Cooling Strategies for Heated Cylinders Using Pulsating Airflow with Different Waveforms

Pulsate flow is an effective technique applied for cooling several engineering systems depending on their pulsate frequency. One very sound external flow pulsation application is heat transfer over heated bodies. In present work, an experimental design and numerical model of controlled pulsating flow according to generated pulsating frequency and wave shape around a heated cylinder were performed. The effects of pulsating frequency, amplitude, and mean velocity on the fluid flow and heat transfer characteristics over a heated cylinder were studied. The wave frequency varied from 2 to 12 Hz, and the amplitude varied from 0.2 to 0.8 m/s. Moreover, different waveforms were investigated to determine their effect on wall cooling. For constant wave frequency and amplitude, the most efficient wave in cooling was the sawtooth wave, with the average wall temperature after 30 s was 1.6 °C cooler than that of the forced convection case, followed by the triangular wave at 1.2 °C less. The heat transfer rate and the flow field were drastically influenced by the variations of these parameters. Optimization was conducted for each wave type to find the optimum wave frequency and amplitude. The optimizing showed that, the most efficient wave was the sawtooth with 12°C temperature reduction compared with that of the forced convection case, followed by the triangular. Furthermore, regression analysis was conducted to estimate the relationships between these variables and surface temperature. It was found that the wave amplitude had a greater role in cooling than that of the frequency

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