PURPOSE: To reduce a temperature of a protective air flow and prevent a dew formation at an outer surface of a rear wall of a thermal insulating wall by a method wherein the rear surface plate forming a narrow passage acting as a part of the second passage may act as a spacer element for preventing a contact between the rear wall of the insulating wall and a cooling device and at the same time the rear surface plate itself is cooled by the cooling device and also as a heat exchanging plate for cooling the protective air flow passing in the narrow passage.
CONSTITUTION: A rear surface plate 40 forming a narrow passage 70 which is a part of the second passage 13 may act as a spacer element for preventing a contact between a rear wall 3A of the insulating wall 3 and a cooling device 9 and at the same time the rear surface plate 40 itself may act as the heat exchanging plate for cooling the protective air flow passing through the narrow passage 70 while being cooled by the cooling device 9. Both side passages 71 formed in spaced-apart from the narrow passage 70 may act to accommodate for the amount of air of the protective air flow being laced and further it may act as the heat exchanging plate for use in cooling the protective air flow passing through both side passages 71. The protective air flow passing through each of both side passages 71 is merged with at the rear part region if the second passage 13 so as to make a uniform air volume and air speed of the protective air stream in the second passage 13.
IKEDA HIDEYA
NODA YASUO
