題組內容

Problem 6
A silicone oil having a temperature of 185 ℃, heat capacity of 5.0 kJ/(kg K) and a flow
rate of 150 kg/min is used for pre-heating the soybean oil (i.e, for biodiesel production)
by using the following heat exchanger (sce the plot shown below).

Based on the design, the temperatures of the silicone oil leaving the shell is preferred
(but not necessary) to be ≦170 ℃. The temperature of the soybean oil entering the
pipes is 20 0C, and the target temperature of the soybean oil at the exit of the tubes/pipes
is ≧80  ℃. Here, the heat capacity of soybean oil is assumed to be 80% of the heat
capacity of silicone oil regardless of the variation in their temperatures. The flow rate
of soybean oil is targeted to be at least 3600 kg/hour.

(c)(Continued on (b)) Fouling is a severe issue to this heat exchanger, resulting in a decline of overall heat transfer coefficient. Through an operation under the minimum flow rate of soybean oil, the predicted overall heat transfer coefficients are linearly decreased to 900 W/m²*K and 800 W/m2*K in the first and the second months, respectively. What is the minimum heat transfer area required to achieve the target temperature of the soybean oil at the exit of the heat exchanger during the 2-month operation (i.e., 80  ℃)?