Melting Snow and Ice

Posted by PITHOCRATES - February 5th, 2014

Technology 101

When Temperatures fall below Freezing Liquid Water turns into Solid Water

You know what the best thing about water is?  You don’t have to shovel it.  Well, that, and its life-giving properties.  Let’s face it.  We couldn’t survive without the stuff.  We couldn’t grow food.  We even couldn’t live without drinking water.  So perhaps its life-giving properties is the best thing about water.  But a close second would be that thing about not having to shovel it.

When it rains water soaks into our green areas.  It runs off driveways and sidewalks into green areas.  And into streets.  Where it runs off into a storm drainage system.  Which takes it to a river or lake.  The rain lets our gardens grow.  And any excess water conveniently just goes away.  We may have a puddle or two to slosh through.  But even those go away without us having to do anything.  Water is nice that way.  As long as the temperature is above its freezing point.

When the temperature falls below the freezing point of water bad things start to happen.  Liquid water turns into solid water.  And hangs around for awhile.  Accumulating.  On our driveways, sidewalks, porches and roads.  It’s pretty much everywhere we don’t want it to be.  Making it difficult to walk.  And drive.  We slip and fall a lot in it.  The sun may melt it a little during the day.  Creating puddles of water where the snow once was. But when the sun sets those puddles freeze.  And become even more slippery.  Making solid water more dangerous than liquid water.  So a big part of making it through winters in northern climes, then, is transforming solid water back into the liquid form.

Even though Bourbon melts Ice Cubes Bourbon would be a Poor Choice to melt Snow and Ice

All material can be in three different stages.  It can be a solid.  A liquid.  Or a gas.  What determines the phase of this material depends on a couple of things.  Mostly temperature and pressure.  And the chemical properties of the material.  At ambient temperature and pressure material typically exists stably in one phase.  Water, for example, is stable in the liquid phase on an 80-degree summer day.  Allowing us to swim in it.  While on a freezing February day it is stable in the solid phase.  Which is why we hold the Winter Olympics in February.  The cold temperatures give us the best solid water conditions.

If we raise the temperature of water we can turn it from a liquid to a gas.  We could also do this by lowering the ambient air pressure.  Such as putting it into a vacuum.  For a liquid remains a liquid as long as the vapor pressure (the tendency for particles to escape from the liquid they’re in) of the liquid is less than the ambient air pressure.  If we lower the ambient air pressure below the vapor pressure of the liquid we can lower the boiling point of that liquid.  This is why different liquids have different boiling points.  They have different vapor pressures.  Oxygen has a very high vapor pressure and requires a high pressure and cold temperature to keep oxygen in a liquid phase.

When we take ice cubes out of the freezer and add them to a glass of bourbon they melt.  Because the ambient temperature outside of the freezer is above the freezing point of water.  So the solid water changes its phase from solid to liquid.  It would follow, then, that pouring bourbon on snow and ice would help melt it.  Of course we don’t do that.  For wasting bourbon like that would be criminal.  Not to mention costly.  Even if you used the cheap stuff.  Making bourbon a poor choice for melting snow and ice.

Salt dissolves into a Brine Solution that lowers the Melting Point of Snow and Ice

We see that a material will change its phase at different temperatures and pressures.  Which is good to know.  But it doesn’t help us to melt snow and ice during winter.  For we can’t lower the atmospheric air pressure to lower the boiling and melting points of water.  And we can’t raise the ambient temperature above the melting point of water.  If we could our winters would probably be a lot more comfortable than they are now.  So because when we can’t change the air pressure or temperature of the ambient environment the snow and ice is in we do something else.  We use chemistry to lower the melting point of snow and ice.  And the most common chemical we use is salt.

To melt snow and ice salt needs heat and moisture.  The moisture comes from the snow and ice.  Or from the humidity in the air.  The heat comes from the warmth of the earth or air.  Heated by the sun.  It also comes from the friction between tires and the road.  When salt comes into contract with water and heat it dissolves into a brine solution.  And this brine solution has a much lower melting point than water.  Which in turn lowers the melting point of the snow and ice it comes into contact with.  Allowing it to be in the liquid phase at temperatures below freezing temperatures.  Melting that snow and ice so it can run off like rain water.

