Triple Expansion Steam Engine

Posted by PITHOCRATES - November 6th, 2013

Technology 101

Pressure and Temperature have a Direct Relationship while Pressure and Volume have an Inverse Relationship

For much of human existence we used our own muscles to push things.  Which limited the work we could do.  Early river transport were barges of low capacity that we pushed along with a pole.  We’d stand on the barge and place the pole into the water and into the river bed.  Then push the pole away from us.  To get the boat to move in the other direction.

In more developed areas we may have cleared a pathway alongside the river.  And pulled our boats with animal power.  Of course, none of this helped us cross an ocean.  Only sail did that.  Where we captured the wind in sails.  And the wind pushed our ships across the oceans.  Then we started to understand our environment more.  And noticed relationships between physical properties.  Such as the ideal gas law equation:

Pressure = (n X R X Temperature)/Volume

In a gas pressure is determined my multiplying together ‘n’ and ‘R’ and temperature then dividing this number by volume.  Where ‘n’ is the amount of moles of the gas.  And ‘R’ is the constant 8.3145 m3·Pa/(mol·K).  For our purposes you can ignore ‘n’ and ‘R’.  It’s the relationship between pressure, temperature and volume that we want to focus on.  Which we can see in the ideal gas law equation.  Pressure and temperature have a direct relationship.  That is, if one rises so does the other.  If one falls so does the other.  While pressure and volume have an inverse relationship.  If volume decreases pressure increases.  If volume increases pressure decreases.  These properties prove to be very useful.  Especially if we want to push things.

Once the Piston traveled its Full Stroke on a Locomotive the Spent Steam vented into the Atmosphere 

So what gas can produce a high pressure that we can make relatively easy?  Steam.  Which we can make simply by boiling water.  And if we can harness this steam in a fixed vessel the pressure will rise to become strong enough to push things for us.  Operating a boiler was a risky profession, though.  As a lot of boiler operators died when the steam they were producing rose beyond safe levels.  Causing the boiler to explode like a bomb.

Early locomotives would burn coal or wood to boil water into steam.  The steam pressure was so great that it would push a piston while at the same time moving a connecting rod connected to the locomotive’s wheel.  Once the piston traveled its full stroke the spent steam vented into the atmosphere.  Allowing the pressure of that steam to dissipate safely into the air.  Of course doing this required the locomotive to stop at water towers along the way to keep taking on fresh water to boil into steam. 

Not all steam engines vented their used steam (after it expanded and gave up its energy) into the atmosphere.  Most condensed the low-pressure, low-temperature steam back into water.  Piping it (i.e., the condensate) back to the boiler to boil again into steam.  By recycling the used steam back into water eliminated the need to have water available to feed into the boiler.  Reducing non-revenue weight in steam ships.  And making more room available for fuel to travel greater distances.  Or to carry more revenue-producing cargo.

The Triple Expansion Steam Engine reduced the Expansion and Temperature Drop in each Cylinder

Pressure pushes the pistons in the steam engine.  And by the ideal gas law equation we see that the higher the temperature the higher the pressure.  As well as the corollary.  The lower the temperature the lower the pressure.  And one other thing.  As the volume increases the temperature falls.  So as the pressure in the steam pushes the piston the volume inside the cylinder increases.  Which lowers the temperature of the steam.  And the temperature of the piston and cylinder walls.  So when fresh steam from the boiler flows into this cylinder the cooler temperature of the piston and cylinder walls will cool the temperature of the steam.  Condensing some of it.  Reducing the pressure of the steam.  Which will push the piston with less force.  Reducing the efficiency of the engine.

There was a way to improve the efficiency of the steam engine.  By reducing the temperature drop during expansion (i.e., when it moves the piston).  They did this by raising the temperature of the steam.  And breaking down the expansion phase into multiple parts.  Such as in the triple expansion steam engine.  Where steam from the boiler entered the first cylinder.  Which is the smallest cylinder.  After it pushed the piston the spent steam still had a lot of energy in it looking to expand further.  Which it did in the second cylinder.  As the exhaust port of the first cylinder is piped into the intake port of the second cylinder.

