Conjugate mixed convection in the entrance region of a symmetrically heated vertical channel with thick walls

•Conjugate mixed convection in a channel under assisted buoyancy is numerically investigated.•The effects of wall conduction and buoyancy force on the flow and heat transfer is studied.•The critical Gr/Re for the flow reversal increases linearly with increasing l*/k*.•The critical Gr/Re for the flow reversal is independent on Re for 200 ≤ Re ≤ 1000.•The effect of wall axial conduction on the heat transfer is obvious at the inlet.

Conjugate mixed convection with buoyancy assisted laminar flow in the entrance region of a vertical channel is considered numerically. The problem is solved by a finite volume method for a thick walled, two-regional channel which has constant and uniform outside wall temperatures. The effects of wall thermal conduction as well as assisted buoyancy force on the flow and heat transfer are discussed in detail. Results are presented for a Prandtl number of 0.7, solid-to-fluid thermal conductivity ratios of 1 ≤ k* < ∞, wall thickness-to-channel length ratios of 0 ≤ l* ≤ 5, Reynolds numbers of 200 ≤ Re ≤ 1000, and for various Grashof numbers. The critical buoyancy parameter (Gr/Re), above which the flow reversal occurs, increases linearly with the increasing l*/k*, while it is independent on the Reynolds number.