Dry ice pneumatic tool

tahanson43206 · 2021-03-27 17:05:06

This starts out for kbd512, because the subject is pneumatic tools, and specifically the use of CO2 as the gas for operating the tool ...

However, several members have commented on pneumatic tools, and all replies are welcome

Here are two posts where kbd512 included the words "pneumatic" and "tool" ..;;

http://newmars.com/forums/viewtopic.php … 63#p152163

http://newmars.com/forums/viewtopic.php … 86#p152086

***
Inspired by the praise of pneumatic tools in this forum and elsewhere, I took the plunge today and invested in a pneumatic reciprocating saw and a small electrinc pump with 3 gallon storage container,. The tool says it is rated for 90 psi, and the pump says it can reach 100 psi, so I figure I'm reasonably likely to be close to the rating for the tool most of the time, because the compressed air is expended at the rate of 8 cubic feet per minute. I'm not expecting a long duration of use for the tool, in a remote location, which is where I'm planning to use it. I'll have to be ** really ** economical with my cuts.

So! Here is my question for kbd512 and the forum....

In reading the instruction brochure after unpacking the tool, I found ** this ** perplexing warning:

Topic: Air Source

Never use oxygen, carbon dioxide, combustible gases or any bottled gas as an air source for the tool. Such gases are capable of explosion and serious injury to persons.

OK ... I can understand worry about combustible gases, and I suppose oxygen could accelerate combustion of any combustible material that might be in the vicinity, which could include hot metal being cut.

What makes NO sense to me is the prohibition against carbon dioxide. A reason not to use ** that ** gas might be the risk of difficulty breathing for the operator, if carbon dioxide is produced at a high rate and the operator takes it in.

However, on Mars, the atmosphere is almost ** entirely ** CO2, so the operator will be wearing breathing gear.

Can anyone think of a reason why this warning might have included CO2, other than the breathing issue?

(th)

SpaceNut · 2021-03-27 18:43:18

Water in the atmosphere is brought into the tank and heat of compression of the water might happen with a spark.

This is why the engine for Mars might be plausible.

tahanson43206 · 2021-03-28 06:18:30

For SpaceNut re #27

Water is apparently a concern for pneumatic tool systems. Water won't ignite, but it can pass through the tool, and I get the impression that is not helpful.

The vendor sells add-on equipment to filter water out of the flow. I'm starting out without any of the offered add-ons. The basic equipment consists of a pump and tank base station, a hose and the reciprocating saw tool.

A minor concern is that the tool is offered with it's own saw blades, and those are designed with fine or coarse settings designed for working with metal such as exhaust pipes. My application is for wood in locations away from utility power. I ** think ** the blade holder might be able to accommodate alternative blades, because it is a simple squeeze device held by set screws.

The instruction manual for the pump recommends it be run with all valves open for 30 minutes before closing valves and building up pressure.

One of the add-ons for the tool is a device to feed oil into the air line. The alternative is for the operator to squeeze some oil into the air intake port of the tool before use. The piston inside the took is getting a heck of a work out, according to the manual. I would think that erring on the side of "too much" oil is a better bet than not oiling at all.

The need for oil would certainly apply to Mars! If there is no oil available from the terrain, and none has been reported so far, then it will have to be made, along with all the other lubricants needed by a civilized society. I'll check My Hacienda to see if we've included lubricants as a specific requirement.

Edit#1: This is for SpaceNut about water in the flow to a pneumatic tool... It wasn't obvious to me why water vapor would be a problem in the flow to a pneumatic tool ... it just passes through the tool and contributes to the push against the piston. However, in looking through the pamphlet on the compressor, I found the answer ... the water filter is sold for customers who are doing airbrush painting. Of course! That makes perfect sense.

The Carbon Dioxide prohibition was probably the legal department trying to prevent lawsuits. Postings on the Internet I've seen so far seem to indicate no problem using CO2 except for (a) the expense and (b) the higher pressure typical of CO2 sold by commercial suppliers.

Edit#2: Now I have a bit of experience with the brand new set of pneumatic tools, and I understand that the teenager who waited on me was woefully ignorant of the requirements for the job I wanted to do. The 3 gallon compressor is (according to the manual) designed for stapler guns and for spray painting. It is undersized for the reciprocating saw. The saw only runs for a few seconds before it exhausts the pressure it needs. It works ** just fine ** while pressure is correct, but stops when pressure falls just a few pounds.

Furthermore, I am perplexed about the need to oil the tool. It was easy to see how oil could be squirted into the aft end of the tool when it came out of the box, but after the pressure fitting is installed (and bolted into place) there is no way to admit oil.

However, everything taken into account, I am just as glad I made this investment in learning/education/experience, because now I've seen the potential of pneumatic tools. The fact that the compressor is undersized is an inconvenience, but it's all I could afford, so I'll just have to be content with 15 second spurts of activity and 5 minutes of recovery between spurts.

That seems to be a pattern for lots of things these days!

