Honeycomb segment

A honeycomb segment comprising outer walls and porous partition walls disposed inside the outer walls and separating and forming a plurality of cells functioning as fluid passages,

• the honeycomb segment having a structure where first cells each open in one end portion on one side and plugged in the other end portion on the other side and second cells each plugged in one end portion on one side and open in the other end portion on the other side are alternately disposed in such a manner that the fluid flowing in the first cells from the one end portion is permeated through the partition walls to flow out inside the second cells as a permeated fluid and that the permeated fluid can be discharged from the other end portion on the other side where the second cells are open;
• wherein a cross-sectional area of the first cells in a cross section cut along a plane perpendicular to a longitudinal direction of the cells is larger than that of the second cells, and the first cells and the second cells are alternately disposed in a first direction and in a second direction perpendicular to the first direction in the cross section,
• a cell structure formed by the first cells and the second cells in an outermost peripheral portion is formed different from that in a central portion, and the second cells in the outermost peripheral portion are formed larger than the second cells in the central portion, and
• the outer walls are linearly formed so as to have a uniform thickness except for corner portions.