Download ENT 211 Tutorial Week 1

TUTORIAL WEEK 1
PLEASE REFER TEXTBOOK FOR DETAILS ON EACH
QUESTION.
Thermal Fluid Science, Cengel, Turner, Cimbala,
3rd Edition.
QUESTION 1-2C
Why does a bicyclist pick up a speed on a downhill road even when he is not
pedalling? Does this violate the conservation of energy principles?
On a downhill road the potential energy of the bicyclist is being converted to
kinetic energy, and thus the bicyclist picks up speed. There is no creation of
energy, and thus no violation of the conservation of energy principle.
Q 1-5C
How does “heat transfer” differ from
“thermodynamics”.
Thermodynamics deals with the amount of heat
transfer as a system undergoes a process from
one equilibrium state to another.
Heat transfer, on the other hand, deals with the
rate of heat transfer as well as the
temperature distribution within the system at
a specified time.
Q 1-6C
What is the driving force for HT, EC and FF?
The driving force for heat transfer is the
temperature difference. (b) The driving force
for electric current flow is the electric
potential difference (voltage). (a) The driving
force for fluid flow is the pressure difference.
Q 1-7C
Why is Heat Transfer a nonequilibrium
phenomenon?
Heat transfer is a non-equilibrium phenomena
since in a system that is in equilibrium there
can be no temperature differences and thus
no heat flow.
1-8C
No, there cannot be any heat transfer between
two bodies that are at the same temperature
(regardless of pressure) since the driving force
for heat transfer is temperature difference.
1-14
The variation of gravitational acceleration above the sea level is given as a
function of altitude.
g = a – bz; a = 9.807 m/s2 & b = 3.32 * 10-6s-2
Determine the height above sea level where the weight of an object will
decrease by 1%?
W = mg = m(a-bz) ; At z = z1 = 0 m, W = mg = ma.
Body weight decrease by 1 %, W2 = 0.99W at z = z2
Altitude at 1% weight reduction?
0.99W = 0.99ma = m (a-bz2)
Therefore,
z2= (a – 0.99a)/b = 29,539 N.
1-17
Throw 5 kg stone upward with a force of 150 N.
g=9.79ms-2
∑F = ma
Y
is positive upwards,
Therefore,
∑F = Fup – Fg= 101.05 N
101.05 N = ma
Therefore, a = 20.2 ms-2
Q 9-3c
WHAT IS NO SLIP CONDITION?
Analysis a fluid in direct contact with a solid
surface sticks to the surface and there is no
slip. This is known as the no-slip condition,
and it is due to the viscosity of the fluid.
There is no such thing as an inviscid fluid,
since all fluids have viscosity.
Q 9-22C
• Viscosity, “stickiness” or “resistance to
deformation” of a fluid.
• Due to the internal frictional force, between
different layers
• Viscosity, cohesive forces between the
molecules, liquids, and molecular collisions in
gases.
Q 9-23C
Fluids ,shear stress, linearly proportional to the
velocity gradient (strain rate) are called
Newtonian fluids.
Q 9-25C
How does viscosity
change with
temperature?in fluid
and gas.
The dynamic viscosity of
liquids decreases with
temperature. (b) The
dynamic viscosity of
gases increases with
temperature.
Q 9-27C
Ans 9-27C (A)
Ans 9-27(B)
QUIZ Q 9-28 Submit before 18/07/08
QUIZ Q 9-29 Submit before 18/07/08