(th)

SpaceNut · 2021-03-28 11:26:45

Here on earth the free air source will also depending on location have the chance to draw in fuel vapors that Mars does have with its seasonal methane releases.

tahanson43206 · 2021-03-28 17:12:21

As a follow up regarding purchase of a pneumatic tool and compressor ...

I observed in testing subsequent to earlier reports that the effective time of operation for the reciprocating saw is about 10 seconds.

Pressure in the compressor tank drops from 90 (or so) to 70 or less within 10 seconds .... I did observe that the tool continues to operate as pressure falls below that point, but only if there is no load on the blade.

I've decided to return the compressor tomorrow, and to take the hit for the re-stocking fee. The compressor is now used, and has to be sold as a return.

Hopefully the store can come out even, and my increased knowledge is a fair trade for the investment.

I'll keep the saw and hose and fittings ... The should work find with an adequately sized compressor and tank.

Come to think of it, it might be possible to rent one from one of the numerous Rent-a-Tool sites in town.

Now ** there's** something to add to My Hacienda! Rental services .... vehicles, mobile homes (as you suggested), tools, ...

Can you think of other items that Mars settlers would need to rent?

OK! I just checked ... we already have:

0066 Vehicle rental
0067 Equipment rental (I was thinking of bulldozers and similar)
0068 A combination of both

OK !!! There are no entries for tool rental

We can also add spacesuit rental

Can you think of anything else ?

(th)

SpaceNut · 2021-03-28 17:22:59

The compressor issue is the size of the tank to provide the cfm for the tool and not just the pressure.

tahanson43206 · 2021-03-28 19:22:24

For SpaceNut re #31

I agree that the size of the tank is the issue. However, in my case, it was the ignorant (a teenager) leading the even more ignorant (me) to the wrong conclusion. The reciprocating saw was clearly marked that it needed 8 cfm, but the teenager did not know enough about the products to understand what that meant, and I certainly did not.

Here is a snipped from the Home Depot Tool Rental web page:

Electric Air Compressor 2.6 CFM
category #05 group #581
The heavy duty 6 Gallon, 165 MAX PSI, compressor is ideal for supporting a variety of pneumatic applications including use with nail guns. With an oil free pump and high output motor, this compressor provides long runtime and quick recovery. The onboard cord wrap provides convenience and easy storage for the jobsite or garage.

The image shows a machine very similar in appearance to the one I brought home.

The same web site offers a gasoline powered compressor that offers 13.5 cfm, and that would do the job, for sure!

Rental Pricing for Grove City #6954
Exact pricing will be determined at the store.
$39 00 4-Hours
$56 00 Per Day

The total cost would be about $100 for a day, because it would be necessary to rent a vehicle from U-Haul to move it around.

This entire episode has been quite enlightening!

***
Now! bringing the entire learning experience back to Mars .... kbd512 has recommended pneumatic tools on multiple occasions.

I have learned of the need for robust supply of high grade lubricating oil as a result of this experience, and I now understand the specifics of gas flow requirements for various tools. I expect that the 8 cfm requirement of the reciprocating saw is at the low end. The next time I'm at Home Depot (which also has a tool rental) I'll investigate to try to learn what various tools require.

It is possible members of the forum (from one of the current 15 actives) can add to the store of knowledge in this topic.

(th)

SpaceNut · 2021-03-28 19:28:21

https://www.quincycompressor.com/know-m … ation/amp/

https://www.vmacair.com/blog/many-cfm-n … age-chart/

https://www.garagetooladvisor.com/air-t … ompressor/

tahanson43206 · 2021-03-28 19:44:29

For SpaceNut ... re Post #33

Thanks for those helpful additions to this topic!

In the second item: https://www.vmacair.com/blog/many-cfm-n … age-chart/

I was surprised to find the reciprocating saw in the far right column ... the little saw I brought home is a toy compared to what that must be.

However, this one is advertised for cutting exhaust tubing, and for that, given the right compressor, I think it would be fine.

As a side note ... I really liked the fine cut that the little saw was able to achieve, during the brief time it was working. I had to finish the job (cutting some roofng material) with an electric saber saw, and the result was jagged in comparison.

I attribute the fine cut to the high rate of cut, compared to the much slower electric saw. The pneumatic tool did not grab the metal, and instead, while it was working, it cut through the sheet metal like butter. The electric saw in comparison made a huge racket and grabbed the metal.

***
I am definitely looking forward to any comments kbd512 might make (and perhaps even GW Johnson bye-m-bye)....

I suppose the Mars tools should be rated in cubic meters per second, so the numbers would be lower.

Never-the-less, whatever the measuring scale, any tools to be configured for Mars would need to operate at a much grander scale than my little experiment.

Edit#1: As a side note but relevant ... the company that (I think) sponsored the second link you provided is offering a spiral compressor that does NOT use a buffer tank! They state in their advertising copy that their product is able to operate in continuous mode and thus able to support tools that need to operate in continuous mode.

By coincidence, that is precisely the kind of pump installed in the perseverance MOXIE experiment.

