omenti

η and cooking meals on car engines

eta

 

Greek letters are used to symbolize so many things that they are almost Rorschach tests.   For me it represents a term in a few very different equations  and a type of particle...  anyone else is likely to see it differently.  You need some context to sort out what it means.  But if you want something that touches all of us - the most general and possible important use - I'll defer to engineering where it represents efficiency.

 

Efficiency can be a bit subtle.  It seems simple  - how much you get out of something divided by how much you put in.  Take a car with an internal combustion engine.  The energy it takes to move it down the road some distance divided by the energy in the gasoline it burns is the efficiency of your car.  Under average highway conditions it's somewhere between 25 and 30 percent.  Energy isn't created or destroyed - it just changes form when work is done.  In this case you get some useful work - moving your car - but the rest goes into heat the engine has to get rid of, heating the road a bit, some noise and so on.  

 

In this fashion you can measure the efficiency of any process that converts energy from one form to another.  One of you is a volleyball player.  The efficiency of a human running around in the sand is something under 25%.  Jumping is roughly the same.  The measure here is how well the muscles convert the energy they're given into work.    A Tour de France cyclist is somewhere near 25% - human muscle efficiency are similar to a car with an internal combustion engine.

 

But it's not that easy.  What if I want to measure how much work a volleyball player does moving in the sand?  Now there's a lot of energy being lost to the slippage of the sand under her feet.  You can measure this in principal, but you can keep asking questions.  For the car you can ask how much energy did it take to mine the oil, turn it into gasoline and ship it to your tank .. what is the well to tank efficiency?   And if you have an electric car what is the efficiency of making and transmitting the electricity and now efficient is the charging process.  Oh - and if you buy a car in the first place how much energy did it take to make it?

 

These questions are part of the necessary context to sort out how much carbon we dump into the atmosphere.  Bottom-up calculations like these are extremely difficult - I spent three months doing one for a telecommunications company - but they illuminate where areas for improvement exist.  Serious global warming models use top-down measurements which are much easier to get right.  They just gloss over a lot of the detail. 

 

My sister had an Easy-Bake toy oven when she was about seven or eight.  It looked like a real oven and used  two 100 watt light bulbs to generate about 350°F to bake little cakes and cookies.  It may have not been the safest toy, but the light bulb as a cheap heating element was genius.

 

Electric lighting  is extremely inefficient.  Incandescents convert about three percent of the energy they use into visible light, CFs average around eight percent and the best LEDs maybe fifteen. Most of us have replaced our incandescent lights with compact fluorescent or led lights to save energy.  But if your goal is baking little cakes or heating the room a bit, inefficiency becomes useful -- the cheap waste heat is put to use.

 

The best fossil fuel and nuclear power plants are about thirty five percent efficient.  The waste heat can be circulated as steam or hot water and used to heat homes, businesses, run industrial processes - even grow hothouse produce in the Winter.  When you add up how the energy is used the effective efficiency of the co-generation plant can rise to sixty to eighty percent. Denmark is the world leader when it comes to doing it at scale - nearly all businesses and housing developments use so-called district heating.  

 

Even your car, assuming it isn't electric, uses co-generation for heating and defrosting.  Of the four gallons of gasoline you burn to go thirty miles or so nearly three heat up the engine block or down the tailpipe as waste heat.  Your car heater taps this powerful water heat (much more powerful than your home water heater) and there are other ways to use the resource.  My father would wrap hamburger, chopped onion, carrots and potato in aluminum foil and tie it to the engine manifold of the old Ford Falcon on our yearly trip to Utah.  Eighty miles at seventy miles per hour was about right in early June.  The downside was the foil wrapping wasn't great plus sometimes it burned.  But as a child of the depression he saw it as a free oven.

 

This kind of thinking can lead to the lowest of the low-hanging fruit when it comes to using less energy to get our work done.  The rub is most of this heat is below the temperature of boiling water and it is increasingly difficult to use heat energy as it gets colder.  When you extract heat energy from something it gets cooler.  The maximum efficiency is the difference between the original temperature - final temperatures divided by the original temperature.¹  You have to get clever if things are cool.

 

Waste heat is good for hot water if you have the infrastructure.  Data centers, sewage treatment plants, industrial air conditioning and refrigeration are good sources.( Cooling is very inefficient and generates an enormous amount of waste heat.²  On a hot Summer day AC increases the temperature of NYC by about 2°F!)  Beyond hot water there are specialized engines that work with fairly cool (boiling water temperatures) to generate electricity.  They're not sensible everywhere, but industrial applications that can use them to reduce power costs and lower carbon emissions at the same time. With realistic carbon taxes these approaches would explode in popularity.

