Energy correlation of heat transfer for drag reduction surfactant solution in a double pipe heat exchanger

In the present study, the effects of surfactant solutions on pressure drop properties and heat transfer characteristics in a double pipe heat exchanger have been investigated. An ionic surfactant (SDS) and two nonionic surfactants (NP-10 and Tween 80) solutions with 0.2 wt% are utilized at different flow rates. The results show that pressure drops for surfactant solutions are lower than those for water at equivalent flow rates. NP-10 demonstrates high drag reduction values, reaching a maximum of approximately 15%, whereas Tween 80 has lower drag reduction values, which vary according to the flow rate. Besides, Nusselt number for water in this study reveals a satisfactory agreement with the predictions derived from the Dittus-Boelter equation with a difference of 2.1%. While NP-10 and Tween 80 addition cause the Nusselt number to decline, SDS does not significantly alter it when compared to water. Energy correlations with high R² values have been developed using experimental data for water and surfactant solutions. Furthermore, enhancement factors (η), the ratio of heat transferred at constant pumping power with and without surfactant, have been calculated. The η values vary within a range of 0.8‒1.1 depending on the flow rate, and for SDS solution, these values are above 1 when the Reynolds number is in the range of 13000–25000. In the case of NP-10 and Tween 80 solution, the η values are below 1 for the whole flow rate range.