Wait. If the force on the flange is in the negative Y direction, and that is DOWN, then the flange is under _compression_ onto its partner, in which case the pressure is holding the joint shut and the bolts can't be under tension. A more advanced answer would require you to find the centres of gravity of the nozzle and the water within to make sure they weren't causing a tipping force on the bolts on the outer part of the curve.
Hey! Just a few questions , hope you can help. Dont we use the sum of forces acting on the fluid = change in momentum and not the sum of the fluid acting on the nozzle or bend? Why was the force acting on the bend due to water changing direction not included?
Great question. This is a control volume (cv) analysis. We only consider forces on the outside of the cv i.e., on the control surface. Notice that the control surface (the dashed line) has been purposely placed on the OUTSIDE of the pipe, where the gage pressure is zero. So, the force of the water on the inside of the pipe bend is an internal force -- inside the cv. Thus, it doesn't enter into the force analysis. Thanks for the question. I should make a point to mention that key detail in my lectures.
As in your Statics course: You start by assuming a direction for the force (which may or may not be correct). You then do the analysis using the assumed direction. If the force comes out positive then the assumed direction was correct. If it turns out to be negative, then the direction of the force needs to be flipped (180 degrees). I hope that helps.
Gauge pressure is defined as the pressure relative to local atmospheric pressure. So P_2=0 gauge. A Bourdon pressure gauge at the outlet would read zero. In these types of momentum problems you have to work in gauge pressure, for reasons that are explained in this video: ruclips.net/video/pk3nFNQRmFU/видео.html
@@DhushanSuresh I think you mean p_1. The problem states that "the gauge pressure is p1=200 kPa". So, the absolute pressure at point 1 would be 300 kPa.
The pressure force acts upward on the nozzle, as shown in the Free Body Diagram. So, the component of F_y (the forced needed to hold the nozzle in place) due to pressure alone must be downward. In contrast, the fluid momentum in the vertical direction increases through the nozzle. This change in momentum requires a force (F_y) in the upward direction to hold the nozzle in place. (Think of trying to hold a jet engine in place.)
Thanks for sharing these videos. I work in the industry and I wish the students know how useful it is to master these concepts.
Thanks! Glad to hear the videos are helpful
Peace be upon you sir... I need the name of the source for the Fluid Mechanics book and the number of copies. Thank you
The textbook (White) is given in the video description. That's the best I can do.
Wait. If the force on the flange is in the negative Y direction, and that is DOWN, then the flange is under _compression_ onto its partner, in which case the pressure is holding the joint shut and the bolts can't be under tension.
A more advanced answer would require you to find the centres of gravity of the nozzle and the water within to make sure they weren't causing a tipping force on the bolts on the outer part of the curve.
You've got this reversed. Fy is the force the bolt applies to the flange to hold it in place.
@@FluidMatters Ah. Okay, my bad.
nerd
Hey! Just a few questions , hope you can help. Dont we use the sum of forces acting on the fluid = change in momentum and not the sum of the fluid acting on the nozzle or bend? Why was the force acting on the bend due to water changing direction not included?
Great question. This is a control volume (cv) analysis. We only consider forces on the outside of the cv i.e., on the control surface. Notice that the control surface (the dashed line) has been purposely placed on the OUTSIDE of the pipe, where the gage pressure is zero. So, the force of the water on the inside of the pipe bend is an internal force -- inside the cv. Thus, it doesn't enter into the force analysis. Thanks for the question. I should make a point to mention that key detail in my lectures.
@@FluidMatters thank you for the clarification, it makes sense now
Nice job... Related to the FBD, do you need to include a Moment, M, along with the Fx & Fy? (assume a direction...?)
This analysis is based on conservation of LINEAR momentum. So the are the forces needed to redirect the jet. No moment.
why the different notations for x components and y components, those components being F(y) = m(v2 - v1) and F(x) = m(x2 - x1)
You must mean F(x)=m_dot(u2-u1). This is because F is a vector. u is the x-component of velocity (and v is the y-component).
Thanks !
Glad to hear the video was helpful! Best of luck with your studies.
sir can u please explain me how to take the direction of force
As in your Statics course: You start by assuming a direction for the force (which may or may not be correct). You then do the analysis using the assumed direction. If the force comes out positive then the assumed direction was correct. If it turns out to be negative, then the direction of the force needs to be flipped (180 degrees). I hope that helps.
Pleas sir I want this book pdf for fluid mechaincs
Sorry. I can't do that.
Peace be upon you sir... I need the name of the source for the Fluid Mechanics book and the number of copies. Thank you
SIR, IN THE QUESTION, ATMOSPHEARIC PRESSURE GIVEN AS 100 KPA SO HOW CAN YOU TAKE P2 GAUGE = 0?
Gauge pressure is defined as the pressure relative to local atmospheric pressure. So P_2=0 gauge. A Bourdon pressure gauge at the outlet would read zero. In these types of momentum problems you have to work in gauge pressure, for reasons that are explained in this video: ruclips.net/video/pk3nFNQRmFU/видео.html
@@FluidMatters thank you for the explanation sir.
@@FluidMatters but as p2 we are using straight 200kpa in that why we are not using relative gauge pressure
@@DhushanSuresh I think you mean p_1. The problem states that "the gauge pressure is p1=200 kPa". So, the absolute pressure at point 1 would be 300 kPa.
@Fluid matters sir can I convert gauge pressure into absolute pressure and then use the equation?
Why is the momentum force in the opposite direction as the pressure force? Seems like they would both be acting in the same direction, no?
The pressure force acts upward on the nozzle, as shown in the Free Body Diagram. So, the component of F_y (the forced needed to hold the nozzle in place) due to pressure alone must be downward. In contrast, the fluid momentum in the vertical direction increases through the nozzle. This change in momentum requires a force (F_y) in the upward direction to hold the nozzle in place. (Think of trying to hold a jet engine in place.)
life saver.finally know why😁