Water hammer occurrence process
Water hammer caused by high condensate speed
Radiant and convective heat losses provoke steam condensation in steam lines. At the beginning of the steam pipeline, condensate appears in the form of fog, then the particles increase to the size of drops, some of them, touching the walls of the pipeline, flow down to its lower part, while a partial filling of the steam pipeline with condensate is already formed.
Since the liquid is more viscous than steam, friction against the walls of the pipeline slows down the flow of condensate, and the high velocity of steam on its surface forms a wave.
At first, it appears in the form of ripples, and then increases to the formation of ridges.
Perceiving a high steam flow rate, the condensate flow acquires significant kinetic energy and has a destructive effect on obstacles in the form of a change in the profile of the pipeline, fittings or equipment.
Elimination of this type of water hammer comes down to ensuring correct drainage of steam pipelines and drying of steam by installing cyclone separators.
Water hammer due to instant condensation of steam
The specific volume of steam is 1000 times the volume of condensate. Steam, falling into a cold liquid, condenses and the space it occupies momentarily becomes a vacuum. A vacuum bubble formed in the condensate leads to a sharp collapse and the appearance of a shock wave with all the ensuing consequences
This type of water hammer is more common, since dealing with it is not an easy task.
Dependence of the condensate temperature on the occurrence of water hammer
It is logical to assume that with an increase in the temperature difference between steam and condensate, the force of water hammer should also increase. However, in the course of research, an interesting pattern was revealed: for example, steam with a temperature of 100 ° C causes the greatest water shocks in condensate with a temperature of 70-80 ° C, and insignificant ones in condensate with a temperature below 60 ° C.
In the above graph, three characteristic zones can be distinguished (from left to right):
- Steam, coming into contact with the coldest condensate, quickly condenses in small portions and does not have time to form large "steam pockets", therefore, water hammer is formed insignificantly.
- In the middle zone, due to the relatively small temperature difference of 20-30 ° C, steam does not condense immediately. This delay contributes to the formation of "steam pockets" of significant size, and as a result - a powerful water hammer.
- On the right side of the graph, steam comes into contact with condensate of the same temperature. In this case, it condenses gradually and no water hammer occurs. This can be seen on the example of a condensate drain , after which the condensate interacts with the flash steam, and there is no water hammer.