The second cylinder is bigger than the first cylinder.  For the steam entering this cylinder is a lower-pressure and lower-temperature steam than that entering the first cylinder.  And needs a larger area to push against to match the down-stroke force on the first piston.  After it pushes this piston there is still energy left in that steam looking to expand.  Which it did in the third and largest cylinder.  After it pushed the third piston this low-pressure and low-temperature steam flowed into the condenser.  Where cooling removed what energy (i.e., temperature above the boiling point of water) was left in it.  Turning it back into water again.  Which was then pumped back to the boiler.  To be boiled into steam again.

By restricting the amount of expansion in each cylinder the triple expansion steam engine reduced the amount the temperature fell in each cylinder.  Allowing more of the heat go into pushing the piston.  And less of it go into raising the temperature of the piston and cylinder walls.  Greatly increasing the efficiency of the engine.  Making it the dominant maritime engine during the era of steam.

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Phase Transition, Expansion Valve, Evaporator, Compressor, Condenser and Air Conditioning

Posted by PITHOCRATES - April 3rd, 2013

Technology 101

We can use Volume, Pressure and Temperature to change Water from a Liquid to a Gas and back Again

Liquids and gasses can do a lot of work for us.  If we can control three variables.  Volume.  Pressure.  And temperature.  For example, internal combustion engines work best when hot.  But excessive heat levels can damage the engine.  So we use a special anti-freeze/anti-boil liquid in the cooling system.  A pump circulates this liquid through the engine where it absorbs some of the excess heat of combustion that isn’t used in pushing the piston.  After leaving the engine it flows through a radiator.  Air blows across tubes in the radiator cooling this liquid.  Ejecting some of the heat of combustion into the atmosphere.  Lowering the temperature of the cooling liquid so it can flow through the engine again and absorb more heat.

Our first cars used alcohol in the winter for a lower freezing point.  So this liquid didn’t freeze in the engine and crack the block.  Letting the coolant flow out.  And with no cooling available the excessive heat levels would damage the engine.  In the summer time we used plain water in the cooling system.  And kept the cooling system sealed and under high pressure to prevent the water from boiling into steam.  But the high pressure often caused a hose or a radiator cap to fail.  Releasing the pressure.  And letting the cooling water boil out leaving the engine unsafe to operate.

If this happened on a hot summer’s day and you got a tow to a gas station you may have sat there waiting for them to complete the repairs.  Sipping on a cool bottle of soda from a refrigerated soda machine.  Soon drops of water would condense onto your cold bottle.  The cold bottle cooled the water in gas form (the humidity in the air) and turned it back into a liquid.  So in these examples we see how we were able to use pressure to keep water a liquid.  And how removing heat from water as a gas changed it back into a liquid.  This phase transition of a material has some very useful applications.

The High-Pressure Refrigerant Liquid from the Condenser loses Pressure going through the Expansion Valve

The phase transition between a liquid and a gas are particularly useful.  Because we can move liquids and gases in pipes and tubing.  Which allows us to take advantage of evaporation (going from a liquid to a gas) in one area.  While taking advantage of condensation (going from a gas to a liquid) in another area.  By changing pressure and volume we can absorb heat during evaporation.  And release heat during condensation.  Allowing us to absorb heat inside a building with evaporation.  And release that heat outdoors with condensation.  All we need are a few additional components and we have air conditioning.  An expansion valve.  An evaporator.  A compressor.  A condenser.  A couple of fans.  And some miscellaneous control components.

We install the expansion valve and the evaporator inside our house.  Often installed inside the furnace.  And the compressor and the condenser outside of the house.  We interconnect the indoor and the outdoor units with tubing.  Inside this tubing is a refrigerant.  Which is a substance that transitions from liquid to a gas and back again at relatively low temperatures.  As the refrigerant moves from the evaporator to the condenser it is a gas.  As it moves from the condenser to the evaporator it is a liquid.  The transition between these stages occurs at the evaporator and the condenser.

The refrigerant leaves the condenser as a liquid under high pressure.  As it passes through the expansion valve the pressure drops.  By restricting the flow of the liquid refrigerant.  Think of a faucet at a kitchen sink.  If you open it all the way the water flowing in and the water flowing out are almost equal.  But if we just open the faucet a little we get only a small trickle of water out of the faucet.  And a pressure drop across the valve.  With the full force of city water pressure pushing to get out of the faucet.  And a low pressure trickle coming out of the faucet.

