★Specialized Examination for Chemical Engineering ★ — One question per day (2016-1-4) — Points are awarded for participation
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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 (2016-1-4): 1. When a fluid flows in a circular straight pipe and has entered the fully turbulent regime, which of the following statements is correct regarding the relationship between λ and Re? A As the Reynolds number increases, λ also increases. B As the Reynolds number decreases, λ increases. C As the Reynolds number decreases, λ remains unchanged. D As the Reynolds number increases, λ first increases and then decreases. 2. After cutting the impeller of a centrifugal pump, if the speed of the pump remains constant, which of the following statements is correct regarding the performance of the centrifugal pump? A Flow rate increases. B Head increases. C Efficiency increases. D Shaft power decreases. Answers: Question 1 – C; Question 2 – D
1. When a fluid flows in a circular straight pipe and has entered the fully turbulent regime, which of the following statements is correct regarding the relationship between λ and Re? A As the CA Reynolds number increases, λ also increases. B As the B Reynolds number decreases, λ increases. C As the Reynolds number decreases, λ remains unchanged. D As the Reynolds number increases, λ first increases and then decreases. 2. After cutting the impeller of a centrifugal pump, if the pump’s speed remains constant, which of the following statements is correct regarding the performance of the pump? A Flow rate increases. B Head increases. C Efficiency increases. D Shaft power decreases
1. In the stagnation region, the friction coefficient decreases linearly as the Reynolds number increases； In the turbulent region, the friction coefficient decreases slowly as the Reynolds number increases ； In the fully turbulent region, the friction coefficient is independent of the Reynolds number. 2. Centrifugal pump cut-off law: head, flow rate, and shaft power vary in the same direction as the impeller diameter
1. As the C Reynolds number decreases, λ remains unchanged. 2. The shaft power decreases in D
1. As the C Reynolds number decreases, λ remains unchanged； In the fully turbulent region, the friction coefficient is independent of the Reynolds number; 2. The power on the D-axis decreases
1. When a fluid flows in a circular straight pipe and has entered the fully turbulent regime, which of the following statements is correct regarding the relationship between λ and Re? A As the Reynolds number increases, λ also increases. B As the Reynolds number decreases, λ increases. C As the Reynolds number decreases, λ remains unchanged. D As the Reynolds number increases, λ first increases and then decreases. 2. After cutting the impeller of a centrifugal pump, if the speed of the pump remains constant, which of the following statements is correct regarding the performance of the centrifugal pump? A Flow rate increases. B Head increases. C Efficiency increases. D Shaft power decreases