View Full Version : vessel size calculation

hardy surya
14-03-2007, 09:17 PM
hello guys,

i need some information about vessel calculation like accumulator, intercooler and receiver (high pressure). i have read ashrae refrigeration handbook but i get no much information about that. pls could you give me the advise information? thanks

US Iceman
15-03-2007, 02:45 AM
Well, you gave a list of three vessels each of which is sized using slightly different methods.

A high-pressure receiver is simply sized on volume. How much storage volume do you need to store at anytime? Determine the volume you want to store and add 20%-30%. The new volume is what you use to select the reciever volume.

The other two vessels are liquid separators. They separate liquid form a vapor stream. In this case you need to determine what the maximum separating velocity is for a given operating pressure. This data is included in the ASHRAE refrigeration manual.

If you take the total connected compressor volume flow (CFM or cubic meters/sec) for the specific cooling load, then divide the volume flow of the compressors by the maximum separating velocity. This gives you the cross sectional area of the separator.

Now you have to decide how much liquid you want the vessel to hold (this called surge volume). This volume divided by the vessel area tells you how much height is needed in that vessel diameter. Now add the separation distance to this height (from the surge volume).

After you make some allowances you have the overall height of the vessel. All of this is described in the refrigeration manual. What I described above is a very breif example.

15-10-2008, 01:54 AM
Us ICeman:

is there any equation for computing surge volumen????

if the compressor in my system is oversized i always have to take its CFM for computing the sectional area of my vessel.

for example the compressor has twice of the capacity necesary.

US Iceman
15-10-2008, 02:31 AM
If you use the compressor CFM (swept volume) that is the safest to use. Because, the actual CFM of vapor will be less due to the volumetric efficiency of the compressor.

The difficult part is deciding which separation velocity to use for the operating temperature and refrigerant. Most of the ASHRAE info is for steady state operation. However, I believe they also state you can use a correction factor of 0.75 to decrease the maximum separation velocity to account for normal operation (which is not steady state).

For the surge volume you should use the largest volume of liquid that could return to the vessel. This typically occurs during defrost, therefore you would need to know the quantity of coils in defrost at a single point in time. Since most coils are bottom fed or flooded my suggestion is to use the total coil volume, because... when the coils need to be defrosted they will contain the highest percentage of liquid (it might be almost 100%).

Hope that helps Luis.

US Iceman
15-10-2008, 02:51 PM
I want to add some additional information to my last post.

In general terms, the cross-sectional area of the vessel should be larger than: the total compressor CFM / the maximum separation velocity (feet/minute).

This will provide some additional safety for operation.

However, it is also important to remember this point; the surge volume required to be stored in the vessel should also be checked to ensure the vessel will have sufficient separation capacity when the vessel has reached the maximum surge volume also.

And, if a horizontal vessel is used, NEVER allow the vessel to fill beyond 1/2 of it's internal diameter. As the liquid level rises, the velocity quickly increases if the CFM is constant.

29-10-2008, 03:20 PM
Hello, I am a new member.
I have a question could anybody help me ? The system consists of 3 x piston compressor with cooling capacity 170kW each (-43/+35oC); 3 contact freezers supplied by NH3 liquid pumps; how to calculate the dimension of HP liquid receiver, Intercooler and Liquid separator (all horizontal). That's kindly appreciate