posted April 20, 2006 08:47 PM               

Two influneces of heat transfer would be;

1) The bigger the difference between the temperature of the water and the metal the greater the heat exchange.

2) Turbulance increaes heat exchange.

I would like to hear more about the "Pulling Water" trick. I'll assume it depends on the position of the pump in the circuit. I would think that having the pump on the outlet would allow "smoother water" on the inlet. Heat exchange would then be slightly reduced on the inlet side of the mold.

I think you can buy cooling water channel inserts which increase turbulance. This would probably wipe out any differences.

posted April 21, 2006 03:45 PM            

Pulling water through a mold is commonplace on what is called Negative Flow water temperature controllers. Most times, they are used when the tool has a leak where the water drip would interfere with the molded part. In this case, some of the new school boys were trying to convince me that pulling the water through the tool from what would normally be the discharge end would result in a different cooling pattern. Particularly in tools where bubblers or other complicated water turbulence devices were installed.

I just do not see it happening. If I push it through the inlet at 8 gallons per minute and 62 degrees or pull it from the discharge end at 8 gallons per minute and 62 degrees, the results should be the same.

Then I am no fluid dynamics genius for sure, so I thought I would ask.

posted April 22, 2006 09:45 AM               

Pulling water must use some type of air chanmber and vacuum to get the effect you are speaking of. To eliminate leaks the air pressure around the tool must be greater than the air pressure in the plumbing. I guess this is like syphoning. I would think the maximum water flow would be reduced in this case.

I think a lot depends on the amount of heat transfered to the water. If the temperautre rise in the water is large, I think the mold performance would change because you would pull different amounts of heat from different parts of the mold. If the rise is small, then the difference would be minimal.