PierArg
Guest
and think that the load losses vary with the square of the speed!
paulpaul
Guest
interesting speech on the ejectors: reminiscences of the studies remind me of them as "static" pumps of food of steam thermoelectric plants. the thermodynamic treatment I remember quite complex, I certainly did not fully grasp it at its time
However sonic speed in certain industrial plants are on the agenda: working in the natural gas sector I often find myself translating gas from high-pressure tanks (200-300 bar) in other at a much lower pressure (some dozens of bars), with expansion reports far superior to the critical one. the result is that the flow is "locked" (choking), and the whistle is remarkable... but nothing more since there is a sudden expansion in the atmosphere.
Actually the venturi tube is the stroking device (also used to measure the flow) that presents the lowest load losses, since the kinetic energy (maximum in the throat section, purchased at the expense of a pressure loss in the convergent tract) is recovered as a large part pressure (if the design is done well) in the subsequent divergent tract. Ultimately, a venturi working under subsonic regime can have efflux coefficients very close to 1.
However sonic speed in certain industrial plants are on the agenda: working in the natural gas sector I often find myself translating gas from high-pressure tanks (200-300 bar) in other at a much lower pressure (some dozens of bars), with expansion reports far superior to the critical one. the result is that the flow is "locked" (choking), and the whistle is remarkable... but nothing more since there is a sudden expansion in the atmosphere.
Actually the venturi tube is the stroking device (also used to measure the flow) that presents the lowest load losses, since the kinetic energy (maximum in the throat section, purchased at the expense of a pressure loss in the convergent tract) is recovered as a large part pressure (if the design is done well) in the subsequent divergent tract. Ultimately, a venturi working under subsonic regime can have efflux coefficients very close to 1.
Er Presidente
Guest
:finger:: finger: finger:
MBT
Guest
We have supersonal jets in the workplace
their noise is covered by much more intense others, but I happened to hear a "bang" at the moment when the jets are lit.
lasts a moment, then turning into a continuous whistle. but, at least in my opinion, it is true.
I'll see if I have a video of the test at the bar, but I doubt it's public.
their noise is covered by much more intense others, but I happened to hear a "bang" at the moment when the jets are lit.
lasts a moment, then turning into a continuous whistle. but, at least in my opinion, it is true.
I'll see if I have a video of the test at the bar, but I doubt it's public.
mambo1988
Guest
the sonic speed of steam water is 650 m/s? ? ?
Considering that the fluid was hypothesized ideal (incomprehensible, absence of losses) would speed be lower? ?
Considering that the fluid was hypothesized ideal (incomprehensible, absence of losses) would speed be lower? ?
Er Presidente
Guest
It is difficult to understand whether it is a wave of discontinuity of pressure (explosion) or a real supersonic bang.
to be sure you should put a microphone moving towards the source and play the bang at lower speed, you could recognize the "transition" feature where the sound would be "inverted" in the sequence immediately before the bang.
p.s.: I understand that I've been as clear as the nebia in London, but I'm having fun like this!
:biggrin:
paulpaul
Guest
the speed of sound in a fluid at the pressure p and density rho can calculate it as
sqrt(k*p/rho)
with k polytropic exponent considering (for saturated steam k you can consider it equal to 1,1 and for a steam overheated about 1.2/1,3
Hi.
mambo1988
Guest
What do you recommend? ? I thought I was close to the solution and instead...:frown:
is this system unrealizable because the speeds are too high? ? ?
helpp me
is this system unrealizable because the speeds are too high? ? ?
helpp me
mambo1988
Guest
can it be that the pressure hypothesized by me is too high considering that the boiler can work max at 6-8 bar, and during the vapor output the pressure decreases? ? ?
then I also obtained the steam flow considering the thermal power (due to the resistances that make the water in evaporated boiler) and the pressure, which is 0.00115 kg/s, the density of the steam obtained it through the temperature (about 120 °c and p=5 bar)
which is about 3.15 kg/m^3.
so I calculated volumetric flow rate and then speed knowing the section, the initial speed is about 8 m/s..
