page_title: CFD in buildings
section_title: Boundary conditions
hierarchical_section_title: CFD in buildings / CFD approach for heat transfer analysis in buildings / Discretization of the governing differential equations for the steady state heat transfer analysis / Boundary conditions
caption_attribution_description: English: Schematic for the FDM formulation of combined convection and radiation on the left boundary of a plane wall
context_page_description: CFD stands for computational fluid dynamics. As per this technique, the governing differential equations of a flow system or thermal system are known in the form of Navier–Stokes equations, thermal energy equation and species equation with an appropriate equation of state. In the past few years, CFD has been playing an increasingly important role in building design, following its continuing development for over a quarter of a century. The information provided by CFD can be used to analyse the impact of building exhausts to the environment, to predict smoke and fire risks in buildings, to quantify indoor environment quality, and to design natural ventilation systems.
context_section_description: Above equation is valid only to interior nodes only. To obtain the solution for exterior nodes we have to apply the boundary conditions (as applicable), which are as follows.
  1.Specified heat flux boundary condition
  When boundary is insulated (q=0)
  2. Convective boundary condition
  3. Radiation boundary condition
  4. Combined convective and radiation boundary condition (shown in figure-4).
  or
  when radiation and convection heat transfer coefficient are combined, above equation becomes as follows; 
  5. Combined convective, radiation and heat flux boundary condition
  6.Interface boundary condition : when there is an interface (in composite walls) of different walls having different thermo-physical properties, the two different solid media A and B are assumed to be perfect contact and thus have same temperature at interface at node m (as shown in figure-5).
  In above equations q_0 = denotes specified heat flux is in , h =convective coefficient,  = combined convective and radiation heat transfer coefficient, = Temperature of surrounding surface, =Ambient Temperature,  = Temperature of at initial node.
  Note: For interior side of wall we can apply the suitable boundary condition from above (as applicable), in that case   will be replaced by  (Room Temperature), = will be replaced by  (Temperature of last node).
caption: Figure-4: Schematic for the FDM formulation of combined convective and radiation on the left boundary of a plane wall
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