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Section 2 - practice problems
Introduktion til vindenergi (46000)
Danmarks Tekniske Universitet
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Concept Review
14-2C What are the primary differences between fans, blowers, and compressors? Discuss in terms of pressure rise and volume flow rate. 14-3C What is the more common term for an energy-producing turbomachine? How about an energy- absorbing turbomachine? Explain this terminology. In particular, from which frame of reference are these terms defined—that of the fluid or that of the surroundings? 14-4C Discuss the primary difference between a positive-displacement turbomachine and a dynamic turbomachine. Give an example of each for both pumps and turbines. 14-6C For a turbine, discuss the difference between brake horsepower and water horsepower, and also define turbine efficiency in terms of these quantities. 14-7C For a pump, discuss the difference between brake horsepower and water horsepower, and also define pump efficiency in terms of these quantities. 14-16C Consider a typical centrifugal liquid pump. For each statement, choose whether the statement is true or false, and discuss your answer briefly: a. at the pump's free delivery is greater than at its best efficiency point. b. At the pump's shutoff head, the pump efficiency is zero. c. At the pump's best efficiency point, its net head is at its maximum value. d. At the pump's free delivery, the pump efficiency is zero. 14-18C Consider steady, incompressible flow through two identical pumps (pumps 1 and 2), either in series or in parallel. For each statement, choose whether the statement is true or false, and discuss your answer briefly: a. The volume flow rate through the two pumps in series is equal to 1 + 2. b. The overall net head across the two pumps in series is equal to H 1 + H 2. c. The volume flow rate through the two pumps in parallel is equal to 1 + 2. d. The overall net head across the two pumps in parallel is equal to H 1 + H 2. 14-93C For each statement, choose whether the statement is true or false, and discuss your answer briefly: a. If the rpm of a pump is doubled, all else staying the same, the capacity of the pump goes up by a factor of about 2. b. If the rpm of a pump is doubled, all else staying the same, the net head of the pump goes up by a factor of about 2. c. If the rpm of a pump is doubled, all else staying the same, the required shaft power goes up by a factor of about 4. d. If the rpm of a turbine is doubled, all else staying the same, the output shaft power of the turbine goes up by a factor of about 8. 14-134 Which quantities are added when two pumps are connected in series and parallel? a. Series: Pressure change. Parallel: Net head b. Series: Net head. Parallel: Pressure change c. Series: Net head. Parallel: Flow rate d. Series: Flow rate. Parallel: Net head e. Series: Flow rate. Parallel: Pressure change
14-144 Which turbine type is an impulse turbine? a. Kaplan b. Francis c. Pelton d. Propeller e. Centrifugal
Problem Review
14-36 The performance data of a water pump follow the curve fit Havailable = H 0 − aV. 2 , where the pump's shutoff head H 0 = 7 m, coefficient a = 0 m/(Lpm) 2 , the units of pump head H are meters, and the units of are liters per minute (Lpm). The pump is used to pump water from one large reservoir to another large reservoir at a higher elevation. The free surfaces of both reservoirs are exposed to atmospheric pressure. The system curve simplifies to Hrequired = (z 2 − z 1 ) + bV. 2 , where elevation difference z 2 − z 1 = 3 m, and coefficient b = 0 m/(Lpm) 2. Calculate the operating point of the pump ( operating and Hoperating) in appropriate units (Lpm and meters, respectively). Answers: 7 Lpm, 4 m
TABLE P14-
, Lpm H, m 20 21 30 18. 40 14 50 7.
Section 2 - practice problems
Kursus: Introduktion til vindenergi (46000)
Universitet: Danmarks Tekniske Universitet
