Method for detecting primary gas flows in flow chambers, use of a gas mixture therefor and gas mixture

A method for detecting primary gas flows (18) in a flow chamber (10), the method comprising:

• causing a primary gas (18) to flow in the flow chamber (10);
• locally seeding the primary gas (18) with a gas mixture (34) including a seed gas that moves with the primary gas (18) and has a refractive index that can be distinguished from the primary gas (18);
• carrying out an imaging detection using an image detector (28) and imaging optics (30) arranged in front of the image detector (28) for performing a background schlieren measurement method to detect a movement of the gas mix re (34) that e of the flow of the primary gas (18);
• and
• the gas mixture (34) being composed in such a way that:
• |mP−Σi=1Naimi|<2 g/mol,
• and
• |n′P−Σi=1Nain′i|>70,
• where mP is the molar mass and n′P is the refractive index of the primary gas, mi is the molar mass and n′i is the refractive index of the i-th gas component of the seed gas, N is the number of gas components of the seed gas, and ai is their respective relative mole fraction in the seed gas,
• so that a co-movement of the gas mixture (34) with the primary gas (18) flowing at a flow velocity of 0.1 to 1.0 m/s takes place without relative movement.