10,000 lb/h of benzene was heated from 60 F to 120 F by heat exchange with an aniline stream that was cooled from 150 F to 100 F. A number of 16 ft hairpins consisting of 2 in. by 1.25 in. schedule 40 stainless steel pipe (type 316, k = 9.4 Btuh.ft.F) were used for this service. Table 1.1 presents the fluids property. Calculate the number of hairpins that would be required assuming benzene flows in the inner pipe in a counter-current flow pattern, the exchanger have at least one hairpin containing 32 ft of pipe and both streams exhibit low fouling tendencies. Data: For 2-in. by 1.25 in. schedule 40 pipe, D, = 1.66 inch-and-D, = 1.38 inch At pipe wall temperature, viscositics of benzene and aniline are 0.47 cP and 2.4 cP respectively External surface area per foot of 1.25-in. schedule 40 pipe = 0.435 ft, Flow area (4) = 0.00826 ft Table 1.1: Benzene and Aniline Property Fluid property (cp) Cr (Btu/lbm- "F) k (Btu/h ft.F) Benzene (ave=90F) Aniline (Tane 125F) = 0.55 0.42 0.092 2.0 0.52 0.100