In the casting processes of parts, the temperature-flow of the die is a main parameter of the casting process.
The simplest way is to check the temperature of the heat transfer medium.
But this do not take a guarantee to have also the right quantity of heat transfer.
Only with flow meters in the return conduction there is a safety to see temperature problems before they will cause to differently parts quality.
The flow meters must be able to be connected in high temperature environment and also for temperature transfer medium like heating oil.