The flow and heat transfer behaviour of channels with dimples and protrusions of spherical and piriform shapes was numerically explored by solving the Navier-Stokes and energy equations with a CFD software, the ANSYS Fluent 19.3, in the range of Reynolds numbers from 8,500 to 59,000. The values of the Nusselt number and friction factors were estimated and the non-dimensional Performance Evaluation Criterion (PEC) was determined to measure the thermal-hydraulic performance. The results reveal that the piriform protruded channel demonstrated a higher thermal performance with Nusselt number values of 36%, 15%, 23%, and 9% than the smooth, spherical dimpled, piriform dimpled, and spherical protruded channels, respectively. This indicates that heat transfer is enhanced by the turbulent mixing caused by the roughened surfaces of the channels. Nevertheless, the smooth channel had the lowest pressure drop with the friction factor of 20%, 7%, 21% and 27% less than that of spherical dimpled, piriform dimpled, spherical protruded, and piriform protruded channels, respectively. In the Reynolds number range, lower Nusselt number ratios and friction factor ratios were observed in the piriform dimpled channel compared to other enhanced-surface channels. The overall performance based on the thermal-hydraulic analysis indicated that the channel with piriform protrusions performed better with the highest PEC value of 3.77 times higher than the smooth-surface channel.
Tubes are commonly employed in heat exchangers for their ease of production and capacity to sustain high pressure. In this study, the heat and flow transfer behaviour of cam-shaped tube bank in staggered configuration at varying angles of attack 0° to 180° was numerically investigated. The study was carried out by solving the continuity, momentum, energy and realizable k-ε transport equations using the finite volume-based ANSYS Fluent solver. This was performed to acquire the friction factor and heat transfer characteristics in the air inlet velocity range of 9 to 15 m/s. The results showed that the cam-shaped tube bank at varying angles of attack provided enhanced heat transfer characteristics relative to the circular tube bank. Also, camshaped tube banks at angles of attack of 90° and 120° exhibited the maximum heat transfer with 33.9 and 32.1% increase in Nusselt number over the circular tubes. Their friction factor was higher by 183 and 140.7%, respectively. The cam-shaped tube banks generally exhibited higher performance than the circular tube bank. Tube banks at angles of attack of 150° and 180° demonstrated higher thermal-hydraulic performance by 167.6 and 284.3% than the circular tubes, respectively. However, the tube banks at angles 90° and 120° exhibited lesser performance by value of 52.6 and 45.1%.
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