6.11. 13,000lb/hr of 26API gas oil (see Example 6.3 in text for viscosities) is cooled from 450 to 350F by heating 57API gasoline under pressure from 220 to 230F in as many 3- by 2-in. IPS double pipe 20-ft hairpins as are required. Pressure drops of 10 psi are permitted along with a minimum dirt factor of 0.004. (a) How many hairpins are required? (b) How shall they be arranged? (c) What is the final dirt