A bypass implements two sub-ducts: A primary and a secondary branch. The flow rate is divided, s.t. the pressure loss in both branches is equal: $$\Delta p_i(\dot{V})=\Delta p_{i,1}(\dot{V_{i,1}})=\Delta p_{i,2}(\dot{V_{i,1}})$$ and $$\dot{V}=\dot{V}_{i,1}+\dot{V}_{i,2}$$
The outlet temperature of a bypass is the mixing temperature of the outlets of the two branches: $$T_{i}=\frac{\dot{V}_{i,1}\cdot T_{i,1}+\dot{V}_{i,2}\cdot T_{i,2}}{\dot{V}}$$ whereas the inlet temperature of the branches is qual to the inlet temperature of the bypass.
The profile of the bypass at its in- and oulet is defined to be equal to the one of the first branch. Graphical visualizations (e.g. Analysis) always show the properties of the first branch.