Fool wrote: ↑Mon May 20, 2024 1:16 pm
The end of the compression stroke and beginning of the expansion stroke is where the displacer is moving away from the hot side pushing the gas to the hot side through the regenerator away from the cold side at the highest rate. The piston is at the top of its travel and is moving at its slowest rate. Any temperature changes are a direct result of heat flow from hot plate, cold plate, and regenerator. Little is a result of volume change or work. Another change in direction of this discussion. Another partial cycle description. Why?
Your characterization is just wrong.
TDC is FULL COMPRESSION.
Heat generated by compression has reached its zenith. Heat of compression is at a maximum.
"Any temperature changes are a direct result of heat flow from hot plate, cold plate, and regenerator. Little is a result of volume change or work."
You are trying to dismiss, ignore, undervalue, heat and temperature changes that are the result of work as if they don't exist or are inconsequential. That is simply not true.
It's like, if I boiled water on the stove, then shut off the stove, you would say there is no heat in the boiling hot water that was added by the stove because the burner was shut off.
The heat of compression at TDC came from compression that just completed.
True, in an LTD type engine with a large volume of air in the displacer chamber and a tiny piston, the heat of compression has little impact. (But still some). That is not necessarily the case in other Stirling engine configurations where the compression ratio is much higher.
At TDC the piston is briefly not moving. Look at the piston's position verses time plot. It is at the top of the sine wave. It moves (rough numbers) 1% for a crank moving 5%. Compression is "over" before TDC, mostly over, especially in a LTD Stirling. At the same time the displacer is moving at its highest rate, (again rough numbers) 5% movement for crank moving 1%. That is also easy to see from a displacer/time plot. Both can also be seen in a position verses crank angle plot. Your choice.
Since the compression is over, mostly, the temperature change, not temperature, will be mostly the result of displacer movement and regenerator interaction. It is not going to be from the mostly "non existent" piston movement/compression. That applies only to the 10° BTDC, and 10° ATDC, (roughly).
Water boils continuously because it has an input of heat from a flame or a red hot stove element. IOW's, from something hotter than the boiling point.
If the burner is turned off, the boiling stops. The pot remains hot for quite some time. That "hot", is not "heat", it is "internal energy". Internal energy is stored energy. It gets there from, something hotter or mechanical force, so it is not heat. It is however, "hot".
It can also get there from electricity, chemical reaction, friction, light and nuclear radiation, to name a few. Hot doesn't necessarily come from heat.
Hot is energy, and never heat. Colloquially, people say, heat is hot, but in engineering that is wrong/misleading. Hot is a measure of internal energy, and is a representation of quality or value of that energy, its availability for use, its potential for "efficiency".
The same amount of energy can be at different temperatures depending on the mass and coefficient of thermal energy specific to the material. M•Cv•T. Larger Mass equates to lower temperature for the same material and quantity of energy, lower quality/value.
The hot pot looses internal energy, slowly, through heat flow to the outside side atmosphere. The burner looses energy faster because it is hotter. It looses it to the air and to the much cooler boiling water pot.
It took me quite a bit of research to eliminate my erroneous mindset that heat is hot. Most engineering books, professors and people, are colloquially challenged, and use heat, hot, internal energy, Q, adiabatic cooling, cooling, heating, work, sink, source, to name a few, "interchangeably". It took me a long time to understand that they are very misleading. It has taken me even longer to understand why, and how. And even longer to accept the correct viewpoint. And I'm still trying to eliminate my own habit of colloquially using the terms interchangeably as I have for so many years. I keep trying to mislead myself to the old ways.
I want to redefine "heat" as "internal energy". And "Flowing energy" as "thermal flow". It would aline it with current colloquial use. Unfortunately it would mess up all the current engineering books and that is way too much inertia to overcome by any good idea. It's like the misleading term 21'st Century, wrong/misleading. We are in the century numbered 20. The same as our calendar date number 2024. Simple, and not, or less, misleading. But it will never overcome the inertia of the fools that want our current century to sound more advanced than it is. I digress. Sorry.
The main point here is that heat is a flow/transfer of internal energy from hotter to colder. Heat is not "energy" any more than a river is water. Energy is what is flowing, like water flowing, but a river, the flow, isn't storage. A lake is storage, hot masses are the lake storing, not heat, but energy, thermal energy expressed as temperature, called internal energy. Perhaps I should open a thread on "The Nature of Thermal Energy, It Isn't Heat." That would allow others to hammer this out in an appropriate thread.
Heat is not energy. Heat is the "flow", of energy. The river is not water. It is the "flow", of water. There are some other big differences between water and energy, it's just an analogy.
As you like to point out the "heat of compression" is "instantaneous" so it stops when the volume change stops.
The gas is being pushed through the regenerator to the hot space at the fastest rate. Compression is zero. Delta energy from compression is zero during this period.
Fool wrote: ↑Tue May 21, 2024 12:15 pm
As you like to point out the "heat of compression" is "instantaneous" so it stops when the volume change stops.
The gas is being pushed through the regenerator to the hot space at the fastest rate. Compression is zero. Delta energy from compression is zero during this period.
Fool wrote: ↑Tue May 21, 2024 5:31 pm
Apparently I need further clarification. Sorry.
You are going to ridiculous, bizarre extremes to "prove" my statement that compression generates heat of compression during compression is "misleading".
Just because heat is also added due to displacer motion is irrelevant to the fact that compression causes heat of compression. Nothing misleading about it.
