[AR] Re: OT Nozzle shapes
- From: Ian Woollard <ian.woollard@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Wed, 13 Nov 2013 21:44:46 +0000
Aren't thin radiators better than thick radiators? Why would you want a
pipe 100 metre in diameter? For example 4 pipes 50 metres in diameter have
the same volume, and PV value and metal weight is the same, but you have
twice the surface area.
What am I missing?
On 13 November 2013 21:25, Keith Henson <hkeithhenson@xxxxxxxxx> wrote:
> Spinning was my first thought, even have some artwork based on the idea.
>
> But, if it will work, it would be less complicated to have a rocket
> type expansion into the low pressure condensing section of ten tubes
> 100 meters in diameter and 2.7 km long. The question: is the momentum
> from the low pressure steam entering the tube enough to sweep the
> condensed water to the far end of the tube where pumps can return it
> for reuse? Sub question, what's the best dimensions for the nozzle?
> Can you get gas this thin to choke in the nozzle?
>
> On Wed, Nov 13, 2013 at 1:08 PM, Carlo Vaccari <airplaniac2002@xxxxxxxxx>
> wrote:
> > Normally, heat pipes are filled with a porous material for capillary
> action.
> > I imagine that's less feasible weight-wise, and it would perhaps require
> > more liquid volume, so I would be inclined to agree that spinning would
> be
> > helpful.
> >
> >
> > On Wed, Nov 13, 2013 at 4:05 PM, Nathan Mogk <nm8911@xxxxxxxxx> wrote:
> >>
> >> For a heat pipe, you don't need to have it spinning. The temperature
> >> gradient will provide the circulation, but perhaps you can get more
> >> circulation by spinning.
> >>
> >>
> >> On Wed, Nov 13, 2013 at 1:13 PM, Ian Woollard <ian.woollard@xxxxxxxxx>
> >> wrote:
> >>>
> >>> Doesn't sound particularly difficult in principle, it's just a heat
> pipe.
> >>>
> >>> Maybe construct it as a round, flat disk with the lasers at the rim,
> and
> >>> spin it around the centre axis.
> >>>
> >>> Make the disk double walled and have ties between the two faces to deal
> >>> with the steam pressure. Or just spot weld it occasionally with
> dimples.
> >>>
> >>> So the water cycle goes, boils at the rim, steam rises up towards the
> >>> axis, condenses against the wall and rains back down towards the rim
> again.
> >>> No pumps. You'll need to score the interior surface of the metal with
> >>> channels to let the water wet it and run back down again otherwise it
> will
> >>> get blown about too much by the steam.
> >>>
> >>> ~300 watts/metre sounds about right; similarish power to that radiated
> by
> >>> the Earth.
> >>>
> >>> You'll possibly also need a sunshade. You'll also have to precess it
> >>> somehow for pointing or use mirrors.
> >>>
> >>>
> >>> On 13 November 2013 05:59, Keith Henson <hkeithhenson@xxxxxxxxx>
> wrote:
> >>>>
> >>>> I have a fairly bizarre problem. Need to get rid of 3 GW of waste
> >>>> heat from lasers in orbit. The pump diodes use a total flow of 60
> >>>> cubic meters per second at 22 deg C inlet and 34 deg C outlet.
> >>>>
> >>>> The heat removed from the local cooling loop for one laser diode, is
> >>>> 1.5 kW, which amount to lowering the temperature of 0.03 l/s by 12
> >>>> degrees to get the water back to 22 deg C. Evaporation takes 2640
> >>>> kJ/kg at that temperature. Injected tangentially into a low-pressure
> >>>> "boiling drum," the pumps could pick up the water from scoops as it
> >>>> swirled around the inside while vapor came off the surface in the
> >>>> center. At that temperature, evaporating water takes 2460 kJ/kg.
> >>>> Lowering the temperature 12 degrees for a kg of water would require
> >>>> removing 4.2 kJ/kg-deg K x 12 deg K or 50.4 kJ. The fraction of the
> >>>> water flow evaporated would be 50.4/2640 or about 2%.
> >>>>
> >>>> Two% of 60,000 liters per second is 1200 liters per second or 1200
> >>>> kg/s. 120 kg/s split into ten radiator sections.
> >>>>
> >>>> It is not clear how to minimize the system mass, but large pipes do
> >>>> not contribute much to the mass since the pressure over 22-degree
> >>>> water is only 2644 Pa. If we allow a ten-degree temperature difference
> >>>> to drive the low-pressure steam into the cooler radiators, they will
> >>>> be at 12 deg C. At that temperature and an emissivity of 0.95, the
> >>>> surface will radiate 355 W/m^2.
> >>>>
> >>>> How to get an emissivity coating on aluminum (or something else) that
> >>>> will radiate well at that temperature is a question that needs more
> >>>> research.
> >>>>
> >>>> Three GW at 355 W/m^2 would take 8.45 square km of area.
> >>>>
> >>>> The original rough partitioning of mass for the LPS gave 6,000 tons to
> >>>> the radiator. As a design-to-mass project, we initially allocate 4000
> >>>> tons to the radiator pressure vessel 4,000 tons of aluminum at a
> >>>> density of 2.7 tons per m^3 is 1481 cubic meters. Li-Al alloys can be
> >>>> 10% lighter and there are substances like graphite and other forms of
> >>>> carbon that are much lighter for the same strength. 1481 cubic meters
> >>>> spread over 8.45 million square meters is 0.175 mm. That is only twice
> >>>> as thick as a soda can.
> >>>>
> >>>> On a per meter basis, and using a 400 M Pa strong aluminum alloy, the
> >>>> maximum hoop stress is 70129 N. The vapor pressure of water at 12 deg
> >>>> C is 1400 Pa. Thus 70129 = 1/2 D x P or D = 2 x 70129/1400, which is
> >>>> almost exactly 100 meters in diameter. Circumference is 314 m, each km
> >>>> of tube would have 0.314 square km of area. For 8.45 square km, the
> >>>> length is 26.85 km. A radiator with ten tubes would be almost 2.7 km
> >>>> in one dimension and, with spacers and reflectors, about 4 km in the
> >>>> other dimension. (See figure C on page 7 of the above URL.)
> >>>>
> >>>> The internal volume of the radiator tubes would be ~212 million cubic
> >>>> meters. Steam at 12 deg C has a density of 0.01067 kg/m^3 and would
> >>>> mass 2262 tons. How much water would stick to the inside is unknown.
> >>>> Only a tenth of a millimeter would increase the mass by 845 tons.
> >>>>
> >>>> The question is how to size the nozzle between the relatively hot
> >>>> steam coming off the evaporator at 22 deg c and 2644 Pa and the major
> >>>> part of the radiator at 1400 Pa and 12 deg C main radiator tube?
> >>>> Secondary to that question is: will the momentum from the steam carry
> >>>> the liquid water to the far end of the radiator in the absence of
> >>>> gravity.?
> >>>>
> >>>> I realize this is way off topic for AR, but it is a physics problem
> >>>> about nozzles and some of you may have some insight into how to solve
> >>>> the problem.
> >>>>
> >>>> Keith
> >>>>
> >>>
> >>>
> >>>
> >>> --
> >>> -Ian Woollard
> >>
> >>
> >
>
>
--
-Ian Woollard
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