Experimental analysis of flow pattern and heat transfer in circular-orifice baffled tubes

An experimental study on the thermal-hydraulic and flow pattern characteristics of tubes with circular-orifice baffled inserts is performed. A geometry with an orifice-to-tube diameter ratio of d/D=0.5 and an interbaffle spacing equal to 1.5D is tested in steady-state conditions. Isothermal friction factor tests in the range 10<Re<2200 allow the laminar, transitional and turbulent flow regimes to be identified. Flow visualization by means of hydrogen bubbles is used to assess the main flow structures and their relation with the onset of transition, which occurs at Re≈160. Heat transfer experiments under uniform heat flux are conducted in order to obtain the Nusselt number as a function of Reynolds number, for 150<Pr<630, using propylene-glycol as the test fluid. Numerical simulations are used to complement the visualization study and explain the role of the flow structures on the thermal-hydraulic behavior.