Thermal Investigation of Heat Transfer Enhancement in a Rectangular Duct Provided with Different Configurations of Semi-Circular Ribs

Abstract

Past research studies have explored the use of continuous ribs (with square or rectangular cross-sections) to improve the thermal efficiency of ducts or channels. Some researchers have also investigated the impact of different rib shapes, such as triangular, semicircular, trapezoidal, and pentagonal, on thermal performance. However, there has been limited research focusing on how various semi-circular rib patterns influence the thermal behavior of rectangular ducts. This study investigates the effects of different semi-circular rib designs on the thermal efficiency and friction factor of a rectangular duct. Six distinct rib configurations, ranging from continuous to hybrid patterns, were applied to the bottom wall of the test section. The thermo-hydraulic performance (η) of the ribbed ducts was measured and compared to that of plain ducts. Experimental results revealed that the ratio of Nusselt numbers ranged from 1.44 to 2.57. The ratio of the friction factor ranged from 2.20 to 4.51. The thermal enhancement ratios for semi-circular rib designs ranged from 1.08 to 1.69 relative to a plain duct. The hybrid rib configuration surpassed all other rib designs, delivering the most significant improvement in thermal performance. This was primarily due to enhanced flow distribution and reduced thermal resistance. The superior performance of the hybrid ribs resulted from their innovative design, which combines ribs truncated at both ends with ribs truncated at the center, creating a unique hybrid rib arrangement from the combined rib design. Across the specified range of Reynolds numbers, the hybrid rib duct demonstrated a thermal performance increase of 1.47 to 1.69 times compared to the plain duct.