Experimental investigation of heat transfer and friction factor characteristics of surfactant solutions

Efforts to achieve optimal results have led modern heat transfer science to focus on creating smaller yet more efficient devices. The double-pipe heat exchanger (DPHE) is widely used across industrial sectors. To elevate DPHE's effectiveness, investigators have introduced diverse approaches for enhancing heat transfer capabilities. These strategies include implementing a chemical compound, including a surfactant and alternative base fluids with better thermal specifications. Nonetheless, scientists were interested in exploring the drag-reduction properties of drag-reducing additives in turbulent pipe flows. Numerous research has advanced our understanding of this topic. Theoretical and experimental studies abound as we seek greater insight into what makes these additives effective at reducing fluidic friction within piping systems by examining changes along the conduits' wall where molecular momentum is transferred between fluids. Experts propose various scenarios that could explain these unique physical behaviors. This study aims to decrease pressure drop in a counterflow double-pipe heat exchanger (DPHE) using surfactant solutions as drag-reducing agents. For this purpose, surfactant solutions were prepared by adding three different surfactants, including sodium dodecyl sulfate (SDS), nonylphenol ethoxylate (NP-10), and polysorbate 80 (Tween 80) at weight concentrations of 0.2% to water, separately. The test rig consisting of a heater, cooler, storage tank, pump, and the test section of a double pipe heat exchanger was set up. While surfactant solutions used as cold fluid passed through the inner tube of the heat exchanger at several flow rates (3, 4, 5, 6, 7, 8 LPM), the flow rate of the hot fluid, distilled water was kept constant at 5 LPM throughout the experiment. The study was conducted in turbulent flow regimes. Pressure drop measurements and heat transfer measurements were carried out simultaneously. The friction factor was calculated from the pressure drop data and compared with the literature. According to the results, the maximum drag reduction was achieved by approximately 15% when using an NP-10 surfactant solution, while Tween 80 surfactant solution yielded the most negligible reduction in drag at 1.10%. In the case of SDS and NP10 solutions, drag reduction increases with the Reynold number until reaching a peak, after which it decreases. However, with the Tween 80 surfactant solution, a decrease in drag was observed as the fluid flow got turbulently. Heat transfer measurements were made for the same surfactant solutions simultaneously with the pressure drop measurements and compared with the results obtained with distilled water. Convective heat transfer coefficients were calculated with the help of the overall heat transfer coefficient. The Wilson plot method and classical internal flow heat transfer correlation, Dittus Boelter correlation, were used to calculate convective heat transfer coefficients. Obtained results were compared to each other. The results obtained for pure water were compared with classical heat transfer correlations. Accordingly, it was observed that the Dittus Boelter correlation showed the closest agreement with the experimental results, with a maximum deviation of 6%. Compared to water at a constant flow rate, Nusselt numbers close to the water were obtained for the SDS solution, while lower Nusselt numbers were obtained for the NP10 and Tween80 solutions. It was observed that the addition of surfactant caused a decrease in pressure drop compared to water at constant pressure and showed a reduced heat transfer.