Ch1 Introduction Importance: 生物醫學－Blood flow； kidney stones； 溺水時急救 打氣等等…… 工業 －引擎、汽車（運輸工具）流線造型、如聯 結車之整流罩等等……、或crude oil across Alaska through an 800-mile-long， 4ft-dia. pipe、航空器、飛機氣動力學等等 …… 自然界 －大氣、海洋、火山爆發、地底岩漿、海岸 消蝕等等…… (Show Transparencies relating to Fluid Mechanics) Solid & Fluid：What is a fluid? From Observation－Solid (hard; not easily deformed); Fluid (Soft; easily deformed; readily move through air)

From Scientific or Engineering Point View － Molecular structure of Materials (Solid vs. Fluid; intermolecular cohesive forces) Thus liquids can be easily deformed (but not easily compressed). Gases：have even greater mlc spacing and freedom of motion with negligible cohesive intermlc forces; very easily deformed (and compressed) and will completely fill the volume of any container in which they are placed. A more specific distinction： How they (gas, liquids, solids) deform under The action of an external load.

Solid (within the limit of elasticity) Shear stress shear modules shear strain of elasticity Fluid a fluid is defined as a substance that deforms continuously when acted on by a shearing stress of any magnitude. plate no slip condition H bubble (velocity) Dimensions, Dimensional Homogeneity, and Units (See the text books; Table 1.1; SI/BG)

Characteristics of A Fluid: Density: (Greek symbol) Specific volume: Specific weight: Specific gravity: S.G.=

unit vectors) Stress at point： tangential stress normal stress Define：tension stress（+） compression stress（-） Fluid in static state

Viscosity: (Solid) shear stress ~ shear strain （ ） (Fluid) shear stress ~ time rate of shear strain（ ） （absolute viscosity） （kinematic viscosity）

Time rate of strain （angular deformation） 1. 2.

Velocity gradient change of velocity in x-direction in Y plane. (SI) (BG) An important parameter for momentum transport (Contact area per second)

Ideal gas law： Non-ideal gas： Compressibility of Fluids： Bulk Modulus Isothermal bulk modulus of elasticity Coefficient of compressibility

Compression and Expansion of Gases： Isothermal process： Isentropic process： （no heat exchanged with the surroundings） Speed of sound Isentropic process (small disturbances more rapidly negligible heat transfer)

Vapor Pressure Some liquid mlc at the surface have sufficient momentum to overcome the intermlc cohesive forces and escape into the atmosphere. pressure is called vapor pressure Appendix B（Tables B.1 & B.2） Boiling：which is the formation of vapor bubbles within a fluid mass, is initiated when the absolute pressure in the Fluid reaches the vapor pressure

Sea Level： T P water boiling 100。C （212。F） 1atm（14.7psi） 10,000ft： water boiling 89.4。C （193。F） 1atm（10.1psi） Cavitation：1.underwater explosion 2.Ship propeller 3.Irregular, narrowed passages of a valve or pump cause structure damage

Surface Tension a liquid/ a gas or between two immiscible liquids, forces develop in the liquid surface－skin. ex：a steel needle will float on water if placed on the surface. and other fluids The difference between the pressure inside the drop and the external pressure The pressure inside the drop＞the pressure surrounding the drop

Continued Surface tension Q: Would the pressure on the inside of a bubble of water be the same as that on the inside of a drop of water of the same diameter and the same temp? Fig.1.7 Effect of capillary action in small tubes. Liquid-gas-solid interface liquid wet solid surface wetting Q－angle of contact

Mercury Non wetting ＊give some example from NCFM Inertial,gravitational&viscous process are much more