(th)

kbd512 · 2021-03-28 21:46:28

tahanson43206,

Unless you're using CO2 in an enclosed space without a positive pressure breathing apparatus (every person working on the surface of Mars would be wearing such a device merely to survive) or working with powdered Magnesium metal, or other similarly exotic materials, then CO2 is not combustible or explosive. I've no idea why they wrote that, but people working with exotic materials should be aware of the hazards of working with said materials. Pure CO will burn in the presence of atmospheric O2, given a suitable ignition source. The presence of water, which is unavoidable, will accelerate the corrosion of air tools, which is why air tools used by professionals are cleaned and oiled after use, as well as inspected for serviceability prior to use.

The primary benefit of air tools is that they will almost always weigh less than equivalently powerful battery / corded electric tools (due to the weight of the batteries or electrical cords), reducing the fatigue experienced by the user who may need to manipulate them for many hours at a time, require less money to transport, and are generally some of the most durable and simplistic power tools available. Since a plethora of tools are required for constructing a second branch of human civilization on another planet, air tools and hand tools are the most practical type of tools for most jobs. Additionally, using air tools reduces the danger of electrocution or ignition of an explosive atmosphere, even though prudence would always dictate that explosive atmospheres are detected and eliminated prior to conducting any repair work. Unlike battery powered tools that are subject to the performance limitations and degradation of batteries, pneumatic tools typically have very long useful service lives with routine maintenance. Since air tools contain no batteries or electronics or electrical connections, the failure modes associated with such devices obviously can't occur when using air tools. The expanding "air" also cools the pneumatic motor in the air tool, and so long as the expelled gas is dry the tool will function in temperature ranges that would render batteries inoperative. Electric motors and batteries used in construction type tools would either need to be oversized to function as heat sinks to contend with the heat they generate, or would require liquid coolant lines connected to a radiator of some kind, whereas the expanding gas cools the pneumatic motor in air powered tools. All that said, there's another practical reason for using CO2-powered air tools. We're going to have to compress truck loads of CO2 to produce rocket fuel to return to Earth, so we may as well use some of that collected CO2 for other purposes, and construction is another worthwhile end use.

There are still lots of uses for battery powered tools, primarily for mobile repair work, where they are more practical than dragging around an air hose and air compressor. Even so, every construction site I've ever seen has an air compressor and air tools present. There must be some reason for that, and it's probably related to the practicality of using hand tools vs electric tools vs air tools for specific tasks. For repairing an engine of some kind, I'd want hand tools. For machining parts for that same engine, you need corded electric tools like CNC machines, mills, lathes, sanders, grinders, drill presses, saws, etc. For moving about a base or a ship and conducting general repair work, I'd want a mix of hand and battery powered tools. For steel fabrication at a construction site, I'd want air tools and a welder of some kind.

tahanson43206 · 2021-03-28 23:31:26

For kbd512 re #35

Thanks for rounded review of tool technologies including strengths and weaknesses and appropriateness for a variety of situations.

I'd have to go back to the opening post to be sure, but I ** think ** the students were demonstrating that dry ice could be heated to produce CO2 gas with sufficient pressure to operate a pneumatic tool. As reported to SpaceNut in several posts in this topic, I had no prior experience with air tools before investing in a small reciprocating saw, a (really) small compressor, and miscellaneous accessories to make it all work.

Because I was "led" on this exercise by a very young, very inexperienced, "sales" person, I went down a path that was not productive from a practical point of view, but it most definitely was productive as a learning exercise.

I'll be taking the 3 gallon compressor back tomorrow, and put up with the restocking fee as the price of the practical lesson. I'm thinking of offering to trade the compressor for a lubrication add-on, that would appear to be necessary because I can see absolutely NO way to lubricate the tool with the brass fitting installed. For those who are not familiar with this kind of fitting (which I was not) there is a seal (a ball bearing) inside the fitting (female) that is (presumably) pushed aside by the male fitting from the air hose when it is inserted.

I'll have to save up for a compressor large enough to sustain flow to this small saw. A suitable compressor (with gasoline engine) is available for rent in a nearby home supplies store, but at $100 for the day (machine plus truck) I'm unlikely to make the investment any time soon.

What I ** can ** say is that i am favorably impressed by the performance of the tool in cutting sheet metal, as compared to the DeWalt power tool I used to finish the job. If memory serves, I ** think ** the rate of movement of the saw blade was on the order of 18,000 per minute. For the brief interval when there was sufficient air to power the tool, it cut through the metal like butter, and left a clean edge.

For Mars, the issue of providing sustained power for ** real ** work is non-trivial. We (forum members) have discussed using CO as a fuel (with Oxygen) for portable engines that would be able to deliver rotating power to various devices. The students (again if my memory is correct) showed that heating dry ice can deliver CO2 gas in sufficient volume and at a sufficient pressure to operate a pneumatic tool.

The energy to heat the dry ice might come from a source of electricity, or it might come from burning CO and Oxygen, or it might come from a nuclear power source, but it has to come from somewhere. I suppose a mirror could deliver photons to a warming chamber if one is patient.

