CE 230-Engineering Fluid Mechanics Week 1 Introduction

Policy Get to know each other Things to know about instructor policy Grading

Basic terminology What is fluid mechanics What is a fluid Difference between solid, liquid and gas

Applications Applications of fluid mechanics in daily life

Fluid Properties

Units Basic Units versus derived units SI versus Traditional units prefixes

What are the units of? Mass Length Time Temperature Weight Pressure Energy Power

Intensive versus Extensive properties Density Specific weight Specific gravity Tables A.2-A.4 at the end of the text Gases, air, water, and some liquids

Example What is the weight of a 1 cubic meter of water if the temperature is 5 C? What if the temperature was 90 C? or 0 C?

terminology Incompressible fluid Compressible fluid Ideal fluid Perfect gas?

Perfect gas law P=ρRT R is the gas constant with units of m.N/kg K or ft lb/slug R See appendix A.2 for R values

Problem 2.6 What is the weight of a 10 cubic feet tank containing oxygen if it is pressurized to 400 psi (absolute pressure) and at a temperature of 70 F? answer 22.5 lb

Elasticity & Bulk modulus The needed pressure change needed to reduce the volume of a fluid E v = -Δp/(ΔV/V) What does it mean if E v is very big? For waterE v = 2.2 GN/m 2

Problem 2.46 What pressure increase must be applied to water to reduce its volume by 1%?

Surface tension Due to unbalanced molecular forces at interface of two fluids. Force /length For water-air surface σ=0.073 N/m This accounts for capillary rise

Estimate the capillary rise of water in a tube of diameter d.

Applications of surface tension Pressure in a droplet Pressure in a soap bubble Cylinder supported by surface tension Ring being pulled out of liquid Capillary rise between two plates

Vapor pressure The pressure at which a liquid boils Function of T (direct proportion) At what pressure does water boil? Table A.5

Example Consider two cases of water boiling in a tea kettle one near the sea and the other on top of a very high mountain. a) compare the value of vapor pressure for both cases b) compare the temperature for both cases does this make sense?

Fluid Properties (2)

Examine velocity distribution in pipe

Viscosity Consider two plates separated be a thin film of fluid. The lower plate is fixed and the upper is moving with a constant velocity. Investigate what is happening in the fluid in terms of flow or stresses.

Viscosity No slip boundary condition Relation between shear stress and velocity gradient Classification of fluids

Mechanisms of fluid resistance to shear stress Particle cohesion Transfer of molecular momentum Influence of temperature on viscosity

Units of viscosity Dynamic viscosity absolute viscosity viscosity Kinematic viscosity

Influence of temperature on viscosity

Classification of fluids according to relation of shear to strain rate

Problems on viscosity Board sliding on an inclined surface separated by a thin film of oil Is there a shear stress in the film? let’s calculate the terminal velocity

Problem # 34

Problem # 39 Calculate the weight of piston given : Terminal velocity μ Spacing between piston and cylinder Piston dimensions

Problem 2.39

Problem 2.41