I'll think...
then I also obtained the steam flow considering the thermal power (due to the resistances that make the water in evaporated boiler) and the pressure, which is 0.00115 kg/s, the density of the steam obtained it through the temperature (about 120 °c and p=5 bar)
which is about 3.15 kg/m^3.
so I calculated volumetric flow rate and then speed knowing the section, the initial speed is about 8 m/s..
I'll think...
paulpaul
Guest
Try to take a look here at the ejectors
http://83.169.19.56/gea/geacategory/219/index_en.htmlfind some theoretical notion on the ejectors always in the book of caput (turbomacchine) for example.
here.
http://www.freestudy.co.uk/fluid mechanics/t2203.pdffind, in the end, an explanation of the same incomprehensible fluid oriented.
do you already know the power of the boiler? at that point the steam flow is actually known (check).
otherwise it is usually a project data: You know how much steam you have to produce and you have to determine the power of the boiler. knowing the mixing ratio with the cleaner you find the scope of this. But it seems to me that certain speeds are indispensable, unless you press the cleaner somehow! But I would crave a little in the dark, I have no direct experience of these machines!
If I can get you a couple of ejector theory pages tomorrow!
Hi.
http://83.169.19.56/gea/geacategory/219/index_en.htmlfind some theoretical notion on the ejectors always in the book of caput (turbomacchine) for example.
here.
http://www.freestudy.co.uk/fluid mechanics/t2203.pdffind, in the end, an explanation of the same incomprehensible fluid oriented.
do you already know the power of the boiler? at that point the steam flow is actually known (check).
otherwise it is usually a project data: You know how much steam you have to produce and you have to determine the power of the boiler. knowing the mixing ratio with the cleaner you find the scope of this. But it seems to me that certain speeds are indispensable, unless you press the cleaner somehow! But I would crave a little in the dark, I have no direct experience of these machines!
If I can get you a couple of ejector theory pages tomorrow!
Hi.
mambo1988
Guest
thanks for the answer, cmq I in practice know the power that I supply to the resistors that wind the boiler which for conduction heat the water in boiler and lead to evaporation... the resistors are 2 from 1200 w a one!
mambo1988
Guest
Thanks for the help shown so far, I'll explain a few things so maybe you're going to direct me to the right path, because maybe I've made some initial imposed data wrong.
then as first I noticed that I made some confusion between saturated steam and overheated steam.
my boiler works maximum at the t of 165° and the max pressure is 6-8 bar... now I wonder in boiler where the evaporation of the water happens I have saturated steam, so I can know the dry saturated steam density that at 160°c to p=6 bar I have a rho(v)=3,3 kg/m^3.(at 150°c to p=4,5 bar I have a rho(v)=
then to know the steam flow as I do? I know the max power of the resistors that are 2400 w...
the steam comes out from the boiler by a tube of 1/4" gas (external diameter=13,16mm).
the internal diamentro I noticed that in the tubes 1/4" is not normalized i.e. changes.. .
so it will also change my initial speed knowing the flow!
said this, I thank you in advance and hope you address me to a solution:finger:
Matteo
then as first I noticed that I made some confusion between saturated steam and overheated steam.
my boiler works maximum at the t of 165° and the max pressure is 6-8 bar... now I wonder in boiler where the evaporation of the water happens I have saturated steam, so I can know the dry saturated steam density that at 160°c to p=6 bar I have a rho(v)=3,3 kg/m^3.(at 150°c to p=4,5 bar I have a rho(v)=
then to know the steam flow as I do
? I know the max power of the resistors that are 2400 w...the steam comes out from the boiler by a tube of 1/4" gas (external diameter=13,16mm).
the internal diamentro I noticed that in the tubes 1/4" is not normalized i.e. changes.. .
