1. Pressure In static Fluids
Fluid Mechanics
Pressure In static Fluids
CHE 312/CHE315
Pressure In static Fluids

2. Objectives Define and classify fluids
Define static Fluids vs. Dynamic Fluids
Explain pressure in a static fluid
Derive the equation of pressure in a static fluids
Show examples of applications of static pressures.
CHE 312/CHE315
Introduction

3. Fluid:
A continuous substance whose molecules move freely past one another and that has the tendency to assume the shape of its container; a liquid or gas.
CHE 312/CHE315
Introduction

4. Types of Fluids:
Incompressible Fluids: Effect of pressure on the fluid is neglected (small) Most liquids are incompressible
CHE 312/CHE315
Introduction

5. Gases are compressible
Types of Fluids:
Compressible Fluids
Gases are compressible
CHE 312/CHE315
Introduction

6. static Fluids vs. Dynamic Fluids
CHE 312/CHE315
Introduction

7. Pressure in A Static Fluid
Furnace duct
Pipe or tube
Dam
Pressure is a Normal Force (acts perpendicular to surfaces)
It is also called a Surface Force
CHE 312/CHE315
Introduction

8. P=F/A P=rgh F =mg P = h ρ g + P0 Pressure in A Static Fluid P0 h P
CHE 312/CHE315
Introduction

9. Pressure in A Static Fluidx z Z
Force Balance
SF =0 DZ
Think-Pair-Share
How many force components are making the balance?
z+Dz
P+DP z P
CHE 312/CHE315
Introduction

10. Pressure in A Static Fluid
Fz+Dz Fz W
Force Balance
SF =0
z+Dz
P+DP z P
Fz =PA
Fz+Dz = (P+DP)A
W = mg =(rV)g =r(ADz)g
Assumptions?
dP+rgdz = 0
DP+rgDz = 0
CHE 312/CHE315
Introduction

11. the vertical height of a fluid that determines the
pressure in fluid, the shape of the vessel does
not affect the pressure.
CHE 312/CHE315
Introduction

12. CHE 312/CHE315
Introduction

13. CHE 312/CHE315
Introduction

14. Introduction Related Links:
CHE 312/CHE315
Introduction

15. Summary
CHE 312/CHE315
Introduction

16. Pressure In static Fluids
2.2C Head of a fluid
Pressures units: Pascal (N/m2), Psi, dynes/cm2, etc…
A common method of expressing pressure, is in terms of head (h) in meter (m) or feet (ft) of a particular fluid:
…………………………………………………………………….
……………………………………………………………………..
Example: Atmospheric Pressure?
CHE 312/CHE315
Pressure In static Fluids

17. Pressure In static Fluids
in SI units
h (m) = P/(r*g)
h (ft) = P*gc/(r*g)
in English units
…………………………………………………………………….
……………………………………………………………………..
Example: Atmospheric Pressure?
CHE 312/CHE315
Pressure In static Fluids

18. Pressure In static Fluids
2.2D Devices to Measure Pressure and Pressure Differences
In industrial processing, it is important to measure and control the pressure and/or the liquid level in a vessel or process.
For Flowing pipes, flow rate is also needed. Thus, pressure measurements are important.
CHE 312/CHE315
Pressure In static Fluids

19. Simple U-tube ManometerPa Pb 4 2 3 1 5 ra rb R Z
Density of Fluid A > Density of Fluid B
A and B are immiscible
Pa is exerted on one arm of the tube
and Pb is exerted on the other arm.
CHE 312/CHE315
Pressure In static Fluids

20. Pressure In static Fluids
Pressure difference between Pa and Pb:
Pressure at point 1: P1=Pa
Pressure at point 5: P5=Pb
At point 2: P2=Pa+(Z+R) rB g
(R: reading of the manometer) Pa Pb 4 2 3 1 5 rA ra rb rB R Z
CHE 312/CHE315
Pressure In static Fluids

21. Pressure In static Fluids
At point 3: P3=P2 Also, P3= Pb+Z rB g + R rA g
Therefore, P3= Pa+(Z+R) rB g = Pb+Z rB g
+ R rA g Pa Pb 4 2 3 1 5 rA ra rb rB R Z
Pa -Pb= R (rA- rB) g (SI ) Pa -Pb= R (rA- rB) g/gC (English )
CHE 312/CHE315
Pressure In static Fluids