Flow channel structure, and mixing method, extraction method, and reaction method for fluids

A flow channel structure for causing a first fluid and a second fluid to flow so as to mix together, comprising a substrate in which a flow channel for causing the first fluid and the second fluid to flow is formed, wherein:

• the flow channel includes a main channel formed on a top surface of said substrate and that permits the first fluid to flow along the top surface of said substrate, a plurality of sub channels formed on a back surface of said substrate facing opposite the top surface of said substrate and that permit the second fluid to flow along the back surface of said substrate, and a plurality of merging portions that penetrate said substrate in the thickness direction of said substrate from the top surface side to the back surface side, and permit merger of the second fluid flowing through the plurality of sub channels with the first fluid flowing through the main channel;
• each of the sub channels has an inlet for introducing the second fluid into the sub channel and an opposite end provided opposite the inlet, wherein an overlap portion of each of the sub channels between the inlet and the opposite end overlaps the main channel and extends in parallel with the main channel when viewed from a direction perpendicular to the top surface of said substrate, and wherein the merging portion coincides with the overlap portion;
• and
• the opposite end of each of the sub channels coincides with the merging portion and includes a wall surface opposing the flow of the second fluid flowing from the first sub channel into the merging portion, such that the second fluid is caused by the wall surface to flow in the thickness direction of said substrate toward the top surface of the substrate.