JRodgers on sun 18 mar 12
Really interesting stuff to me. Learned about this first in college
physics, then later in more depth when attending aircraft mechanic
school, and finally in the greatest depth of all when I had to teach it.
Bernoulli's applied to all carburetion back in the day and where
airplanes were concerned every good aircraft mechanic had to have an
absolute understanding of the principle. The principle is applied not
only to the engines but in many other areas of airplanes. In fact, the
principle is the basis of flight.
With a good understanding of Bernoulli's it for sure gives one better
control of one's gas kiln. ie, the more you know - the better off you are.
John
On 3/18/2012 3:43 PM, mel jacobson wrote:
> if you like technical science you can read this.
> nils really means turbulence and the creation of it.
> when you constrict the exit twice it seems to speed
> up the turbulence. it works. and, more heat stays in the
> kiln than you let out. a kiln is a box, that stores heat, energy,
> and builds to a pre/determined temperature. heat in, fumes
> out, temp builds. if you do it right you get great pots.
>
> i talked today via phone to nils for a time, and then called
> feriz delkic and talked about kilns. we do have a meeting of the
> minds.
>
> here is a simple explanation of venturi.
> but, we really don't care so much...the double flue exit works
> like magic. and many many of these kilns are in use by happy potters.
>
> this is for fluids, but the effect is much that same for gas/heat /energy=
.
>
> i have all three my degrees in art/education and craft. i am not a
> physicist.
> but, i can make a rather good kiln.
>
> The Venturi effect is a jet effect; as with a funnel the velocity of
> the fluid increases as the cross sectional area decreases, with the
> static pressure
> correspondingly decreasing. According to the laws governing
> fluid dynamics, a
> fluid's velocity must
> increase as it passes through a constriction to satisfy the
> princ=
iple
> of continuity, while its pressure must decrease to satisfy the
> principle of
> ical_energy>conservation
>
> of mechanical energy. Thus any gain in
> kineticom/Kinetic_energy?qsrc=3D3044>
>
> energy a fluid may accrue due to its increased velocity through a
> constriction is negated by a drop in pressure. An equation for the
> drop in pressure due to the Venturi effect may be derived from a
> combination of
> Bernoulli's
> principle and the
> continuity equation.
>
> The limiting case of the Venturi effect is when a fluid reaches the
> state of choked flow,
> where the fluid velocity approaches the local speed of sound. In
> choked flow the mass flow rate will not increase with a further
> decrease in the downstream pressure environment.
>
> However, mass flow rate for a compressible fluid can increase with
> increased upstream pressure, which will increase the density of the
> fluid through the constriction (though the velocity will remain
> constant). This is the principle of operation of a
> de Laval nozzle.
> Increasing source temperature will also increase the local sonic
> velocity, thus allowing for increased mass flow rate.
>
> Referring to the diagram to the right, using Bernoulli's equation in
> the special case of incompressible flows (such as the flow of water
> or other liquid, or low speed flow of gas), the theoretical pressure
> drop at the constriction is given by
>
> http://www.visi.com/~melpots/
> clayart page below:
> http://www.visi.com/~melpots/clayart.html
>
mel jacobson on sun 18 mar 12
if you like technical science you can read this.
nils really means turbulence and the creation of it.
when you constrict the exit twice it seems to speed
up the turbulence. it works. and, more heat stays in the
kiln than you let out. a kiln is a box, that stores heat, energy,
and builds to a pre/determined temperature. heat in, fumes
out, temp builds. if you do it right you get great pots.
i talked today via phone to nils for a time, and then called
feriz delkic and talked about kilns. we do have a meeting of the
minds.
here is a simple explanation of venturi.
but, we really don't care so much...the double flue exit works
like magic. and many many of these kilns are in use by happy potters.
this is for fluids, but the effect is much that same for gas/heat /energy.
i have all three my degrees in art/education and craft. i am not a physici=
st.
but, i can make a rather good kiln.
The Venturi effect is a jet effect; as with a funnel the velocity of
the fluid increases as the cross sectional area decreases, with the
static pressure
correspondingly decreasing. According to the laws governing
fluid dynamics, a
fluid's velocity must
increase as it passes through a constriction to satisfy the
princip=
le
of continuity, while its pressure must decrease to satisfy the
principle of
al_energy>conservation
of mechanical energy. Thus any gain in
kinetic/Kinetic_energy?qsrc=3D3044>
energy a fluid may accrue due to its increased velocity through a
constriction is negated by a drop in pressure. An equation for the
drop in pressure due to the Venturi effect may be derived from a
combination of
Bernoulli's
principle and the
continuity equation.
The limiting case of the Venturi effect is when a fluid reaches the
state of choked flow,
where the fluid velocity approaches the local speed of sound. In
choked flow the mass flow rate will not increase with a further
decrease in the downstream pressure environment.
However, mass flow rate for a compressible fluid can increase with
increased upstream pressure, which will increase the density of the
fluid through the constriction (though the velocity will remain
constant). This is the principle of operation of a
de Laval nozzle.
Increasing source temperature will also increase the local sonic
velocity, thus allowing for increased mass flow rate.
Referring to the diagram to the right, using Bernoulli's equation in
the special case of incompressible flows (such as the flow of water
or other liquid, or low speed flow of gas), the theoretical pressure
drop at the constriction is given by
http://www.visi.com/~melpots/
clayart page below:
http://www.visi.com/~melpots/clayart.html
John Britt on mon 19 mar 12
Turbulence is not venturi.
john britt pottery
ivor and olive lewis on tue 20 mar 12
Dear Mel,
The description of a Venturi speaks of a pipe with a diminishing diameter
connected without a break to a short parallel section that flares outwards
again. It is not possible to apply scientific equations for a streamline
system to a non streamline system since it does not comply with the
definition of a venturi.
It seems to me as though we have a big box connected by a small aperture to
a small box. This leads through an even smaller opening to a discharge pipe=
.
The net effect is to reduce the rate at which super hot gases flow from the
main chamber because the smaller box acts as an intercooler. Cooling
increases the density of exhausting gas. This will induce back pressure.
Greater energy retention within the kiln chamber makes for better firings.
Economy, Efficiency and Ecology.
So, has anyone done a direct comparison between kilns of identical
proportions and thermal mass, the first without a plenum chamber and the
second with the plenum chamber.
Sincere regards to the three of you.
Ivor.
Ivor Lewis,
REDHILL,
South Australia
.
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