Question

A 25-mm-diameter hot surface at $T_{s} = 85^{\circ}C$ is cooled by an air jet exiting a 5-mm-diameter round nozzle with a velocity of 35 m/s and temperature of 25$^{\circ}C$. The nozzle exit is 25 mm from the hot surface. Determine the percentage change in average heat transfer coefficient at the hot surface if the air is replaced with carbon dioxide or helium. Use material properties from reputable tables.

$What\; is \; \frac{h_{He}-h_{_{air}}}{h_{air}} \; in \;percentage\; form?$

7.80 A 25-mm-diameter hot surface at T, 85°C is cooled by an air jet exiting a 5-mm-diameter round nozzle with a veloc- ity of 35 m/s and temperature of 25°C. The nozzle exit is 25 mm from the hot surface. Determine the percentage change in the average heat transfer coefficient at the hot surface if the air is replaced with carbon dioxide or helium. Use the material properties from your own search. what is (h-He-han/hair in % (note: answer is in percentage)

Answer 1

olution = 25mm 1.5 12.5 mm 2 usselt number is Qiven as S405 xo 0.55\リ2 =251.515

029iS O.2333) (259.S1S0. 7o35 0.00S 2. O. 6788 de Gx ID O.60 0.6785 0,005 51249-294 .L.x 100 % Peecentage Chan