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Introductions / Re: Greetings All
« Last post by PK on Today at 07:59:58 PM »
I don't fully understand though. Why would I not get enough flow?

Apologies if this is (as we say in my country) telling you how to suck eggs, but a simple explanation will probably be useful for the non rocket nerds  of this non rocketry forum.

In the simplest sense, a rocket motor cooled by one of it's propellants (usually the fuel because hot oxidiser is nasty) flows that propellant over the outer walls of the chamber at a rate and velocity sufficient to
a: Extract enough heat from the chamber walls to prevent them from melting,
b: Not raise the temperature of the propellant past it's boiling point at the local pressure.

IPA has a fairly low boiling point at the 300-400psi you are going to see inside your cooling channels (I'm assuming that you'll pressurise the fuel tanks to 600+PSI), so you need to flow a lot of it to remove enough heat without getting local boiling and hence hotspots. This is one of the reasons kerosene is a popular fuel. You do this by increasing the velocity of the fuel in the cooling jacket, which increases the pressure drop which drops the boiling point..... welcome to rocket design.

This isn't a too much of a problem until you consider that nitrous oxide doesn't have a lot of oxygen in it, so you don't need a lot of fuel (by weight) to run near a stoichiometric point OTTOMH it's about 6:1.
Again this doesn't sound so bad, because less fuel == less burning == less heat right?  The kicker is that the decomposition of N2O is reasonably exothermic, so you are getting heat from a process that doesn't require fuel flow. That extra heat generally means that you'll struggle to get enough fuel flow to cool the chamber without boiling.

All biprops also use boundary layer cooling, which might get you out of trouble as much by increasing the fuel flow rate as by direct shielding of the walls.



Now this is a lay mans description. There is, of course, maths to work all this stuff out.

Quote

 And are you saying you built a Nox cooled motor?

Well, it was a NOX cooled motor for about 4 seconds, then it was a self digesting fireball, then a bucket of molten shrapnel.

I've built a radiation cooled NOX biprop that worked, but it was done before we figured out how to do reliable ignition so it was a pig to start...
I'll have a pic somewhere, but it was based on this:



PK
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CNC / Re: first cnc
« Last post by tom osselton on Today at 06:44:31 PM »
Well it gets delivered tomorow around 10 am, then we shall see what power it needs they told my son 220 he's thinking single phase to the transformer I'm thinking 3 phase if so we will need a converter. What would be a good choice in that respect balanced for cnc and we will be adding a mill shortly too. Heres the plate on the transformer.
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Mod-Ups! / Re: Case Hardening Experiments Mod-Up
« Last post by fatal-exception on Today at 05:16:27 PM »
Hey guys, I know this is about home brew case hardening experiments, but on the last McMaster Carr order I put in, I got a 1lb jar of Cherry Red. I have to say, it works like a charm (doesn't smell so good..:D) . I've done a bunch of mild steel parts and also some parts from 12L14. Nice thing is, there's no catastrophic cracking from quenching.  :beer:
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Project Logs / Re: New Tractor Shed
« Last post by awemawson on Today at 04:26:54 PM »
Oh yes Pete, it's getting a bit like the Grand Canyon  :bugeye:

... but we need more earth to level off the rest of it and form a consistent batter to the slope. When that's done and it's been adequately compacted I urgently need to get some foliage growing on it to keep it in place.

There will be a standard stock fence enclosing the little L shaped paddock behind the shed, with gates (4 foot to right of front and 10 foot on the diagonal corner ) and it will be a handy place to corral stock for short periods such as shearing and lambing.

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Project Logs / Re: New Tractor Shed
« Last post by Pete. on Today at 04:17:12 PM »
That drop down to the stream is looking steep enough to warrant a fence now Andrew :thumbup:
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Project Logs / Re: New Tractor Shed
« Last post by awemawson on Today at 04:10:53 PM »
Having clad the rear wall we were able to get the downspouts fitted, and as rain is forecast overnight we have fitted temporary 90 degree bends and pipe leading away from the building. Eventually there will be roddable traps where the 90 degree bends currently are.

Then we need to add a fair amount of height to bring ground level behind the shed up to meet the concrete floor. To this end I've ordered yet more lorry loads of earth - another four eight wheeler loads  :bugeye:
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Project Logs / Re: New Tractor Shed
« Last post by awemawson on Today at 04:06:08 PM »
So as promised a few pictures of the rear wall cladding going on. Rather repetitive I'm afraid but at least it's now done  :thumbup:
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Electronics & IC Programing / Lithium phone battery sizes
« Last post by picclock on Today at 03:22:05 PM »
Hi All

I am trying to make a chart of the capacity and size of lithium phone batteries for my projects. Phone batteries are the lowest cost lithium cells and can be very useful for home brew projects. Chargers are available for very little money <1, and they can supply a wide range of voltages with low cost step up convertors.

I can do 4 atm

HTC Hero  1.5Ah stated Actual not measured dims 50x80x10mm
Note III 3.2Ah stated Not measured dims 60x81x4mm
HTC Desire Z 2.45Ah measured 1.3AH @1A dims 64x44x4mm
HTC BM59100 HTC WINDOWS PHONE 1.7AH stated not measured dims 80x41x3mm  Weird connector so not very good.

Any other info will only make the list more comprehensive

Best Regards

picclock
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You can buy a thing called a "big head" fasteners, it's basically a bit of perforated stainless with a nut welded to it, bond this to the existing grip with epoxy, then laminate over it creating a captive nut.

Alternatively, bond on a piece of tufnol, whale or 10G40 would be my grade of choice here, the drill and tap it once the adhesive has set. Tufnol will give a better bond to epoxy than s/so, and is non conducting, so no galvanic corrosion
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Introductions / Re: Greetings All
« Last post by British Reaction Research on Today at 02:03:16 PM »
Hi PK,

Thanks very much for your interest and your comments.

I don't fully understand though. Why would I not get enough flow? And are you saying you built a Nox cooled motor?

Sorry for being slow on the uptake,

Carl.
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