In order to maintain pump power requirements per unit flow rate below an acceptable level, operation of the oil pipeline of the preceding problem is subject to the constraint that the oil exit temperature Tm,o exceed 110°C. For the values of Tm,j Ts, D, ti, z, L, and k; prescribed in Problem 8.63, operating parameters that are variable and affect Tm,o are the thermal conductivity of the soil and the flow rate of the oil. Depending on soil composition and moisture and the demand for oil, representative variations are 0.25 < ks < 1.0 W/m ∙ K and 250 < mo < 500 kg/s. Using the properties prescribed in Problem 8.63, determine the effect of the foregoing variations on Tm,o and the total heat rate q. What is the worst case operating condition? If necessary, what adjustments could be made to ensure that Tm.o > 110°C for the worst case conditions?