SearchTerm:Tools review of a variety of tools and applications that might be used on Mars

http://newmars.com/forums/viewtopic.php … 30#p178030 kbd512 post just ahead of this one

(th)

tahanson43206 · 2021-03-29 07:40:07

This topic was started with a report of a student investigation of possible use of dry ice to provide CO2 for a pneumatic tool.

It is possible for members of this forum to carry out original research as a follow on to the student project.

As a starting point, I have come into possession of a small reciprocating saw able to operate reliably at 90 psi at a flow rate of 8 cfm.

For those who may not be familiar with the abbreviations, psi is the pressure measurement of pounds per square inch, still used in the United States.
cfm is an abbreviation for cubic feet per minute, also still used in the United States.

If a member of the forum were to post the metric equivalents that would be helpful.

The quest is to see if dry ice can be heated at a rate sufficient to operate an 8 cfm tool at 90 psi for an hour.

Energy is invested in making dry ice on Earth by withdrawing thermal energy from carbon dioxide gas, and that energy is restored to the dry ice to release the gas for use in a tool.

On Mars, dry ice is made available in quantity by the environment, but the energy to convert the solid back to a gas must still be invested by the operator of the tool.

It should be possible to compute the quantity of dry ice that would be needed to deliver 8 cfm for 60 minutes, and the amount of energy that would be needed to warm the solid to change it's state to gaseous.

There are two expenses already identified: The cost of dry ice, and the cost of energy to warm to solid to release the gas.

However, in addition, as the student experiment showed, there is the cost of the container to hold the gas until it is needed, and any hardware needed to perform the heating.

Edit#1: Google came up with this web site to convert 8 cfm to cmm :

About 188,000 results (0.42 seconds)
Please share if you found this tool useful:
Conversions Table
7 Cubic Feet Per Minute to Cubic Meters Per Minute = 0.1982 400 Cubic Feet Per Minute to Cubic Meters Per Minute = 11.3267
8 Cubic Feet Per Minute to Cubic Meters Per Minute = 0.2265 500 Cubic Feet Per Minute to Cubic Meters Per Minute = 14.1584
13 more rows
Convert Cubic Feet Per Minute to Cubic Meters Per Minute

The challenge of this post is to deliver 60*.2265 cfm from dry ice. [13.59 cubic meters]

Let's round that number up to 14 cubic meters to be delivered from the system over the course of an hour.

The pressure needed is 90 psi: Per Google: [6.20528 bar] [620528 pascals]

If the gas delivery system produces 14 cubic meters in an hour, then it would be helpful to know what temperature was reached to achieve a pressure of 6.2 bar.

From that (I presume) it should be possible to compute the amount of energy needed to change the phase of dry ice to the needed gas.

Edit#2: Asking Google about price:

$1.00 to $3.00 per pound
How much does dry ice cost? Dry ice is generally priced by weight, but the exact cost varies from one retailer to the next. On average, the price ranges between $1.00 to $3.00 per pound.
Dry Ice FAQs | All About Dry Ice: Cost, Quantities, & More ...
cryocarb.com › dry-ice-faqs

So how many pounds of dry ice are needed to make 14 cubic meters?

And how much energy is needed to achieve the phase change?

What kind of equipment is needed to accept the heating and to deliver the needed pressure in a controlled manner?

I am anticipating a quiet burning heater method, such as natural gas or propane.

This would be a quiet machine, and it would produce less pollution than would be the case for a gasoline powered compressor.

If a member of the forum decides to package a solution to the proposed exercise, please do so in a manner that could be found easily for future reference.

A complete solution would show:

The components required (tanks, burners, support structure, regulators, anything I've overlooked)

The quantity of fuel required (natural gas, propane, other)

Anything I've overlooked.

Reminder: the challenge is to deliver 8 cfm for one hour, using dry ice as the starting point, and assume a remote location for the site.

What would you need to successfully complete the job as stated?

(th)

tahanson43206 · 2021-03-29 09:26:08

This post is offered to bring focus to the potential business opportunity here on Earth, for a dry ice pneumatic tool gas supply system.

Assuming the fuel used to change the phase of the CO2 from solid to gaseous is natural gas or propane, (or hydrogen at the green extreme) then the output of the process would be less polluting than would be the case for a gasoline or diesel powered engine.

Furthermore, the mechanism would almost totally silent. The only sound would be that produced by the pneumatic tool itself, so there might be a use case for such a silent gas delivery system.

Mechanically, such a system might be attractive because of it's simplicity.

There may be other advantages I haven't thought of.

A distinct ** disadvantage ** is the perishable nature of dry ice. The dry ice needs to be transported to the work site rapidly to reduce loss during transit, and then used promptly. In that respect, it would be similar to ready-mix concrete, which is prepared at a facility, transported without delay to the job site in vehicles that keep the mix stirred, and then used immediately at the job site.

