Question

a. Discuss why car inside temperature is high when you park the car outside in a sunny day even under the shade and the relation with glass transmissivity (Greenhouse effect). [5 marks]

b. A double walled spherical tank is used to store iced water at O'C. The tank internal diameter is 2 m and wall thickness is 0.5 cm. The inner and outer walls are separated with the 2 cm thick space. The air between the two walls of the tank is evacuated in order to minimize the heat transfer. The surfaces surrounding the evacuated space are polished so that each surface has an emissivity, e = 0.15. The temperature of the outer wall of the tank is measured to be 20"C. Assume the inner wall of the steel tank is at 0"C and conduction resistances of the walls are negligible. Determine:

The rate of heat transfer to the iced water írÍ the tank [5 marks]

ii. The amount of ice at 0"C that melts during a 24 h period. [5 marks]

c. A thermocouple is used to measure the temperature of hot air flowing in a duct, whose walls are maintained at 000 K shows a temperature reading of 700 K. lf the emissívity of the thermocouple junction ís 0.6 and the convection heat transfer coefficient is 100 Wlm2.K, determine the actual temperature of air. [5 marks]

Answer #1

In casting furnace, the combustion gases are separated from
the
surrounding air by a wall with a thickness of 12 cm, 1.2
W/m.K, and 0.85
as emissivity. Calculate the inner surface of the wall since
the outer
surface temperature of the inner wall, where the air has 273 K
and 25
2
W/? . ? as a coefficient of convective heat transfer.
Problem #2 (5 points)
Expect that

Steam at an average temperature of ?∞= 400°C flows through a
steel pipe. The inner and outer radii of the pipe are r1 = 4 cm and
r2 = 4.5 cm, respectively, and the outer surface of the pipe is
insulated with a layer of 50 mm thick-calcium silicate of thermal
conductivity of k = 0.5 W/m.K, and is maintained at 350 °C. If the
convection heat transfer coefficient on the inner surface of the
pipe is h = 65...

10. Air is to be heated by passing
it over a bank of 2.8-m-long tubes inside which steam is condensing
at 90ºC. Air approaches the tube bank in the normal direction at
20ºC and 1 atm with a mean velocity of 5.2 m/s. The outer diameter
of the tubes is 1.6 cm, and the tubes are arranged staggered with
longitudinal and transverse pitches of SL = ST= 4 cm. There are 30
rows in the flow direction with 10 tubes...

You want to limit the heat flux density (heat
intensity) by a wall to 10 W / (m2). The outside temperature is 4 °
C and the internal temperature 37 ◦C.
How thick should a steel wall (λ = 17, 3 W / (m · K)) be to meet
requirements?
How thick must a mineral wool disk (λ = 0, 038 W / (m · K) be) to
give the same greatest heat intensity?
Disregard the heat transfer rates between...

1-The temperature value inside a reactor in the treatment plant
is 30 0C during operation. The outdoor temperature in the winter
period is 5oC. The wall thickness of the reactor is 0.10 m and its
area is 20 m2. Air and reactor wall heat transfer coefficients and
conductivity are given below.
reactor = 20W / m2.K, creator = 0.8 W / m.K; outdoor environment =
10 W / m2.K
a. Under these conditions, calculate the heat loss value from the...

A house with 200-m2 floor space is heated with geothermal water
flowing through pipes laid in the ground under the floor. The walls
of the house are 4 m high, and there are 8 single-paned windows in
the house that are 1.2 m wide and 1.8 m high. The house has R-4
insulation (where R= 1/U is the overall unit thermal resistance(the
R-value) and U is the overall heat transfer coefficient) in the
walls and R-5 on the ceiling. The...

Consider the BVP or the steady-state temperature u(x,y,z) in the
airspace between two infinite (in the y and z directions) stone
walls that are perpendicular to the x-axis, and are 5 centimeters
apart from each other (ie the wall surfaces in contact with the air
space are 5 cm. apart), with the first (or left) wall located at
x=-1 cm. and the second (or right) wall at x= 4 cm, where ux = -10,
and u=100, respectively. Temperature is measure...

a) A vertical plate of 700 mm wide
and 120 cm height is maintained at a temperature of 95oC
in a room at 25oC with an air conditioning with velocity
of 36000 cm/min. Calculate the heat transfer coefficient and
convective heat transfer rate.
(b) Two concentric cylinders are
located in a large room. Determine the view factors for the two
cylinders when the length is 20 cm, the inner radius
(r1) is 5 cm and the outer radius (r2) 10...

1.
Consider a 1.8-m high and 1.5 m-wide double-pane window
consisting of two 4-mm thick layers of glass (k = 0.78 W/m°C)
separated by a 10-mm wide stagnant air space (k = 0.026 W/m°C). The
room is maintained at 20°C while the temperature of the outdoors is
-10°C. Take the convective heat transfer coefficients on the inner
and outer surfaces of the window to be 10 W/m2°C and 40 W/m2°C,
respectively.
Determine the steady rate of heat transfer through this...

You are working for a camping gear manufacturer and your boss
has asked you to design a new portable cooler. The portable cooler
will have the shape of a rectangular prism, with a height of 25 cm,
a width of 20 cm and a length of 35 cm. The walls of the cooler
will be composed of a thin inner liner (negligible resistance to
heat transfer), a gap containing water, and an outer insulating
wall having a thickness of 20...

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