★Note: Specialty Exam for Chemical Engineering ★ — One question per day (2015-12-3) — Increased participation
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This post was last edited by zshiwei2008 on 2015-12-8 08:45. Points system for the daily question: Participation – 1~3 points; Correct answer – 5 points; In-depth analysis – 5~10 points. The answer is provided the next day. Due to limited capabilities, I am unable to provide more in-depth explanations for each question; therefore, on the second day, in addition to offering reference options, I will also remove the restriction on reading replies. I hope that all candidates can learn from one another and improve together! Daily Question (2015-12-3): 1. When heating crude oil with saturated water vapor, what is the most effective measure to reduce the total thermal resistance? ( ) A. Increase the vapor flow rate. B. Use pipes with a high thermal conductivity. C. Increase the crude oil flow rate. D. Replace smooth pipes with threaded pipes to improve the heat transfer surface structure. 2. When two fluids exchange heat in a tubular heat exchanger and the temperatures of both fluids change, which operating mode should be used to achieve a greater driving force for heat transfer? A. Co-current B. Counter-current C. Cross-current D. All of the above. Reference answers: Question 1: C; Question 2: B. Many students below have provided very good analyses
1. C. Increase crude oil flow rate； Using pipes with a high thermal conductivity can also increase the overall heat transfer coefficient, but the thermal resistance of these pipes is much lower than that of crude oil; therefore, it has little impact on the overall heat transfer coefficient ； Changing the structure of the heat transfer surface hardly affects the heat transfer coefficient (the flow state of high-viscosity fluids has an impact on the heat transfer coefficient). 2. B. Counterflow
I believe the answer to both questions is D； The owner does a great job running this section! I hope more people will get involved to cultivate more professionals in this field; of course, I also need to work hard.
1. When heating crude oil with saturated water vapor, the most effective measure to reduce the total thermal resistance is (B). A. Increase the steam flow rate. B. Use tubes with a high thermal conductivity. C. Increase the crude oil flow rate. D. Replace smooth tubes with threaded tubes to improve the heat transfer surface structure. 2. When two fluids exchange heat in a tubular heat exchanger and the temperatures of both fluids change, (D) operation mode should be used to achieve a greater driving force for heat transfer. A. Co-current B. Counter-current C. Cross-current D. All of the above
1. When heating crude oil with saturated water vapor, the most effective measure to reduce the total thermal resistance is (B). A. Increase the steam flow rate. B. Use pipes with a high thermal conductivity. C. Increase the crude oil flow rate. D. Replace smooth pipes with threaded pipes to improve the heat transfer surface structure. 2. When two fluids exchange heat in a tubular heat exchanger, and the temperatures of both fluids change, then (B) operation mode should be used to achieve a greater driving force for heat transfer. A. Co-current B. Counter-current C. Cross-current D. All of the above
1. C. －－－2, B. －－－－－－－－－－－－
1. When heating crude oil with saturated water vapor, the most effective measure to reduce the total thermal resistance is ( ). C. Increase the crude oil flow rate. 2. When two fluids exchange heat in a tubular heat exchanger, and the temperatures of both fluids change, then ( ) operation mode should be adopted to obtain a greater driving force for heat transfer. B. Backflow