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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The Creative Destruction of the Internet may put Best Buy Stores out of Business

Posted by PITHOCRATES - August 11th, 2012

Week in Review

Best Buy and Circuit City were once fierce competitors in retail electronics.  Big box stores that carried an amazing range of consumer goods from televisions to car stereos to cameras to computers to refrigerators.  Their marketing plan?  Trade volume for margin.  They sold at low prices with low profit margins that mom and pop stores could not match and remain profitable.  But because of their high volume Best Buy and Circuit City could make a profit with those small margins.  Which they padded with those extended warranties.  It was a successful business model.  For awhile.  Circuit City is no longer with us.  And now Best Buy is struggling (see Best Buy founder proposes taking retailer private by Dhanya Skariachan and Nadia Damouni posted 8/6/2012 on Reuters).

Best Buy Co Inc (BBY.N) founder Richard Schulze on Monday made a bid to take the struggling U.S. electronics retailer private just months after being forced out as chairman.

If Schulze succeeds, it could result in the world’s biggest leveraged buyout of the year. But early reaction suggests he faces an uphill battle in taking his once wildly successful company in a new direction…

Best Buy has been closing stores, cutting jobs and trying out a new store format to improve business. It has faced criticism for being too slow to react to a changing retail world, where many use Best Buy as a “showroom” to try out gadgets and then buy them online or elsewhere for less.

It takes money to maintain inventory.  And every Best Buy store has inventory.  It’s a huge cost.  But it also gives them purchasing power.  This is why the mom and pop stores went bye-bye.  With their low sales volume they had small purchasing power.  So the little they bought came at higher unit costs than Best Buy’s.  Which meant they had to charge higher prices to cover those costs.  And now it’s happening again.  Only it’s online sales that are squeezing the profits out of Best Buy.  From suppliers that have no retail stores.  And a more consolidated inventory.  With no sales force or cashiers to pay.  They have high sales volume and low operating costs.  So now Best Buy is getting a taste of what it was like for the mom and pop stores.

We call this creative destruction.  And it’s a good thing in capitalism.  Everyone agrees.  Having a cell phone is better than having a pager that displays a phone number to call.  Then finding a public telephone to make that call from.  Cell phones have hurt the pager industry.  Just as digital cameras have hurt the instant camera industry.  Just like the MP3 player has hurt the compact disc industry.  Which hurt the cassette tape business.  Which hurt the 8-track tape business.  And now the Internet is hurting the big box retail industry.  We call this progress.  And it’s what the people want.  Because it’s the people driving this change.  They’re the ones buying the cell phones, digital cameras, MP3 players, compact discs and cassette tapes.  And it’s the people who are now shopping online.

New technology is always replacing old technology.  When it does it destroys a lot of jobs.  But it also creates a lot of new jobs.  Yes, it’s sad to see some of our favorite businesses go out of business.  But they only go out of business because there is something better out there attracting our business away from those old businesses.  And the day we stop wanting this is the day we give up our smartphones.  Or whatever will have replaced our smartphones in the future.


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Weights and Measures

Posted by PITHOCRATES - November 9th, 2011

Technology 101

Flying Airplanes Require Careful Calculations and Exacting Measurements

How do you buy your gasoline?  Well, if you’re in the U.S., you buy it by the gallon.  And you choose your gas station by the price per gallon.  Typically choosing the cheapest price per gallon you can find.  Even if it means 20 minutes of additional drive time.  Because you want to get as much value as you can when you spend your money.  But have you ever wondered how much gas you’re really getting?

Actually the chances are pretty good that you’re getting what you’re paying for.  The next time you pump gas take a look at the pump.  You should see a tag from the Department of Weights and Measures.  This tag says an inspector filled up a 5-gallon test can and verified the pump metering.  If you see this tag you should be getting what you paid for.  And you should see this tag.  Because they test every gas pump.

Have you ever flown in an airplane?  If you’re a regular flier you probably notice that ticket prices go up when oil prices do.  Why?  Because jet fuel is the greatest expense of flying.  For it takes a lot of jet fuel to make those heavy planes fly.  And one of the heaviest things on a plane is that fuel.  So they try to carry as little fuel as possible.  Which requires some careful calculations.  And some exacting measurements.  Because a jet plane running out fuel while flying can’t continue to fly for much longer.

Egypt, Sumer and Harappa Developed a System of Weights and Measures to Build and Trade

Life as we know it would be pretty difficult without a reliable system of weights and measures.  Something we take for granted these days.  I’m sure you don’t give it a second thought when you pump your gas.  Or sit in an airplane accelerating down a runway.  But none of this would be possible without weights and measures.

There would be no economic activity, either.  Without being able to measure lengths, areas or volumes there would be no building.  And one thing we’ve learned from the Subprime Mortgage Crisis is that building houses IS the U.S. economy.  But it would be hard to build a house if different suppliers sold 2X4s in different lengths.  Or if there were no standard sizes of hot water tanks.  Or if there was no standard size of drywall.  Or no way to measure how much water to mix with gypsum to make wet plaster.

Of course, we would never have gotten to the building process.  Because we couldn’t trade without weights and measures.  We have to measure raw materials before we can trade them.  And assign a unit price.  Calculating prices per unit goes back to the beginning of civilization.  All the way back to Egypt.  Sumer.  And Harappa.  Who all developed systems of weights and measures to build.  And to trade.

Setting Unit Prices for Raw Materials and Finished Goods made Trade Possible and Efficient

Money made trade easier.  But without a system of weights and measures trade would not have been possible.  Even with money.  Because you can’t count everything.  You don’t count grain.  You weigh it in bulk.  You don’t count olive oil.  You measure it by volume.  And you don’t count seed-holes.  You calculate how much seed by weight is required to sow a field based on the calculated area of that field.

Setting unit prices for these goods made trade possible.  And efficient.  It allowed traders to find the best value.  By comparing unit prices.  Much like we do today when choosing a gas station.  All thanks to those reliable weights and measures.


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