attacking global warming with deep insight from a brewery

The 1970s were marked by two dramatic energy disruptions that shook the world.  Petroleum became much more expensive and a geopolitical weapon. Small cars suddenly became popular and American drivers began to look to countries that made them.  In the US large sums flowed into energy R&D.  Much of it went into shale oil, but alternate energy labs appeared.  Electricity from wind and solar were far from practical, but there was a mini-boom in solar hot water heating.  It turns out you need solid engineering if you're going to water running in panels on your roof.  Unfortunately there was a lot of poor engineering, short module lifetimes, and water damage. 

 

Since then we've seen dramatic reductions in the cost of electricity from wind and solar energy.  Expanding these sources to levels needed to deal with global warming is extremely challenging - too challenging given the current political climate.  It's important to remember that electricity is just a way to move from a generator to a load.  It's very practical, but also ephemeral.  Storage is expensive as is the infrastructure to efficiently move it from where it's produced to where it's needed.

 

Electricity demand represents about a fifth of the world's primary energy supply.  This will grow with electrification in transportation, but the numbers are so staggeringly huge that it will be awhile before the needle moves.  Solar, wind and nuclear are the primary non-fossil fuel sources.  Two are growing and one is shrinking.  But even if all electricity came from clean sources it would just be a fifth of the primary energy supply.  

 

Thermal energy demand is larger at a bit more than a third of the supply worldwide. Space and water heating, industrial processes, cooking and so on.  In homes it's much higher than a third usually running above sixty percent.  Thermal energy can and is electrified, but you have to deal with the inefficiency of making, transporting and then converting the energy. Wouldn't it be neat if you could do it directly without the intermediate step?

 

You can and you have.  All of us have sat inside on cold sunny days next to the window enjoying the heat.  Insulated homes and insulating windows can dramatically drop external energy requirements.  Solar hot water heating is dramatically better than it was forty years ago and is required by code in a few regions.  But what intrigues me is the direct mechanical production of heat.

 

An apple rolling off a dinner table hits the floor with about a joule of kinetic energy.  The energy unit is named in honor of the son of a prominent brewer and followed his father into the family business.  The family had money and the young James Joule was tutored by John Dalton and a few other great scientists of the day.  Science became his hobby and passion.   In the 1840s he built early electric motors to see if it made sense to replace the brewery's steam engines.  It was far too early, but he established himself as a solid amateur scientist.  With this mindset and approach he set himself to was understanding the economics of brewing.  It would change the world.

 

He worked in many areas, but this most important work was on the convertibility of energy from one type to another.  The caloric theory of heat was accepted wisdom - basically heat was conserved and couldn't be created or destroyed.  While wrong, it led to the creation of some rather beautiful mathematics.  Joule found something deeper and more accurate -  that energy could be converted from one form to another.  As it happened brewers had the best thermometers allowing careful measurements to figure out what was really happening.  He mechanically did work to water by stirring it and showed a unit of work heated the water by the same unit.   The energy increase of the water by heating was equivalent to the work done by the mechanical stirring.   He had made the leap to the conservation of energy and created the basis for the first law of thermodynamics.

 

It's neat to think about a simple extension of his apparatus.  Put a mechanical stirrer inside an insulated box and spin it with a wind turbine.  Mechanical energy from the wind is directly converted to heat and can be used for home hot water or space heating.  

 

The sketch is just a simple version.  Vertical axis turbines aren't that efficient, but that may not be a major issue. While big turbines are more efficient,  it is impractical to move hot water far enough to make it practical.  The natural size of these units may be home with a small turbine or, where district heating is popular, a medium sized wind turbine.

 

The back of the envelopes are interesting.  A cubic meter of water (a metric ton or 1000 liters or about four average bathtubs) can hold up to about 90 kWh of heat energy.. enough for a two days for a family of three or four.  It's fine if the wind is intermittent.  When it blows, heat is added to the water.    Getting the size right for a household and location would require a fair amount of experimentation and modeling, but this is the sort of work that would probably be crack for mechanical engineering grad students.  It's a great exercise in systems optimization.

 

Here's a simple simulation for a small half meter radius turbine in a location with an average wind speed of 16 miles per hour over two days.  The first graph is wind speed.  The second is the mechanical power delivered to the mixer in the water.  Note that power increases quickly with windspeed (you know this if you've held your hand out of a car window or biked into the wind)  The last is the water temperature given good, but not fantastic insulation.   The water gets hotter and keeps its heat in spite of a very bursty power source.

 

There are a lot of ways to tap energy.  The direct conversion of mechanical energy to heat is particularly attractive given the enormous worldwide heat use.  This may be a good technique in some cases and there are undoubtedly others.  It's not very technical - heavens - it was easy in the 1800s and it's remarkable no one stumbled on it earlier - the technical capability to do this goes back about a millennia.   Now we have the capacity to measure and model as well as utilize a wide range of materials and construction techniques.  It may be interesting again.

 

There are a variety of mechanisms to deliver energy in some practical form for us to use.  Many are more efficient as centralized sources and some are better at smaller scales.  This is one that works best when highly distributed. 

 

 

Comments

[G Vesonder]

This sounds like a great senior design project for our mechanical engineers!

[steve crandall]

Yeah .. understanding some basics about wind, water, heat transfer but on an inexpensive and manageable scale. Then instrumentation and testing and thinking about how you'd improve your design.

I'd use an electric motor I could carefully control rather than a windmill to understand things later on. Maybe play with a kilowatt or two max and tell them to think in terms of a stove's heating element.