As the Warm Air blows across the Evaporator Coil any Humidity in the Air will condense on the Coil

As the liquid leaves the expansion valve at a lower pressure it enters the evaporator coil.  A fan blows the warm air inside of the house through the evaporator coil.  The heat in this air raises the temperature of the refrigerant.  And because of the lower pressure this heat readily boils the liquid into a gas.  That is, it evaporates.  Absorbing heat from the warm air as it does.  Cooling the air.  Which the fan blows throughout the ductwork of the house.

As the gas leaves the evaporator it travels through a tube to the condenser unit outside.  And enters a compressor.  Where an electric motor spins a crankshaft.  Attached to the crankshaft are two pistons.  As a piston moves down it pulls low pressure gas into the cylinder.  As the piston moves up it compresses this gas into a higher pressure.  As the pressure rises it applies more pressure on the spring holding the discharge valve closed.  When the pressure is great enough it forces open the valve.  And sends the high-pressure gas to the condenser coil.  Where a fan blows air through it lowering the temperature of the high pressure gas enough to return it to a liquid.  As it does it releases heat from the refrigerant into the atmosphere.  Cooling the refrigerant.  As the liquid leaves the condenser it flows to the expansion valve to repeat the cycle.  Over and over again until the temperature inside the house falls below the setting on the thermostat.  Shutting the system down.  Until the temperature rises high enough to turn it back on.  A window air conditioner works the same way.  Only they package all of the components together into one unit.

There is one other liquid in an air conditioning system.  Water.  As the warm air blows across the evaporator coil any humidity in the air will condense on the coil.  Like on a cold bottle of soda on a hot summer day.  As this water condenses on the evaporator coil is eventually drips off into a pan with a drain line.  If the evaporator is in the furnace this line will likely run to a sewer.  If the evaporator is in the attic this line will run to the exterior of the house.  Perhaps draining into a gutter.  If it’s a window unit this line runs to the exterior side of the unit.  These simple components working together give us a cool and dehumidified house to live in.  No matter how hot and humid it gets outside.

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Trade, Steam Power, Reciprocating Steam Engine, Railroading, Janney Coupler and Westinghouse Air Brake

Posted by PITHOCRATES - January 25th, 2012

Technology 101

Early Cities emerged on Rivers and Coastal Water Regions because that’s where the Trade Was

The key to wealth and a higher standard of living has been and remains trade.  The division of labor has created a complex and rich economy.  So that today we can have many things in our lives.  Things that we don’t understand how they work.  And could never make ourselves.  But because of a job skill we can trade our talent for a paycheck.  And then trade that money for all those wonderful things in our economy.

Getting to market to trade for those things, though, hasn’t always been easy.  Traders helped here.  By first using animals to carry large amounts of goods.  Such as on the Silk Road from China.  And as the Romans moved on their extensive road network.  But you could carry more goods by water.  Rivers and coastal waterways providing routes for heavy transport carriers.  Using oar and sail power.  With advancements in navigation larger ships traveled the oceans.  Packing large holds full of goods.  Making these shippers very wealthy.  Because they could transport much more than any land-based transportation system.  Not to mention the fact that they could ‘bridge’ the oceans to the New World.

This is why early cities emerged on rivers and coastal water regions.  Because that’s where the trade was.  The Italian city-states and their ports dominated Mediterranean trade until the maritime superpowers of Portugal, Spain, The Netherlands, Great Britain and France put them out of business.  Their competition for trade and colonies brought European technology to the New World.  Including a new technology that allowed civilization to move inland.  The steam engine.

Railroading transformed the Industrial Economy

Boiling water creates steam.  When this steam is contained it can do work.  Because water boiling into steam expands.  Producing pressure.  Which can push a piston.  When steam condenses back into water it contracts.  Producing a vacuum.   Which can pull a piston.  As the first useable steam engine did.  The Newcomen engine.  First used in 1712.  Which filled a cylinder with steam.  Then injected cold water in the cylinder to condense the steam back into water.  Creating a vacuum that pulled a piston down.  Miners used this engine to pump water out of their mines.  But it wasn’t very efficient.  Because the cooled cylinder that had just condensed the steam after the power stroke cooled the steam entering the cylinder for the next power stroke.

James Watt improved on this design in 1775.  By condensing the steam back into water in a condenser.  Not in the steam cylinder.  Greatly improving the efficiency of the engine.  And he made other improvements.  Including a design where a piston could move in both directions.  Under pressure.  Leading to a reciprocating engine.  And one that could be attached to a wheel.  Launching the Industrial Revolution.  By being able to put a factory pretty much anywhere.  Retiring the waterwheel and the windmill from the industrial economy.

