Experimental Investigation of Heat Transfer in Low Frequency Pulsating Turbulent Flow in Circular Pipe

Heat transfer characteristic of low frequency pulsating turbulent water flow in a vertical circular pipe which is heated at uniform heat flux, are experimentally studied under different conditions of Reynolds number, pulsation frequency and relative amplitude. The experiments are performed with the Reynolds number range of 3000 to 20000, pulsation frequency range of 0.033 to 0.1 Hz, and the relative amplitude range of 0.1 to 0.8. This pulsating flow situation is used to simulate the phenomenon happened in the ship power system which is induced by ocean conditions. The effects of pulsation on heat transfer characteristics are presented in terms of relative local and mean Nusselt numbers defined as the ratio of the local and mean Nusselt numbers for pulsation flow to that of the ordinary steady turbulent flow with the same time-averaged Reynolds number Re_ta. The results show that the relative local Nusselt number is strongly affected by Reynolds number, pulsation frequency and relative amplitude. The phenomena that the Nusselt number would increase or decrease with the increase of the Reynolds number are both observed and the variation is more notable in the entrance region than that in the fully developed region. The relative mean Nusselt number decreases initially as the Re_ta increases, and then recovers gradually, but finally it has the tendency to decrease again. With the increase of pulsation relative amplitude, the relative mean Nusselt number increases at first and then decreases. And for the Reynolds number range of 3176 to 6670, heat transfer enhancement is observed as the pulsation frequency raises, but complete contrary phenomena appears at Reynolds number range of 11904 to 15844. The obtained heat transfer results are analyzed and seem to be qualitatively in accordance with previous investigations.