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## Main Question or Discussion Point

I have a closed system (a wind tunnel with entrained air) where a high speed air flow sucks up ambient air to provide a combined flow of the 2 air streams over the model. The resulant flow has a mass flow rate equal to the combination of the 2 air streams.

However in calculating the velocity of the combined flow there seems to be 2 answers.

If I use momentum then m1*v1 + m2*v2 = (m1+m2)*v3

but if I use energy then m1*v1^2 + m2*v2^2 = (m1+m2)*v3^2

m1 and v1 being the high speed air mass rate and velocity and m2 and v2 are the entrained air stream mass rate and velocity. v3 is the needed velocity after mixing.

Both equations are Laws of conservation but in this instance which one is correct and why. There seems a lot of history about which is correct but no real conclusion is drawn.

Many thanks for any guidance.

ohms

However in calculating the velocity of the combined flow there seems to be 2 answers.

If I use momentum then m1*v1 + m2*v2 = (m1+m2)*v3

but if I use energy then m1*v1^2 + m2*v2^2 = (m1+m2)*v3^2

m1 and v1 being the high speed air mass rate and velocity and m2 and v2 are the entrained air stream mass rate and velocity. v3 is the needed velocity after mixing.

Both equations are Laws of conservation but in this instance which one is correct and why. There seems a lot of history about which is correct but no real conclusion is drawn.

Many thanks for any guidance.

ohms