You who read this, may be an engineer, a mechanic, an inventor, a student, or even someone without an engineering background. My observation is that the general public has little knowledge of basic science and even engineers and other professionals often lack in basic insights, in spite of being advanced in their specific fields. This often leads to unfeasible projects and wrong choices, based on wrong assumptions, that no computer can correct.
I myself am a graduated engineer on B.Sc level in both mechanics and electrics. Nevertheless, most of what I know worth knowing as an engineer today, I learned from practical experience and backing it up with own theoretical studies afterwards. It forced me to focus on basics. When you have the basics right, the rest is just methodology, where the computer can be very helpful, but don’t let it “think” for you!
If you have no engineering background, why would you need to have some basic knowledge of all this, you may ask? Well, we live in a technological society and so we are confronted with technological matters and products, that we need to understand the basics of to make proper choices. Ever bought expensive “energy-saving” lamps, while in the same time needing to heat your home? Do you think hydrogen and/or fuel cells are energy sources? Do you think energy can be produced and consumed? Would you invest money in solar panels, or other renewable energy technology for your home? The more these kinds of things apply on you, the more you need to read this article.
The Laws of Newton
The metric, or SI system of units is based on the laws of Newton and so is most of modern mechanics and dynamics. They are essential for basic understanding:
- 1. A mass object persists in its momentary motion to speed and direction, unless it is forced to change it by external forces working on it.
- 2. The acceleration of an object is proportional with the force F working on it and inverse proportional with its mass m. Hence, the acting force is given by: F = m.a
- 3. A force acting on an object, will yield a counter force of the same strength in the opposite direction: action = reaction.
Although these laws sound simple, they are often wrongly applied, or overlooked. Especially the third law appears to be the most fundamental one, still not fully understood by Science and subject for discussions on the highest levels (how can you move a table for example, as it pushes back with the same force?).
Power and Energy.
Power and energy are very often mixed up. For example a lightning, causing a tree to split into half, is very powerful, but it has very little energy, because it lasted only a fraction of a second. Energy is the range of power and time. Power is expressed in Watt and energy in Joule - 1 Watt thus is 1 Joule per second, inversely 1 J = 1 Ws (Watt second). If you during one hour would apply a power of 1000 Watt (1 kW = 1 kJ/s), which approximately is what a flat iron takes, the energy involved is 1 kWh and this is thus equal to 3600 kJ. If you instead would develop that energy in one second, the power becomes 3600 kW, or 3.6 MW - a small power plant! If thus a lightning would have a power of say 10 GW and lasted 1 millisecond (it looks much longer, because of the glowing air around it), it contained an amount of energy of just 10 MJ = 10,000 kJ, not more than 2.8 kWh, or to power a flat iron for around three hours! If you in brochures would read dimensions like kilowatt per hour, or horsepower per hour, you can know that the author has no idea what he/she is talking about.
Energy is also the range of force and traveled way. If you lift up a mass of 1 kg to a height of 1 meter, the force needed for that is the range of mass and gravity acceleration, as per Newton’s second law. On Earth, gravity acceleration is 9.8 meter per second square, which we can round to 10. The lifting force then becomes 10 kilogram meter per second square, which is called the Newton (N) and the work done is then 10 Nm (Newton meter), which is 10 Joule: 1 J = 1 Nm.
The same confusing exists around temperature and energy. What would you rather have in your hand, a 1 inch red glowing sewing needle, or a 4 inch red glowing bolt? Though both have the same temperature, the needle will just cause you a blister, whereas with the bolt, you won’t have a hand any more. The bolt contains much more energy (more mass) than the needle and that makes the difference, not the temperature.
If you would be interested in a solar panel to heat water in your home, the temperature it can yield is therefore not that important. You pay for energy instead and that is what you want to save on. Ideally, a solar water heater should work on a low temperature, so it doesn’t loose too much heat through its insulation and produce a larger water flow instead. You then save more energy = money, because of the higher efficiency on which your solar panel works. To reach your desired water temperature in the kitchen and bathroom, you can heat additionally with say an electrical heater. Combination with a heat pump, also taking up heat from your warm waste water, would give the absolute best results (but high installation costs). Read more about that at the end of this article.
However, manufacturers of solar panels optimize on temperature, which is a good selling argument for the energy-unaware public. At higher temperatures, the size and thus the costs of the whole installation, including storage tank, become lower, which also sells better. They don’t talk very much, or at all about efficiency, being the relationship between how much solar energy hits the solar panel and how much of that you can use in the end. They talk about capacity instead - solar energy is “free”!
