Experimental investigation of the thermal–hydraulic performance of hook-shaped fins and dimples

• Novel and cost-effective extended surfaces, GRIPMetal, are investigated. • Experiments were conducted at low Re . • Thermal performance of GRIPMetal peaked at the smallest tip-clearance. • Empirical correlations predicted performance with errors < 4.1 % ( Nu h ) and 10 % ( f h ). • GRIPMetal outperformed existing surface enhancement techniques by 13 %−91 %. In forced convection, arrays of extended surfaces are commonly used to increase heat transfer rates because they increase specific surface area, improve fluid mixing, and generate turbulence which results in higher heat transfer coefficients. The objective of this work is to comprehensively quantify the heat transfer coefficient and pressure drop of arrays of hook-shaped fins and dimples, trademarked as GRIPMetal. Experiments were conducted by pumping water through a rectangular channel to cool heated GRIPMetal surfaces on one side. The channel height was varied to adjust the tip clearance above the arrays. Three sizes of GRIPMetal arrays were tested across a range of Reynolds numbers ( Re ) from 600 to 12,000. The Nusselt number ( Nu ) and friction factor ( f ) were used to evaluate the thermal–hydraulic performance of the arrays and to quantify their effectiveness relative to a flat surface. The overall thermal–hydraulic performance factor ( η o ) was employed, and empirical correlations were developed to describe Nu and f for the arrays. All the GRIPMetal arrays exhibited higher thermal performance than a smooth surface, with Nu ranging from 2.4 to 5.7 times higher, depending on the array type, Re , and channel height. However, the pressure drop was also higher than that of a smooth channel. Despite the pressure drop penalty, the overall thermal-hydraulic performance of the arrays was always higher than that of the smooth surface—the lowest performance factor was 1.4 for the mini arrays. GRIPMetal outperformed other similar heat transfer enhancement techniques explored in the literature, suggesting its potential to serve as a low-cost heat transfer enhancement method.