Exam 1 Flashcards
Definition of a fluid
A substance that deforms continuously when acted upon by a shearing stress of any magnitude (i.e., they will flow).
g
9.8 m/s^2; 32.2 ft/s^2
Deg R
deg R = deg F + 459.67
1 lb
1 lb = (1 slug) (1 ft/s^2)
Weight (W)
W = mg
1 N
1 kg *m/s^2
1 watt (W)
1 W = 1 J/s
1 J (joule)
1 J = 1 N * m
1 Pa
1 N/m^2
sea-level atmospheric pressure
14.7 psi
101 kPa
specific mass
density (rho) = mass/volume
specific weight
(gamma) = rho * g
specific gravity
SG =rho/rho_water
= gamma/gamma_water
shear stress
(tau) = mu* du/dy,
where mu = viscosity
du/dy = velocity gradient
Newtonian fluids
shearing stress is linearly related to the rate of shearing strain (velocity gradient);
i.e., tau vs du/dy is linear
no-slip condition
fluid “sticks” to a surface (U=0)
direction of shear stress on a surface
same direction as velocity
Reynold’s number
ratio of inertia to viscous forces. dimensionless.
Re = (fluid density*average velocity * characteristic length)/mu
Bulk modulus
A property used to describe compressibility
Ev= -dp/(dV/V) or dp/(drho/rho)
where dp is the differential change in pressure needed to create a differential change in volume (dv) of a volume (V)
(negative sign is because an increase in pressure will cause a decrease in volume)
Large values for the bulk modulus indicate that the fluid is…
relatively incompressible (i.e. it takes a large change in pressure to create a small change in volume).
When does boiling occur?
When the absolute pressure within a fluid reaches the vapor pressure.
Surface tension
the intensity of molecular attraction per unit length along any line in the surface
The value of surface tension _____ as temperature increases.
decreases
Definition of pressure
Normal force per unit area
Pascal’s law
The pressure at a point in a fluid at rest, or in motion, is independent of direction as long as there are no shearing stresses present.
What is a surface force, and what are the 2 types
Force proportional to the area. Normal force (pressure force sigma or P) Tangent force (shear stress force tau)
What is a body force?
Force proportional to the volume (weight = gamma * volume)
pressure variations for a fluid
pressure does not change in x direction (dp/dx=0)
pressure does not change in y direction (dp/dx=0)
pressure is a function of gamma in z direction (dp/dz=-gamma).
in an incompressible fluid: moving upwards, pressure ____.
decreases.
moving downwards, pressure ____.
increases
moving horizontally, pressure ______.
does not change.
kinematic viscosity
= dynamic viscosity (mu)/density
speed of sound
= sqrt(Ev/rho)
speed of sound in solids > liquids> gases
