I don't think I've seen this referenced before, and I thought Neal aficionados might be interested in it.
I've come across a newspaper article from 1940 concerning Neal's experiments that appears to be describing his "Model 39." There's not a whole lot to the article, but it does report that the tank pressure of this later - and smaller - engine design was 150 pounds.
On the negative side, despite the passage of an additional 6 years of development since he patented his original design in 1934, Neal is reported to have said "that there is more work to be done before it will be ready for the market."
The news item is titled "Experiment May Change Industry" and appears near the middle of page 6 of the May 30, 1940 issue of the Camden News:
EDIT: Hmm. I guess that didn't work... Still looking into how to share the article.
Maybe use a screen clip program. There are several around, Apple has one built-in, am thinking windows might have one too. If you can read it clearly on your screen, should be able to get a clip of that. Or go caveman style, with a picture using camera or phone!
Post by Uncle Buddy on Dec 19, 2020 23:46:22 GMT -8
Renny, thanks for joining the forum. By coincidence I found the same article a while back and will post a copy so you don't have to. Don't go anywhere, I'm preparing to post a few more that I just found a few days ago.
Renny, thanks for joining the forum. By coincidence I found the same article a while back and will post a copy so you don't have to.
It seemed like a simple enough thing to use the site's "clipping" tool to highlight the part of the page you want to share, then get a link to post that will let people go to there and see that portion of the page highlighted as the clipping. Not sure what I was doing wrong.
Post by Uncle Buddy on Dec 20, 2020 18:37:22 GMT -8
I don't use the clipping tool, I use the print/save button and then to add titles or crop or resize or whatever, I use a paint program. You can use MS Paint for simple stuff but I usually use an old program called JASC photopaint. The clippings above were done in a hurry, the bibliographical data is in the title of the .jpg. Also browsers these days have a printscreen function and the keyboard has a printscreen button so you could copy stuff without letting the website keep statistics on what you were copying, but I don't worry about that.
Two takeaways: First, they clearly confirm (as is stated perhaps a bit more vaguely in the patent) that the compressor cylinders are working only against the pressure of the atmosphere. This seems to indicate that their sole job is to pull a vacuum, rather than doing any actual compression. Yes?
Second, they are also clear in describing the function of the heater as being to warm the moisture in the compressed air entering the motor. Why do they specify "moisture", instead of just generally stating that it warms the air? Would the air drop below freezing if not for the heater, and start forming frost on the motor intake port? Seems like an odd place for it.
Post by Uncle Buddy on Dec 29, 2020 20:09:42 GMT -8
I'm not sure what you mean by "pulling a vacuum". Compressors get their work done for free by atmospheric pressure on the intake stroke. The moving piston is trying to create a vacuum but this work is negated by the positive work done by ambient pressure rushing in behind the piston, so the cylinder is filled more or less for free.
There's an interesting engineering paper in the collection which is now kept at archive.org called Reheating Compressed Air. An experiment was done with mixtures of compressed air and steam, pure steam, and pure air to see which mixture ran an expansion engine most efficiently. If I recall, the most efficient mixture was 90% air and 10% steam. I don't recall if this was thermal efficiency or mechanical efficiency. I think the study was done in 1924?
Someone named Eric S Buck who used to write to me and might be a member of the forum has a patent on a wet compressor, he is sure that keeping the water in the air is a better idea. His patent explains why.
Anyone who's worked in a shop knows that compressor tanks have to be drained of water so they don't rot. Special equipment is used to extract water from the air. In some places this is important, like maybe a photo lab or the space shuttle. I've never bothered with it. I think maybe Neal's reason for keeping the air wet and then stating that he was heating the water in the air is that water holds a lot more heat than air, and holds it longer. Which is why they say steam engines are "better" than air engines. Air gets cold very fast. Actually that can work to our benefit since it means the air can become a sponge for ambient energy. For example, it's been suggested that putting a little puff of 600 psi into a cylinder just before the compression stroke would refrigerate the atmospheric air just intook, so that at the end of the compression stroke most or all of the compression heat would still be in the air. Vs the usual method of compressing air till its hot and letting all the compression work dissipate.
For anyone who still entertains the notion that a double check valve might have undocumented special properties, has the influence of H2O content in the air been considered? What would be the effect on a water-hammer or similar phenomenon if cold air from the tank were reheated and had water content, vs. cold air alone?
