Kiš, PetarPetarKišHerwig, HeinzHeinzHerwig2022-09-062022-09-062011-10-14International Journal of Computational Fluid Dynamics 25 (7): 387-399 (2011)http://hdl.handle.net/11420/13555The balance equations for mixed convection in plane channel flow, based on the Boussinesq assumption for buoyancy, are carefully analysed by considering the two limits of pure forced and natural convection. Additional information about the flow is gained from the mechanical energy equation and the entropy equation (the second law of thermodynamics). Since the Boussinesq approximation assumes ε = δT*/T* → 0, i.e. a vanishing dimensionless temperature difference between the hot and the cold wall, certain inconsistencies in modelling the flow appear for ε ≠ 0. They are identified and discussed with respect to their importance. Numerical solutions gained by a direct numerical simulation (DNS) approach give detailed information about the friction factors and Nusselt numbers including the influence of those terms in the equations that turn out to be the source of the inconsistency in the modelling for ε ≠ 0. © 2011 Taylor and Francis Group, LLC.en1029-025720117387399Taylor & Francisdirect numerical simulationforced convectionnatural convectionNusselt numberfriction factorPhysikTechnikIngenieurwissenschaftenJournal Article10.1080/10618562.2011.609276Other