Basic Chemical Engineering Knowledge: One Question per Day: February 22, 2012
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This post was last edited by 328104062 on 2012-2-23 16:13. Multiple-choice questions on fluid transport: 13. Under normal conditions, the viscosity of a liquid increases as the temperature rises ( ). A. Increase B. Decrease C. Remain unchanged 14. The higher the vacuum level inside a device, the greater the absolute pressure inside that device ( ). A. Greater B. Smaller C. Closer to atmospheric pressure. 15. When a fluid flows laminarly inside a circular straight pipe, the resistance is proportional to the flow velocity’s ( ), while when it flows in a fully turbulent state, it is proportional to the flow velocity’s ( ). A. Square B. Fifth power C. First power 16. When water flows steadily and continuously in a vertically oriented pipe with constant diameter, its flow velocity ( ). A. The flow will become faster. B. The flow will become slower. C. It remains unchanged. PS: 1) Those who provide a detailed analysis, discussion, or derivation process will be awarded 10-15 wealth points or 1-2 charm points:victory:. 2) Please hide your replies. The method to do this is: http://bbs.hcbbs.com/thread-492556-1-1.html. Do not edit your replies after posting them{:1_90:}, and also avoid copying others’ answers, as that will result in a deduction of points:funk: ； Indicate the question number when answering; otherwise, it will be difficult to determine whether the answer is correct: handshake. 3) The reference answers will be available once you reply; those who want to confirm their answers may refer to o. 4) Please also avoid submitting answers maliciously multiple times; if it is due to an operational error, please contact the forum moderators or administrators: call:. Otherwise, points will be deducted. Reference answer: BB CA C
This post was last edited by qq201088 on 2012-2-22 00:27. Analysis for 13.B: In liquids, the molecules are close together due to short distances between them. An increase in temperature raises the kinetic energy of the molecules, facilitating their movement relative to one another; as a result, the dynamic viscosity of the liquid decreases； Gas molecules are far apart from each other and relatively independent; an increase in temperature raises the kinetic energy of the molecules, but it also increases the frequency of collisions between them, which in turn increases the dynamic viscosity of the gas. 14.B Explanation: Absolute vacuum is defined as -0.1 MPa, and gauge pressure = absolute pressure – 1 atmosphere. 15.C A Explanation: When a fluid flows laminarly within a circular straight pipe, the resistance is proportional to the first power of the flow velocity; when it flows in a fully turbulent state, the resistance is proportional to the square of the flow velocity, ΔE = kv². For more details, see… 16.C Explanation: When the state of the fluid does not change, the flow velocity depends only on the volumetric flow rate and the cross-sectional area through which the fluid flows.
1.B 2.B 3.C A 4.C
The answer is as follows: 1: B； 2: B ； 3: A, B ； 4: C
13. Under normal conditions, the viscosity of a liquid increases as the temperature rises (B). 14. The higher the vacuum level inside the equipment, the greater the absolute pressure (B) within it. 15. When a fluid flows laminarly in a circular straight pipe, the resistance is proportional to the flow velocity to the power of (C); when it flows in complete turbulence, it is proportional to the flow velocity to the power of (A). 16. When water flows steadily and continuously in a vertically oriented pipe with constant diameter, its flow velocity (C).
13 A 14 B 15 AB 16 C
13、B； 14、B ； 15、C, A ； 16、C
13, B 14, B 15, C A 16, C
1.B. Decreases. Reason: As the temperature of the liquid rises, the distance between molecules increases, resulting in weaker forces between them; hence, the viscosity decreases. 2.B. Becomes smaller. Reason: Vacuum degree = atmospheric pressure – absolute pressure. 3.C. To the first power; A. To the square. 4.C. Remains unchanged