I was just asked this question…

To determine the correct size chiller you must first calculate the cooling time, total amount of heat to be removed, the cooling power, the cooling power per line, and the required volumetric flow rate.

A basic way to calculate the cooling time for this purpose is to use a common rule: 2 X [wall thickness (mm)]^2

To calculate the total amount of heat to be removed use the equation:

Q= (combined mass of the parts and feed system) x Cp x (Tmelt -Teject)

Where: Cp is the specific heat of your plastic, Tmelt is your melt temperature, and Teject is the temperature of your parts at ejection. This answer should be in Joules. 

After calculating the amount of heat to be removed divide it by your cooling time to get an answer in the units of J/s or Watts. This is the power you will need to cool your part. 

The cooling power per line can be calculated by dividing the power you need to cool your part by the number of cooling lines in the part. Example: You had a 1000W estimate for the required power to cool your part and you have 4 cooling lines. The result is 250 W per cooling line.

To calculate the volumetric flow rate you will need to cool your parts you must:

Divide the cooling power per line by: [allowable increase in coolant temp x density of the coolant x specific heat of the coolant]

This calculation should result in a number with the units of m^3/s or ft^3/s. 

You can now use the estimated coolant flow rate to determine which machine will meet your needs. 

-Andy