Experimental investigation on the convection heat transfer enhancement for heated cylinder using pulsated flow

The paper presents experimental results regarding heat transfer behavior of a cylinder in cross pulsating flow and focuses on heat transfer characteristics enhancement obtained using a novel and peculiar type of pulsation technique able to generate variable pulsate signals with different frequencies. The pulsating flow tunnel features a square cross section of 200 mm × 200 mm and 1600 mm length, while the testing apparatus utilizes a station of normally closed (NC) solenoids and a vacuumed plenum chamber which can generate a time dependent flow inside the tunnel. Effects of pulsating frequency in the range 1–12 Hz and Reynolds number in the range 1.02–2.04*104 on convective heat transfer for both a horizontal and vertical heated cylinder are carried out. A cylindrical cartridge heater is embedded into the cylinder with two insulated ends to generate a constant heat flux of 33 W in all the experimental runs. The surface temperature of the cylinder was measured using an array of k-type thermocouples around the cylinder circumference and recorded in a real-time data logger. The results show that the measured velocity and convection heat transfer coefficient are very sensitive to the frequency of crossflow pulsation. In addition, the influence of pulsating frequency on the local and average of heat transfer coefficient is discussed in detail. Results also demonstrate that maximum enhancement in heat transfer for the horizontal and vertical setup occurs at a frequency of 9 Hz compared to steady forced convection, with 8.33% and 11.11% increment in heat transfer respectively.