The warmer it is when it snows the quicker salt will melt that snow.  While the colder it is the longer it takes to melt.  If it gets too cold (around 15 degrees Fahrenheit) salt proves to be ineffective.  In temperatures below 15 degrees Fahrenheit other chemicals work better.  Such as calcium chloride.  But calcium chloride is more costly than sodium chloride (salt).  Ambient temperatures, time of day, sunny or cloudy, wind, etc., all determine the chemical to use.  And the amount of chemical to use.  They consider all of these factors (and more) before sending those ‘salt’ trucks out on the roads.  Allowing us to drive in the worst of winters just as we drive in the best of summers.  It may take more time.  And there may be a little more cussing.  But we still go to work, take our kids to school, go shopping, etc., when it snows.  Thanks to chemicals.  Chemistry.  And the people that put those chemicals and that chemistry to work.


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Another Electric Car bursts into Flames

Posted by PITHOCRATES - October 5th, 2013

Week in Review

One thing we learned from Breaking Bad was to respect the chemistry.  And that’s what batteries are.  Chemistry.  The kind of chemistry that’s a little on the dangerous side.  Unlike gasoline.  Which we can store relatively safely in tanks under our cars.  Where little chemistry goes on inside our gas tanks.  To use that gasoline to power our cars we have to do a couple of things.  We have to aerosolize it.  Combine it with oxygen.  Compress it.  Then ignite it.  Then and only then does it release its incredible energy.  Producing great heat in the engine.  But not the gas tank.  Which needs no cooling system.  It’s a little different in an electric car.

In a battery the chemistry is all local.  It produces electricity—and heat—where the chemicals are stored.  In the battery.  One of the problems with electric cars is their limited range.  And you fix this problem with bigger and more powerful batteries.  That can produce a lot of electricity—and heat—as they charge or power the car.  Making battery cooling a requirement for safe battery use.  To keep those chemicals under control.  But sometimes these chemical reactions go out of control.  Causing fires as cars re-charge in their garages.  Causing fires that grounded the new Boeing 787 Dreamliner.  And this (see Hot Wheels! Tape of Tesla Fire Has Stock Tanking by Dan Berman, Hot Stock Minute, posted 10/3/2013 on Yahoo! Finance).

Tape of a Tesla (TSLA) on fire is giving new meaning to the term “hot wheels.” The video was shot on Tuesday after a Model S sedan went up in flames…

In an e-mail sent to The New York Times, Tesla spokeswoman Elizabeth Jarvis-Shean wrote that the fire was caused by the “direct impact of a large metallic object to one of the 16 modules within the Model S battery pack.” The e-mail went on to say, “Because each module within the battery pack is, by design, isolated by fire barriers to limit any potential damage, the fire in the battery pack was contained to a small section in the front of the vehicle.”

Contained to a small section?  It looks like the fire engulfed the whole car.  All because of some metal debris thrown up from the roadway.  Of course, a way to protect against something like this in the future is to add a metal shield that can take a direct hit without damage.  Adding a thick piece of metal under the car, though, adds weight.  Which, of course, reduces range.

This is a problem with electric cars.  Improving safety results in a reduction in range.  Because it adds weight.  It adds weight, too, with gasoline-powered cars.  But one full tank of gas can hold a lot more energy that all the batteries can on an electric car.  And when you run out of gas all you have to do is stop at a conveniently located gas station and fill up.  Which takes about 10 minutes or so.  Unlike a recharge of an electric car.  Which can take anywhere between a half hour (with a high-voltage fast charger) to overnight in the garage plugged into a standard outlet.  Which is why electric cars are more of a novelty.  Those who have them typically have other more reliable cars for their main driving needs.  For though gasoline-powered cars catch fire, too, when they’re not on fire you know you’re going to get home.