Next to consider is Pressure. Usually it is that of a fluid, like a gas. It is expressed in Pascal (Pa) which is force (N) per unit of area and thus 1 Pa = 1 N/sqm (Newton per square meter). Atmospheric pressure at sea level is roughly 100 kPa, thus 100,000 N/sqm. In technical descriptions it is also often called the bar - 1 bar is thus atmospheric pressure. Pressure can also be seen as stress in materials, tension. In the SI system of units, pressure and tension are thus both expressed in Pascal.
Then there is contact-pressure. This is what makes a knife work. The sharper a knife, the smaller its edge area (A) is and for a given force (F), the contact-pressure (F/A) becomes larger, also expressed in Pascal. With this, all units in the SI-system are given. It has only three basic units, the kg for mass, the meter for length/distance and the second for time. No conversions are needed
Circular Motions.
From Newton’s third law follows the perception that on an object in mechanical rotation, two forces are working, a centripetal one, pulling the objects towards the center of rotation, and a centrifugal one, tending to push it out radially away from that center. If the mechanical contact with the center of rotation suddenly is broken, in that very moment no forces are working on the object any longer and thus it will move as per Newton’s first law, meaning it keeps its speed in the direction it had in the moment just before losing contact. That speed was directed tangentially and thus the object will “fly out” in the tangential direction, not radially. In fact, centrifugal forces do not exist, because then there would be no resulting force to keep an object in its circular path - only the centripetal force exists. This is a hot discussion point in Science - Newton’s third law.
Hence, when you are in a car that makes a sharp curve, your body does not push against the inside of the car (centrifugal), but the inside of the car pushes your body into the curve (centripetal). As per Newton’s first law, your body wants to keep its direction of motion, straight ahead, just before entering the curve - it’s called inertia. There is only one force, the centripetal one (free motions in gravitational fields, such as orbits of planets and satellites, are described in General Relativity, which we won’t discuss here).
From this follows the notion of “inertial” systems, which are frames of reference in which Newton’s laws are valid. An accelerated system is thus not an inertial system, because motions described in it, would not follow Newtonian laws. This causes a severe point of confusion, as follows:
If you are an inventor of “fantastic” mechanical machines, your really should understand the implements of impulse. Impulse (p) is the amount of motion, being the range of speed (v) and mass (m), which is equal to the range of working force (F) and the working time (t): F.t = m.v = p. An impulse has a direction, which (kinetic) energy has not and therefore impulses can have a positive or a negative sign between opposite directions of motion. Because impulse is a function of force (the time-derivative of it), Newton’s third law requires that the sum of all impulses of moving components within a system (machine) must be zero. However, many inventors, not being aware of this, “create” a resulting impulse, that accelerates the system.
What they do is mixing up reference systems and impulse with energy. If you consider a mechanical system (machine), that has a certain total mass, but also internally moving parts, the resulting impulse of those parts, the sum of all impulses, will be zero relative the system’s center of gravity, but not necessarily relative a resting frame of reference (an observer) in which the whole system (machine) may be moving (at constant speed). The sum of kinetic energy of all the internally moving parts, is of course a positive value (negative energy is less than nothing). This value is the system’s internal (kinetic) energy. Since this internal energy is needed to keep the internal parts moving, there cannot be any energy left to accelerate the system (machine) as a whole. On the contrary, energy must be applied all the time to overcome the friction that the internally moving parts are subjected to, otherwise they would come to a halt. This applied energy converts to heat.
Sadly, there are several patents on according designs, claiming to be “inertial drives” for space-ships or whatever. Their inventors, some of which may have ruined their private economies on this, were not confident with the basics of dynamics, as outlined above. See some of those unfortunate examples here: http://jnaudin.free.fr/html/IPEmain.htm
Mechanical Engineering Concepts
Now, imagine you had a ball that is perfectly spherical and a table that is perfectly smooth, so when the ball is placed on the table, the contact area becomes a dimensionless point - zero whatever. Then the contact-pressure F/0 becomes infinite, regardless how light the ball is - something must break. No material could withstand an infinite contact-pressure and from this follows that not even with the most fantastic materials, yet to be developed, a frictionless machine could ever be built (that would require ideal point and line contacts).
Some inventors have a problem with that, like a patent I once saw, where a 15 cm (6 inch) diameter cylinder was rotating at 1500 rpm in a somewhat larger cylinder, supported by a number of smaller rollers in the size of just a few millimeters - it looked like a ball-bearing in cross section. These rollers would rotate at roughly 50,000 rpm. You look in any bearing table what the admissible speeds are and you would see that this design exceeds the limits by far; self-destruct through friction!
Another problem that many inventors have is judging leakage potential. Leakage is a function of pressure ratio, not of pressure difference and it varies to the third power with the clearance gap between the boundaries. It means that the same sealing device, that would leak in an however deep submerged submarine, would leak more in a space craft, because there the pressure ratio to vacuum is infinite - many don’t seem to know that. In addition, even less known, is that the best sealing is obtained with a single, unbroken sealing line, ideally a circle.
