Validation of a new methodological approach for the selection of wire-coil inserts in thermal equipment

The use of wire-coils is especially relevant at low Reynolds numbers (below the critical number to turbulent flow in smooth tubes) according its inherent positive features such as advance transition onset and, if they present suitable geometric characteristics, establishment an extended transitional a interval [ReCL-ReCT], with predictable friction coefficient and Nusselt number. This paper presents experimental validation new methodology based on evaluation non-dimensional geometry-based parameter: TSP (Transition Shape Parameter) that allows predict evolution wire-coil inserts enables compute extension region. close relationship between hydraulic thermal performance makes this valuable tool for selecting most appropriate geometry given tubular heat exchanger. It observed promote increase transfer, value ReCL wire coil must be less than operating range equipment. Thus, ReCL-ReCT insert should fall into range. In order validate methodological approach, application harp-type solar collectors typical [40–6000] presented. Four representative wire-coils, wide geometrical characterized by values 759, 196, 35.3 3.1 (exhibiting significant differentiated behaviours their factor curves numbers) were inserted inside risers modified collector experimentally tested laboratory conditions. Static temperature different locations absorber plate, pressure drop measured obtain riser covering laminar, low-turbulent regions. For general constraints TSPW02=196 ReCL=663 ReCT=2286 Nu¯w02/Nu¯s=2.21 Re=300-3000 f¯w02/f¯s=3,82. However, case study presented (a collector) it feasible third TSPW03=35.3 due early transition, ReCL=364 ReCT=2324, Nuw/Nus=1.35 Re=300 high augmentation f¯w03/f¯s=18.84. also promotes highest reduction. greatest reduction [700–2000], reaching approximately 6 °C, which represents 15 %.