Question

“A pipe is carrying hot water through a cold storage facility. The ambient air in the cold storage has temperature of ?5?C. To maintain uniform temperature in the cold storage, blowers installed in the facility induce a 3 m/s velocity to the cold air (which can be assumed to be flowing across the water pipe). Hot water inside the pipe has a mean velocity of 0.5 m/s. The internal and exter- nal diameter of the pipe are 8.4 cm and 10 cm. The effective thermal conductivity of the pipe material is 60 W/m?C. The mean temperature of the hot water in the pipe entering the cold storage is 50?C. Also assume that the water flow is fully developed. Neglect radiation. For the purpose of convection coeffi- cient calculations, assume the bulk-mean temperature of hot water to be same as inlet mean temperature (50?C) and the outer surface temperature of the pipe is very close to the bulk mean temperature of water.”

(a) Calculate the Grashof number and show whether the use of a forced convection correlation was appropriate for evaluating external convection

(b) Assume that the surface and mean temperatures remains same. Assume the emissivity of the pipe surface is 0.5. If instead of 3 m/s air the cold storage was quiescent, what is the rate of heat transfer from a 10-m long section of the pipe to the atmosphere?.

Answer 1

pietui Canng a coster ald toge facly e locit ea) SOC Do dl 10 1S39 x 10 auium NY 2 구구 , 83 10 783

시 Duo --th;' d /being cooled ) ;8 265. 28 2.06 9064 ㅈ0.42 6 0 1.97 xo 00115丨 9.90 x10s I. OIS 97 - -0256 0 0 63 aut

Pole es untF eus O-1635 ง. 294x10-3 2. 2quxto 33 S. xIO ケー7 22 o eau accuuDho Mot ai d 12.