Cooling circuit parameters

The flow rate of the coolant is an important aspect to consider when preparing a Cool analysis. If the flow rate of the coolant is not known, you can use the Reynolds number to define the flow rate.

This topic provides you with some issues to consider when deciding on a coolant control method.

Coolant control issues

The mold designer should know what the available coolant flow rate is before designing the mold. The mold design can be modified in the early stages to take account of the availability of coolant at the plant.

In the cooling circuits, the cooling medium must absorb the heat by convection. This means that the flow must be turbulent. The power required to pump coolant around the system is proportional to the cube of the flow rate. This means that doubling the water flow requires eight times the pumping power. The use of excessively high flow rates is a costly waste of energy.

Coolant control options

The following options are available:

Specified pressure.

A total pressure for the cooling circuit. The Cool analysis determines the corresponding flow rate using the physical properties of the coolant and the coolant temperature.

Specified flow rate.

The flow rate of coolant that can be set on the molding machine.

Specified Reynolds number.

When you do not know the flow rate or the total pressure through the circuit, and want the Cool analysis to determine a suitable flow rate, based on a minimum Reynolds number to be achieved in the cooling circuit. The recommended setting is 10,000.

Note: When using parallel cooling circuits, you may not be able to achieve the required Reynolds number in all branches.

Total Flow-rate (All Circuits).

When the individual circuit pressure or flow rates are not known, and you want to specify the total flow rate through the cooling system. The total flow rate is divided among the circuits according to their pressure drops. Circuits with a low pressure drop receive more of the flow rate, and circuits with a higher pressure drop receive less.

Note: If you choose this option, ensure you specify the same total flow rate value for all coolant inlets in the model.

Reynolds number

Once turbulent flow has been achieved, an increase in flow rate makes little difference to the rate of heat extraction. Therefore, set the flow rate only to achieve the ideal Reynolds Number with minimum variations. The Reynolds Number is a ratio that defines the rate of fluid flow and is assigned to cooling circuits when the flow rate is not known.

When running an analysis, we recommend using a Reynolds number of 10,000, however, to represent turbulent flow, then check this result to ensure minimum variation. Don't aim for a Reynolds number greater than 10,000.

If you have parallel cooling channel circuits, it may be difficult to achieve minimum variation of the Reynolds number throughout all the branches. If this is the case, consider changing the circuit layout. If there is a large variation in cooling channel diameter, there may be excessive variations in the Reynolds number. If this occurs, either adjust the cooling channel diameter, or reduce the minimum Reynolds number (ensure the Reynolds number is always greater than 4000, which is considered fully turbulent).

Effect of parallel cooling circuits on flow rate

The following problems can arise when using parallel cooling channels:

• The flow rate in each branch is reduced as extra branches are added. This reduces cooling efficiency, unless the total flow rate is increased.
• The flow rate can vary from one branch to another, causing non-uniform cooling. To minimize this, you can adjust the bore of the varying branches to balance the coolant flow.
• If one branch gets partially blocked by debris, the flow rate in that branch can be dramatically reduced while increasing slightly in the other branches. This also causes non-uniform cooling.