The Industrial Revolution exploded economic activity.  Making goods at such a rate that the cost per unit plummeted.  Requiring new means of transportation to feed these industries.  And to ship the massive amount of goods they produced to market.  At first the U.S. built some canals to interconnect rivers.  But the steam engine allowed a new type of transportation.  Railroading.  Which transformed the industrial economy.  Where we shipped more and more goods by rail.  On longer and longer trains.  Which made railroading a more and more dangerous occupation.  Especially for those who coupled those trains together.  And for those who stopped them.  Two of the most dangerous jobs in the railroad industry.  And two jobs that fell to the same person.  The brakeman.

The Janney Coupler and the Westinghouse Air Brake made Railroading Safer and more Profitable

The earliest trains had an engine and a car or two.  So there wasn’t much coupling or decoupling.  And speed and weight were such that the engineer could stop the train from the engine.  But that all changed as we coupled more cars together.  In the U.S., we first connected cars together with the link-and-pin coupler.  Where something like an eyebolt slipped into a hollow tube with a hole in it.  As the engineer backed the train up a man stood between the cars being coupled and dropped a pin in the hole in the hollow tube through the eyebolt.  Dangerous work.  As cars smashed into each other a lot of brakemen still had body parts in between.  Losing fingers.  Hands.  Some even lost their life.

Perhaps even more dangerous was stopping a train.  As trains grew longer the locomotive couldn’t stop the train alone.  Brakemen had to apply the brakes evenly on every car in the train.  By moving from car to car.  On the top of a moving train.  Jumping the gap between cars.  With nothing to hold on to but the wheel they turned to apply the brakes.  A lot of men fell to their deaths.  And if one did you couldn’t grieve long.  For someone else had to stop that train.  Before it became a runaway and derailed.  Potentially killing everyone on that train.

As engines became more powerful trains grew even longer.  Resulting in more injuries and deaths.  Two inventions changed that.  The Janney coupler invented in 1873.  And the Westinghouse Air Brake invented in 1872.  Both made mandatory in 1893 by the Railroad Safety Appliance Act.  The Janney coupler is what you see on U.S. trains today.  It’s an automatic coupler that doesn’t require anyone to stand in between two cars they’re coupling together.  You just backed one car into another.  Upon impact, the couplers latch together.  They are released by a lifting a handle accessible from the side of the train.

The Westinghouse Air Brake consisted of an air line running the length of the train.  Metal tubes under cars.  And those thick hoses between cars.  The train line.  A steam-powered air compressor kept this line under pressure.  Which, in turn, maintained pressure in air tanks on each car.  To apply the brakes from the locomotive cab the engineer released pressure from this line.  The lower pressure in the train line opened a valve in the rail car air tanks, allowing air to fill a brake piston cylinder.  The piston moved linkages that engaged the brake shoes on the wheels.  With braking done by lowering air pressure it’s a failsafe system.  For example, if a coupler fails and some cars separate this will break the train line.  The train line will lose all pressure.  And the brakes will automatically engage, powered by the air tanks on each car.

Railroads without Anything to Transport Produce no Revenue

Because of the reciprocating steam engine, the Janney coupler and the Westinghouse Air Brake trains were able to get longer and faster.  Carrying great loads great distances in a shorter time.  This was the era of railroading where fortunes were made.  However, those fortunes came at a staggering cost.  For laying track cost a fortune.  Surveying, land, right-of-ways, grading, road ballast, ties, rail, bridges and tunnels weren’t cheap.  They required immense financing.  But if the line turned out to be profitable with a lot of shippers on that line to keep those rails polished, the investment paid off.  And fortunes were made.  But if the shippers didn’t appear and those rails got rusty because little revenue traveled them, fortunes were lost.  With losses so great they caused banks to fail.

The Panic of 1893 was caused in part by such speculation in railroads.  They borrowed great funds to build railroad lines that could never pay for themselves.  Without the revenue there was no way to repay these loans.  And fortunes were lost.  The fallout reverberated through the U.S. banking system.  Throwing the nation into the worst depression until the Great Depression.  Thanks to great technology.  That some thought was an automatic ticket to great wealth.  Only to learn later that even great technology cannot change the laws of economics.  Specifically, railroads without anything to transport produce no revenue.

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