Question

A 25 mm diameter egg roll (k = 1 W/m degree Celsius) is roasted with the help of microwave heating. For good quality roasting, it is desired that temperature at the center of roll is maintained at 100 degree Celsius when the surrounding temperature is 25 degree Celsius. What should be the heating capacity in K W/m of the microwave if the heat transfer coefficient on the surface of egg roll is 20 W/m? degree Celsius? a) 113.31 k W/m b) 213.31 k W/m c) 313.31 k W/m d) 413.31 k W/m

Answer #1

A house has a composite wall of wood (exterior) (k = 0.12 W m-1
K -1 , 20 mm thick), fibreglass insulation (k = 0.045 W m-1 K -1 ,
70 mm thick) and plasterboard (interior) (k = 0.25 W m-1 K -1 , 10
mm thick). Determine the total heat loss through the wall when the
inside temperature is 20 °C, the outside temperature is -10 °C, the
inside heat transfer coefficient is 15 W m-2 K -1 ,...

A stainless-steel fin (k = 16 W/m. °C) has a length of
15 cm and a square cross section 12.5 by 12.5 mm attached to a wall
maintained at 250 °C. The heat-transfer coefficient is 40 W/m. °C,
and the environment temperature is 90 °C. Calculate the percentage
increase in heat transfer after attaching the fin.

A 4-mm thick, 20cm diameter cast iron frying pan (K =
55 W/mK) is heated on a traditional stovetop range. Under certain
stovetop settings, the temperature on the bottom surface of the pan
(in contact with the heating element) is measured to be
160°C and that on the inside of the pan (cooking
surface) is 150°C. Using the heat diffusion
equation, find an expression (specific solution) for the
temperature distribution across the thickness of the pan.

2.1Consider a solid cylindrical rod of length 0.15 m and
diameter 0.05 m. The top and bottom surfaces of the rod are
maintained at constant temperatures of 20oC and 95oC, respectively,
while the side surface is perfectly insulated. 2.1.1 Draw a diagram
to represent the situation described above. (3) 2.1.2 Determine the
rate of heat transfer through the rod if it is made of copper, k =
380 W/m? oC. (4) 2.1.3 Determine the rate of heat transfer through
the...

An aluminum fin 1.6 mm thick surrounds a tube 2.5 cm
in diameter. The length
of the fin is 12.5 mm. The tube-wall temperature is 200◦C, and the
environment
temperature is 20◦C. The heat-transfer coefficient is 60 W/m2 · ◦C.
Consider the heat dissipated in a pipe 1.20 m long if the fins are
4.2 mm apart from center to center
Explain your procedure with formulas

To harden a steel sphere having a diameter of 50.8 mm, it is
heated to 1033 K and then dunked into a large water bath at 300 K.
Determine the time for the center of the sphere to reach 366.5 K,
and the temperature at 10 mm from the centre. The surface
coefficient can be assumed as 710 W/m^2.K and k=45 W/m.K and
alpha=0.0325 m2/h.

Liquid water flows in a long pipe of internal diameter of
D = 0.01 m at a mean velocity of V = 0.065 m/s.
The pipe is maintained at a constant and uniform surface
temperature. Assume the flow is both hydrodynamically and thermally
fully developed. For simplicity, evaluate the properties of water
at 300 K.
Calculate the convective heat transfer coefficient of the flow
inside the pipe in W/m2K?

A 1-shell-2-tube pass heat exchanger
is made of a steel alloy (thermal conductivity 45.4 W/(m K). It is
used to cool distilled water from 34oC to
29oC using water which flows inside tubes with an outer
diameter of 19 mm and an inner diameter of 16 mm. The number of
tubes in the shell is 160 (80 per pass). The mass flow rate of
distilled water in the shell is 76180 kg/h. The cold water enters
the heat exchanger at...

Used engine oil flows at 0.025 m/s through a 12.5-mm-diameter
tube. The oil enters the tube at a temperature of 27 ºC, while the
tube surface temperature is maintained at 87º C. Determine the oil
outlet temperature for a 100-m and the total heat transfer.

Consider an aluminum pin fin (k = 240 W/m·K) with a 2 mm by 2 mm
square cross-section and a length of 4 cm that is attached to a
surface at 100o C. The fin is exposed to air at 25o C with a
convection heat transfer coefficient of 20 W/m2 · o C. Determine
the rate of heat transfer and the tip temperature of the fin for
the following cases:
(a) Convection from the fin tip.
(b) Adiabatic tip...

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