low-pressure

area (because the compressor is sucking gas out of that side)

• The liquid boils and vaporizes- its temperature dropping

– This makes the inside of the refrigerator cold

• The cold gas is sucked up by the compressor, and the cycle repeats

• Refrigeration cycle converts mechanical energy into heat-a reverse heat engine

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Air Conditioning-A Reverse Heat Engine• The cold side of an air conditioner contains

the evaporator and a fan that blows air over the chilled coils and into the room

• The hot side contains the compressor, condenser and another fan to vent hot air coming off the compressed refrigerant to the outdoors

• In between there is an expansion valve. It regulates the amount of compressed liquid refrigerant moving into the evaporator

• Once in the evaporator, the refrigerant experiences a pressure drop, expands and changes back into a gas

• The compressor is actually an electric pump that pressurizes the refrigerant gas as part of the process of turning it back into a liquid

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• Reducing the temperature of a volume of humid air causes it to release a portion of its moisture

• Air conditioner cycle converts mechanical energy into heat are “reverse heat engines”

Heat Pump-A reverse Heat Engine

• Heat pump is a device that uses a small amount of energy to move heat from one location to another-

• Heat pumps are typically used to pull heat out of the air or ground to heat a house or office building

• They can be reversed to cool a building• Heat pumps , air conditioners and refrigerators operate in very similar ways• They are all “reverse heat engines”

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Review• Energy and its different forms• Source of energy• Conservation of energy• Water and wind• Combustion• Heat engines• Thermodynamics-Heat Engines• Steam engines-piston• Steam turbines• Piston internal combustion

engines

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• Gas turbine engines• Jet engines• Rocket engines• Firearms• Electrical energy• Atoms , electrons• Electric fields • Electric current• Electric potential-voltage• Magnetism

Review

• Generators• Motors• Batteries• Fuel cells• Thermoelectric effect• Photoelectric effect• Photovoltaic effect• Radiation• Light• Incandescent light• Fluorescent light• LED light

• Radioactivity• Nuclear fission• Nuclear fusion• Telephone• Microphone• Speaker• Television• Radio• Microwave oven• Refrigeration• Air Conditioning• Heat Pumps

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Conversion process Energy efficiency

Gas turbine up to 40%

Gas turbine plus steam turbine (combined cycle) up to 60%

Water turbine up to 90% (practically achieved)

Wind turbine up to 59% (theoretical limit)

Solar cell 6–40% (technology dependent, 15% most often, 85–90% theoretical limit)

Fuel cell up to 85%

World Electricity generation 2008 Gross output 39%, Net output 33%.

Combustion engine 10–50%

Electric motors 70–99.99% (above 200W); 50–90% (between 10–200W); 30–60% (< 10W)

Household refrigerators low-end systems ~ 20%; high end systems ~ 40–50%

Incandescent light bulb 0.7–5.1%,5–10%

Light-emitting diode (LED) 4.2–14.9%,up to 35%

Fluorescent lamps 8.0–15.6%, 28%

Low-pressure sodium lamps 15.0–29.0%,40.5%

Metal halide lamps 9.5–17.0%,24%

Switched-mode power supply currently up to 95% practically

Electric heaters 100% (all energy is always converted into heat)

Firearm ~30% (.300 Hawk ammunition)

Electrolysis of water 50–70% (80–94% theoretical maximum)

Thermodynamics in Action-No Free Lunch

20OLLI Fall 2019

Automobile Energy Conversion

• Battery -Chemical to Electrical• Starter Motor- Electrical to

Mechanical-- Electromagnetic fields

– Solenoid and motor

• Engine -Chemical to Thermal-Combustion

– Spark from electromagnetic fields in coils

• Engine -Thermal to Mechanical -Expansion of gases driving pistons

– Waste heat transferred to atmosphere Radiator and Exhaust

• Motion of the Automobile-Mechanical

• Accessories’ Power- Mechanical to Electrical

– Hydraulic power steering- different type of mechanical

• Aerodynamic Drag-Mechanical to Thermal via Friction

• Braking- Mechanical to Thermal-via friction in braking system

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Automobile Energy Conversion

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Energy Conversion at Home

• Water Heater– Gas fired water heater-Combustion/Thermal– Electrical water heater-Resistance/Thermal

• Home Heating– Gas furnace-Combustion of Natural Gas-Thermal– Electric Furnace-Resistance Heating from Electric Current– Heat Pump-Transfer of Thermal Energy from Outside to Inside-Compressor

mechanically driven by Electric Motor• Air Conditioning

– Transfer of Thermal Energy from Inside to Outside-Compressor mechanically driven by Electric Motor

• Refrigerator– Transfer of Thermal Energy from Inside Refrigerator to Outside Refrigerator

mechanically driven by Electric Motor

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Energy Conversion at Home

• Telephone– Mechanical (Sound) to Electrical -Microphone– Electrical to Mechanical (Sound) -Speaker

• Radio– Electrical (Radio Waves) to Mechanical (Sound)

• Television– Electrical (TV Signal) to Light via TV Screen

• Dishwasher– Electrical to Thermal and Mechanical

• Clothes Washer– Electrical to Mechanical

• Clothes Dryer– Electrical to Thermal and Mechanical– Chemical (Gas) to Thermal

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Energy Conversion at Home

• Toaster– Electrical to Thermal and Mechanical (Pop up?)

• Microwave Oven– Electrical to Electromagnetic Radiation to Thermal

• Mixers– Electrical to Mechanical

• Woodworking Equipment– Electrical to Mechanical– Chemical (Battery) to Electrical to Mechanical

• Lawn Mower– Chemical to Thermal to Mechanical

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Energy Conversions

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Energy Conversion is everywhere !

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Energy Conversion is everywhere !

You Can’t get away from it!