FLOW PASSAGE WASHING METHOD

PROBLEM TO BE SOLVED: To propose a flow passage washing method for effectively removing a foreign substance adhered on a wall face of a flow passage even in the flow passage having a complicated structure.SOLUTION: The flow passage washing method includes steps of: injecting a washing material 4 in the liquid state into a flow passage 1 (injection step); then, cooling down the washing material 4 injected into the flow passage 1 to a temperature below or equal to a freezing point (cooling step) and the washing material 4 in the flow passage 1 becomes solid-liquid two-phase fluid containing solid component 4a by the cooling; and reciprocating and flowing the solid-liquid two-phase fluid of the washing material 4 in the flow passage 1 and scrubbing and washing a wall face 3 of the flow passage 1 (washing step).