But this time, we no longer speak of condensation but of solidification: water always present in the form of gas in the air is transformed into crystals! This phenomenon is often seen in winter, it is the white frost… The frost point is, in fact, the temperature below which the air no longer has enough energy to keep the water it contains in the form of vapor. What the preceding explanation does not say is that this dew point, its calculation and its implications are valid only for a positive air temperature… This is the practical case, for example, when you want to know if you can repaint your window shutters: you must ensure that there is a good gap (at least 5 ☌) between the air temperature and the dew point, otherwise if the surface you are about to paint is a bit cold… You now have an idea of what will happen! Frost point This dew point is of relatively high importance for all processes that require to occur in dry conditions.
This is what happens at night when our cars are covered with dew… Another example of this is when you blow air (which comes out of your lungs at a temperature of 33-34 ☌ and almost saturated of water vapor) on a colder surface than the dew point of the air you exhale – for example a window glass when it is colder outside than inside: the water vapor in this air that you exhale condenses, forming micro-droplets on this surface: the moisture! This condensation, again, occurred because the air (out of your lungs) is locally cooled in contact with the glass, to pass below its dew point. Below the dew point, the energy associated with the molecular agitation becomes too low and the water, present in the form of gas (vapor), condenses and forms droplets: it’s dew! All this occurs at constant pressure, but in the case of atmospheric pressure and short observation times, a possible variation in pressure is relatively negligible.Įxample of directly observable effect: if the outside temperature is 12 ☌ and the dew point is at 10 ☌, it is sufficient that I put to air an object which have a temperature lower than 10 ☌ so that it is instantly covered by water droplets, the presence of this object having the effect of a local temperature fall of the air (near the object’s surface). The dew point is the temperature below which the air has no longer enough energy to maintain the water it contains as vapor. About temperature, humidity… and pressure Print run of 1500.Maybe have you ever asked, while using Weather Station, what are the dew and frost points? To better understand what these two indicators are and what they show, here is a small explanation. Single territory for trade global for academic. Print and/or digital / eBook, including for use in on-line academic databases. Image for Magazines and Journals Book use Image for Website or Social Media Magazines and Journals Web display, social media, apps or blogs.
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