42
votes
Why use steam instead of just hot air?
Because boiling a volume of water creates a much bigger volume of steam this volume increase is about 1700 times.
According to the gas laws doubling the absolute temperature of a volume of gas only ...
- 5,751
37
votes
Why did steam locomotives not transfer power by cogwheels?
Steam piston engines can generate a lot of torque from stationary and the pistons can be physically remote from the boiler, so in most cases it is most convenient to have the pistons directly drive ...
- 15.2k
27
votes
Accepted
Why use steam instead of just hot air?
I would say that using a warm pressurized gas is not very feasible.
Ratchet freak already mentioned how you can get much more volume out of heating water into steam than just heating up air until it'...
- 992
15
votes
Why use steam instead of just hot air?
Hot air engines are feasible, and have a 200 year history behind them, starting in 1816 with the Reverend Robert Stirling.
The other answers are largely correct : steam offers more energy per unit ...
- 1,620
14
votes
Why did steam locomotives not transfer power by cogwheels?
Here is a picture of the crankshafts inside a modern internal combustion engine:
The purpose of these is to convert the back-and forth motion of the piston into rotational motion. It's very much the ...
- 239
12
votes
Accepted
Why did steam locomotives not transfer power by cogwheels?
I would like to point out that modern cars do not use cogwheels for transmission, they use shafts. Cogwheels are used for the gearing and differential.
But bar mechanisms were used mostly because ...
- 3,597
12
votes
Accepted
Why is using steam to rotate a turbine more efficient?
The main reason is that a turbine requires a pressure drop to extract energy from the working fluid. The drop in temperature that is observed in a turbine is a result of the expansion of the fluid; ...
- 3,044
10
votes
Why use steam instead of just hot air?
There are really countless possible answers to this. I'd like to add one that hasn't been made clear yet.
If you are doing a closed cycle, where you aren't letting steam/gas out into the atmosphere, ...
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9
votes
Accepted
Why use steam water and not other fuild in steam engines?
There's some interesting information on a number of alternative working fluids here, including ammonia, alcohol, mercury, sulpur dioxide, freon, and many others.
Refrigerants are used today in ...
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7
votes
Why use steam instead of just hot air?
While toy steam engines often require that one pre-fill the boiler, and then only operate until the boiler is nearly empty, most practical steam engines require that every gram of steam which leaves ...
- 369
7
votes
Accepted
On steam locomotives with six driving wheels, why are the rear set of wheels placed further apart from the other two?
In the ones pictured, there are no trailing axles - they are a 2-6-0 and a "tenwheeler" 4-6-0 respectively. The ones shown have the firebox between the two rear drive axles. .That was an ...
- 4,607
6
votes
Accepted
How in Rankine cycle the turbine generates more power than the pump takes?
Pressure is force/area, if the area offered by the pump impeller is smaller than the area against wich the steam must force its way out of the boiler, and both the turbine and the pump are linked, ...
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5
votes
Why did steam locomotives not transfer power by cogwheels?
for a while, steam locomotives actually used gears and cylinder/piston sets which drove crankshafts. These were called geared locomotives and they were used to haul heavy loads up particularly steep ...
- 14.3k
4
votes
Why did steam locomotives not transfer power by cogwheels?
Steam generates full torque at zero speed as has been mentioned elsewhere, so like in an electric car (which has very much the same sort of characteristic), there is little to be gained from a gearbox,...
- 241
4
votes
Why is more steam required to turn a steam turbine when electric power consumption is higher
Because you can't get something for nothing?
If the generator is generating more electrical power then that energy has to come from somewhere.
The more power you try to pull from a generator the ...
- 766
4
votes
estimating the surface area of a steam coil immersed in a tank
One thing to consider is that pipes used for heating like this are normally « finned » to increase the surface area - fins can be small discs fitted to the pipe or even wire loops - both increase the ...
- 15.5k
4
votes
Why is using steam to rotate a turbine more efficient?
You are almost describing a gas turbine engine. These are used to generate electrical power, and also to power aircraft. But, in a gas turbine the output of the combustor is at high pressure, and ...
- 257
4
votes
Why is using steam to rotate a turbine more efficient?
Heating water to make steam is not necessarily more efficient, but a lot more practical. What you describe is how internal combustion engines work, for example, so it's a valid concept. However, ...
- 11.4k
4
votes
How in Rankine cycle the turbine generates more power than the pump takes?
The main reason is that it takes much less energy to compress a liquid than a gas by the same pressure difference. The pump takes a little bit of energy to compress the water, but a huge amount of ...
- 3,044
4
votes
Why do steam and diesel engines have differing cylinder configurations?
The maximum efficiency of either the Diesel or a steam engine cycle is (assuming you can treat steam as an ideal gas): $$\eta_{Diesel} = 1 - \frac{1}{(\frac{V_{Max}}{V_{Min}})^{k-1}} \left[\frac{r_c^...
- 5,343
4
votes
Why use steam instead of just hot air?
For Air:
Consider the ideal gas law PV = nRT rearranged to be V = (nRT)/P.
n and R are considered constant, and for our purposes, P is also constant. Thus, to increase the volume, (i.e. create a ...
- 41
4
votes
Why use steam instead of just hot air?
Do a web search on "Rankine cycle".
The real key is that in a practical heat engine, you need to pump in cold working fluid, heat it, let it do work (and cool) as it expands, and then repeat.
If you ...
- 2,472
4
votes
Why use steam instead of just hot air?
As said, boiling water creates much more gas. To make a useful engine for the kind of applications that steam engines are used in, you want to build lots of pressure to be able to move heavy stuff, e....
- 141
4
votes
Were steam locomotive fitted with centrifugal governor?
A governor is a poor application for steam locomotives because the throttle is constantly adjusted by the driver. Speeds, loads, and steam pressure change constantly, plus a major part of driving a ...
- 6,544
4
votes
On the steam locomotives, why was the driver's cabin not located in the front of the boiler for better visibility?
There have been some locomotives with this design, it's called "Cab forward."
As the article says, Southern Pacific railroad in the US had some cab forward locomotives, which solved crew ...
4
votes
Accepted
How long a spiral copper tube would need to be in a monotube boiler in order to achieve 0.02 kg of steam per second?
I'm not going to answer your question, because no wall thickness or length of tube will meet your needs.
Coiled copper is for cooling something, not for making steam. You can cool hot water by ...
- 6,544
3
votes
Rate of flow of steam going from one pressure to another
You can use the Hagen-Poiseuille equation to determine the flow rate as a result of a pressure gradient. A caveat in using this equation is that the flow has to be laminar, i.e. inertial effects can ...
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3
votes
Rate of flow of steam going from one pressure to another
You stated that most things you found are too complex for your basic understanding, is it safe to assume that the answer you are seeking may be an educated guess? If so I would go with Bernoulli
$$g ...
- 1,734
3
votes
Which has more density: 100 °C steam or 100 °C dry air?
There's an air of 'lmgtfy' about this question...
Wolfram Alpha is a great resource for quickly finding information like this.
You can see that the steam is significantly less dense than the air, at ...
- 7,726
2
votes
Accepted
Steam sterilization of whey in a bioreactor
It all depends on the sterilization level you want to achieve. As you say, you would need to know the death kinetics parameters, or equivalently the log-decimal reduction time (D) and how it changes ...
- 335
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