Heat transfer enhancement in air channel by longitudinal vortexes

Numerical investigation of heat transfer is carried out in an air channel of the rectangular cross section (0.005 × 0.031) m with the length of 0.175 m. The lower surface of the channel is uniformly heated up to 343 K, and the air flow temperature at the channel entrance is 293 K. Two flow rates Q = 0.0010044 and 0.00209 m 3 /s are considered. The heat transfer between the channel surfaces and the cooling air flow enhances by vortex generators (VG) placed at a heated and an opposite surfaces. These generators are formed by two rectangular plates arranged vertically on the surface and at an angle of attack α = 15° to the flow. The plate height is h = 0.002 m and its length is 0.015 m. The VGs at the heated surface creates a pair of longitudinal vortexes that generates behind the plates a common flow to the surface while a pair of longitudinal vortexes at the upper surface creates the common flow away from it. Interaction of longitudinal vortices and secondary flows created by them with the main flow enhances mixing inside the channel and heat exchange with surfaces. Investigation was carried out by the RANS method at Re = 1300–2600 based on the VG height and the flow velocity at the channel entrance. It is shown that the thermal power of the channel with VG at the lower surface increases relative to that in the smooth walls channel by 17–23 % for the considered flow rates. If VG are placed at the both surfaces, the channel thermal power increases by 27–32 % depending on the flow rate.