The cooling medium (in this case, water) in plastic injection molding flows through the hose to cool the mold. There are two types of cooling medium flows: turbulent and laminar. Laminar flow is a state in which the water slowly forms a layer in the hose. The flow is fast at the center of the hose, and the flow rate of the cooling water decreases as the distance from the center increases. On the other hand, turbulent water flows in the hose fast with swirling, so the flow velocity is uniform over most cross sections of the hose.
In either case of laminar flow or turbulent flow, there is a place where water stagnates (boundary film) very close to the pipe wall (mold surface). Since the film tends to be difficult to conduct heat, it is said that the thinner the film, the better the heat transfer. On the other hand, the turbulent flow thins the film that hinders heat transfer, so the heat of the medium can be transferred quickly. Therefore, turbulent flow that can smoothly transfer the heat of the medium is preferable as the mold cooling medium.