Help With Injection Moulding Cooling

[icecube51]

maybe consider "reverse osmosis" water?
and as i understand,is when the chilled water entering the mould machine,it become so hot that it would return instead of going forward,so you have to install or very heavy circulation pump or heavy duty pression pumps?

Ice

[Peter_1]

I should do what the client is asking for, even it's an energy wasting system or a short sight vision.
Install more chillers, make a closed loop system of it and install some HP pumps (for example Grundfoss CR pumps) working parallel so that you have some redundancy or one VFD controlled and 2 full speeds. Hitachi has a VFD which can control this without additional electronics (up to 4 compressors or pumps).

Don't argue with your client any longer them, make that you earn money now.
Install an isolated tank of +/- 500 l with a centrifugal pump and let the chiller cool this reservoir.
Then a second loop with a 3 way bypass with the HP pumps to the molds.
There is circulating a schematic on this forum, I think from a Norwegian or Danish poster.

[Peter_1]

Perhaps this can help
http://www.mcquayservice.com/mcquayb...G_31-003-1.pdf -

[Gary]

Gary you have not been on site! I have, the flow is next to nothing through the heat exchanger.

The tubes are probably clear and the scale has built up around the ends before water has a chance to enter the tubes. I have had this problem many times both on water cooled condensers and chilled water evaporators. Hence the low leaving water temperature and poor flow. You are confusing the issue!

Some of us do actually know what we are doing!

Don't take it personally. There are other people watching and learning. They need to know which symptoms indicate flow problems (delta-T) as well as which symptoms indicate scale build-up/heat transfer problems (approach).

[Peter_1]

Was thinking th same Gary.

[Gary]

Let's see if I am visualizing this system correctly:

Warm return water flows from the processes to the return ring/loop, then from the opposite side of that return ring/loop to the warm tank. From the warm tank, the water flows through the chiller to be cooled, then through the cold tank to the supply ring/loop. From the opposite side of that supply ring/loop, the cold water flows to the processes.

The pump is between the warm tank and the chiller.

There is a spring loaded pressure relief bypass from the supply ring/loop to the return ring/loop.

Does that sound about right?

[icecube51]

and install some HP pumps (for example Grundfoss CR pumps) working parallel so that you have some redundancy or one VFD controlled and 2 full speeds. Hitachi has a VFD which can control this without additional electronics (up to 4 compressors or pumps).

make sure they are strong enough to overcome the going pressure rate.

Ice

[icecube51]

Let's see if I am visualizing this system correctly:

Warm return water flows from the processes to the return ring/loop, then from that return ring/loop to the warm tank. From the warm tank, the water flows through the chiller to be cooled, then through the cold tank to the supply ring/loop. From that supply ring/loop, the cold water flows to the processes.

The pump is between the warm tank and the chiller.

There is a spring loaded pressure relief bypass from the cold ring/loop to the hot ring/loop.

Does that sound about right?

is there not going to be a chilled water tank needed?

Ice

[Gary]

is there not going to be a chilled water tank needed?

Ice

I'm thinking that's the "cold tank".

On the other hand I may be entirely wrong in my understanding of how the system is piped?

[icecube51]

sorry Gary ;-{

[TRASH101]

From your description of the system it should be possible to close the system but is the existing ring (which I believe is acting as supply buffer tank/ low pressure header) big enough to take the new load and is it likely that all the injection circuits will be running at once.

The warm tank could pose more of a problem because if you upgrade the chillers then you`ll definately have to up the flow rate which will mean you might end up drawing off from the cold tank to maintain the warm tank under low load conditions.

I can see why it is designed as an open system and closing it without a complete redesign may prove to be..............interesting

It would be really helpful if you could draw up a schematic.

[TRASH101]

Its making a little more sense now

I think if you look at just the chillers, cold tank and warm tank as being the primary circuit and close it as you would any normal chilled water circuit the the take off from the cold water tank must be big enough to compensate for no warm return from the process (might need a one way valve in it) work out if you need an expansion vessel on the warm tank and or invertor drive your pump feeding the chiller from the discharge to ensure your vol remains constant, depending on system characteristics the cold to warm take off might want to have a modulating valve on driven by cold tank pressure.

Hope that might put you on the right path. Its a bit difficult to say without seeing the system and shed loads of calcs.

Don`t forget that if youre going for vt on the process take offs then you need the temp diffs for the process water to size and select your valve arrangement.

[Iceman1956]

Hi Refrigerologist Only just picked up on your post, and have quickly scanned what has been said.
There are two points that do not seem to have been asked or questioned. Your existing chiller are likely to have shell and tube evaporators ? the new chillers you are looking at will have Plate type heatexchagers ?
The second item is are you keeping a primary loop through chillers and back to the buffer tank ?.
Providing the primary and secondary loop feed directly from the buffer tank you will not have any problems with a sealed system, as any imbalance is cancelled out within the buffertank. We have completed many such modifications over my 35 years in process cooling, with no problems.

Ensure New Pumps match design flow for new chillers as Plate type HeatX have greater PD across them from Shell and tube.
Flow to process should be from base of buffer tank, as should the return from chiller. Flow to chiller should be from top of buffer tank as should the return from process.