There are acoustic engines that use heat alone to generate the pulsation in the system. I've momentarily forgotten what they're called. Tommy probably knows. Thermoacoustic engines and refrigerators, maybe. The heat has to be applied in the right part of the line. Constantinesco probably discussed this also in his patents and textbook. This is high tech stuff, I think it was being worked on by the military for some reason.
By "pulling a vacuum" what I mean is that instead of compressing air, I think maybe Neal was using those cylinders as a sort of vacuum pump, drawing the pressure in the top half of the cylinders down to near-vacuum on each stroke.
In this way the pistons would be "pumping against only the atmospheric pressure of 15 pounds" as it says in the articles, but the "pumping" (what I call pulling) would be done on the downstroke.
Post by Uncle Buddy on Jan 9, 2021 19:35:48 GMT -8
Do you think the two sides of the piston worked differently? You said the top half.
Your idea is interesting. I believe that if you lower the pressure by 10 psi you're going to lower the temperature dramatically. Maybe you've already said all this but my memory is no good. The atmosphere doesn't need a serious vacuum in order to enter the cylinder, in a normal compressor it enters on its own volition anyway. But if the check valve had a strong spring on it, the air would wait and enter only when a partial vacuum was inside the cylinder. It would thus be refrigerated. Which I think is good, it's the sort of thing Tesla discussed in his 1900 article on solar air engines. Also it's been said Lee Rogers was refrigerating his cylinder by injecting a puff of high pressure air just before compression stroke. Also Obid Smith said one of the principles of his engine involved maintaining an even temperature throughout the expansion/compression process.
What I'm getting at is that if the air starts out cold before the compression stroke, then a lot of the compression heat will have nowhere to go. It will not dissipate as it does in a normal compressor. No compression heat will leave the system until the temperature inside the piston goes over ambient temperature. If it only goes over ambient temperature a little bit, there won't be time for all of it to dissipate, because if you refrigerate the inside of the cylinder, you'll be refrigerating the cylinder walls also.
This would make the intake stroke of the compressor extremely noisy. Neal's grandson did in fact say that one reason Neal felt his working engine was not ready for market was that it was extremely noisy. It would be noisy anyway with 14 to 28 intake strokes per revolution, but with the implosive intake system you mention, it would be hellishly loud, I think.
ALTERNATE EXPLANATION from NEAL patent. Simons textbook is 1914, it contained no new information at that time, it is a textbook for working level mining/industrial applications. Neal's patent was 20 years later, so safe bet that those working with air would be using either Simon's text of another very similar.
Read Simon's Adiabatic Compression explanation, begins on page 28 through 34. In particular, make note of formula 45, Net work per stroke. Also make note of formula 46, Mean Gage Pressure for adiabatic single-stage compression and delivery.
Remember that Energy and Work are the same thing, two words used, but same thing.
Neal's machine has 1 motor cylinder which must provide enough energy so as to operate 7 compressor cylinders. That leads to the question: How much energy is needed by a single compressor cylinder? Formula 45 will give the energy requirement for that single compressor cylinder.
But, formula 45 follows the graph of Figure 7 on page 32. This is a complicated graph, many parts.
If I want to know the total energy needed, it is much simpler to use the formula 46. This is simply Force x Distance. Or more properly Pressure * Area * Distance. The mean pressure.
Think about Neal's statement in the patent. He says the compressor is pumping against 15 pounds or 1 atmosphere. To me, he is referring to formula 46. To me, he is saying the compressor is working against 1 atmosphere gage (mean pressure).
That is the alternate explanation to consider.
What values in formula 46 will provide an answer of working against 1 atm gage? That is 2 atm absolute.
Spending some time with algebra, it turns out to be P2/P1 = 4.86. That is equivalent to 56.7 psig. Subtracting the weight of the steel check-ball and the spring, you are left with 50 psig. I think the static pressure in the branch pipe is designed to be 50 psig.
At that pressure, the remaining volume in the compressor cylinder is 0.3232. In other words, it required piston travel over 0.677 of the volume in order to reach the 50 psig and open the inlet check valve. Piston has travelled 2/3 of the distance before check valve opens.
What is the temperature when check valve opens? You can use Simons formulas on page 27-28, or use his handy table in the back of the book. You tell me on this one.
