6.5. 12,000lb/hr26API lube oil (see Example 6.3 in text for viscosities) is to be cooled from 450 to 350F by heating 42API kerosene from 325 to 375F. A pressure drop of 10 psi is permissible on both streams, and a minimum dirt factor of 0.004 should be provided. (a) How many 20 -ft hairpins of 21/2 - by 11/4-in. IPS double pipe are required? (b) How shall they be arranged, and (c) what is the final dirt factor