Vibration in refrigerant piping

Here is another topic that will surely put you to sleep. Or, maybe it will keep you awake during the night.:D

I have long been fascinated by the impact of vibration and noise in refrigerant piping. As you will see in the files below the manufacturers are aware of this and are offering some general guidance on this particular subject.

In general terms, the problem is associated with the acoustic velocity (speed of sound) of the refrigerant for the specific operating condition. The other important aspect is the frequency of the gas pulsations from the compressor.

Screw compressors should be treated differently than reciprocating compressors since the gas pulsations are different for both types and are also dependent on rotating speed.

By determining the above you can then calculate the "piping lengths" to minimize the impact of vibration and the resulting noise.

The information below is not a set of documents that provides all of the information, but they are sufficient to show an interesting concept to consider.

http://www.carlylecompressor.com/Fil...f?SMSESSION=NO
(740 kb)

http://www.bitzer.de/_doc/s/st-630-1.pdf
(323 kb)

Recently we have adopted a new refrigerant piping, at least on the discharge. It is a flexible pipe, imported in Italy by WIGAM, and helps reducing pulsation and noise very much.

http://www.wigam.com/web/prodotti.as...odice=infinity

The corrugated tubing used is probably providing sufficient resistance to disturb the pulsations to reduce the vibrations and noise. This would have a similar effect as using an orifice plate to restrict the pulsations.

This tubing looks very similar to what I remember from the past. Copeland used to have a flexible tubing that was used for the Sentronic oil safety switch. This was much better than the old style capillary tubes with flare nuts.

We order these at a company +/- 1 km from our company
http://www.sisahp.be/products/specifiek.php

Used those some times, but they're sometimes not flexible enough to bend them some times/day in small diameters like in a sliding counter.
We get the couplings and the hose separately, we install them without crimping and thereafter, we go back to crimp them.
We also use the system of Burgaflex (The Netherlands) http://www.burgaflex.com/burgaflex.html a litlle bit more expensive but more flexible.

Personally, I find mufflers not that usefull but an oil separator solved already twice a pulsation problem heard especially in the condensor coil where we selected a low noise.
But all the noise was coming form the pulsations in the discharge line (discharge in 1 case selected at 7 m/s to avoid pulsations)

Sometimes it is not just the speed of the refrigerant moving in the tubing. The speed of sound in the refrigerant depends on the quality (liquid or vapor).

The frequency of the gas pulsations and the speed of sound in the refrigerant can also cause vibrations.

Vibration can be generated by mechanical forces or by acoustics also. The oil separator probably reduced the vibration because of the larger volume of the oil separator relative to the discharge line.