Patent reading is something I avoid as recreation. They're written in a humorless formal style that's perhaps a shade more entertaining than Vogon poetry. Sometimes you have to go through them trying to sort out the claims and their feasibility. I generally translate them into images and numbers I can understand in the process of plowing through. It was during that process that my jaw dropped. Someone had successfully patented something that was clearly impossible. It violated the underlying physics - the patent office usually catches these mistakes early on. Someone had already spent a fair amount of change. At least I could alert my client.
The patent was trying to harvest waste energy. That's all and good - more of it should be done, but it claimed to be more efficient that was possible.
A good deal of engineering is concerned with efficiency. The story of the steam portion of the Industrial Revolution amounted to increasing the efficiency of extracting energy from fossil fuels. Steam engines are a case in point. There was a huge need for them pumping water from mines and the early engines made an impact even though they were extremely expensive to run. James Watt and others came up with clever hacks and improvements continued for over two centuries. (The chart shows how much energy can be extracted from a kilogram of coal. The highest level corresponds to an efficiency in the mid forty percent region)
There are many forms of energy... heat, light, motion, electric, chemical, nuclear, gravitational , and so on. These are usually grouped into two types when considering how work is done: kinetic and potential. In general something happens when energy moves from one form to another. But what is energy? The dictionary and some high school science texts say it's the capacity to do work. OK .. so what's work? Dictionaries often say it's a measure of energy transfer when an object is moved. Nothing like circular arguments, eh? During the 19th century the definition was a point of contention in physics, but before going into that consider a roller coaster.
Roller coasters are great ways to explain the transfers between kinetic and potential energy. If there wasn't any friction or wind resistance you could start a car off at the highest peak and it would move around the track coming back to where it started. Gravitational potential energy would turn into kinetic energy as the car dropped and the kinetic energy would turn back into potential energy as it went uphill. Of course there is friction from the wheels against the track and air resistance. The wheels, axle bearings and track heat up, pieces vibrate, air swirls and sound is generated. If you add all of these up you can account for the total energy of the system. You might even be able to harvest some of these, but in general that's a difficult task.
Much has been and is being done on recovering lost energy. Regenerative braking in electric cars, using waste heat from power plants to heat buildings (combined heat and power), etc. Unfortunately there are limits to how much can be recovered. As the waste heat is closer in temperature to its surroundings, the less efficient extraction will be. This was a fatal error in the patent I looked at. It assumed air temperature was much colder than it really is.
Back to a definition of energy. Emmy Noether showed that for every conserved quantity in physics there's a corresponding symmetry and visa versa. Noether's theorem is central to physics. It's one of those things that makes you gasp when you first realize how it works. Among other things it shows time invariant processes are those that conserve energy. If you fall off a building at noon or two o'clock the result will be the same. Falling under the influence of gravity doesn't depend on time and energy is conserved. Unfortunately really diving in requires some serious math. You can get an idea of what's going one from this non-mathematical discussion by a physics grad student. So if you're curious and remember some high school physics:
In the meantime note that we waste an incredible amount of energy. Not only are we staring down the barrel of global warming, but paying for energy is expensive by itself. There's a lot of low-hanging fruit out there. The problem is often getting people to imagine.
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