CAPE-OPEN

I defined these streams--Stream 1: Gas A, Gas B; Stream 2: Liquid C; Stream 3: Gas A, Gas B, Liquid C.

With the Mixer Unit, I am not able to connect Stream 1 and Stream 2 as inlets without an error dialog:

...please make sure to connect materials of the same type to these ports.

The help system tells something different:

In COFE, by default you are only allowed to connect material streams of the same material types to a unit operation. This is to prevent errors by unit operations that are not aware of stream types. For each unit operation, you can change this option from the Ports page of the unit operation dialog.

The Port Operations dialog only shows:

All material connections must be of the same stream type

I can find no way to change the default to allow streams of different material types. What am I missing here? Can I mix input Streams 1 and 2 to obtain output Stream 3?

COFE may allow you to attach different thermodynamic stream types to a unit operation, but the mixer itself does not. It requires consistent thermodynamics, at least a consistent set of compounds on all streams.

Presuming you have 2 feed streams, and one of the feed streams has the same thermo as the product stream, you can use a StreamConverter unit to convert the other stream to the same thermo.