Heat transfer principles
Two substances must have different temperatures to transfer heat. Heat always flows from the warmer substance to the colder. The more significant difference, the faster it equalises.
Almost all heat transfer in Dairies take place in direct or indirect heating, e.g. a Pasteuriser unit can have a small soldered PHE where steam goes direct in the water, the water gets hot and used indirectly in The pasteuriser team to heat the milk to desired pasteurising temperature.
The same thing happens in milk cooler e.g. in the milk reception, the only difference is in the media — Ice water, not steam.