The Rapid heating and cooling circuit Reynolds number result is calculated from the diameter of the cooling channels, the flow rate and the viscosity of the fluid in the channels, and shows the turbulence of the fluid flow in the heating and cooling circuit for both dual domain and 3D analyses. This result is generated from a rapid mold heating and cooling simulation using a Transient Cool analysis.
Effective heat extraction requires flow to be turbulent. The onset of turbulence in water is between 2300-4000. A Reynolds number of 4000 is considered fully turbulent, but it is good practice to use a Reynolds number of 10,000 to represent turbulent flow when running an analysis.
Using this result
The Rapid heating and cooling circuit Reynolds number result is best used in conjunction with the data in the analysis log. The analysis log indicates when the program transitions to the next step and thereby helps you understand what is happening when looking at the Reynolds number result.
Turbulent flow is preferred for heat transfer applications. However, the higher the Reynolds number in the circuit, the more energy is required to pump it through the circuit. Hence the ideal Reynolds number for heat transfer is 10,000. The pumping losses associated with Reynolds higher than 10,000 outweigh the heat transfer gains that can be achieved with higher Reynolds numbers.
Increasing the length or number of the channels improves the area available for heat transfer. This results in a higher pressure drop in the channel. If the diameter of the cooling channel is increased, a higher flow rate is required to achieve turbulence. Thus, a balance has to be struck between the diameter and length of the cooling channels, and the pressure and volume characteristics of the cooling pump.
When looking at the Rapid heating and cooling circuit flow rate result, there are three times when there is measurable Reynolds number; during the primary air purge, when coolant is flowing through the lines, and during the secondary air purge. During the two air purges, the Reynolds number is extremely high, due to the high air pressures required for purging the circuits. When coolant is flowing, it should drop to 10,000 or so. There is no reading when the circuit is heated.
to animate the result, and see how the circuit Reynold number changes over the duration of the cycle. Things to look for
When viewing the result, watch for the following.
- When coolant is flowing, the Reynolds number is sufficiently high to maintain turbulent flow.
- There are no sections of the circuit where the Reynolds number becomes sufficiently high to stress the cooling pump.
- There are two occasions when the Reynolds number rises to an extreme value, representing the two air purges. If these Reynolds numbers are too high, check the pressure boundary conditions used for the air purges on the circuit.
- The timing of these changes are as you expect.