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[FAQ]

If mass-flow-inlet boundary type is used, it probably suggests the presence of a compressible flow (ideal-gas law). When using the ideal-gas law and turning off flow equations, the temperature will not get updated from the profile at the mass-flow-inlet boundary. One option is therefore to change the mass-flow-inlet to a velocity-inlet type (value of cell velocities will be unaffected since flow is off), and the temperature profile will get applied as expected. The other option that would work is to set a constant density or incompressible-ideal-gas fluid while retaining the mass-flow-inlet boundary type. This would, however, alter the density values in each cell which in turn may affect the transient behavior of energy equations. The reason for this kind of behavior is that the mass-flow-inlet type and ideal-gas law calculations are coupled with the temperature input. For a given mass flow rate value (density*face-area*velocity), the velocity at the inlet should be updated if the temperature changes. This is required since ideal-gas law would control the density value. Turning off flow would not allow the node velocity values to update. Hence it does not allow the temperature to update. Ideally, it is suggested to solve compressible flow equations with the flow kept on. Sometimes, rather the energy equation is turned off if density variations are expected purely from pressure changes in a nearly iso-thermal flow.