Thermal performance of channel flow with detached and attached pin-fins of hybrid shapes under inlet flow pulsation

A newly devised hybrid pin-fin array composed by the attached rhombuses and the hexagon pin-fins was proposed for heat transfer enhancements. The flow pulsation at channel entrance was stimulated by venting the airflow periodically at the frequencies of 1/4, 1/6 and 1/12 Hz with the time-mean Reynolds number, Re, controlled at 1500, 2000, 5000, 10,000, 15,000 and 20,000 to give rise the Strouhal number, Sr, in the range of 0.00028–0.017. At each Re and Sr tested, the open period of vented flow was adjusted to 1/4, 1/2 or 3/4 pulsation cycle to alter the pulsating waveform. A selective set of full-field Nusselt number distributions and Fanning friction factors illustrated the general and individual hydrothermal impacts in association with Re, Sr and the frequency and waveform of the pulsating flow. As Sr increased continuously, the area-averaged time-mean Nusselt numbers were initially reduced but recovered and then raised above than the steady-flow references. The Fanning friction factors of pulsating flows were initially reduced and then increased from the steady-flow baselines as Sr increased. With the significant heat transfer elevations by the present pin-fin array from the smooth tubular flow references, the thermal performance factors at Re≥5000 were above unity. Two sets of empirical correlations were devised for evaluating the time-mean area-averaged Nusselt numbers and Fanning friction factors of the present pin-fin channel with steady and pulsating flows.