An object of irregular shape has a characteristic length ofL = 1 m and is maintained at a uniform surface temperatureof Ts = 325 K. It is suspended in anairstream that is at atmospheric pressure (p = 1 atm) andhas a velocity of V = 100 m/s and a temperature ofT? = 275 K. The average heat flux from thesurface to the air is 12,000 W/m2. Referring to theforegoing situation as case 1, consider the following cases anddetermine whether conditions are analogous to those of case 1. Eachcase involves an object of the same shape, which is suspended in anairstream in the same manner. Where analogous behavior does exist,determine the corresponding value of the average heat or masstransfer convection coefficient, as appropriate.
(a) The values of Ts,T?, and p remain the same, butL = 2 m and V = 50 m/s.
(b) The values of Ts andT? remain the same, but L = 2 m,V = 50 m/s, and p = 0.2 atm.
(c) The surface is coated with a liquid film that evaporatesinto the air. The entire system is at 300 K, and the diffusioncoefficient for the air–vapor mixture is DAB =1.12 × 10?4 m2/s. Also, L = 2 m,V = 50 m/s, and p = 1 atm.
(d) The surface is coated with another liquid film for whichDAB = 1.12 × 10?4 m2/s,and the system is at 300 K. In this case L = 2 m,V = 250 m/s, and p = 0.2 atm.
