Mould Cooling

[processtech]

Hi,
In the set up of cooling for a new mould, do you work out the required water velocity ,depending on lane diameter and based on a Reynolds number of 4000.
Can it be that you could be running a mould and Re may be 10000, where a lower powered pump may be sufficient.
This is something I have been thinking about lately.
How in depth does one need to go with calculations, How does one combine multiple velocities to one output/feed from the chiller.This may not be clear on what I am trying to say
Regards,
processtech

[brentb]

Various sites have tables listing coolant passage diameters, and flow rates (at different temperatures) needed to achieve turbulent flow.

I think Mold Masters and Bill Tolbins site (WJT Associates) are some that list them.

Once you get turbulent flow, the law of diminishing returns apply.

If you can't find the tables, give us the ID of the mold passages and temps you run and we will give you a flow that you should need.

KOM

brent

[processtech]

Thanks for that info brentb, I will look up those tables.
What is the law of diminishing returns?
What I am really looking at is energy efficiency of the cooling process. Why run a larger chiller if we can get away with a smaller one!
If I take each lane individually and take the formula Re = (density x Velocity x diameter)/Kinematic viscosity, using 4000, work back to a required velocity, I know this will not account for friction losses, etc. in the lane & hosing, but should be close enough. Then combining this into one feed from the chiller. We would be looking to do this for all new moulds, at the minute the chiller is connected up, and we record the volumetric flow rate, the inlet/outlet temperatures. I could calculate the water velocity from this, but do you know how to merge multiple velocities? if that makes sense.
Processtech

[Suhas]

Cool Stuff Processtech! that is the way to go. Here is the Cheat Sheet for you. I hope you can read it since I am trying to copy and paste and it is not doing it well. Rewrite this in a table using the '-' as separators. I can also send you this in excel if you want.
Water Temp (deg F) Pipe Dia in inches
1/4 - 3/8 - 1/5 - 3/4
(0.25 in)- (0.375 in)- (0.5 in)- (0.75 in)
60 - 0.35 - 0.53 - 0.71 - 1.06
80 - 0.27 - 0.41- -0.54 -0.81
100 - 0.22 - 0.32 -0.43 -0.65
125 - 0.17 - 0.25 -0.33 -0.50
150 - 0.13 - 0.20 -0.27 - 0.40
175 - 0.11 - 0.17 -0.22 - 0.34
200 - 0.09 - 0.14 -0.19 - 0.28

Other points:
> Try to test the lines with all the lines connected and with water. Flow (water and plastic or any fluid) will take the path of least resistance. If may get misled if you only test the flow with only one line running the water.
> Above a Re = 5000 (with a safety factor) the cooling is not going to get better. So yes, does not matter if it is 5000 or 20000. I also recommend that you record the actual mold temps about an hour in to productions and then again after 4 and 8 hours of continuous running to see if the temps have risen. If they have, then your cooling is not effective.
> The difference between the In and Out lines should not be more than 3 or so deg F. You can have a big mold, with one water line running turbulent flow - not enough, need more line.

Hope this helps.
Regards,
Suhas

[processtech]

Hi,
Thanks for that Suhas, I put those into excel, is that the flow in gpm? that would be great if you could send me that in excel. I have attempted in calculating the Re for the 0.25 diam pipe at 100 °F. I have converted all to si units, I may have went wrong in my calculations but I am getting a Reynolds number of 4.22. at a flow of 0.22 gpm.

I wonder do these tables account for the diameter change from the hoses to the fittings on the tool, then to cooling passage diameter?

Yes when I do fit the flowmeter, to determine the flowrate, I do have all other lanes flowing, from the recent tools we have validated, there has been little increase in temperature, but if I was to reduce the flow, we may see a differ?

Regards,
processtech

[Suhas]

I am sending you a message here with a link. Let me know if you do not get it.
Thanks,
Suhas

[processtech]

Thanks for that

[processtech]

Had a look at those, it has confirmed that my calculations are correct. Is it standard enough to just focus on the lane diameter within the mould and ignore the diameter of the hoses from the stacks.
If I estimate a required flow for each lane and combine this to give a total flow, and add a safety factor can this be used in specifying a new pump for chiller?
Processtech