Posted by Randy on September 22, 2010, 4:57 am
> Well, at least it's new to me - and although I'm working in a solar
> context, it's just another (external combustion) heat engine. I posted
> this query to news:alt.solar.thermal and am drawing a blank, but knowing
> that there're folks here with steam experience, I'll try here as well.
> This is part one of what I think will be a 3-part inquiry...
> My starting point is a solar trough like that shown at
> http://www.iedu.com/DeSoto/Fluidyne/Heat/V1/
> For the sake of discussion, let's replace the copper target pipe with
> one made of unobtanium which, as everyone knows, can withstand infinite
> pressure but is horribly expensive.
> For part 1 of my project, I want to completely fill the pipe with water
> and cap both ends with unobtanium fittings.
> As the seventh photo on the web page shows, the trough can heat the
> target to 384°C - well above the boiling point of the water inside the
> pipe. I've been thinking about turning the mirror 90°, so that my trough
> will be 8' wide and 4' long - to push the temperature up to near 575°C...
> My understanding is that above ~373°C the physical properties of the
> liquid and vapor phases are identical and that, in fact, any discussion
> of 'liquid' and/or 'vapor' is meaningless. Can anyone verify and/or
> improve my understanding?
> And, most important of all, if my pipe contains some volume /V/ of
> water, does anyone know how to calculate pressure /P/ as a function of
> temperature /T/ so I can think about using something less expensive than
> unobtanium?
> --
> Morris Doveyhttp://www.iedu.com/DeSoto/
Why just 1 copper pipe?, split the entry & exit into three with a
(what do you call those things?) splitter?
Then you'd get more water heated at the same time with a sweet low
tech efficiency increase of about 2/3.
R.
Posted by Randy on September 22, 2010, 5:12 am
> > Well, at least it's new to me - and although I'm working in a solar
> > context, it's just another (external combustion) heat engine. I posted
> > this query to news:alt.solar.thermal and am drawing a blank, but knowing
> > that there're folks here with steam experience, I'll try here as well.
> > This is part one of what I think will be a 3-part inquiry...
> > My starting point is a solar trough like that shown at
> > http://www.iedu.com/DeSoto/Fluidyne/Heat/V1/
> > For the sake of discussion, let's replace the copper target pipe with
> > one made of unobtanium which, as everyone knows, can withstand infinite
> > pressure but is horribly expensive.
> > For part 1 of my project, I want to completely fill the pipe with water
> > and cap both ends with unobtanium fittings.
> > As the seventh photo on the web page shows, the trough can heat the
> > target to 384°C - well above the boiling point of the water inside the
> > pipe. I've been thinking about turning the mirror 90°, so that my trough
> > will be 8' wide and 4' long - to push the temperature up to near 575°C...
> > My understanding is that above ~373°C the physical properties of the
> > liquid and vapor phases are identical and that, in fact, any discussion
> > of 'liquid' and/or 'vapor' is meaningless. Can anyone verify and/or
> > improve my understanding?
> > And, most important of all, if my pipe contains some volume /V/ of
> > water, does anyone know how to calculate pressure /P/ as a function of
> > temperature /T/ so I can think about using something less expensive than
> > unobtanium?
> > --
> > Morris Doveyhttp://www.iedu.com/DeSoto/
> Why just 1 copper pipe?, split the entry & exit into three with a
> (what do you call those things?)splitter?
> Then you'd get more water heated at the same time with a sweet low
> tech efficiency increase of about 2/3.
> R.
Manifold, was the word I was looking for.
Posted by Morris Dovey on September 22, 2010, 7:23 am
On 9/22/2010 4:12 AM, Randy wrote:
>> Why just 1 copper pipe?, split the entry & exit into three with a
>> Manifold.
The plan is to produce heat by focusing solar radiation with a parabolic
trough-type reflector, and the trough only has a single focus line -
which means it can only heat one target efficiently.
On the other hand, it may turn out to make sense to use a manifold in
order to use multiple cold heads - but for now I'm trying to keep all of
the flow(s) in a single line. T's, L's, and Y's (and manifolds) all
produce energy losses that I'd prefer to avoid.
>> Then you'd get more water heated at the same time with a sweet low
>> tech efficiency increase of about 2/3.
