A type-302 stainless steel tube of inner and outer diameters D_i = 22 mm and D_o = 27 mm, respectively, is used in a cross-flow heat exchanger. The fouling factors, R''_f, for the inner and outer surfaces are estimated to be 0.0004 and 0.0002 m² ? K/W, respectively

(a) Determine the overall heat transfer coefficient based on the outside area of the tube, U_o. Compare the thermal resistances due to convection tube wall conduction, and fouling.

(b) Instead of air flowing over the tube, consider a situation for which the cross-flow fluid is water at

15?C with a velocity of V_o = 1 m/s. Determine the overall heat transfer coefficient based on the outside area of the tube, Vo. Compare the thermal resistances due to convection, tube wall conduction, and fouling.

(c)?For the water-air conditions of part (a) and mean velocities. U_m,i of 0.2. 0.5, and 1.0 m/s. plot the overall heat transfer coefficient as a function of the cross-flow velocity for 5 s; V_o 30 m/s.

(d) For the water-water conditions of part (b) and cross-flow velocities, V_o' of 1, 3, and 8 m/s, plot the overall heat transfer coefficient as a function of the mean velocity for 0.5 u_m,i 2.5 m/s.

Transcribed Image Text:

Fouling Rj, factors Tube, SS302 Rii Water T- 75°C -0.5 m/s D, D. V= 20 m/s T= 15°C Air