User Name Remember Me? Password

 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum Jul 18th 2019, 07:47 AM #1 Junior Member   Join Date: Jul 2019 Posts: 1 Energy conservation in mixing streams Is it correct to apply two separate Bernoullis equation - for sections 1-3 and for 2-3? Why/why not? I ve seen such solution to this problem on the internet but I have some doubts. I think that energy between sections 1 and 3 is not conserved because of energy exchange with the other stream. Energy conservation for the whole system Q1(v1^2/2 +p1/rho)+Q2(v2^2/2 +p2/rho)=(Q1+Q2)(v3^2/2 +p3/rho) is not enough to determine (p3-p2) needed for Y momentum conservation. system of: v1^2/2 +p1/rho +deltaE=v3^2/2 +p3/rho v1^2/2 +p1/rho -deltaE=v3^2/2 +p3/rho needs an additional equation as well I would be thankful for every help   Jul 18th 2019, 08:20 AM #2 Senior Member   Join Date: Oct 2017 Location: Glasgow Posts: 474 You also need to consider the continuity equation: $\displaystyle Q_3 = Q_1 + Q_2$ $\displaystyle Q_3 = A_1 v_1 + A_2 v_2$ Since each pipe has the same diameter, $\displaystyle A_1 = A_2 = A$ and since $\displaystyle Q_3$, $\displaystyle A$ and $\displaystyle v_1$ are known, $\displaystyle v_2 = \frac{Q_3}{A} - v_1$ That's one less unknown, so you should be able to solve for $\displaystyle p_2$ and $\displaystyle p_3$. You will get some head loss at the junction, but for an estimation you can assume that the head loss is negligible. topsquark likes this. Last edited by benit13; Jul 18th 2019 at 08:39 AM.  Tags bernoulli, conservation, energy, fluid, mixing, streams Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post Charles Energy and Work 4 Dec 15th 2015 08:19 AM zijincheng Advanced Thermodynamics 4 Jun 19th 2015 10:26 AM Momentous Energy and Work 6 Jul 8th 2013 12:01 PM chino109 Advanced Mechanics 11 Oct 1st 2010 07:15 AM werehk Advanced Mechanics 1 Jan 8th 2009 02:21 AM