(th)

Calliban · 2021-03-29 09:53:37

Things in favour of compressed air tools:

(1) High power to weight - electric motors are heavy and cabling usually weighs more than air hoses needed for any given power output at 100psi;
(2) Simplicity and low cost of tools - air motors are usually simple expanders.

Downsides:

(1) Capital cost of the receiver and compressor. If the compressor can easily adjust load to accommodate the needs of the tools, then the receiver tank can be small. It is usually there to accommodate the inertia of the compressor and prime mover so that you don't get an unacceptable pressure drop when using high-demand tools. On the other hand, if compressor power is limited and the tank is being used for significant energy storage, then it may be very pricey.

(2) Poor overall energy efficiency. Air tools are simple adiabatic expanders. For every 1kW of mechanical power output at the tool, some 8kW of mechanical energy are needed at the compressor. Trying to do something clever like interstage heating of the air, would ruin the power-weight ratio of tools. Compressed air has advantages over direct electric, provided that primary energy is cheap.

On Mars, a number of factors may tip the economic balance in favour of compressed air tools. Air motors are simple enough to be 3d printed, cast or machined from steel, plastics or aluminium magnesium alloys. The only things that might not be simple to make on Mars are bearings.

Energy efficiency may not matter, as liquid CO2 is likely to exist beneath ground in many places at depths greater than 50m. We can drill to access it and it will come out of the ground under its own pressure. We can ship it to a base using steel or plastic pipes. It can be stored as a pressurised liquid in tanks or underground cavities and night time cold can be used to keep it liquid. Solar heat or nuclear waste heat can be used to boil it and even superheat it at very high pressures. The only primary energy used is low grade heat, which should be relatively plentiful. The mechanical energy needed to inject liquid into the boiler can be provided by the expansion energy of the CO2.

A hybrid system would have benefits on Mars. A set of small, but high-power gas turbines could be used to generate both compressed gas and electric power. A high pressure turbine would receive supercritical CO2 at a pressure of ~300bar, with back pressure being about 60bar. A medium pressure turbine would receive CO2 at 60bar and exhaust at ~10bar (145psi). Between each turbine, there would be a reheater and taps that would draw a portion of reheated CO2 at medium and low pressures into receiver tanks. Medium pressure CO2 would provide power to fixed equipment through under floor pipes. Low pressure CO2 would be routed through flexible pipes to manifolds feeding hand tools.

For remote work on distant sites, a small diesel generator could be used to generate primary power through the engine itself and then secondary power, using engine waste heat to boil CO2. The outlet from the medium pressure turbine could be routed through a receiver tank containing a reheater. This would double as a compressed gas reservoir for air tools. The liquid CO2 could either be piped to site or delivered in steel bowser tanks, maybe 200,000 litres each.

For tools used in workshops, it may be possible to discharge exhaust CO2 into an overhead plenum. This would be a thin plastic or concrete duct with a weighted pressure-operated valve at the end of it. The valve will lift when pressure between the inside of the duct and Martian atmosphere exceeds 50KPa, venting waste CO2 into the Martian atmosphere. This ensures that CO2 does not contaminate the air that people breathe.

Last edited by Calliban (2021-03-29 10:07:09)

tahanson43206 · 2021-03-29 10:04:03

For Calliban re #39

Thank you for your contribution to this topic!!!

Your review of currently available options seems comprehensive (at least as I read it for the first time just now).

The purpose of ** this ** topic is to discuss use of dry ice to provide CO2 for pneumatic tools.

I've just received a price quote from a local vendor:

Dry ice is available for $2.00 per pound under 20 pounds, and $1.00 per pound over that weight.

If you'd be willing to help this specific topic to advance, I am looking for help estimating the quantity of dry ice that would be needed to operate a tool that takes 8 cfm for one hour, or 8*60 or 480 cubic feet of gas maintained at 90 psi for that entire hour.

I am thinking about what it would take to demonstrate the practicality of this idea on Earth, as a precursor to deployment of the idea on Mars.

As you know, there is a naturally provided supply of dry ice on Mars, due to the ambient low temperatures, and the properties of carbon dioxide.

It has been proposed (see post #1 of this topic) to use dry ice as the working "fluid" for a gas supply for pneumatic tools on Mars.

As discussed earlier in this topic, while the supply of dry ice on Mars is "free" (as a service of the environment) there is a cost to anticipate in converting the solid to gaseous form. The energy needed can come from CO-O2 burners, or perhaps electric heating, or perhaps from solar energy via mirrors.

The challenge is to design a system that can deliver 8 cfm for an hour, while holding a steady 90 psi delivered to the tool.

I'm hoping this challenge will be of interest to you, or perhaps to someone you may know.

