Question

Problem 1 A pipe of outside diameter d=30 mm is exposed to the cross air flow at 20°C, velocity of the air is 5 m/s, and the temperature of the outside surface of the pipe is 80 °C. Determine: a) An average coefficient of heat transfer from outside surface of the pipe to the air. b) The heat flux exchanged per unit length of the pipe.

use dimensionless equations

Answer 1

problem o: Given data Diameter d = 30 mm d = 0.03 m = Ambient temperature Too= 20°C 3 velocity 5 m18 surface temperature Ts = 80°c velocity Voo find out: 0 Average heat transfer Coefficient Chl Heat Flux per unit length (W) 2) Solve At bulk mean temperature Tom た。 = Tot Ts २ 50°C 20+ do 2 Tom = T At 80+20 50c At soc for air

& Density T1092 kg/m3 si & Dynamic viscosity u = 1.963x10-5 Kg Thermal Conductivity K= 0'02735 W/mK → Prandte number Pg= 0.7228 Reynold number of pipe (Re) Re= 8 Vood T u 11092% 5X0:03 1.963x10-5 U Re 8344.37 7 4000 Turbulent pipe flow NUS Selt Dumber M correlation for turbulent pipe flow M Nu = 01023 8 Rooi Proiu 5 NUZ 01023X68344. 3700*8*10.72287014 NU- r 27.69

b= Average heat transfer Coefficient TT ba Nuk d T h 27.69%0.02735 ll 0:03 ha 25.25 W b Heat flux (9 A qa h A (AT) = =hx TdLL (Ts - To L=1m per unit length 25125X TX 0'03X1X ( 80-20) wim 2 142.78 - m2 per - h AT= 25.254 ( 80-20) 1515 m2