Why do thick clouds of steam come out of sewer grates from time to time?
In Kingston Ontario, the sewer grates in the sideswalks will sometimes jet out big white clouds of steam. The speed of the stream suggests that it is being forced out. This lasts for at least 10 minutes at a time and there is no smell. What is the cause and purpose of these jets of steam?
because the air is colder than the water in the sewer.
its warmer than the air
That could depend on the time of year and the location of the grates. It can get very cold in Kingston Ontario, right? The grates are part of a street drainage system where cleanout pits and connecting pipes are located well below grade, where it remains above freezing due to surrounding ground water. Ground water remains at the average temperature of all water entering the ground during the year where the minimum temperature is 32F (ice can’t flow into the ground). The stale air in the system should become saturated with water vapor at the system temperature. If a wind causes cold air to blow into one or more grates, it can drive saturated water vapor out of one or more other grates where it will condense into “steam” in the colder (freezing?) air. Depending on location, a nearby building may be connected to discharge clean hot waste water into the system rather than into the sanitary waste system. Such discharge may cause a plume of steam to rise even in above freezing weather.
condensation, its the same as when you breathe when its cold out, the air leaving the sewer is warmer then the air it is entering into, thus effectively making the water in the air condense