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The experimental and numerical results on the flow structure and heat transfer in a bubbly polydispersed upward duct flow in a backward-facing step are presented. Measurements of the carrier fluid phase velocity and gas bubbles motion are carried out using the PIV/PLIF system. The set of RANS equations is used for modeling the two-phase bubbly flow. Turbulence of the carrier fluid phase is predicted using the Reynolds stress model. The effect of bubble addition on the mean and turbulent flow structure is taken into account. The motion and heat transfer in a dispersed phase is modeled using the Eulerian approach taking into account bubble break-up and coalescence. The method of delta-functions is employed for simulation of distributions of polydispersed gas bubbles. Small bubbles are presented over the entire duct cross-section and the larger bubbles mainly observed in the shear mixing layer and flow core. The recirculation length in the two-phase bubbly flow is up to two times shorter than in the single-phase flow. The position of the heat transfer maximum is located after the reattachment point. The effect of the gas volumetric flow rate ratios on the flow patterns and maximal value of heat transfer in the two-phase flow is studied numerically. The addition of air bubbles results in a significant increase in heat transfer (up to 75%).

Experimental investigations of heat transfer from the heated wall to the two-phase bubbly flow were performed in vertical annular channel using air-water system. The IR-thermography and miniature temperature sensors were used to measure heat transfer coefficients. The influence of bubbles on heat transfer is shown in comparison with the case of single phase flow. The presence of bubbles in the flow leads to heat transfer intensification in the annular channel even for low void fractions.

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The flow structure and heat transfer in bubbly flows in a sudden duct expansion were studied. The data was obtained both in a pipe and a flat channel with a sudden expansion. Measurements are performed using shadow photography and PIV/LIF system. For modelling two-phase bubbly flow the set of RANS equations is used. Reynolds stress transport model is used to predict the turbulence of the liquid phase. The influence of sudden channel expansion on the distribution of bubbles and it`s velocity is shown. It is shown, that in the pipe with sudden expansion there are not a strong influence of bubbles on the hydrodynamical structure and heat transfer in the flow recirculation zone. In a contrast, in the vertical channel with back facing step the strong increasement of void fraction were found in similar region. It can result in increasement of heat transfer.