Heat transfer deterioration has been observed by researchers in turbulent upward flows under the effect of buoyancy. This is a problem for industrial applications since deteriorated heat transfer requires heat exchangers of increased volume and cost. Passive heat transfer enhancement in turbulent mixed convection upward flows through a uniformly heated pipe is studied numerically, using RANS modelling. A constant properties approach is implemented, using the Boussinesq approximation to predict the influence of buoyancy. Turbulence is modelled using two different models, the “Menter shear stress transport turbulence model” and “Spalart-Allmaras” model. Numerical simulations of air flows are conducted at a turbulent Reynolds number of 𝑅𝑒=5300, at a uniform pipe wall heating rate of 𝑞𝑤𝑎𝑙𝑙=1285 𝑊/𝑚2. The effect of transverse rib geometries on heat transfer is studied for various pitch-to-diameter, 𝑝/𝐷, and depth-to-diameter, 𝑒/𝐷, ratios, with ranges equal to 𝑝/𝐷= 1−1.75 and 𝑒/𝐷 = 0.1 −0.175. The effect of ribs on heat transfer is compared to the effect on flow friction, using the overall enhancement ratio, 𝜂. Results show that transverse rib geometries can lead to a maximum overall enhancement of 𝜂=2.20 and 𝜂=2.30 depending on the turbulence model. Recommendations for further research are presented in the end.