Experimental correlations for oscillatory-flow friction and heat transfer in circular tubes with tri-orifice baffles

Abstract

Experimental results of isothermal pressure drop and convective heat transfer coefficient are presented for a smooth tube with tri-orifice baffle inserts, under net and oscillatory flow conditions. Using propylene-glycol as working fluid, net Reynolds numbers in the range Ren=10−600 are reproduced, allowing to describe Fanning friction factor in the laminar, transitional and turbulent regimes, with an onset of transition at Ren≈100 in steady-state conditions. Oscillatory Fanning friction factor for 20<Reosc<200 is also reported, based on the maximum oscillatory pressure drop obtained by statistical fitting of the signal. Nusselt number under uniform heat flux conditions is obtained for superimposed net and oscillatory flows in the ranges 10<Ren<600 and 10<Reosc<440, with Prandtl number in the range 190<Pr<470. The existence of buoyancy effects in steady-state conditions and its vanishing with oscillations is analyzed. The oscillatory flow promotes a 4-fold increase of heat transfer for Ren<20. For Ren>100, the effect of the flow oscillation on heat transfer enhancement is negligible.