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Several of industrial applications such as electronic devices, heat exchangers, gas turbine blades, etc. need cooling processes. The internal cooling technique is proper to some applications. In the present work, computational simulations were made using ANSYS CFX to predict the improvements of internal heat transfer in rectangular ribbed channel using different coolants. Several coolants such as air, steam, air/mist and steam/mist were investigated. The shear stress transport model (SST) is selected by comparing the predictions of different turbulence models with experimental results. The results indicate that the heat transfer coefficients are enhanced in ribbed channel at injection small amount of mist. The heat transfer coefficients of air/mist, steam and steam/mist increase by 12.5%, 49.5% and 107% than that of air, respectively. Furthermore, comparing with air, the air/mist heat transfer coefficient enhances by about 1.05 to 1.14 times when mist mass fraction increases from 2% to 8%, respectively. For steam/mist heat transfer coefficient increases by about 1.12 to 1.27 times higher than that of steam over the consider range of mist mass fraction.

This study investigated heat transfer characteristics on various shaped ribs on the lower channel wall using steam and steam/mist as cooling fluid. The lower wall is subjected to a uniform heat flux condition while others walls are insulated. Calculations are carried out for ribs with square ribs (case A), triangular ribs (case B), trapezoidal ribs (case C) and (case D) cross sections over a range of Reynolds numbers (14000–35000), constant mist mass fraction (6%) and fixed rib height and pitch. To investigate turbulence model effects, computations based on a finite volume method, are carried out by utilizing three turbulence models: the standard k-ω, Omega Reynolds Stress (ωRS) and Shear Stress Transport (SST) turbulence models. The predicted results from using several turbulence models reveal that the SST turbulence model provide better agreement with available measurements than others. It is found that the heat transfer coefficients are enhanced in ribbed channels with injection of a small amount of mist. The steam/mist provides the higher heat transfer enhancement over steam when trapezoidal shaped ribs (38°, case C).

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