Hope this helps.

[Refrigerologist]

Thanks for all the ideas and assistance.

I have since spoken with the guy who originally designed the system! He has told me that in order to ensure that the water temperature at each mould head remains constant, the chilled water loops are fed via pressure pumps and the flow pipe is a complete loop. The return water path is via each mould head unless the pressure increases to a point where the spring loaded pressure relief valve opens and allows water to flow directly to the return circuit.

He has advised us not close the system due to balancing problems.

We are going replace the existing plastic water tanks with GRP insulated tanks and install process chillers with shell & tube heat exchangers. We will be recommending water treatment of the ingoing make up water to help prevent scaling in the tubes.

[Refrigerologist]

Let's see if I am visualizing this system correctly:

Warm return water flows from the processes to the return ring/loop, then from the opposite side of that return ring/loop to the warm tank. From the warm tank, the water flows through the chiller to be cooled, then through the cold tank to the supply ring/loop. From the opposite side of that supply ring/loop, the cold water flows to the processes.

The pump is between the warm tank and the chiller.

There is a spring loaded pressure relief bypass from the supply ring/loop to the return ring/loop.

Does that sound about right?

Sorry for not replying earlier, but I have been on holiday in Ireland, and the Guiness has been good!

Yes, I think your despcription is about right. It may be a bit academic now as we have decided to keep with an open system but treat the make up water.

[Refrigerologist]

I should do what the client is asking for, even it's an energy wasting system or a short sight vision.
Install more chillers, make a closed loop system of it and install some HP pumps (for example Grundfoss CR pumps) working parallel so that you have some redundancy or one VFD controlled and 2 full speeds. Hitachi has a VFD which can control this without additional electronics (up to 4 compressors or pumps).

Don't argue with your client any longer them, make that you earn money now.
Install an isolated tank of +/- 500 l with a centrifugal pump and let the chiller cool this reservoir.
Then a second loop with a 3 way bypass with the HP pumps to the molds.
There is circulating a schematic on this forum, I think from a Norwegian or Danish poster.

I haven't been arguing with my client. What makes you think I have been? They asked if we could close the system. We said we could, every one I have spoken to says we can, now the client is no longer sure and does not understand fluid dynamics very well. So we have decided to leave it as an open system and treat the water instead. A far easier install, but actually more expensive as we must now use shell and tube heat exchangers in place of plate type.

Thanks for all the ideas and advice though!

[Electrocoolman]

Hi Refrigerologist and guys,

Have just picked up on this thread and one thought has occurred to me....with reference to the supply loop.....

Although the supply ring is pressurised by the pressurisation pumps (which should be VSD controlled in this day and age) the water in the supply loop will surely have a temperature variation around it, as there is no mention of a circulator pump, and as you mentioned machines being turned off....will not the flow and thus temperature vary according to demand? Maybe this is not percieved as a problem?....perhaps the loop is only small?

You mention project costs are tight and funds limited....are there any goverment tax incentives on Guernsey for energy saving projects (as on the mainland)..?.(ie Enhanced capital Allowance)...just another thought!

[US Iceman]

He has advised us not close the system due to balancing problems.

How will the system be closed if it has storage tanks in it? The tanks will most likely be open to atmosphere, but the piping would essentially be a closed loop (except hydraulically).

[Magoo]

Your initial major problem is the water quality, as in high calcium content, (hard water). I would definitly recommend converting to a closed loop water system, with high circuit flow rates and a high water chiller by-pass rate. In effect the chiller is trimming the loop temperature, and the low delta tee system water is doing the work. You must add to system a pressure compensation vessel on the primary pump circuit to handle the changes in system and elliminate pipe hammer, the heat exchangers at the moulding machines should have rapid response 3 way by-pass vavs. then you maintain a constant loop volume flow.
First thing to address in the obvious scaling problem in existing system. Ridlime is an excellent product, and eco friendly, add lots of flushing. Next is the problem with closed circuit water cooling systems is the water quality and PH control. Basically you have a perfect low voltage battery, as in dissimilar metals and temp variations and an electrylite (water), so PH and water conditions are important. Cathodic corrossion is un-cool and can send companies broke, because all of a sudden everythings is leaking water and the refrig system is full of water, result no production and huge repair and recovery costs.
Down the track a bit you should recommend a dry cooler with water additions to elleviate the chiller loads, depending on local ambient conditions and wet buld conditions.
magoo

[brunstar]

you will be best to use one buffer tank so that you are constantly mixing the water down through the chiller, otherwise it will be too high on the return to the chiller.
So basically buffer tank flow and return to the moulds then flow and return to the chiller.

[Refrigerologist]

Hi guys, an update is long overdue!

Thanks for the comments and advice.

The client has now gone out for a requote, and I am not hopeful of getting the job, but that could now be a blessing!

Anyway the contractor who has now quoted has chosen a plate heat exchanger system on the same open loop system, so I am expecting them to have some serious problems as the water is not treated and the old shell and tubes are fouled with scale deposits!

[US Iceman]

You may be thankful you don't get the job. Loosing a job is bad enough. Getting a bad job can be even worse.