Heat transfer enhancement in a single-pipe heat exchanger with fluidic oscillators

Abstract

The current experimental study investigates the effects of installing three types of fluidic oscillators—feedback-free, single-feedback loop and two-feedback channel—on thermal performance of a single-pipe heat exchanger. Results are presented as Nusselt number and friction coefficient at the Reynolds number range of 5600–16,400 and two surface thermal conditions: (a) constant continuous heat flux (CCHF) and (b) constant periodically interrupted heat flux (CPIHF). All the three fluidic oscillators have the same square exit throat with the length of 5.67 mm and the same outer diffuser with the depth of 5.67 mm and 45° diverging angle which overlap the tube’s inner diameter. In the case of CCHF, up to 37%, 83%, and 23% heat transfer enhancement are observed for feedback-free, single-feedback loop and two-feedback channel fluidic oscillators, respectively. In the case of CPIHF, feedback-free and two-feedback channel fluidic oscillators showed no merit relative to the plain tube, but single-loop feedback fluidic oscillator still gives up to 57% thermal performance enhancement. Since fluidic oscillators are no-moving-part devices capable of generating self-induced self-sustained oscillating flows, the current study indicates the high capability of the fluidic oscillators for the passive heat transfer enhancement of heat exchangers.