so it will also change my initial speed knowing the flow!
said this, I thank you in advance and hope you address me to a solution:finger:
Matteo
paulpaul
Guest
energy conservation equation? this time in thermal form though:
cdc + gdz + dh = dq - dqa
applied between the free water fur and the vapour outlet duct. We consider the system already in balance, that is to the pressure and temperature of operation. from the tables of the steam that I have, at 6 barg (7 bara) I have a saturation temperature of 165 °c (as it turns out to you).
dz = 0 for aeriforms are usually overlooked the differences in quota
dc = 0 (you may consider the output speed on the section but for now we say it is not known)
dh = variation of entalpia, which in this case coincides with the ethalpy of vaporization, which from the tables in these conditions is worth 2066 kj/kg.
dq = heat transferred to water
dqa = heat loss that does not go into the fluid, it is losses for convection and irradiation to the environment, conduction on the walls of the machine, etc.
suppose that dqa = 0.1dq
multiplying both members by course (m) you should get
mdh = p
m = p/dh = (2,4*0,9)/ (2066) = 3,76 kg/h
very similar to yours!
for the tube... yes, at the same external diameter you find tubes of different thickness! plays between steam speed (some tens of m/s) and its resistance to find the appropriate thickness!
cdc + gdz + dh = dq - dqa
applied between the free water fur and the vapour outlet duct. We consider the system already in balance, that is to the pressure and temperature of operation. from the tables of the steam that I have, at 6 barg (7 bara) I have a saturation temperature of 165 °c (as it turns out to you).
dz = 0 for aeriforms are usually overlooked the differences in quota
dc = 0 (you may consider the output speed on the section but for now we say it is not known)
dh = variation of entalpia, which in this case coincides with the ethalpy of vaporization, which from the tables in these conditions is worth 2066 kj/kg.
dq = heat transferred to water
dqa = heat loss that does not go into the fluid, it is losses for convection and irradiation to the environment, conduction on the walls of the machine, etc.
suppose that dqa = 0.1dq
multiplying both members by course (m) you should get
mdh = p
m = p/dh = (2,4*0,9)/ (2066) = 3,76 kg/h
very similar to yours!
for the tube... yes, at the same external diameter you find tubes of different thickness! plays between steam speed (some tens of m/s) and its resistance to find the appropriate thickness!
paulpaul
Guest
If you use a tube of 1/4''' equivalent to a dn6 you can find it easily in thicknesses of about 1 mm (the 6x1 metric is very widespread, I think even the imperial has its equivalent - I used them two years ago as tubes for the instrumentation of a machine that the customer wanted taxically imperially). look at the catalog of the tca for example to see which tubes you can find. in this case (6x1) the speed of the steam is approximately 22 m/s...
mambo1988
Guest
I picked up the old dispenses of "machines" and found some useful formulas regarding the nozzles.
in particula I found a formula regarding the critical pressure (pc)=p1*0,5(approximately depends on k=rappor between the specific heats)...so in my case if I have p1=6 bar the critical pressure is reached to 3 bar, it seems very strange since cmq then the fluid comes out to 1 bar....
but is it possible that I reach the sonic conditions? ? Intuitively it seems very strange....
in particula I found a formula regarding the critical pressure (pc)=p1*0,5(approximately depends on k=rappor between the specific heats)...so in my case if I have p1=6 bar the critical pressure is reached to 3 bar, it seems very strange since cmq then the fluid comes out to 1 bar....
but is it possible that I reach the sonic conditions? ? Intuitively it seems very strange....
mambo1988
Guest
possiamo trascurare cdc???
mambo1988
Guest
What could happen if mach>1? ? in the end also in the steam plants are used a convergent divertenge to have expansion of the steam from 250 bar to 0,5 bar....li that happens to me seems very strange, that from 6 bar to 0.8 bar I reach the sonic conditions...to the end the environment is 1bar, I would be in trans-sonic environment even if I did not use this tube venturi
mambo1988
Guest
guys thank you very much, today I finally made crafty a venturi tube, it works perfectly blend! Now I just have to understand why it works, and what I did wrong in calculations
paulpaul
Guest
Let us know how you made it!