(th)

Calliban · 2021-03-29 11:02:30

A few articles that you may find useful.
https://www.lowtechmagazine.com/2018/05 … onomy.html
https://www.lowtechmagazine.com/2018/05 … orage.html
https://www.lowtechmagazine.com/2016/03 … works.html

tahanson43206 wrote:

As discussed earlier in this topic, while the supply of dry ice on Mars is "free" (as a service of the environment) there is a cost to anticipate in converting the solid to gaseous form. The energy needed can come from CO-O2 burners, or perhaps electric heating, or perhaps from solar energy via mirrors.
(th)

Quite so. But if you look at the CO2 phase diagram, the minimum temperature needed to generate CO2 gas at the pressure needed for air tools (10bar) is -40C.
https://www.researchgate.net/figure/Pha … _320352662

So your heat could be daytime ambient heat, or heat gathered by simple, flat-plate collectors. Powerplants usually generate waste heat, which must be disposed of. On Earth, this typically gets dumped into rivers, the sea or atmosphere. On Mars, if large quantities of liquid CO2 are available, the waste heat can be used to generate extra power, before being dumped into the atmosphere at low temperatures and pressures. A nuclear reactor could be very efficient on Mars and solar power plants can be built to operate at much reduced temperatures, without sacrificing efficiency.

If the goal is to provide gaseous CO2 for air tools, then the design project is quite simple as supply pressure need not exceed 10bar. The source of heat needs to have temperature greater than 233K, but need not be a high temperature heat source. Ideally, CO2 should be injected into the boiler as liquid using a centrifugal pump. That way, you don't need to power down every time you refill the vessel with dry ice. The boiling liquid within the boiler can then be dried using swirl vanes which separate vapour particles. This ensures that all of the CO2 reaching the air tools is dry. Heat can be delivered to the boiler by plastic pipes carrying brine from flat plate solar panels or waste heat from a nuclear or radiothermal heat source.

Last edited by Calliban (2021-03-29 11:40:46)

tahanson43206 · 2021-03-29 11:39:29

For Calliban re #41

I only have time (right now) to look at the first article you showed, from 2018 Low Tech Magazine.

That is a very ** nice ** summary of the history of compress air machinery and applications, from bellows 4000 years ago through a city wide system in Paris through today's energy storage systems in Germany and the US.

The inefficiency of the air storage system is prominently shown in the article.

Despite this, I see a potential advantage for a system based upon dry ice as the working "fluid" and a burner system using natural gas, propane or (at the extreme) perhaps even Hydrogen.

Such a system would be silent, compared to an internal combustion engine.

I'm not sure how the bulk of the supplies and equipment would compare to an all-electric solution.

In the present instance, I am pursuing the question of what it would take to drive a tool that needs 8 cfm at 90 psi (6 bar or so) for an hour.

A local vendor offers dry ice for $1.00 per pound in lots exceeding 20 pounds.

I am wondering how to compute the amount of dry ice that would be needed for the specified application.

In addition to the cost of dry ice, there is the cost of natural gas, propane or hydrogen.

Propane seems (to me at least) the most practical fuel for the present study, because it is so widely available for home grill use.

It may be possible to compute the amount of propane that would be needed to perform the required heating.

The nature of the hardware is unclear (to me for sure) ...

There would be a reservoir which would admit dry ice through an intake port, and deliver gas at 90 psi from an output port.

There would need to be an arrangement for delivering heat to the reservoir.

There would need to be gas pressure regulators and some sort of feedback mechanism to control heating, much as a gasoline powered compressor turns on or off depending upon sensor readings of pressure inside the tank,

Edit#1: After re-reading the above after doing something else, i realized how similar the description is to a traditional steam engine.

There is a boiler where water is converted to steam (liquid to gas). There is an external supply of heat (coal or some other fossil fuel). The gas is admitted to a machine that includes a piston. The exhaust from the piston goes to the atmosphere. There are gauges and control valves to regulate pressure.

Edit#2: Here is a site which offers a list of Pneumatic tools and there air flow requirements

https://www.engineeringtoolbox.com/air- … d_847.html

I am still looking for a way to determine what size compressor is needed for the 8 cfm reciprocating saw described earlier in this topic.

A compressor that delivers 11 cfm continuously runs $900 (base price plus tax) at a local store.

A comparable compressor can be rented for a day for $50 or so, but it is so large a renter would need to rent a truck for another $50 or so.

Edit#3: Here is a link to a pdf that is written for planning a permanent air supply system, such as a repair facility or a factory.

https://www.cagi.org/pdfs/CAGI_ElectHB_ch4.pdf

I am still looking for a way to compute the amount of time a particular compressor tank will supply air given air flow of 8 cfm at 90 psi, which is the rating of the reciprocating saw I now have on hand.

Today I traded in the 3 gallon compressor, which was sized for a paint sprayer. It only had a .6 CFM rating. I had an opportunity to inform the teenager who had given me poor advice on Saturday of the need for greater cfm, and of the need for an oil injection device, which was in stock.

I don't have a compressor at this point, but I ** do ** have the oil injector accessory.

(th)

SpaceNut · 2021-03-29 19:07:09

10 bar is 147 psi of which the regulated psi to the tool is 90 psi.

The trouble is you want a volume that is 8 cubic feet a minute for 60 minutes leaves a matching volume still in the tank at the 90 psi.

