Heat transfer in fluids is very important in many industrial heating and cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. When a fluid flows in a channel, transversal ribs can be used as fins and break the laminar sublayer creating local wall turbulence. However, as a consequence the presence of the ribs can significantly augment pressure drops. In this paper a numerical investigation is carried out on forced convection in channels heated by a constant heat flux. Also conductive effects are taken into account. The fluid is air and properties are assumed as function of temperature. Ribs of the same material of the channel walls are introduced and several arrangements are analyzed. The investigation is accomplished by means of the commercial code Fluent. A turbulence model is used. Results are presented in terms of temperature and velocity fields, average heat transfer coefficients, friction factor profiles and pressure drops. The aim of this study is to find arrangement of ribs such to give high heat transfer coefficients and low pressure drops. The maximum Nusselt number and friction factor have been detected for dimensionless pitches equal, respectively, to 12 and 10.

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