I wish! The total energy available is determined by the reflector's
capture area, and the temperature produced by that energy is determined
by the width of the capture area and the width of the area on the pipe
onto which the solar radiation is focused.
If heat were being applied in a combustion chamber, then multiple pipes
would make a lot more sense - and in that context I think your
suggestion might be spot-on.
--
Morris Dovey
http://www.iedu.com/DeSoto/
Posted by Jim Wilkins on September 22, 2010, 7:47 am
> On 9/22/2010 4:12 AM, Randy wrote:
> >> Why just 1 copper pipe?, split the entry & exit into three with a
> >> Manifold.
> The plan is to produce heat by focusing solar radiation with a parabolic
> trough-type reflector, and the trough only has a single focus line -
> which means it can only heat one target efficiently.
> On the other hand, it may turn out to make sense to use a manifold in
> order to use multiple cold heads - but for now I'm trying to keep all of
> the flow(s) in a single line. T's, L's, and Y's (and manifolds) all
> produce energy losses that I'd prefer to avoid.
> >> Then you'd get more water heated at the same time with a sweet low
> >> tech efficiency increase of about 2/3.
> I wish! The total energy available is determined by the reflector's
> capture area, and the temperature produced by that energy is determined
> by the width of the capture area and the width of the area on the pipe
> onto which the solar radiation is focused.
> If heat were being applied in a combustion chamber, then multiple pipes
> would make a lot more sense - and in that context I think your
> suggestion might be spot-on.
> --
> Morris Doveyhttp://www.iedu.com/DeSoto/
Is your pipe diameter large enough to permit a circular reflector that
doesn't need to track the sun as precisely?
http://www.appropedia.org/Understanding_Solar_Concentrators
The 'Cusp' is the Involute curve.
jsw
Posted by Morris Dovey on September 22, 2010, 8:36 am
On 9/22/2010 6:47 AM, Jim Wilkins wrote:
> Is your pipe diameter large enough to permit a circular reflector that
> doesn't need to track the sun as precisely?
It could be made large enough, but that would lower the temperature (and
therefore the efficiency) that could be achieved.
_Tracking_ is a PIA, but tracking _precision_ isn't a problem.
> http://www.appropedia.org/Understanding_Solar_Concentrators
> The 'Cusp' is the Involute curve.
Hmm - that article looks like a porkbarrel/earmark project handed to
some senator's niece's SO. (sorry)
Given that the mirrors tend to be an expensive component of just about
any concentrator, that Trombe-Meinell cusp design doesn't produce much
"bang for the buck" for anything beyond DHW. Take a close look at what
they call "temperature" in Table 1...
BTW, the numbers in their "Table 1" don't make any sense whatever. The
author/reviewers demonstrate Sturgeon's Law.
--
Morris Dovey
http://www.iedu.com/DeSoto/
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> context, it's just another (external combustion) heat engine. I posted
> this query to news:alt.solar.thermal and am drawing a blank, but knowing
> that there're folks here with steam experience, I'll try here as well.
> This is part one of what I think will be a 3-part inquiry...
> My starting point is a solar trough like that shown at
> http://www.iedu.com/DeSoto/Fluidyne/Heat/V1/
> For the sake of discussion, let's replace the copper target pipe with
> one made of unobtanium which, as everyone knows, can withstand infinite
> pressure but is horribly expensive.
> For part 1 of my project, I want to completely fill the pipe with water
> and cap both ends with unobtanium fittings.
> As the seventh photo on the web page shows, the trough can heat the
> target to 384°C - well above the boiling point of the water inside the
> pipe. I've been thinking about turning the mirror 90°, so that my trough
> will be 8' wide and 4' long - to push the temperature up to near 575°C...
> My understanding is that above ~373°C the physical properties of the
> liquid and vapor phases are identical and that, in fact, any discussion
> of 'liquid' and/or 'vapor' is meaningless. Can anyone verify and/or
> improve my understanding?
> And, most important of all, if my pipe contains some volume /V/ of
> water, does anyone know how to calculate pressure /P/ as a function of
> temperature /T/ so I can think about using something less expensive than
> unobtanium?
> --
> Morris Doveyhttp://www.iedu.com/DeSoto/