Did I make a mistake on the math? Please double check.
Neal Alternate Explanation, continued, Look in Simons, page 163, Table III. This was used in the old days since nobody had a pocket calculator and regular working folks did not use slide rules. Notice columns 6 and 7. There we see the mean pressure shown. Why so much emphasis on this mean p value? Because it gives a simple number related to energy used, to the work required, in simple generic terms. Back in the old days, the mean pressure was a commonly used term. You do not see it in modern times. This table shows how important that mean p number was for the typical user back then, it is shown prominently in the table columns 6 and 7. For example, 55 psig adiabatic compression, mean pressure is 29.11 - 14.7 = 14.41 psig Same as what Neal says in patent. Using the formulas give accurate result of 56+ psig for mean p of one atmosphere. Either way is close enough.
ALTERNATE EXPLANATION from NEAL patent. Let's step back in time to early 1930's. Here is how I believe the air machine designers would do their planning work. Will use Simon's text as a good example of the state of the art at that time. Using Neal's patent statement, we arrive at the compressor pressure ratio of 4.86, for an exit pressure of 50 psig. The energy requirement for that compression using EQ 45, is 2*P*V. P is 1 atm and V is the compressor cylinder volume. There are 7 compressor cylinders to 1 motor cylinder. Now, total compressor energy requirement is 14*P*V. This is the energy needed from the motor cylinder. The motor cylinder, as drawn on patent, has no cutoff. The energy supplied from the motor cylinder is seen at Simons top of page 106, simply V*(P1-P2). Neal's motor cylinder is a little larger volume than is the compressor, but for this estimate I will just say all the volumes are equal. To follow what happens, we have three locations of interest. #1 is the storage tank leading to the heater. #2 is exiting the heater and entering the motor. #3 is exhaust from the motor.
At #1, the pressure from news articles was sometimes 135 and sometimes 150 psi. For this estimate, I will say it is 150 psia and 135 is psig. That is 10.2 atma, say 10 atm for this estimate. Storage tank temperature is 68F = 293K.
At #2, will use the letter m to indicate when entering the motor. When the air passes from storage tank to motor, it first passes through the heater. See Simons EQ 11 which gives the heated temperature based upon the increased pressure after heating, Pm. That is Tm=293*(Pm/10)^(2/7)
At #3, will use the letter e for motor exhaust. Neal states the motor exhaust air must be kept above freezing, this makes sense. Pick an exhaust temperature, say 39F = 277K. Use EQ 11 again for the temperature cooling through the motor. Te=277=Tm*(Pe/Pm)^(2/7)
We already found the energy required from motor to be 14*P*V with P being one atm. If we assume motor and compressor cylinders are same size, then for the motor, Pm-Pe = 14 atm.
The algebra is as follows: Take the Te formula from #3 above. Get the Tm formula from #2 and substitute it into the above formula which eliminates the variable Tm. We just found out that Pm-14 = Pe, so substitute that also into the first formula to eliminate the variable Pe. Now notice the first formula only has one variable, that being Pm. Work the numbers on your calculator, to find Pm = 22.2.
Put this into the formula at #2 above, to find that Tm = 368K = 95C = 203 F. Also since Pm - 14 = Pe, then Pe = 8.2 = 106 psig.
Finally, in summary the storage tank is at 135 psig and room temperature. The heater increases temperature to 203 F and this increases the pressure to 22.2 atma = 311 psig. Motor exhaust is 39F temperature and pressure of 8.2 atm = 106 psig.
You can check your work with Simons EQ 14. 22.2*(277/368)^(7/2) = 8.2 atm at exhaust.
To make this estimate more accurate, need to add the electrical generator load and the water pump load to the work required from the air motor cylinder, remembering that this work is shared between all four of the motor cylinders.
Another step needed, is to estimate the amount of torque on the steel of the crankshaft, which might help to explain why Neal spent much time talking about the crankshaft being carefully balanced.
Stepping back to look at the big picture. We now have the compressor creating 50 psig and the storage tank at 135 psig. Motor uses tank air, with preheating, to run the seven compressors and keep exhaust above freezing temperature. The part we have not discussed is the missing step of going from 50 psig to 135 psig, that is where the "secret valve" comes into the picture.