Question

The heat flux, q, is 6000 W/m2 at the surface of an electrical resistance heater. The heater temperature is 120C when it is cooled by air at 70C. (a) What is the average convective heat transfer coefficient, ? (b) What will the heater temperature be if q is reduced to 2000 W/m2?

Answer #1

Consider a surface of area 26 m2 at which the
convection and radiation heat transfer coefficients are 13.05
W/m2·K and 20.39 W/m2·K, respectively. Assume
the medium and the surrounding surfaces are at the same
temperature. Determine the single equivalent heat transfer
coefficient (in W/m2·K). (Round the final answer to two
decimal places.)

Consider the electrical heater of Problem 7.49. If the blower
were to malfunction, terminating airflow while the heater continued
to operate at 1000 W/m, what tem- perature would the heater assume?
How long would it take to come within 10 C of this temperature?
Allow for radiation exchange between the heater ( 0.8) and the duct
walls, which are also at 27 C.
7.49) Along,cylindrical,electricalheatingelementofdiameter
D 10 mm, thermal conductivity k 240 W/m K, den-
sity 2700 kg/m3, and specific...

Air at a pressure of 1 atm and a temperature of 15C is in
parallel flow at a velocity of 10
m/s over a 3-m long flat plate that is heated to a uniform
temperature of 140 C.
(a) What is the average heat transfer coefficient and heat transfer
rate for the plate?
(b) What is the local heat transfer coefficient and heat flux at
the midpoint of the plate?
(c) Plot the variation of the heat flux with distance...

An insulated copper wire with a length of 1.2 m carries 20 A of
current. The copper is 1 mm in diameter and the insulation (k=0.13
W/m. ºC) has a thickness of 0.8 cm. The wire has electrical
resistance of 0.0321 Ω. Air at 25 ºC blows in crossflow over the
wire to produce an external convective heat transfer coefficient of
219 W/m2. K. Assuming the copper is isothermal, find the copper
temperature. Take the electrical resistivity of copper to...

A can of soft drink, 12-cm high and 6-cm diameter, is initially
at 20°C. It is placed in a refrigerator where the air is at 0°C.
The convective heat transfer coefficient associated with the outer
surface of the can is 10 W/m2 °C. Assuming the properties of the
drink to be those of water and that the heat capacity of the
container is negligible, estimate the time taken for the
temperature of the drink to reach 5°C.
USING EES PLEASE

A process fluid having a specific heat of 3500 J/kg?K and
flowing at 2 kg/s is to be cooled from 80 °C to 40 °C with chilled
water, which is supplied at a temperature of 15 °C and a flow rate
of 2.5 kg/s. Assuming an overall heat transfer coefficient of 2000
W/m2?K, calculate the required heat transfer areas for the
following exchanger configurations: (a) Parallel flow; (b) Counter
flow; (c) a 1-2 shell and tube exchanger with the water...

A long cylinder 11 cm in diameter is initially at a uniform
temperature of 427 C and has a density of 7250 kg/m3, thermal
conductivity of 16.7 W/m-K, and a specific heat of 540
J/kg-K. The cylinder is suddenly plunged into water with a
temperature of 27 C, giving a convective heat transfer coefficient
of 380 W/m2-K.
a) Determine the surface and centerline temperatures of the
cylinder 12 minutes after immersion.
b) Calculate the heat transferred from the cylinder during this...

A thin metallic wall may be constructed using copper (properties
are given in the table). The piping is required
to have a radius r = 0.008 m and carries steam at 385 K. The wall
is inside a room surrounded by air at a temperature
of 298 K. The wall is insulated with a material (properties are
given in the table).
Properties
Copper
Insulation material
Thermal Conductivity (W/m per ˚C)
385
0.071
Density (kg/m3)
8940
453
i. If the external...

1. In an industrial process, a tank containing 200 liters of
water at 372 K at a constant pressure is used as a thermal energy
storage device. The device is used to heat a residential space that
is maintained 293 K. There is a negligible change in the volume of
the water. The water is stirred during this process to maintain a
uniformly distributed temperature. During the process, the
convective heat transfer coefficient between the water and the
space is...

16a) A triple glazed window consists of 3 clear glass
panes of 4 mm thickness each, separated by two
air cavities of 13 mm each in thickness. The
window area is 1.0 m2
. If the thermal conductivity
of the glass panes is 0.8 W•m-1•K-1 and of the air
cavities is 0.026 W•m-1•K-1 what is the total
thermal resistance of the window?
(A) 2.452 K•W-1
(B) 0.015 K•W-1
(C) 1.015 K•W-1
(D) 6004 K•W-1
16b)A heater provides 305 W of...

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