Therefore, the reciprocating circular piston machine will always prevail over any rotational displacement concept, that contains several broken (discontinuous) sealing lines. These rotational concepts can be used and are used in low-duty applications, where they have their advantages, such as in air-driven hand tools, industrial compressors, etc, but not in heavy-duty combustion engines. This is why the Wankel never became commercial, except a few years in cars from German NSU, that went bankrupt on it in the 1970-ies.
One can see the most ‘horrible’ designs in various patents, the worst I saw being an engine, consisting of a torus shaped tube, with a slot over its inner length to let through a piston rod, attached to a circular piston moving in that torus, while flat plates were sliding radially in and out the torus to form alternate compression and expansion chambers - at best a good cream-wiper (but it got a gold medal in an inventors contest - its glorious funeral)!
Many inventors have tried to find a linear transmission, that can replace the pendulous crankshaft. It has various disadvantages, such as causing vibrations of higher order, but most of all causing side-forces on the pistons, resulting in excessive wear and leakage there. I once read a statement from a development manager at Volkswagen in Germany, that the crank mechanism alone stands for 20% of the fuel consumption. All alternative designs I have seen, indeed convert the linear piston motion into a rotating one on the shaft and without causing side forces on the piston, but instead they generate the same or higher side forces on sliding parts elsewhere in the design, causing excessive friction and wear there - definitely no fuel savings. I have found a design that does not contain any sliding parts, but consists of rotating components only (I got the idea, when I was with my kids in a merry-go-round). Had I only come up with this a good 100 years ago, I could have made it, but now the pendulous crankshaft is so well established in automated production lines, that it can’t be changed any more. I almost hade it made with Compair-Reavel in the UK, around 20 years ago, but also they found it in the end too costly too change their production line - my bad luck!
Thermodynamics
Another basic thing, often misunderstood, is that energy can’t be “used up”. Surely, the gasoline you put in your car is used up, but the energy it developed is still there, to stay around for all eternity. All the chemical energy that was stored in the original fuel, is converted to heat. Firstly at high temperatures in the car’s engine, but then decaying to heat at ambient temperature. The rest is also converted to heat by friction, the tires on the road, the transmission, air resistance, etc. All energy that we “use” with our technology, finally decays to heat at ambient temperature, even the light from your lamps at home does that.
So is there the term “waste heat”, as opposed to “useful heat”.What is useful? Take “energy-saving” lamps for example. If you live in a cold climate, where you have to heat your home, a normal cheap hot glowing light bulb actually delivers 100% useful energy, 5% of which is light, the rest is heat, that helps heating your home, but this is not what you are told. Only the 5% light is brought forward as “useful” and you are told that you are “wasting” 95% with a normal glow bulb. Only in warm climates, especially third-world countries with very expensive electricity, or in cooled rooms, the use of energy-saving lamps makes sense!
The misconception by the public is that useful energy is “consumed” and waste energy is not. The real situation is that the useful energy is just used, but not “consumed” and is wasted after usage just the same. That’s why your energy bill comes back every month - nothing of what you used, is left. Therefore you read everywhere about “energy production” and “energy consumption”, not in the least used by decision makers in energy politics! It indicates that there is no basic understanding in public society, what energy is about and so unfeasible projects are initiated, wasting time and (your tax) money.
The First Law of Thermodynamics says that energy cannot be created (produced), nor destroyed (consumed). We can only convert energy from one form to an other and the Second Law of Thermodynamics says that it all finally must decay to heat at ambient temperature and so it does. Even though many know this, that is end of story for them, as far as the First Law is concerned. However, the scientific definition of the First Law says that if you add energy to a system to bring it in an other condition, you must remove the same amount of energy to bring it back in the original condition. Naturally, because if we could remove more, energy would be created from nothing and if less, energy would disappear into nothing. This formulation has great consequences, as follows:
Let’s consider an ideal hydrogen (water) engine, by which we pour water in it on one side and the same water AND useful mechanical energy comes out on the other side. Because the engine returns the same water as was applied (firstly as steam, but than condensing to water at ambient temperature), there cannot be a net output from the engine - it would have been created from nothing. If there is an output anyway, this means that the according energy had to be applied as well, not only the water. Indeed, we must apply energy to split the water in hydrogen and oxygen. If that could be done at an efficiency of 100% (electrolysis has only 60%), then that energy could appear as mechanical work on the shaft. This then means that the hydrogen only was an energy converter, definitely not an energy source!
Hydrogen does not occur in free form on Earth, like fossil fuels do and therefore hydrogen can never be an energy source. Give me a dollar for every article that says different and I will be well off!If there would be a method to obtain free hydrogen at considerably less energy input than what combustion with oxygen gives in output, yes, then it would become an energy source, but such a method has not yet been found.
