Chapter 2 Flashcards
Can you draw the diagram for a zoomed in small volume of fluid from a cubical container?
Yes or no
What is the body force in this situation?
Related to the weight of the fluid, is equal to the weight of the fluid particles contained in the small volume.
dW=dm.g=rho.dV.g
What are the six surface forces?
L&R, F&B, T&D
How to get an expression for x and y direction resultant force?
L: Fl=Pl.dy.dz R: Fr=Pr.dy.dz dFx=Fl-Fr=(Pl-Pr)dy.dz F: Ff=Pf.dx.dz B: Fb=Pb.dx.dz dFy=Fb-Ff=(Pb-Pf)dx.dz
How to get an expression for resultant z direction force?
T: Ft=Pt.dx.dy
D: Fd=Pd.dx.dy
dFz=Fd-Ft-weight=(Pd-Pt)dx.dy-rho.dV.g
Prove horizontal pressure is constant?
The fluid is at rest so is in equilibrium.
dFx=0,dFy=0 …. Pl=Pr,Pb=Pf
Find an expression for pressure variation in vertical direction?
dFz=0…… dP/dz=-rho.g
What is gamma?
Specific weight=rho.g
Application of pressure variation in vertical direction expression in an incompressible fluid how to get a new expression for calculating pressures at different heights?
Draw diagram…
Integrate dP/dz=-rho.g between z1&z2:
P2-P1=-rho.g(z2-z1)=-rho.g.h
P1=P2 + rho.g.h
What is pressure head?
Pressure head, H=(P-Po)/gamma
Application of pressure variation in vertical direction expression in an compressible fluid how to get a new expression for calculating pressures at different heights?
PV=mRT => m/V= P/RT => rho=P/RT….. Plugging this into dP/dz=-rho.g and integrating with g,R,T constant (isothermal) eventually gives P1=P2.e^g(gh/RT)
If P2=Po (z2=h) which is the same as Patm, what is pressure at depth H? (Compressible)
P=Po.e^(gH/RT)
What is gauge pressure?
Pgauge=Pabs-Patm
Is absolute pressure always positive or negative?
Positive
When is gauge pressure positive/negative?
Positive when Pabs > Patm and negative when Pabs<Patm
If gauge pressure is positive/negative when happens to fluid?
Positive: blowing , fluid will come out of the system to the atmosphere
negative: suction , fluid will go into the system from the atmosphere
What shape is a piezo meter? Related equations for this?
L
Pa=gamma.h + Patm
Pgauge=Pa-Patm=gamma.h
Limitations of a piezo meter?
Pcontainer>Patm only
Fluid pressure inside the container must be small so that the height of the column is reasonable otherwise a long tube is needed
Suitable only for liquid
