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Old Jan 18th 2019, 04:54 AM   #1
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Electricity production from steam - help

First topic here in the forum, thanks for having me!

Recently i've developed some curiousity over how steam based electricity is produced. and i have some questions i'm hoping to help me understand the mechanims of it. My physics backround is dull because i had hard time with it in school growing up but i will do my best to learn it!

I want to create electricity using a saturated steam turbine, that's need 10-12bar of pressure, in temperature of 200-220 celsius in the rate of 0.05kg of steam per second.

What is the most efficient way to create steam that has these properties?
For example let's say everything takes place on sea level, in room temperature (24c), as a boiler, i will use a 2cm diameter, 10 cm in length steel tube that has molten salt in 280 celsius in it, and pour 10ml of purified water, in 20 celsius on the tube from all around it at the same time. this tube is inside a container measuring 20X20x20cm.

1. how much time will it take to create steam with these properties?
2. how can one calculate it?
3. how much heat will be lost from the steel tube and the molten salt through the process until the steam reach these properties?
4. are there benefits to using different settings (thicker/longer/different material tube, increasing container's volume?
5. how much time will it take to fresh molten salt to heat the steel tube after being cooled off by the poured water?
6. is aluminium more efficient than steel in keeping the heat?
7. is there a constant way to predict Leidenfrost effect of the poured water?
8. is this way efficient to create steam with these properties, in the shortest amount of time?
9. how to direct the steam out of the container towards the turbine in the required pressure? is there a fixed nozzle's sizes for that?
10. let's say i use gas to heat up the molten salt. what is the most efficient way to heat the salt with gas? pressure of the flame, air mixture in the tank, nozzle size?

will appreciate any help!
sorry for the long post and for the "language", i really don't know how to answer these stuff in a way that i can understand... is there a good place to learn this stuff?

Thank you!
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Old Jan 21st 2019, 08:46 AM   #2
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A lot of these questions might be considered "engineering" rather than "physics"
My main concern would be the estimated 10-12bar of pressure,
this is enough to be deadly dangerous!

However to start you off:
Question 1 can be determined from the specific heat capacity and the latent heat of evaporation.
Basically the specific heat capacity details how much heat energy is required to raise the temperature of (1kg) water by 1 degree (Celsius),
so you can then work out how much energy is required to raise it to 100deg (Celsius)
You then need energy (latent heat of evaporation) to turn the liquid water into gaseous water (steam)
you then need more energy to raise the temperature of the steam from 100 to 200 Celsius.

Subtract this energy from the energy of your molten salt pipe.
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Old Jan 21st 2019, 07:58 PM   #3
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Originally Posted by physicsnub View Post
.... let's say i use gas to heat up the molten salt. what is the most efficient way to heat the salt with gas? pressure of the flame, air mixture in the tank, nozzle size?
It makes no sense to use gas to heat salt then salt to heat water ... More efficient to use gas to heat water (a boiler) ...

Efficiency is dependent on how high you can get the pressure ... As Woody has pointed out this is very dangerous.

I've often wondered why there aren't add ons for diesel generators ... Diesel (or petrol) is burnt in a standard IC(internal combustion) engine and turns a generator , the waste heat is usually lost via the radiator , (fan assisted air flow). The pressure in the radiator is about 2 atms.(30psi) ... Remove the radiator and produce steam ...and run the engine hot ... this will increase the efficiency of the IC generator , but will also give a source of steam at perhaps 5 or 10 atms which can drive a primitive steam engine , of turbine....

You could also use the exiting gas from the IC engine (700C ?) to heat water and generate steam.

A typical IC generator (around 10Kw) may have an efficiency of perhaps 35% ... if you can harness some of the 65% that is wasted then you could make an important breakthrough ... an extra 5% in electrical output is realistic.
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Last edited by oz93666; Jan 21st 2019 at 08:33 PM.
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Old Jan 22nd 2019, 10:02 AM   #4
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Like Oz my first reaction is
Are you sure you want to go this way?

I am guessing there may be other constraints that are not evident from your post,
but I think you might want to look carefully at the premise of your project.

I don't want to pry too much, but can you tell us any more about what the final aim might be?
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Old Jan 23rd 2019, 02:15 AM   #5
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It seems that molten salt is being researched as a heat transfer fluid:

https://reader.elsevier.com/reader/s...10FD637A6BAB39

I think you might find some answers by reading the papers published by this author and the references therein.

Last edited by benit13; Jan 23rd 2019 at 02:18 AM.
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Old Jan 23rd 2019, 07:05 AM   #6
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Well ... there's nothing new or magical about molten salt ... it has it's uses in a few specific applications .. solar trough concentrators which operate at around 300C , the alternative, pressurized water would require thick pressure pipes running down the focus .. expensive and thermally resistant to collecting solar radiation ...

You must be clear about why you would even consider molten salt .. for most applications it only wastes power.
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