Instead of splitting water, hydrogen can be obtained from natural gases, such as methane. It shows however that the overall efficiency of such a hydrogen loop in a combustion engine would have a somewhat lower overall efficiency than using the natural gas (or bio-gas) directly in a combustion engine. Moreover, hydrogen is a very tricky gas to store and to handle. Not only is it very explosive, but it tends to exude through most metals as well. It is very voluminous, around ten times more than air and thus needs to be brought on high pressures to keep the volume down and that takes a lot of compression energy. Liquefying it would even take more energy, plus a temperature problem for storage as well. There are materials that can absorb hydrogen gas at a lower temperature and give it off again at a higher temperature, surely the better way, but also not very cheap and practical in a distribution system. All together, there is no economy in hydrogen engines, but it may have an environmental advantage - the only viable argument for using it, provided the consumer wants to pay the higher costs, do you?
The same can be said from fuel cells, working on hydrogen - they produce water (steam) and need a steady supply offresh hydrogen and oxygen to work continuously- whereto get how? Yes, the energy that fuel cells are supposed to “produce”, originally came from fossil fuels to manufacture the input hydrogen. Can we call that “non-pollutant” energy? A fuel cell is NOT an energy source, just an energy converter.
The importance of using spontaneity in physical processes is largely unknown, because it has to do with entropy, something not explained very well in schools. So I had to learn in practice, by trial and error, that if you want to separate fluids from each other, you must try to find a design by which this happens as spontaneously as possible, for example with “smart” piping, rather than using filters. The more you try to force it about with various design details, the more you will lose in efficiency - you “produce” entropy as it wrongly is called. The more you force about a process (introduce “irreversibilities”, as it is called correctly), the greater the change of entropy is, the lower the efficiency becomes. Entropy is an essential part of the Second Law of Thermodynamics, not to say the whole of it, but yet there is no general agreement among scientists, what entropy actually is - very confusing.
The Second Law is actually not a “real” law, because it is based on observations only, not on any physical principle. This means that if the observations would change, the Second Law would have to change too, but this hasn’t happened yet, which makes it a law. In everyday life we experience that most things don’t happen spontaneously, only accidents, or coincidences in general, do (”Murphy’s Law”). If we want things to happen, we usually have to do work for it. Hence we could formulate the Second Law as: “for free only the Sun goes up”. On the internet, this formulation of the Second Law is widely violated by millions of web sites, trying to let you believe that for a small investment, you can become rich very soon. But that is not engineering (rather “religion”), so I leave you with that.
In engineering, especially when it comes to renewable energy sources, the Second Law is also widely violated, or rather ignored. Oh yes, solar energy is free, but you can’t use it for free, why not? Because it is widely spread in Nature and thus the effort to collect it into one point of usage and to present it in a usable form, is very large and you have to pay for that effort. Using fossil fuels is cheaper and easier and that’s what we do instead. The same would be valid for nuclear power, but there the “environmentalists” have been successful to obstruct it - with thanks from the Arab oil sheiks.
Renewable energy is something the Second Law is very much against, because it wants to spread it out in the environment, not to collect it for our use. Therefore these renewable energy sources are high-entropy ones, meaning you must do a lot of work to make use of them (low efficiency). There is one exception though and that is hydro-electric power. The forces of nature actually do all the work for us, by collecting rain water in high situated reservoirs, ready for us to use; they are low-entropy sources. But also here the “environmentalists” choose to favor the oil sheikhs instead.
Next would be heat pumps, which are inverted refrigerators. A heat pump absorbs heat from the environment, usually from the ambient air, by generating a cold surface there. This surface is small, but it actually collects heat from large, remote areas, brought by the wind. Also here, the forces of nature do the collecting work for us, a second exception on the rule (compare with a storm blowing aside of your wind propeller, without affecting it, or the Sun burning a hole in the ground next to your solar panel, also without affecting it).
The heat pump, as the name says, pumps up the ambient heat to a higher temperature that we can use, for example to heat water. Also its drive power is given off as heat at usage temperature, is thus no loss (where it is in a refrigerator) and so a heat pump can give off between 3 and 4 times more energy than what it takes to run it. If all the billions of dollars that to date and ongoing are wasted on wind propellers and solar collectors of various kinds, would have been used to provide all households with heat pumps, many power plants could have been shut down by now and no more oil would be burned in homes for heating. This however is a truth with modification. A huge polluting industry, likely using fossil fuels, would be behind all those heat pumps, but that would be the same also for wind propellers, solar panels and the production of hydrogen and fuel cells, all having to be financed by the consumers and making profit as well - the Second Law all right:”For free, only the Sun goes up”
Rudolph N. J. Draaisma
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