A comprehensive investigation has been carried out to analyze the fluid and heat flow during mixed convection in entrapped triangular cavities for heat disposal (case 1: hot inclined and cold horizontal wall) and heat recovery (case 2: cold inclined and hot horizontal walls) to/from the industrial fluids via heatline approach. Galerkin finite element method is employed to solve the governing equations and the results are illustrated for various Grashof numbers (103 ≤ Gr ≤ 105), Prandtl numbers (Pr=0.026 and 7.2) and Reynolds numbers (1 ≤ Re ≤ 100). At Re=1 the symmetric fluid circulation cells occur whereas, the asymmetric fluid circulation cells occur at Re ≥ 10 and Gr=105 in both the cases and both Pr. The conduction dominant heat transfer is observed at Pr=0.026 and Gr=105 involving all Re. In contrast to Pr=0.026 the heat flow field is highly influenced by the fluid flow field at Pr=7.2 for all Re and Gr=105. In the upper cavity, the average Nusselt number of the top wall (Nut¯) is higher at Re → 0, Gr=105 for the case 1, and at Re=100Gr=103 for the case 2 involving Pr=7.2. In the lower cavity, the average Nusselt number of the bottom wall (Nub¯) is higher at Re=100Gr=103 for the case 1, and at Re → 0, Gr=105 for the case 2 involving Pr=7.2. © 2017 Taiwan Institute of Chemical Engineers