Fig. 2 shows the schematic and computational domains for different channel configurations considered in this ZM336372 study, whereas near wall mesh for a circular cross-section is shown in Fig. 1d. The computational domain creation and discretization was performed using Gambit 2.3.16 preprocessing software. Channel configurations considered in this study are circular, square, rectangular, triangular and trapezoidal cross-sections as shown in Fig. 2. Since the flow is low Reynolds number, higher mesh density was used near the wall to adequately capture the near wall effects on the flow field. The geometrical dimensions for cross-sections other than the circular were calculated such that the expansion ratio and the outer surface area are conserved for all geometries. The governing equations together with the relevant boundary conditions are solved using finite volume solver FLUENT 13. The elliptic 3-D governing equations of fluid flow and heat transfer are computed using a sequential (segregated) 3-D double precision parallel computing solver. The convergence criterion of 10−6 is set for the energy equation, whereas the criterion for all other equations including continuity, specie and turbulence is 10−3. All governing equations together with constitutive relations and appropriate boundary conditions are discretized using a second-order upwind scheme. The pressure–velocity coupling is handled by using the Semi-Implicit-Method-for-Pressure-Linked-Equations (SIMPLE) algorithm.