351-375 Flashcards
- If the speed of a pump is higher than the designed speed, cavitation will
a. not occur
b. occur
c. may occur and may not occur
d. sometimes occur and sometimes not
b. occur
- If the net positive suction head (NPSH) is greater than the required suction head of the pump, cavitation will
a. not occur
b. occur
c. may occur and may not occur
d. sometimes occur and sometimes not
a. not occur
- In order to avoid cavitation, the NPSH of an installation should be at least than __________ the required NPSH of the pump.
a. equal or greater
b. equal or lower
c. lower
d. equal
a. equal or greater
- Net positive suction head (NPSH) can be increased by which of the following:
a. increasing the height of the free fluid level
on the supply tank
b. reducing the temperature of the fluid
c. using larger pipe size in the suction side
d. all of these
d. all of these
- If Hb is the pressure head corresponding to absolute pressure on the surface of the fluid, Z is the height of the fluid surface above or below the pump centerline, hf is the total friction head loss and Hv is the pressure head corresponding to the vapor pressure of the liquid. What is the available NPSH of the pump?
a. NPSH = Hb-Hv-Z + hf
b. NPSH = Hb-Hb-Z- hf
C. NPSH = Hb + Hv - Z-hf
d. NPSH = Hb + Hv - Z+hf
b. NPSH = Hb-Hb-Z- hf
- If Pb is the Absolute pressure on the surface of the liquid, Z is the suction lift of the pump, hf is the total friction head loss and Pv is the vapor pressure of the liquid at the Determine existing temperature. corresponding NPSH of the pump.
a. NPSH = (PB - Pv)/w + Z+hf
b. NPSH (PB - Pv)/w + Z-hf
c. NPSH = (PB + Pv)/w + Z-hf
d. NPSH = (PB + Pv)/w +Z+hf
b. NPSH (PB - Pv)/w + Z-hf
- If cavitation will occur, the available NPSH is insufficient. Which of the following is a remedy to overcome cavitation?
a. decrease the available NPSH
b. increase the required NPSH
c. increase the available NPSH
d. none of these
c. increase the available NPSH
- Regardless of its rotative speed, the value of the specific speed of a given impeller of a centrifugal pump is:
a. Varying
b. constant
c. unity
d. increasing
b. constant
- Specific speed of a centrifugal pump is to its operating speed.
a. indirectly proportional
b. directly proportional
c. inversely proportional
d. unity
b. directly proportional
- What is the effect on saturation pressure if the temperature of the fluid is increased?
a. there is no effect
b. saturation temperature increases
c. saturation temperature decreases
d. saturation temperature remains the same
b. saturation temperature increases
- What is the effect on saturation temperature if the pressure of the fluid is increased?
a. saturation temperature increases
b. saturation temperature decreases
c. saturation temperature remains the same
d. there is no effect
a. saturation temperature increases
- The capacity of a centrifugal pump, Q, is proportional to the speed N in the same pump.
a. directly
b. indirectly
c. Inversely
d. inversely and indirectly
a. directly
- The capacity of a centrifugal pump, Q, is proportional to the impeller diameter D at the same pump.
a. directly
b. indirectly
c. inversely
d. inversely and indirectly
a. directly
- What is the pressure present inside the casing of an impulse turbine?
a. vacuum
b. atmospheric pressure
c. above atmospheric
d. zero
a. vacuum
- Compare the refrigerating effect per unit mass of refrigerant for a saturated cycle and for a superheated cycle that produces useful cooling, for the same vaporizing and condensing temperature.
a. for a superheated cycle
b. lower for superheated cycle
c. greater for saturated cycle
d. lower for saturated cycle
a. for a superheated cycle