A steel casting cools to 90% of the original temperature difference in 30min in still air. The same casting is cooled to 90% of the original temperature difference in a moving air stream. the convective heat transfer coefficient in the moving air is 5 times that of still air. the time in minutes to cool the casting in moving air is ................ The same casting is cooled to 90% of the original temperature difference in a moving air stream. The convective heat transfer coefficient in moving air is 5 times that of still air. The time (in minutes) to cool the casting in moving air is