IST / DEQ
Mestrado Integrado em Engenharia Química
Mestrado Integrado em Engenharia Biológica
Mestrado em Engenharia e Gestão da Energia
Fenómenos de Transferência I
2014-2015 1º Semestre
1º Teste / 30.10.2014 / 19:00 h Duração 1:30 H
Docentes: Alda Simões; João Fareleira; Teresa Reis
nº:
Name:
Course:
Parte A
There is only one correcy answer for each question. All the calculations should be made on this sheet. The
use of calculators is not allowed until delivery of this sheet.
For each right answer: +1,00 (for each wrong: -0,25)
-3
3
1. Taking the density o fair as constant and equal to 10 g/cm , what is the approximate thickness of the atmosphere of
-2
our planet? (take 1 atm=100 kPa and g=10 m s ).
i.
10 km
ii.
100 km
iii.
1000 km
iv.
10000 km
v.
None of the above.
2.
Consider the equation for diffusional transport of heat:
In which
is the heat transferred per time unit. What are the dimensionally correct units for the thermal
conductivity, k?
-1
-1
i.
Js m K
-1
ii.
WmK
-2 o -1
iii.
cal m C
-1
-1
-1
iv.
erg s m ºC
-1 -1
v.
Nsm K
3.
The viscosity of water at 20°C is:
i.
1 stoke
ii.
1 centistoke
iii.
1 poise
iv.
1 centipoise
-3
v.
1 g cm
4.
The expression “developped flow” means:
i. There is no accumulation
ii. The flow is incompressible
iii. The velocity profile does not change along the flow direction.
iv. The velocity profile is flat.
v. The flow lines are parallel.
5.
A fluid is forced to flow inside the tube of the figure, from left to right. The work done to overcome the friction at
the walls is null.
Which of the sections has the highest pressure?
i.
A
ii.
B
iii.
C
iv.
D
v.
They are all the same because there is no friction.
6.
The fluids that have decreasing apparent viscosity with time under constant agitation rate are called:
i. Thixotropic
ii. Pseudoplastic
iii. Reopectic
iv. Newtonian
v. Bingham plastic
7.
Consider the scheme in the figure, in which water flows with no friction, and consider g=10 m/s e 1atm=100000 Pa.
At point A, the pressure is 9.5 atm and the water velocity is 10m/s. What is the velocity at point C?
i.
2.5 m/s
ii.
5 m/s
iii.
10 m/s
iv.
20 m/s
v.
40 m/s
8.
For the same figure, the pressure at C is:
2
i.
0 N/m
2
ii.
100 000 N/m
2
iii.
150 000 N/m
2
iv.
800 000 N/m
2
v.
1 100 000 N/m
IST / DEQ
Mestrado Integrado em Engenharia Química
Mestrado Integrado em Engenharia Biológica
Mestrado em Engenharia e Gestão da Energia
Fenómenos de Transferência I
2014-2015 1º Semestre
1º Teste / 30.10.2014 / 19:00 h Duração 1:30 H
Docentes: Alda Simões; João Fareleira; Teresa Reis
Read carefully. Justify clearly your replies and show clearly your calculations.
I (6,0 val)
Water flows, in the horizontal, with a velocity of 20 m/s through the pipe bend (90º elbow) shown
in the figure. The gage pressure on section 1 is 140 kPa. If the friction is neglected, what will be the
horizontal force necessary to maintain the pipe bend in position?
Pipe diameter: 5 cm
1
water = 1000 kg/m3; μwater = 1.0 mPa.s
2
II ( 6,0 val)
A cylindrical tank contains air, oil and water. On the oil a pressure of 35 kPa gage is maintained.
What is the velocity and the flow rate of the water leaving if we neglect both friction everywhere
and the kinetic energy of the fluid above elevation A? The jet of water leaving has a diameter of 1 ft
water = 1000 kg/m3; μwater = 1.0 mPa.s
oil = 800 kg/m3
1 ft=0.3048 m