A hot surface at 150°C is to be cooled by attaching 30 mm-long
aluminum pin fins (k= 237 W/m·K) having
the square cross-section (3-mm x 3-mm) as
shown in figure. The temperature of the
surrounding medium is 25°C, and the heat
transfer coefficient on the surfaces is 30
W/m2
·K. Determine the rate of heat transfer
from the surface for a 57-mm x 53-mm
section of the plate. Also determine the
overall effectiveness of the fins

The frequency of a given region of the electromagnetic spectrum ranges from 3 × 1016 − 3 × 1019 hertz. which type of wave is found in this region? a. x-rays b. ultraviolet rays c. infrared waves d. radio waves

Asheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200oc and is permitted to achieve a steady-state diffusion condition. the diffusion coefficient for nitrogen in steel at this temperature is 6 x 10- 11 m2 /s, and the diffusion flux is found to be 1.2 x 10-7 kg/m2 -s. also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3 . how far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3 ? assume a linear concentration profile.

Engineers find a new metal that is stronger than steel but much lighter. this material is also significantly cheaper than what is currently used for most aircraft, available in large quantities, and easy to manufacture. the engineers are excited because this new material will lower the costs of buying and operating airplanes for companies. what is probably the best step for the engineers to make next?