PURPOSE: To promote heat exchanging efficiency between a fluid inside a heat exchanger tube of a multi-tubular heat exchanger and a fluid flowing outside said heat exchanger tube to restrain pressure drop from becoming larger, by inserting a spiral plate in an axial direction of tube into a gap existing outside a heat exchanger tube within an outer shell.

CONSTITUTION: The heat exchanger comprises tube plates 3 for securing heat exchanger tubes 2 thereto and a plurality of spiral plates 4 inserted in an axial direction of said heat exchanger tubes 2 into the space existing between the outside of a plurality of heat exchanger tubes 2 and the inside surface of a cylindrical shell 1. By the presence of the spiral plates 4 being inserted, rotational motion of fluid occurs, causing agitation therein, so that the temperature distribution of the fluid approaches to uniformized one, resulting in an abrupt change in the temperature of the fluid near the heat exchanger tubes 2, leading to a very large temperature gradient, heat flow per unit surface of the heat exchanger tubes 2 becoming large and surface resistance thereof becoming low. Furthermore, since reversion in the flow direction does not occur, increment in pressure loss can be limited to a small amount.