Why is it that the higher the boiler pressure, the more difficult it is to separate steam from water, and the easier it is for steam to contain water?
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This post was last edited by zgj2405 on 2011-6-26 at 18:43. Why is it that the higher the boiler pressure, the more difficult it is to separate steam from water, and why does steam tend to contain more water?
Reasons for water in steam from high-pressure boilers. As the pressure in the boiler increases, the boiling point of the boiler water rises; simultaneously, the surface tension of the boiler water decreases. This makes it easier for small droplets to form as the water evaporates, and these droplets can be carried away. At the same time, as pressure increases, the density difference between steam and water decreases, making it difficult to separate them, and steam tends to carry water droplets. The higher the pressure, the greater the density of the steam, and the kinetic energy of the steam flow increases, making it easier for water to be carried along. So when the steam flow velocity is constant, the higher the pressure, the easier it is for the steam to carry water.
As the operating pressure of the boiler increases, not only does the saturation temperature of the boiler water rise, but the molecular thermal motion of the water also intensifies and the forces between molecules weaken. Additionally, due to the increased density of steam, the magnesium oxide composite air ducts cause the steam in contact with the water surface to exert a greater attraction on the water molecules, resulting in a decrease in the surface tension of the boiler water. The result is an increase in the number of small water droplets in the steam space of the drum. As the operating pressure of the boiler increases, the density of steam rises, while the density of the boiler water decreases due to the rise in saturation temperature. As the density difference between steam and boiler water decreases, the ability of steam to carry water droplets increases, while the gravitational separation effect that relies on this density difference weakens. For these two reasons, the higher the operating pressure of the boiler, the more difficult it becomes to separate steam from the boiler water, and the easier it is for the steam to contain water.
This post was last edited by zgj2405 on 2011-6-28 20:42. Therefore, boilers under high pressure usually come equipped with superheaters in order to increase the dryness of the steam...:lol
Firstly, there is steam separation; it must be saturated steam. When the pressure of saturated steam increases, its temperature necessarily rises as well； Secondly, the density of water decreases as temperature rises, while the density of steam increases as temperature rises ； Finally, as the densities of the two approaches each other, separation becomes increasingly difficult, and it is easier for the steam to carry water.
The last edit to this post was made by zgj2405 on 2011-6-28 at 20:42. Reply to 6#: Step stop. In power station boilers, the superheater serves to heat saturated steam to superheated steam at a certain temperature, thereby improving the efficiency of the power station. In industrial boilers, superheaters can also be installed as per the user’s requirements, but the steam temperature generally does not exceed 400°C.