 

On the horizon are a variety of methods of mining low grade waste heat turning it directly into electricity.  Some are used now -- thermoelectrics are the go-to method for generating power from heat in space - any spacecraft with a nuclear generator uses them.  And some developing world stoves generated electricity to charge lights and phones.  They're getting better and cheaper, but are still aways off from general use. Thermoacoustics, thermovoltaics, and thermoionics are other promising approaches that are being looked at- the sort of thing DARPA-E was focused on until the current administration came in with a buzzsaw.  But this is a very exciting area.  Imagine the potential for cutting back on fossil fuel power plants by half without impacting power output.

__________

¹ It gets a little technical and I'm simplifying, but the highest efficiency of a heat engine is the Carnot efficiency which is  (T_h - T_c )/Th where T is degrees above absolute zero.  So the efficiency of going from boiling to room temperature is about (373-273)/373 - about 27% .. in practice it will be much lower.  For an efficient engine you want a very high working temperature and a very cool heat sink.  Cars need radiators and power plants use super heated steam.

² Apple and Facebook are leaders on datacenter waste heat capture.

the critical edge in a major sport

The other day I was in a Manhattan library wearing the t-shirt of my undergrad school.  As luck would have it someone noticed it.  She was from the same school - her Ph.D. was in mechanical engineering - and a most interesting conversation followed.  It turns out she happens to work on suspensions for one of the more famous Formula One teams. 

 

Formula One may be the most form of auto racing. Four wheels hanging out in the breeze and an open cockpit, its roots go back to Grand Prix racing about ninety years ago.  After WWII it was associated with some of the most famous car makers and drivers.  It has enormous popularly worldwide with something like a half billion people following any given race and over 300 million fans who follow most of the season. Good drivers make in the eight figures and some have career earning exceeding a billion dollars.  A massively important form of sports entertainment larger than the NBA and NFL combined. 

 

F-1  technology side has made huge advances over the years.  Thanks to tire, suspension and aerodynamic advances the cars can corner with lateral accelerations over six times that of gravity.  That's more than an astronaut experiences during re-entry and on par with the limits of a jet fighter.  Top speeds are on the order of 240 miles per hour on relatively twisty tracks.  Teams spend a lot of money - she said an average team might have 100 engineers, technicians, physicists and mathematicians - over a third with Ph.Ds. - working on every little bit of vehicle performance.  Cars get much better during the racing season not making improvements every race means almost certain failure.  She said a few American universities major talent suppliers - notably Caltech and MIT - but England is the real ground zero for car design and tuning talent from a half dozen schools.  

 

So there's this question.  How much success is the driver and how much is the car?  The feeling is the driver, even though operating a car under such conditions probably is an athletic performance, is less important than the car.  Put a great driver in a lesser car and they might improve the performance of the car a bit, but they'll never win.  A lesser driver in a great car probably won't win, but will place much higher one might expect.   But there's a human story and sport is all about human performance.  You probably won't see much interest in autonomous cars zipping around a circuit even though they might outperform humans.  

 

But there's another story.  The master designers and aerodynamics people are very important, but there are enough very good ones and enough viable approaches that the top half dozen teams are on fairly equal footing. the most important person on the team, and sometimes it is two people, is the strategist - usually a mathematician or physicist. 

 

The cars are rich data sources sending hundreds of channels of telemetry for analysis giving the state of almost anything you can image about the car.  Additionally tracks, weather, cars, tires, competition and tactics and strategy are all modeled ahead of time.  Variables are thrown into the mix that makes the strategist even more important.  Tires are a good example.  There are three levels of grip... the grippiest tires wear very quickly, the least grippy more slowly. You have to use at least two during a race meaning a pit stop with a tire change is necessary. Additionally there are two types of rain tires.  It's an exercise in modeling and game theory sorting out how this will play out. The most consistent factor in winning races appears to be the strategist.  Three of the top ten are women.

 

As the sport changes to stay relevant hardcore fans are being challenged to examine some of the race data during the race .. there's thought about making it part of the race itself, but keeping the competition level high and the fans engaged is the key point.   One thing she mentioned is heart rate and blood pressure telemetry from the pit chief as a car comes into the pits at 70mph stopping a few inches away as he has a few seconds to make the swap.  

 

There are a lot of interesting things you can say about this type of data and its analysis.  The fact that some believe understanding it is more important than the driver speaks volumes. Some of the teams monetize this by letting their largest sponsors in on their technics of dealing with rapid change and strategy and tactics.  A few of the analysts have been loaned to these sponsors for non-trivial sums to look into their businesses. 

 

It makes you wonder about other sports.   It would be interesting to create a plot with understanding of athletic performance (including psychological elements) along one axis and understanding of strategy along the other.   Understanding hydrodynamics created a revolution in swimming along the first. A deep data and model driven understanding of strategy has driven Formula One performance along the second.  How much potential does a given sport have?