Heat transfer and crisis in swirl flow boiling

The lecture considers general features of swirl flows. For single-phase convection, both theoretical and experimental results obtained up to-day give rather clear understanding of the main mechanisms of energy and momentum transfer in tubes with twisted tape inserts. At one-side heating the high temperature azimuthal gradient exists at the inside surface, that requires the well-founded choice of reference temperature for physical properties used in calculations of HTC. Heat transfer in boiling of subcooled liquid in swirl flow at uniform heating can be successfully described by superposition of the known predicting equations for single-phase convection and nucleate boiling. Under one-side heating condition different heat transfer modes are observed along the circumference of the cooled channel. Practical recommendation on the prediction of HTC at nucleate boiling of subcooled liquid in swirl flow at one-side heating has been given in this paper. Boiling crisis in swirl flow at uniform heating can be prevented either by centrifugal body forces or by single-phase convection from the bubbly layer surface at the heated wall to the cold flow core. The greater from heat fluxes controlled by these two mechanisms determines CHF. At one-side heating in swirl flow CHF is essentially higher than under uniform heating condition. Based on the experimental measurements, the conclusion is stated that at high flow velocity and high liquid subcooling in swirl flow the thermodynamical limit of CHF has been achieved. (C) 2005 Elsevier Inc. All rights reserved.