Page V - 6 
Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
“snap” to the nearest grid line in the final model. This type of allowance is often acceptable when 
setting up room geometries. The exact location of an item need not be clearly defined. 
Below is a list, with brief descriptions, of the boundary conditions relevant to the approach taken 
in this study, referred to in the sections of this report. 
Rectangular 
Obstructions 
Rectangular obstructions are three-dimensional, solid, 
rectangular objects, with faces aligned with x, y and z. 
Friction at all surfaces exposed to fluid is included. There are 
a number of possible thermal specifications: 
• Fixed uniform heat flux at all surfaces 
• Fixed uniform surface temperature 
• Solve in solid (to investigate conduction through solid) 
External Walls 
External walls are walls at the edges of the solution domain, 
or exceptionally internal walls for which solution is required 
only on one side and “external” conditions can be applied on 
the other side. Surface friction is evaluated automatically and 
there are a number of thermal options: 
• Prescribed heat flux 
• Prescribed inner wall surface temperature 
• Prescribed external temperature with detail of the heat 
transfer through the wall 
Exhausts 
Exhausts represent any outflow of air, usually when driven 
using mechanical means. The flow rate is specified as: 
• Fixed mass flow rate (kg/s) 
• Linear pressure drop/flow rate fan characteristic 
• External static pressure 
Openings 
Openings are any opening through which fluid can enter or 
leave the domain as a result of pressure differences. The 
temperature and angle of flow of incoming air can be 
specified. It is also possible to represent, for example, a grille 
across the opening by setting a pressure drop (see 
Resistances). 