480 x 2 = 960 cm with the full tank psi of 180

The compressor normally does not want to run more than a 50% duty cycle to allow head to cool.

So if you run the compressor for 1/2 hour at 180 psi once half the tank is used the start it you would just keep up with its use.

tahanson43206 · 2021-03-29 20:12:34

For SpaceNut re #43

Thanks for adding insights to help with understanding this technology.

Your insight about wanting the pressure in the tank to be 90 psi after one hour of delivery is helpful!

Something that just occurred to me is that the air exhausting from the tool is at 1 bar (14 psi). About 5 bar are consumed in operation of the tool.

In the tank, the molecules are compressed and loaded up with kinetic energy they trade with each other as they collide inside the tank.

I presume that the number of molecules that escape through the tool in one minute at 8 cfm is the number of molecules inside ???

I just realized I have no idea what is meant by the term: "8 cubic feet per minute".

I asked Google to show the number of cubic feet in a gallon: The result is: 0.133681

So the compressor I brought home was 0.40 cubic feet (3 gallons).

The tool operated normally for 10 seconds before the pressure dropped below a useful level.

The term cubic feet per minute is meaningless in the absence of pressure.

The web site at the link below seems to be trying to make sense of the expression ...

https://sciencing.com/calculate-cubic-f … 31117.html

My first reading of the text at the web site left me unsure of what to make of it, since the emphasis seemed to be computing velocity.

Here is a mystery:

https://engage.aiche.org/communities/co … viewthread?

3. RE: SCFM as molar flow

Venkat Subramanian
Posted 01-05-2019 00:06
SCFM is volumetric flow rate of gas: Standard Cubic feet per minute at STP conditions.
Volumetric Flowrate, V = (N(molar flow rate (moles/minute)/density of gas or vapor)
--
Best Regards
Venkat Subramanian

The hint there is that the flow rate should be measured at Standard Temperature and Pressure.

If I am interpreting that hint correctly, then the 8 cfm figure should be understood as referring to 8 cubic feet of gas at STP passing through the tool in a minute.

it should be possible to arrive at a count of molecules that pass through the tool in one minute, if that hint is correct (or my interpretation is correct).

Given the number of molecules needed by the tool in one minute, it should be possible to multiple ** that ** number by 60 to arrive at the number that need to be in the tank. ** That ** number should then yield a volume at a pressure necessary to hold those molecules.

And, taking your hint as a guide, whatever the number is, there need to be enough molecules left in the tank after 60 minutes to be able to power the tool at 90 psi.

***
Here is a snipped from Wikipedia that appears to suggest that cfm measurement is done at STM

https://en.wikipedia.org/wiki/Cubic_foot

Standard cubic foot
Main articles: Standard cubic foot and Standard cubic foot per minute
A standard cubic foot (abbreviated scf) is a measure of quantity of gas, sometimes[clarification needed] defined in terms of standard temperature and pressure as a cubic foot of volume at 60 degrees Fahrenheit (15.56 °C; 288.71 K) and 14.7 pounds per square inch (PSI) (1.01 bar; 101.35 kPa) of pressure.[citation needed]

If this additional hint is correct, it should be possible to determine the number of molecules needed by the tool to operate normally.

60 times that number of molecules would be needed to operate the tool for an hour.

However, as you have pointed out, that number is NOT the number that needs to be in the tank, because there still need to be enough molecules left after operation for one hour to provide 90 psi at the exit port.

(th)

tahanson43206 · 2021-03-30 09:02:48

For SpaceNut (and anyone else who may be interested) ....

This topic is about enlisting dry ice as an agent to drive pneumatic tools. I'd like to see the topic develop and grow over time, until we have at least one working prototype of a functional system somewhere on Earth.

If anyone who is not currently a member of the forum would like to participate, please read Post #2 of the Recruiting topic, and then contact NewMarsMember * gmail.com.

I'd like to begin with hard facts, courtesy of the manufacturer of a reciprocating sheet metal pneumatic saw that I have available for experiments.

The specification for this tool is to receive a volume of air flowing at the rate of 8 cubic feet per minute, at a pressure of 90 psi.

Per this site: https://www.asknumbers.com/cfm-to-m3min.aspx

1 cfm is equal to .0283 cubic meters per minute
8 cfm is equal to .2265 cubic meters per minute

At this point, my understanding is that the cfm measurement assumes STP (Standard Temperature and Pressure), but I am most definitely open to correction on that point.

Assuming for the moment that my understanding is correct, the quantity of matter (number of molecules) that needs to pass through the tool should be a fixed, knowable number. Whatever that number is, it should be invariant. It should be the same on Mars, the Moon or anywhere.

However, the ambient pressure on Earth is 1 bar, and the 90 psi value equates to (about) 6 bar, so the pressure difference enlisted by the tool designers is 5 bar. As I understand the situation right now, the tool designers made the dimensions of the parts and their behavior so that optimum performance is achieved with a pressure difference of 5 bar at standard temperature and a flow rate of 8 cfm.

