申論題 - 阿摩線上測驗

申論題資訊

試卷：110年 - 110 國立清華大學碩士班考試入學試題_化學工程學系:輸送現象及單元操作#104976
科目：清大◆化工◆輸送現象及單元操作
年份：110年
排序：0

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.

申論題內容

(b) To simplify the analysis, we choose the method for the study of a double pipe heat exchanger. The cold flow (in the tubes/pipes) is assumed to be in the inner pipe (10 cm in diameter) of this double pipe heat exchanger, and the hot flow in the shell is assumed to be in the outer tube (20 cm in diameter) of this double pipe heat exchanger. The overall heat transfer coefficient is 1000 W/m²*K. The streams of silicone oil and soybean oil are counter-current. What is the heat transfer area required to achieve the minimum target temperature of the soybean oil at the exit of the pipes (i.e., 80 ℃, when flow rate of soybean oil is at the minimum value)?

Is the final temperature of the silicone oil leaving the shell below 170 ℃? Full derivations to the answers are required.