i. Module 4 Fluids and Thermodynamics ... - Workforce 3 One

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The instructor will use a Syringe to ignite a few strands of cotton, todemonstrate the heating of a gas at increased pressure. Cotton placed atthe bottom of the tube ignites in a flash as the plunger causes rapidcompression of the gas inside the tube. If the cotton alone doesn’t workuse a match head.Also see a demonstration at:http://www.teachertube.com/view_video.php?viewkey=b9537c8753c09e08d4dfThis is a demonstration of what is called adiabatic compression where noheat is lost to the outside environment, in which the compression has tobe so fast that practically no heat generated by the compression isallowed to escape.The fire syringe demonstrates the relationship between pressure andtemperature. When the pressure on a gas is increased, the particles(atoms and molecules) are forced to move in a smaller space. This canbe shown when a ping-pong paddle is lowered onto a bouncing ping-pongball. The intervals between the ball striking the paddle decrease as thepaddle is lowered. The French scientist Joseph Gay-Lussac concluded thatequal volumes of all gases expand the same with identical increases intemperature. This is known as the Gay-Lussac's Law.This also explains how canning creates a vacuum seal. As the temperature inside the jardecreases and atmospheric pressure seals the lid tightly.The Diesel EngineDiesel engines rely on the relationship between pressure and temperature. There are nospark plugs in a diesel engine. The fuel is sprayed into the cylinder of compressed airwhere, because of the relationship between pressure and temperature, the fuel ignites andthe expanding gases from the ignition forces the engine piston downward.The diesel engine uses a four-stroke combustion cycle justlike a gasoline engine.Intake stroke -- The intake valve opens up, letting in airand moving the piston down.Compression stroke -- The piston moves back up andcompresses the air.Combustion stroke -- As the piston reaches the top, fuelis injected at just the right moment and ignited, forcingthe piston back down.Exhaust stroke -- The piston moves back to the top,pushing out the exhaust created from the combustion outof the exhaust valve.See:http://auto.howstuffworks.com/diesel1.htmhttp://library.thinkquest.org/C006011/english/sites/diesel.php3?v=2Module 4 Student Guide Fluids & Thermodynamics Page 8
Lesson 4: Fluid PowerActivity 1: Fountain Connection: Air Pressure, vacuum and compressionUse the soda bottles and plastic tubes to demonstrate how a water fountain worksPerform this as a demonstration and discuss with the class.1. The clear plastic tubes have holes drilled near the one end. Insertthis end into the connector approximately ¼ inch.2. Clean out two PLASTIC 2-liter soda bottles and remove the labelsusing hot air from a hair dryer. The plastic tubes can be shortenedto fit smaller bottles. Do not cut the ends with the small holesdrilled into it.3. Some soda bottles have separate molded bottoms. It is best toremove this piece for a better view of the fountain. This base can beremoved more easily if it is heated first with hot water or a hairdryer to soften the glue. Press the two bases together to make astand to hold the bottles upright (Figure 2) or, most of the base canbe cut away leaving just the flat section attached.4. Fill one bottle ¾ full with clear or colored water and connect the twobottles together.5. The fountain will erupt every time you turn the bottle over.BackgroundHero of Alexandria described a water fountain that used compressed air to lift water to apoint higher than its origin. The result was a fountain that seemed to defy both logic andthe laws of nature. A closer study of your fountain will reveal the principles of operation.When the bottles are inverted1. Gravity pulls the water from the upper bottle down through the lower tube andcompresses the air to the tower bottle.2. When water leaves the upper bottle, a decrease to pressure, or partial vacuum, isformed.3. Air is then forced from the lower bottle, up the fountain tube, and takes the place ofthe water as it leaves the upper bottle.If you examine the clear tubes near where they enter the bottle connector, you will be ableto see several small holes.4. When the bottle is turned over, water runs into these small holes and is pushedupwards by the air with enough force to form the fountain at the top of the bottle.This is the same type of action that moves water in fish tank filters and some typesof coffee percolators.5. The tube to the lower bottle has no effect on the formation of the fountain. Try itwith one tube removed.Vacuum and Compression Demonstration:1. Start the fountain and unscrew the lower bottle.2. Lift the fountain up. Air rushes up the fountain tube and takes water with it. Place atray underneath to catch any spilled water.Demonstrate how using compressed air will lift water to a point higher than its origin1. Cut the base off a third bottle and replace this for the upper bottle.2. Hold your finger on the hole of the tube and fill this open bottle with water.3. Let go of the tube and the fountain will start.Module 4 Student Guide Fluids & Thermodynamics Page 9
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