Influence of a novel serrated wire coil insert on thermal characteristics and air flow behavior in a tubular heat exchanger

The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchangers is constantly being studied and presented. In this work, a novel wire coil turbulator was developed to have characteristics that are different from those previously proposed. It is based on the concept of a combination of a coiled wire structure with a continuous V-shaped rib turbulator, which was referred to as a serrated wire coil (SWC). In the paper, the turbulent air flow behavior and heat transfer characteristics in a tube heat exchanger with SWC insert was investigated experimentally under isothermal-flux condition. Ambient air was used as a working fluid in a turbulent flow regime with Reynolds numbers (Re) ranging from 5114 to 14,752. The SWCs were inserted into test tubes with three different coil diameters (DC) of 34.4, 41.2 and 47.9 mm (or diameter ratio, DR = DC/DT = 0.68, 0.81 and 0.94) and four different pitch lengths (PC) of 10, 20, 30 and 40 mm (or pitch ratio, PR=PC/DT = 0.1969, 0.3937, 0.5906 and 0.7874). The experimental results of heat transfer and friction loss were presented as dimensionless parameters, Nusselt number (Nu) and friction factors (f), respectively. It was observed that the Nu increased with a decrease in pitch length and an increase in coil diameter. While the f decreased with an increase in both pitch length and coil diameter. Under the scope of this study, it was found that the insertion of the coils increased the Nu and f above the smooth tubes by approximately 1.75-2.46 times and 3.31-8.16 times, respectively. The empirical correlations of Nu and f for tubular heat exchanger inserted with SWC under the scope of this study were developed and showed error within +/- 4 % for Nu and +/- 12 % for f. The maximum thermal performance enhancement factor (eta) for this work was about 1.41 for the SWC with DC = 47.9 mm and PC = 10 mm at Re = 5114. In addition, the Nu, f and eta obtained in the optimal conditions of this work were compared with previous work.

Automated summary

The experimental study involved the insertion of a novel wire coil turbulator, referred to as serrated wire coil (SWC), into a tube heat exchanger to enhance heat transfer performance. Results showed significant improvement in heat transfer efficiency with SWC inserts, supported by developed empirical correlations with acceptable error margins.