HEAT TRANSFERBKFZ4Z? Tutorial4

Question 1

Two parallel surfaces each 1.83 x 1.83 m square are spaced 0.91 apart. The surfacetemperature of Ar is 81 1K and that of ,A2 is 533 K. Both are black surfaces.

a) Calculate the radiant heat transfer between the two surfaces.

b) Do the same as for part a) but for the case where the two surfaces are connected by

nonconducting reradiating walls.

c) Repeat part b), but ,A1 has an emissivity of 0.8 and Az and emissivity of 0.7.

Question 2

Two pf ane disks each 1.25 m in diameter are parallel and directly opposite each other. They are

separated by a distance of 0.5 m. Disk 1 is heated by electrical resistance to 833.3 K. Bothdisks are insulated on all faces except the two faces directly opposite each other. Assume thesurroundings emit no radiation and that the disks are in space. Calculate the temperature of disk

2 at steady state and also the electrical energy input to disk 1. (Hint: The fraction of the heat lost

from area number 1 to space is 1-Fd.

Question 3

Two disks each 2.0 m in diameter are parallel and directly opposite each other and are

separated by a distance of 2.0 m. Disk 1 is held at 1 000 K by electric heating and disk 2 at 40Q

K by cooling water in jacket at the rear of the disk. The disks radiate only to each other and tothe surrounding space at 300 K. Calculate the electric heat input and also the heat removed bythe cooling water.

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