Pressure In static Fluids
Fluid Mechanics Pressure In static Fluids CHE 312/CHE315 Pressure In static Fluids 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 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 Types of Fluids: Incompressible Fluids: Effect of pressure on the fluid is neglected (small) Most liquids are incompressible CHE 312/CHE315 Introduction Gases are compressible
Types of Fluids: Compressible Fluids Gases are compressible CHE 312/CHE315 Introduction static Fluids vs. Dynamic Fluids
CHE 312/CHE315 Introduction 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 P=F/A P=rgh F =mg P = h g + P0 Pressure in A Static Fluid P0 h P
CHE 312/CHE315 Introduction Pressure in A Static Fluid
x 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 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 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 CHE 312/CHE315 Introduction CHE 312/CHE315 Introduction Introduction Related Links:
CHE 312/CHE315 Introduction Summary CHE 312/CHE315 Introduction 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) inmeter (m) or feet (ft) of a particular fluid: . .. Example: Atmospheric Pressure? CHE 312/CHE315 Pressure In static Fluids 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 Pressure In static Fluids
2.2DDevices 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 Simple U-tube Manometer
Pa 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 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 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