MyQuestionIcon

1

You visited us 1 times! Enjoying our articles? Unlock Full Access!

Radiative Heat Transfer Laws - I

A small hot s...

Question

A small hot surface at temp 425 K having an emissivity of 0.85 dissipates heat by radiation into a surrounding area at 400 K. The equivalent radiation heat transfer coefficient in $W / m^{2} K i s$

A

13.5

Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses

B

6

No worries! We‘ve got your back. Try BYJU‘S free classes today!

C

11

No worries! We‘ve got your back. Try BYJU‘S free classes today!

D

8

No worries! We‘ve got your back. Try BYJU‘S free classes today!

Open in App

Solution

The correct option is A 13.5
$Rediative heat transfer = ε σ A (T_{1}^{4} - T_{2}^{4})$

$= h_{r} A (T_{1} - T_{2})$

$ε σ (T_{1}^{2} + T_{2}^{2}) (T_{1} + T_{2}) (T_{1} - T_{2}) = h_{r} (T_{1} - T_{2})$

$h_{r} = ε σ (T_{1}^{2} + T_{2}^{2}) (T_{1} + T_{2})$

$= 0.85 \times 5.67 \times 10^{- 8} (425^{2} + 400^{2}) (425 + 400)$

$h_{r} = 13. 54 W / m^{2} K$

$h_{r} = radiative heat transfer corfficient.$

Suggest Corrections

thumbs-up

0

Similar questions

Q. A steam pipe

(ε = 0.9)

of 0.4m diameter has a surface temp of 500 K. The pipe is located in room at

27^{o} C

, and the convection heat transfer coefficient is

25 W / m^{2} K .

. The rate of heat loss from the pipe if the combined heat transfer coefficient by radiation and convection is

39 W / m^{2} K

Q. A hot plate of area 0.2

m^{2}

is maintained at a temperature of

59^{o} C

by a 100 W heater when the room temperature is

20^{o} C

. The appropriate convection coefficient is 2.512

(Δ T)^{1 / 4} W / m^{2} K

. Taking heat transfer from plate is by convection and radiation, the percentage of heat lost by radiation is

Q. The outside dimensions of a small cubical furnace constructed of fire clay bricks (K=2 W/mK) are 0.5 m x 0.5 m x 0.5 m, the walls are being 0.1 m thick. The temperatures at the inside and outside surface temperatures are

500^{o} C

50^{o} C

respectively. Also the heat transfer coefficient for top surface is

12 W / m^{2} K,

bottom surface is

8 W / m^{2}

K and side surface is

15 W / m^{2} K

with surrounding temperature taken as

35^{o} C

. The heat transfer from the cube to the surrounding is

Q. The hot gases enters a parallel flow heat exchanger at

425^{o} C

260^{o} C

, heating 25kg/s of water from

32^{o} C

82^{o} C

. For a surface area of

370 m^{2}

, what is the overall heat transfer coefficient in

(W / m^{2} K)

Q. The average heat transfer coefficient on a thin hot vertical plate suspended in still air can be determined from observations of the change in plate temperature with time as it cools. Assume the plate temperature to be uniform at any instant of time and radiation heat exchange with the surroundings negligible. The ambient temperature is

25^{\circ} C,

the plate has a total surface area of

0.1 m^{2}

4 k g .

The specific heat of the plate material is

2.5 k J / k g K .

The convective heat transfer coefficient in

W / m^{2} K,

at the instant when the plate temperature is

225^{\circ} C

and the change in plate temperature with time

d T / d t = - 0.02 K / S,

View More

Join BYJU'S Learning Program

similar_icon

Related Videos

lock

Radiative Heat Transfer Laws - I

OTHER

Watch in App

explore_more_icon

Explore more

Radiative Heat Transfer Laws - I

Join BYJU'S Learning Program

CrossIcon