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Lithium Ion Battery Fires ground entire Boeing 787 Dreamliner Fleet

Posted by PITHOCRATES - January 20th, 2013

Week in Review

The big drawback for electric cars is range.  For after a battery powers all the electrical systems (heating, cooling, lights, etc.) what charge is left is for going places.  And if that place is more than 30 miles away few people will feel comfortable taking a chance that they will have enough charge to drive there and back.  Unless that trip is to work where the car can recharge for 8-9 hours while at work.

Range anxiety is the greatest drawback to an all-electric car.  For if you run out of charge there is only one way to get your car home.  With a tow truck.  For you can’t walk to a gas station and ask for a can of charge to pour into the battery.  Charging needs an electrical source.  And time.  So the Holy Grail of the all-electric car industry is a battery that can hold a lot of charge.  But is small and does not weigh a lot.  And can be recharged in a very short time.  Right now that Holy Grail is the lithium ion battery.

But there is a cost for this Holy Grail.  There is a lot of chemistry to do this.  Chemistry that can produce a lot of heat.  Catch fire.  And explode.  Which has happened in some electric cars.  As well as in some airplanes (see Bad Batteries Seen as Best Case for 787 Overcoming Past by Susanna Ray, Alan Levin & Peter Robison posted 1/18/2013 on Bloomberg).

Other aircraft bleed air off the engines for a pneumatic system to power a variety of critical functions, such as air conditioning. That diverts power from the engines that they could otherwise use for thrust, and means they use more fuel.

With an electrical system for the jet’s other needs, the engines become much more efficient. The 787 uses five times as much electricity as the 767, enough to power 400 homes. To jump- start a so-called auxiliary power unit that’s used on the ground and as a backup in case all the plane’s generators failed, Boeing decided on a lithium-ion battery because it holds more energy and can be quickly recharged, Mike Sinnett, the 787 project engineer, said in a briefing last week.

Those capabilities also make lithium-ion cells more flammable than other battery technology, and they can create sparks and high heat if not properly discharged. Chemicals inside the battery are also flammable and hard to extinguish because they contain their own source of oxygen, Sinnett said.

A couple of battery fires have grounded all Boeing 787 Dreamliners.  The last commercial jetliner to receive such an order was the McDonnell Douglas DC-10.   Which happened after an engine came off while taking off at O’Hare International Airport in Chicago.  Due to a maintenance error in changing out the left engine and pylon.  Causing the plane to crash.  After investigation they found the slats did not mechanically latch into position.  When the engine ripped out the hydraulic lines the slats retracted and the wing stalled.  The plane slowly banked to the left and fell out of the sky.  Killing all on board.  The DC-10s were grounded worldwide until the hydraulic lines were better protected and the slats latched to prevent them from retracting on the loss of hydraulic pressure.  Now no 787s have crashed.  But few things are deadlier to an airborne aircraft than a fire.  For there is nothing pilots can do other than to continue to fly towards an airport while the plane is consumed by fire.

Stored chemical oxygen generators in the hull of ValuJet Flight 592 were stored improperly.  They were activated.  Producing oxygen by a chemical reaction that generated a lot of heat.  The heat started a fire and the oxygen fueled it.  Once the pilots were aware of the fire they turned to the nearest airport.  But the fire consumed the airplane and fell out of the sky before they could land.  Killing all on board.

Fire on an airplane rarely ends well.  Which explains the grounding of the entire 787 fleet.  Because these lithium ion batteries run very hot when they make electricity.  And they can generate oxygen.  Which is the last thing you want on an aircraft.  However, both Airbus and Boeing are using them because they are the Holy Grail of batteries.  They’re small and light and can hold a lot of charge and nothing can recharge as fast as they can.  Which is why they are the choice for all-electric cars.  Even though some of them have caught fire.  This is the tradeoff.  Smaller and lighter batteries are smaller and lighter for a reason.  Because of powerful chemical reactions that can go wrong.  So to be safe you should park your electric car outside and away from your house.  In case it catches fire you’ll only lose your car.  And not your garage or house.  Or you can stick to the gasoline-powered car and not worry about battery fires.  Or range.


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