An ice slurry is produced at the triple point of water in a freezer vessel having vertical freezer tubes on which feed water falls as an outside film and coolant tubes on which cold coolant falls as an outside film, with the liquid coolant and liquid feed distributed to the tubes by a pan over the tubes. The resulting warmer coolant flows to a collecting pan at the vessel bottom and then through an outlet for withdrawing the coolant from the vessel, while the ice slurry is withdrawn through an outlet at the vessel bottom.