<p>The extremal intensification of turbulent heat exchange in a narrow plane-parallel channel with an inclined trench of optimal length, placed on its heated wall, as a result of the formation of a tornado-like vortex structure and a transverse lumped pressure drop in the leading part of the trench was investigated. Correlation between the increase in the indicated drop to a large value and the increases in the length of the trench to 0.1 in the case where the trench shape is close to the shape of a spherical dimple and to 0.34 in the case of a long trench with a depth of 0.39, inclined to the channel wall at an angle of 45°, has been established. It is shown that, as the length of a trench in the channel increases, a detached turbulent flow in it is intensified, and the maximum velocities of the reverse flow and of the secondary swirling flow reach 0.43 and 0.83, respectively, compared to 0.27 for a spherical dimple. The minimum relative friction and the maximum relative heat transfer in the central cross section of the trench at its inlet are stabilized at a level of –1.6 and 1.6 in the case where the trench has a length larger than 4. A maximum relative heat transfer from the channel region of variable area with a long inclined trench, having spherical ends, is attained in the case where the trench has a length of 3, and this maximum exceeds the maximum relative heat transfer from the analogous channel region with a spherical dimple by 1.4–1.5 times.</p>