As regards the term cdc: integrated, taking 22 m/s, does 0.5*c^2 = 0.5*22^2 = 242 j/kg which if related to the evaporation ethpia (about 2000 kj/kg) seems to me to be negligible in the budget.
Try to see here
http://www.cheresources.com/compressible_flow.shtmlIf you can clarify some doubts about the motions of incomprehensible fluids! I would try to consider the isothermal flow, from the boiler to the tube exit. know the flow rate (it is fixed by the power) and the length of the pipe: pressure downstream and loss for sudden expansion at the exit of the pipe. You should trace the load loss in the tube and the number of machs on the output section!
However, if you do not use a convergent/divergent and parts from a subsonic speed upstream of the tube, the maximum you can have is ma=1 after a certain length (rho decreases for load losses, so c increases to have the constancy of the flow), also for very low discharge pressures.
small ot
take into account that gasdynamics (which I do not know if not in the most elementary bases) is not normally treated in normal course of machines, if not regarding the classic equation of st. venant and the behavior of convergent/divergent in sonic conditions: is an extremely complex science, where the studied phenomena escape the intuition.
is considered "high-tech", with applications to aerial and spatial propulsion and modular fluid turmoil that only few manufacturers in the world realize: I would like to know a lot more but time ahimè does not help!
As regards the term cdc: integrated, taking 22 m/s, does 0.5*c^2 = 0.5*22^2 = 242 j/kg which if related to the evaporation ethpia (about 2000 kj/kg) seems to me to be negligible in the budget.
Try to see here
http://www.cheresources.com/compressible_flow.shtmlIf you can clarify some doubts about the motions of incomprehensible fluids! I would try to consider the isothermal flow, from the boiler to the tube exit. know the flow rate (it is fixed by the power) and the length of the pipe: pressure downstream and loss for sudden expansion at the exit of the pipe. You should trace the load loss in the tube and the number of machs on the output section!
However, if you do not use a convergent/divergent and parts from a subsonic speed upstream of the tube, the maximum you can have is ma=1 after a certain length (rho decreases for load losses, so c increases to have the constancy of the flow), also for very low discharge pressures.
small ot
take into account that gasdynamics (which I do not know if not in the most elementary bases) is not normally treated in normal course of machines, if not regarding the classic equation of st. venant and the behavior of convergent/divergent in sonic conditions: is an extremely complex science, where the studied phenomena escape the intuition.
is considered "high-tech", with applications to aerial and spatial propulsion and modular fluid turmoil that only few manufacturers in the world realize: I would like to know a lot more but time ahimè does not help!
mambo1988
Guest
Hi, guys thank you again for all the tips, in practice at the end only managed to size the tube is the system works pretty well... .
i.e. the venturi effect (I used a dark converging, and then a softer divergent to regain the same intial conditions), works perfectly if at the exit of the divergent is present immediately the external environment, instead of aspiring, expels steam in the restricted section) if at the exit of the venturi tube is connected a tube more or less long 1 m (which would serve me).
I did several experiments and noticed that the suction system works up to a tube length tot connected to the venturi (10-15 cm) exceeded this length, the effect vanishes....
Could I fix the system? ? ?
i.e. the venturi effect (I used a dark converging, and then a softer divergent to regain the same intial conditions), works perfectly if at the exit of the divergent is present immediately the external environment, instead of aspiring, expels steam in the restricted section) if at the exit of the venturi tube is connected a tube more or less long 1 m (which would serve me).
I did several experiments and noticed that the suction system works up to a tube length tot connected to the venturi (10-15 cm) exceeded this length, the effect vanishes....
Could I fix the system? ? ?