Your attacking my character implying I'm being intentionally "misleading" which is ridiculous and IMO INSANE.
You are obsessed, consumed by this agenda to nullify, debunk, mischaracterize, disprove, whatever, every word that comes out of my mouth, no matter how innocuous, or how true.
The heat of compression does not disappear at the full completion of the compression stroke. Your trying to say it does is what is being not only misleading but ridiculous and irrational.
In the past I didn't always get what you (Tom) were talking about. But I think I've come to a similar conclusion as you during my recent research.
I've been looking into Tesla turbines in great detail and have a configuration in mind that eventually might work as an ambient heat engine.
This is going away from Stirling engines, but fits this topic.
What if, for a "cold hole", we were to create a vacuum. But a continuous vacuum between a pump and a turbine.
The pump would draw in fluid through a nozzle onto a turbine. The turbine in turn powers the pump and hopefully has some leftover.
The nozzle, if sized correctly, will squeeze the fluid and turn all the stored kinetic energy in the same direction and give the fluid speed onto the turbine. Because the fluid is pulled through the nozzle into a vacuum it gets cold but fast. Then it does work on the turbine, which heats it up a little before being pumped out again.
As Tom mentioned somewhere earlier in this thread, this theoretically would also work better with a load.
And I didn't used to think this would work in ambient air, because the pump will have to pump it into ambient air pressure. But what this pump basically does is put back in the heat so the fluid goes back to ambient pressure. If the pump alone had to do this it wouldn't work, but this thread made me realize that the pump can take ambient heat to bring the fluid back up to pressure.
So basically cooling ambient air while having work output.
I've started ordering parts to do the first experiments on this contraption.
The first goal would be to make this work with a bigger temperature differential. But after that I'm going for the full Monty.
I recently found an old dirt devil vacuum powered brush head attachment. It has a squirrel cage style fan blade and a belt drive to a brush head. It has a surprising amount of torque.
Just for fun I hooked it to the vacuum and ran it up for a few minutes loaded and unloaded while checking temperature with the ir gun.
No change at all. I kind of expected something. Maybe a much larger vacuum is needed but the ambient air is being made to do work on the blades. Perhaps a few blades in series would be needed to see a reduction in temperature.
VincentG wrote: ↑Thu May 23, 2024 6:49 am
I recently found an old dirt devil vacuum powered brush head attachment. It has a squirrel cage style fan blade and a belt drive to a brush head. It has a surprising amount of torque.
Just for fun I hooked it to the vacuum and ran it up for a few minutes loaded and unloaded while checking temperature with the ir gun.
No change at all. I kind of expected something. Maybe a much larger vacuum is needed but the ambient air is being made to do work on the blades. Perhaps a few blades in series would be needed to see a reduction in temperature.
I don't think IR cameras can "see" air or gas temperature. Gases don't emit IR, except CO2 If I recall.
Also, high velocity air traveling in a tube tends to flow down the center, not contacting the walls, unless the tube is bent.
I'm not sure those are actual reasons. Coincidentally, I did a similar test with my shop vac, looping the exhaust back to the intake, then just crimping the hose.
I through the high pressure side felt a little warmer than the low pressure side to my hand, but could not see any difference with the IR camera.
The fact that the low pressure side was not insulated could be a factor also, surrounded by "hot' ambient air, a slight cooling would be re-heated immediately by the ambient surroundings, the heat is replaced almost instantly, without insulating the hose and in your test, the entire fan/squirrel cage brush head and hose would have to be insulated.
This guy gets a little drop in temperature, but he doesn't have his turbocharger insulated either, so the expansion is mostly isothermal. For the expansion to be adiabatic the turbine needs to be insulated and also given some time to cool down. He would get better results if the turbocharger were insulated.
Also turbochargers get hot on the high pressure side and there is not good thermal separation.
For example, me just stepping on the vacuum hose to kink the hose without insulating the hose, well, at best that would be a degree or two of Joule Thomson cooling. With no turbine and no insulation, just isothermal expansion. The gas heats up as fast as it cools down.
Also, how is the brush head "loaded"? By using the brush? I don't know, just asking but is heat from friction being generated making the brush head hotter?
Kind of like electricity. You can't maintain a voltage difference if the wires are not insulated. Thermal "short circuiting" all over the place.
Another interesting point, in an air liquefaction machine, a similar setup, but the cold exhaust from the turbine is recirculated through the compressor, so each loop around gets progressively colder.
A complete refrigeration cycle for cooling is actually mostly a heating process.
Not "heating" by adding heat but making hotter by compression.
That is, the gas or air is first compressed to make it hot.
The gas gets hot in the pipes and then the pipes are cooled with a fan.
So really, the vacuum exhaust should be captured in a pipe that can be cooled before being expanded through the turbine, fan, brush head turbocharger or whatever.
Cooling the compressed hot air before expansion is part of the cycle.
This might be interesting to experiment with. About $200 on eBay. Nice to see Tesla turbine/generators becoming available anyway.
Rated as 50 to 100 watt.
Compress_20240523_120109_9621.jpg (9.35 KiB) Viewed 1688 times
Again, not a recommendation. I have no experience with the product or the sellers. It may be junk, but this is the first time I've seen Tesla turbines and generators of any kind so readily available, ever.
Not in my budget, I just sent for the turbine without the generator. I kind of wish I had seen this first.
I've been watching a lot of YouTube and Patreon builders who are experimenting with the turbines. All very promising.
I do plan on building my own, because it's a very interesting path. And also, ebay isn't really an option in Vietnam hehe.