refrigeration hammering

[mahesh]

what is ammonia liquid hammering?

[taz24]

what is ammonia liquid hammering?

I know others on this site will have the exact definition, but I know it as one of two things.

1 It is the noise and vibrations that the liquid makes when it is pumped through a system. The hydrolic effect you could say.
2 It is also the effect of liquid traveling down an empty pipe and the hammering against a stop of somekind, such as a valve or a bend.

Not very technical but thats how I understand it to be.

Cheers taz.

[Andy P]

what is ammonia liquid hammering?

Dear Mahesh,

This is a little more complicated than you might think. Many people are familiar with "water hammer" where a sudden change in velocity can cause pressure shock waves in water pipes, and they assume that liquid hammer is the same. However the hammering in ammonia pipes is caused by the sudden collapse of small gas bubbles in a liquid pipe - usually due to a sharp increase in pressure. As the bubble collapses the liquid in the pipe "hammers" against itself. You might think that this would not be too severe, but the impact produced can be sufficient to fracture pipes or valves and can cause big leaks. The liquid is incompressible so the hammering is transferred to the wall of the pipe.

It can be avoided by using 2-step solenoid valves to give a slight increase in pressure before the main valve opens.

I hope this helps

cheers
Andy P

[taz24]

Dear Mahesh,

This is a little more complicated than you might think.
I hope this helps

cheers
Andy P

I told you someone would be able to give you an exact definition

Cheers taz.

[US Iceman]

One of the first things in understanding this is to see how the different types of transients occur. As Andy P mentioned, you have "vapor propelled" and "condensation induced" (a fancy way of saying similar to cavitation).

Single phase liquid lines are the easiest to deal with as essentially all you have do is slow down the control valve response speed. High velocity liquid flow that is suddenly stopped has a lot of energy that can make pipes jump, or break.

The far more tricky issues relate to pipes that contain two-phase flow, whether intentional or not.

In my mind, the major source of problems revolve around hot gas defrost lines. These lines are usually considered dry, but very seldom is that the case.

Condensation of vapor during the off-cycle will accumulate in the headers and suddenly accelerate when defrost is initiated. Therefore it becomes imperative to provide some means of draining the condensate.

The hammering noise is the energy being transferred from the fluid to the pipe. If the pressure spike is lower than the burst pressure, the pipe jumps around.

If the energy transferred is greater than the burst pressure of the pipe, then the pipe ruptures.

A really good question Mahesh.

PS. Welcome to the RE forums.

Regards,
US Iceman