The goal of this topic then, would be to design, build, test and demonstrate a source of gas (CO2 in this case) able to sustain a pressure of 90 psi at the exit port and a flow rate of 8 cfm using dry ice as the "working fluid" (it is of course a solid) and propane (for convenience) as the source of energy to drive the system. The complete system needs sensors and control subsystems able to regulate the flow of heat and dry ice into the boiler to sustain the required outputs.

SpaceNut ... do you have access to any resources in your local community who might be interested in this challenge, and willing to contribute in some way?

The immediate question that I ** think ** needs to be answered is:

What is the number of molecules of gas that must be delivered to the tool to achieve optimum performance at 90 psi and 8 cfm at STP?

From that number I would expect to be able to work backward to compute the amount of dry ice needed over the course of an hour, and the amount of heat energy needed, and ultimately, the amount of propane needed.

In the case of Mars, the heating would be performed by oxidation of CO, which is readily available on Mars.

Edit#1: It should be understood that this is intended to be an "Open Source" activity. No Intellectual Property rights should be claimed by any individual or organization for work done in development of the proposed system. The concept started with a student experiment that was published for anyone to review, and this topic should (and I hope ** will **) continue in that mode.

(th)

kbd512 · 2021-03-30 11:30:25

tahanson43206,

SCFM assumes STP conditions, because Standard Cubic Feet per Minute accounts for gas mass variation associated with volume / pressure / temperature / humidity changes, unlike CFM. SCFM is expansion of pressurized air or other gas to 1 bar under STP conditions. Ultimately, we're talking about the mass flow rate of the gas in question. Since the ambient pressure at Mars sea level is 6 millibars, less mass is required to produce the same amount of power if the temperature and pressure of both systems remains the same.

tahanson43206 · 2021-03-30 12:54:32

For kbd512 re #46

Thanks for taking a look at this topic, and for clarifying the meaning of SCFM !! That definitely helps.

In the case of the particular tool I'm studying, the difference between the recommended supply pressure and the ambient pressure (ie, sea level) is 5 bar.

In the case of Mars, I would assume the same performance could be achieved by dropping the tank pressure from 90 psi to 75 or thereabouts.

Does that sound about right to you?

And! can you point to a reference where I can dig out the mass flow for this particular tool?

It needs 8 cfm at 90 psi, which should translate to a mass flow of (some quantity) of gas that would be invariant across planets.

(th)

kbd512 · 2021-03-30 14:31:49

tahanson43206,

That's about right if we're talking about "air". You can calculate mass flow rate based upon SCFM. 1 SCF of "air" weighs about 0.0807 pounds and 1 SCF of CO2 weights about 0.1144 pounds. If an air tool requires 10 SCF of air per minute, then it's consuming 0.807 pounds of air per minute to drive the tool. In your example, if it's consuming 8 SCFM, then that's about 0.6456 pounds of air per minute.

However, CO2 is also more significantly affected by temperature changes during expansion than compressed air is, so I think we'd need to heat the CO2 prior to discharging it through the air tool's impeller. Discharging our CO2 fire extinguishers always (very briefly) left little bits of dry ice "flakes" or "foam", which was fine for extinguishing small fires, but not so great for driving air tools.

I've forgotten almost everything I knew about this stuff, to be honest, but it boils down to mass flow rate. The mass of expanding gas is driving the impeller (supplying the "horsepower"- the tiny flying ponies, if you will, or maybe the "pegasuspower", I like that) in the air tool. If you supply a certain mass of gas moving at a given velocity, and it's also important that the gas remains a gas after significant expansion (not a given with CO2), then that's what counts. You'd need less gas volume if the gas was LCO2 vs compressed air, but then you probably need a portable heat source such as a RHU as well.

Nothing about living on Mars could ever be easy, could it?

Well, at least there's no EPA there.

tahanson43206 · 2021-03-30 15:24:42

For kbd512 re #48

Thanks for the additional tip to pursue!

Going with the numbers you provided, the supply will need to hold .807*60 or 48.42 pounds of air (staying with air for the moment) to supply the tool, assuming there is no resupply. A machine large enough to sustain that 8 cfm continuously was priced at $800 or so at the local store, and the tank was large (although not the largest) which I assume was sized to act as a buffer for the pulses of air from the piston pump.

In pursuing this topic, I'll try to work with the lead you've provided to see if I can work out requirements for a dry ice heated by propane system.

Your point about the temperature of the CO2 as it leaves the supply system is helpful. Some of the energy from the propane heater could (presumably) be used to insure the CO2 is at room temperature (or there-abouts) when it leaves the tank.

(th)

SpaceNut · 2021-03-30 16:34:43

Part of the flow rate is the hose diameter inside as well as it connection to the tank as its how you control the level of psi to the tool.

The use of the expansion tank will be needed to control the levels of pressure and it gives the time to heat a volume to gain pressure before it exits.

Here is a com to psi conversion
http://azglassclasses.com/Reference/CFM-PSI.htm

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