Guys, please help me with a question on chemical engineering principles
Thread Content
Tianjin University version – Basic Examination Questions 11.1: In fluid transfer machinery, question 11-3 involves using an IS80-65-160 type water pump to transport clean water at 40 degrees Celsius (with a density of 992.2 KG/cubic meter) from an open reservoir to a certain workshop; the flow rate required is 45–60 cubic meters per hour. The head loss in the suction pipeline within this flow range is 1 to 1.8 meters: the required net positive suction head (NPSH) of the pump is 3 meters. The atmospheric pressure in the area where the pump is to be installed is 98.1 kPa, and the saturated vapor pressure of water at 40 degrees Celsius is 7.38 KPa. Therefore, the allowable installation height for the pump is ( ) A. 3.72 meters B. 4.52 meters C. 5.52 meters D. 9.32 meters. My calculation was as follows: Hg = (Pa – Pv) / pg – NPSH – Hf0 – 1 = (98100 – 7380) / (992.2 * 9.81) – (3 + 0.5) – 1.8 = 4.02 meters. This value isn’t among the options provided, so I chose option A. I’m not sure how to carry out this calculation; I would be very grateful if anyone could help me understand it
What you have calculated now is the maximum allowable installation height of 4.02 meters. What the ontology requires is the allowable installation height, that is, the practical installation height that is feasible. Here, there is an installation height coefficient of 0.5 to 1 meter. This is also for the safe operation of the pump. Allowed installation height = Maximum allowed installation height – (0.5～1); the result obtained in this way is A.
The calculation is correct~~~ The maximum allowable height comes out to be 4.02 meters, and among the four options, only answer A does not exceed this maximum value; therefore, answer A is correct! ! ~~
Support your algorithm, and then consider what was said on the second floor.
Change your calculation method to: Hg = (Pa – Pv) / (pg – NPSH – Hf0 – 1) = (98100 – 7380) / (992.2 * 9.81) – 3 – 1.8 = 4.52 meters. 4.52 meters represents the maximum allowable installation height; this value is calculated based on the pressure at the pump inlet, whereas during operation the lowest pressure is actually at the center of the pump. Therefore, the actual installation height must be less than this maximum allowable value. As mentioned by the people above, a safety installation height factor of 0.5 to 1 meter is required. Therefore, only A is correct; its value should be less than 4.02 meters, not equal to 4.02 meters.