steam generator project

[salvatore87]

I made the changes you had suggested to me,cmq on the superheater page you will find the total surface of the generator, and the losses in the pipes and the cloak

 

[paulpaul]

in fact I was wrong was not in bar but in pascal excuse me then excuse if to calculate re use de, then also in the calculation of he I have to use it (he=nu*conducibility/de) right?

Yes, the characteristic length is the same for both the number of reynolds and the number of nusselt!

 

[salvatore87]

As for the capacitor, do you think it is possible to work with a pressure of 0.5 bar?

 

[salvatore87]

the capacitor comes out of me 150 tubes from 40mm power 18mw, air flow 893kg/s, 1bar condensing p, air dye=20c; air output=40c

 

[paulpaul]

As for the capacitor, do you think it is possible to work with a pressure of 0.5 bar?

depends on the temperature of the cooling fluid: I would consider an approach deltat of 10-15 °c in the case of water, then determine the condensing temperature (and pressure from tables or mollier, since the variance is 1).

Normally the large water-cooled capacitors of thermoelectric power plants work on the 35 °C (then 0.06 absolute bars). have systems for the continuous removal of uncondesirables (which also serve at the first start to create the vacuum). steam side cape, cooling water side tubes.

if you work on air probably the temperature will be higher. for air are used tubes (tube side steam) whose exchange coefficients can be obtained from the literature for numerous geometries (kays & london is a bible in this regard). the outside air is in forced convection, moved by fans. If for example you have air at 20 °C (it seems unpreservative if you are in puglia...) the condensing temperature may be around 40 °C (on air/gas exchangers or air/vapore you hold a generally higher approach than on liquid/gas). at 40 °c I read from the tables of the saturation steam approximately 0.07 bar.

it could be more realistic in the puglia an external air of 45 °c, which would correspond a tsat of 65 °c and a psat of 0.25 bar.

 

[salvatore87]

But I have noticed that with those powers working at 0.25bar will give me a very large exchange surface at least 4-5 times that calculated on the steam generator that is 500m2.......ecco because in the end I opted for a tdi condensation of 100c to 1 bar. regarding the ambient temperature, look that bari is cold in winter!!! I think it's too much to risk 45 degrees of average. Then I noticed something strange. since I have a very high air flow (which would further increase if I followed your pressure indications) the maximum speed is about 75m/s, but the losses are low (0,07bar). Is it possible to have such a speed of air? ?

 

[paulpaul]

If you use air, I expect large surfaces. you use the fins for this. How did you find him? I attach an experimental graph to a battery of tubes, characterized by two different steps and a certain geometry of the tube and fins. many other graphs are available for different geometries. with this you can determine, according to the number of reynolds (in which the characteristic length is the 4rh hydraulic diameter that you find at the bottom of the figure) , the friction coefficient and the external convection coefficient, expressed as a product between the number of prandtl elevated to 2/3 and the number of stantons. the speed to be used both in the number of stantons and in the number of reynolds is given by v = mass flow/(rho*a) in which to is the free flow area always reported in the figure as a relationship between this and the total frontal area.
as you can see at the bottom of the figure, you can have an exchange surface per beam volume unit of 299 m2/m3 (for this particular geometry).

said this, even here you have to look for a great anyway, I have not calculated anything or at least it is my intention to do it, it is too late now! :wink:

My 45°C were a tmax, not a tmedia, so as to put me in the minimum entalpic jump conditions on the turbine.
I wanted to identify the maximum condensation pressure in the worst weather conditions. If you have colder air, it will increase the actual power of the turbine. to check the exchange surfaces. for an indicative calculation you can actually take an average, type 20 °c as you said.

regarding air speed: what area did you consider to calculate it? Can't you play on the deltat by throwing out the hottest air by reducing your flow? air speed should not exceed 20 m/s in bulk/out of the unit.

 

[salvatore87]

but how do you calculate the frontal area?

 

[salvatore87]

After calculating that term from the function chart of the stanton number, I used the st=nu/(re pr) report to calculate nu and finally he cono the usual relationship where I used 4rh, right?

 

[paulpaul]

Hi.
Consider that that graph is only an example, it is not said to be the most correct geometry for the application. However, you can keep it as a reference.
yes yes: st = nu/(re*pr), but also st = h/(cp*rho*v), with v calculated as above.

the front area calculates it as a rectangle so you have about 20 m/s on it and then imagine to "fill it" with your pipes.

v. for example qui

 

[salvatore87]

then I calculated the frontal area of the book, as (passo*n. tubes along the vertical*length beam(hypotized)).
After I calculated the minimum surface of passage, through sigma, and then the speed.
then from the chart I got the adimensional quantities,as specified above, and finally he.
This is the total surface of heat exchange. But I have noticed that if I echo the lateral surface of the tubes as a stot*(1-0,825) as the book indicates, it does not coincide with the one obtained from my configuring (300 tubes*de^2/4*3,14*length beam), but it is far greater! This is a countersensitivity! at most should be less.

 

[salvatore87]

cmq I solved the problem before, don't worry I had made some confusion with the accounts......senti right by curiosity I send you the file where I calculated capacitor+the components of the evaporator, of course I do not claim that I check if the calculations are correct, but only if the characteristic quantities are plausible. if something is not clear, I will give you a prospect, with the only characteristics that interest you.
I apologize if I ask you so much, but the availability you showed me, it is impossible to think about getting it from a university professor

 

[paulpaul]

quiet, I am passionate about matter (which largely coincides with my work) and it doesn't cost me any trouble! what is missing is time, in fact the times I write to are often impossible as you have seen! the important is not the "correct" resolution of the problem but to understand what assumptions should be done, since in the project the degrees of freedom (as you have seen) are many.

As soon as I can look at it, but you know I'm not an expert on exchangers! I have designed some of the water/gas type and participated in the design of other air/gas (so no steam) for high pressures, but only because taken between head and neck:biggrin:

surely find many competent people on the topic here!

 

[salvatore87]

quiet, I am passionate about matter (which largely coincides with my work) and it doesn't cost me any trouble! what is missing is time, in fact the times I write to are often impossible as you have seen! the important is not the "correct" resolution of the problem but to understand what assumptions should be done, since in the project the degrees of freedom (as you have seen) are many.

As soon as I can look at it, but you know I'm not an expert on exchangers! I have designed some of the water/gas type and participated in the design of other air/gas (so no steam) for high pressures, but only because taken between head and neck:biggrin:

surely find many competent people on the topic here!

What do you do in your job?

 

[paulpaul]

What do you do in your job?

gas compression machines and plants, for use mainly in the oil and gas sector.
As soon as I can answer you in the other 3d you opened.

 

[salvatore87]

gas compression machines and plants, for use mainly in the oil and gas sector.
As soon as I can answer you in the other 3d you opened.

Thank you! I thought I could find more people prepared on my subject, in that section... besides you obviously. . .