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A method and apparatus are disclosed for managing thermal energy transfer between a mold, die or cavity and a thermal transfer fluid. The thermal energy being exchanged with the mold, die or cavity is calculated in real time as a function of the temperature differential between inlet and outlet flui

A method and apparatus are disclosed for managing thermal energy transfer between a mold, die or cavity and a thermal transfer fluid. The thermal energy being exchanged with the mold, die or cavity is calculated in real time as a function of the temperature differential between inlet and outlet fluid temperatures, the volumetric rate of fluid delivery, and known characteristics of the fluid. The rate of thermal energy exchange is controlled by varying the fluid delivery rate in accordance with a desired thermal energy exchange profile.

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1. A method of controlling a thermal exchange liquid as it is circulated through an injection mold, die, or barrel (herein referred to as a “process”), the method comprising: establishing an energy set point, the energy set point being a desired rate of thermal energy exchange with the process;circu

1. A method of controlling a thermal exchange liquid as it is circulated through an injection mold, die, or barrel (herein referred to as a “process”), the method comprising: establishing an energy set point, the energy set point being a desired rate of thermal energy exchange with the process;circulating the thermal exchange liquid through the process at a selected flow rate using a positive displacement pump coupled to a motor having a programmable and controllable speed which is independent of variations in line voltage;sensing an actual process inlet temperature and an actual process outlet temperature for the thermal exchange liquid;determining an actual flow rate of the thermal exchange liquid;computing an actual rate of thermal energy exchange between the thermal exchange liquid and the process according to the actual inlet and outlet temperatures and the actual flow rate; andcomputing and making an adjustment to the selected flow rate so as to correct the actual rate of thermal energy exchange to the energy set point. 2. The method of claim 1, wherein determining the actual flow rate of the thermal exchange liquid includes determining a pumping speed of the positive displacement pump. 3. The method of claim 1, wherein correcting the actual rate of thermal energy delivery to the energy set point includes adjusting a time average of the thermal energy exchange rate to be substantially equal to the energy set point. 4. The method of claim 1, wherein correcting the actual rate of thermal energy exchange to the energy set point includes: calculating an average thermal energy exchange rate during a first time interval;andadjusting the flow rate at the beginning of a second time interval so as to cause a net average thermal energy exchange rate over the first time interval and the second time interval to be substantially equal to the energy set point. 5. The method of claim 1, wherein determining an actual thermal energy exchange rate includes: measuring an inlet pressure of the thermal exchange liquid; andcalculating an inlet mass flow rate of the thermal exchange liquid according to the inlet pressure, the fluid flow rate, and known properties of the thermal exchange fluid. 6. The method of claim 1, wherein the energy set point is a constant energy exchange rate. 7. The method of claim 1, wherein the energy set point is a thermal energy exchange rate profile. 8. The method of claim 7, wherein the thermal energy exchange rate profile is calculated so as to maintain a desired temperature versus time profile for the process. 9. The method of claim 1, wherein the thermal exchange liquid is one of water and oil. 10. The method of claim 1, wherein the thermal exchange liquid is continuously delivered to the process inlet. 11. The method of claim 1, wherein the thermal exchange liquid is delivered to the process inlet in pulsed bursts, the flow rate of the thermal exchange liquid being an average flow rate. 12. The method of claim 1, further comprising: displaying the actual thermal energy exchange rate on a display visible to an operator. 13. A system for controlling a rate of thermal energy exchange between a thermal exchange liquid and a process comprising an injection mold, die, or barrel as the thermal exchange liquid is circulated through the process, the system comprising: a process comprising a mold, die, or barrel;a positive displacement pump coupled to a motor having a programmable and controllable speed which is independent of variations in line voltage, the positive displacement pump being in liquid communication with the process and being able to circulate the thermal exchange liquid through the process at a selected flow rate;a flow rate determining mechanism for determining an actual flow rate of the thermal exchange liquid;inlet and outlet temperature sensors which are able to determine an actual process inlet temperature and an actual process outlet temperature respectively for the thermal exchange liquid; andan energy exchange controller which computes an actual rate of thermal energy exchange between the thermal exchange fluid and the process according to the actual process inlet and outlet temperatures and the actual flow rate of the thermal exchange liquid, establishes an energy set point, and computes and makes an adjustment to the selected flow rate so as to correct the actual rate of thermal energy exchange to the energy set point, the energy set point being a desired rate of thermal energy exchange. 14. A method of controlling a thermal exchange liquid as it is circulated through an injection mold, die, or barrel (herein referred to as a “process”) comprising: establishing an energy set point, the energy set point being a desired rate of thermal energy exchange with the process;circulating the thermal exchange liquid through the process at a selected flow rate using a positive displacement pump coupled to a motor having a programmable and controllable speed which is independent of variations in line voltage;determining a process inlet temperature set point for the thermal exchange liquid;controlling an actual process inlet temperature of the thermal exchange liquid so as to minimize its deviation from the process inlet temperature set point;sensing an actual process inlet temperature and an actual process outlet temperature for the thermal exchange liquid;determining an actual flow rate of the thermal exchange fluid;computing an actual rate of thermal energy exchange between the thermal exchange fluid and the process according to the actual inlet and outlet temperatures and the actual flow rate; andcomputing and making an adjustment to at least one of the selected flow rate and the process inlet temperature set point so as to correct the actual rate of thermal energy delivery to the energy set point.