- The thermal pattern on a heated wall was studied for the flow of water and drag-reducing surfactant solutions in a channel. The wall of the channel was made of a thin foil, which was heated by direct current. The temperature of the foil, which reflects the local flow velocities, was measured by an infrared technique with high spatial and temperature resolution. The microstructure of the surfactant solution was studied by direct imaging cryogenic temperature transmission electron microscopy (Cryo-TEM). The most prevalent structures observed are thread-like micelles, which have been suggested to cause the modification of the thermal patterns.