Well........... being technically correct. With natural gas there are three types of gas used in old cities, primarily because of the presence of cast iron pipes that are sealed with oakum and lead the same way that cast iron drain pipes are sealed. Most areas with steel or plastic pipes are supplied with dry gas, any water in it will be accidental such as in new piping or where the line is punctured letting water in. Old areas are supplied with "humidified" gas where they add some steam to keep the oakum moist, or they add oil vapour to do the same job. In older cities you will see small iron fittings in the street or sidewalk that say "drip". These are not a comment on the local people but a low point in the underground piping where water or oil accumulates from condensing of the injected steam or oil. At regular intervals, the gas utility will access these drips to pump out excess water or oil.
The Colonel is correct. The products of combustion of gas (or any hudyocarbon) are Carbon Dioxide and WATER VAPOR. (With incomplete combustion you would also have some soot, which is unburned carbon, and some Carbon Monoxide, which is combustable.) If the stack temperature (flue temperature) is low enough, the Relative Humidity will hit 100%. That means some of the water vapor will condense into liquid water vapor droplets. This is what you see coming out of the chimney. If the flue gas is too hot, the water vapor will mix with the dry air outside before condensation can occ. Or if it occurs, the vapor clout will be so dilute you won't be able to see it.
Ok. I see I have created quite a war here. So why is it that My huge boiler puts out no vapour, steam, "cloud", but my neighbors wimpy water heater puts out a huge "cloud". Furthermore, lets say I like the cloud, what can I do to cause the cloud when I install a new water heater with b vent? What can be done to avoid the visible cloud with b vent on a cold day? Thanks
Your huge heater is putting out the vapor, but it may be condensing inside the chimney and just dropping down to the ground inside. Most chimneys have a longer run than the high efficiency heaters that go out the side of the house.
Most people and dictionaries will flunk the physics, chemistry, and engineering tests about it also. You can join most people and dictionaries, or you can be correct.
His boiler isn't condensing any moisture. The mass of water vapor expelled isn't the issue. Temperature and absolute humidity are of primary importance.
True in absolute terms but not comparative. He wants to know why one type of heater makes more visible condensing vapor than the other. Assuming they are burning about equal amounts of fuel, under equal weather conditions, why does one seem to be more visible than the other type? You did not answer that but I'm sure you will. .
Suppose that one system cools the exhaust gases just to the point of condensing moisture in the vent pipe but without actually condensing any. This mixture will be at 100% RH. For the sake of argument alone let's set the temperature of the outlet at 120ºF. Now suppose the other system only cools the exhaust gas down to 150ºF at the outlet. The RH of the exhausted gas in this system will thus be less than 100%. We are assuming that both systems have burned gas at exactly equal rates. Both will have produced the same quantity of water vapor as byproduct, and the absolute humidity of the gasses in both vent pipes will thus be the same (neglecting differences in density due to temperature differences). The dewpoint will thus also be the same for the outlet gasses of both. The difference between these systems is that the first system's gasses are already *at* dewpoint, while the second system's gasses must drop
30ºF before getting to dewpoint. IOW, if the gasses of these system were to both drop 5º in temp in the first few inches of travel after leaving their respective pipes, then the first will be condensing moisture and the second will still have 25 more degrees to drop before it could condense its moisture. If the gasses from the second system travel sufficiently far to drop to 120ºF, where it could begin producing fog, then it will instead have mixed with the ambient air causing its absolute humidity to drop, which in turn reduces the dewpoint required to produce fog. And if it mixes sufficiently with the ambient air as its temp drops, then the required dewpoint may be pushed to well below the ambient temp, thus preventing any possibility of producing fog.
The biggest fog producer of all systems will be the first system described above. If you drop the outlet temp of the vent below the saturated temp described for it, then condensation will be occurring in the unit and/or vent pipe. The loss of moisture from the gasses will cause the absolute humidity of the output to be lowered. It will still be at dewpoint as it leaves, as in system1, but it will also be closer in temp to the ambient temp and won't therefore cool as quickly. Thus for maximum fog adjust the outlet temp such that the RH is at 100% but with no condensation actually occurring within the system. Outdoor ambient conditions also play a big part in fog formation from flue gasses.
That is what I was trying to say, except in simpler terms. Your descriptions is much more accurate and finally should settle the OP's question. thank you.
physical chemistry and in engineering, steam refers to vaporized water. It is a pure, invisible gas (for mist see below), which at standard atmospheric pressure has a temperature of around 100 degrees Celsius, and occupies about 1,600 times the volume of liquid water (steam can of course be much hotter than the boiling point of water; such steam is usually called superheated steam).
Ah, Ed. I'm disapointed. Of all the people who would know the diff between quotes and parenthases. But at least you didn't say "quote unquote" which many folks use incorrectly. A typical usage would be that the person said, quote unquote, you're fat. Now, in this usage, there is no quoted text.
Anyhow, (paranthetically), I think you're right about stem being invisible. And you can quote me as agreeing with you.
Uh, no. The ninety percenter has a drain, and much of the water vapor is condensed and run down the drain. So, and 80 percenter dumps much more water vapor up the stack.
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