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
- What is the effect of superheating the suction vapor with regards to the work of compressor per unit mass of refrigerant circulated?
a. Decreases
b. remains the same
c. proportional
d. increases
d. increases
- Compare the efficiency (COP) of a refrigeration cycle if the condensing
temperature is increased.
a. decrease in efficiency
b. increases in efficiency
c. efficiency remains the same
d. varies directly
a. decrease in efficiency
- It is important to take some moisture from the air to dehumidify it and the relative humidity reaches high levels. To do this, it requires cooling the air
a. at wet-bulb temperature
b. above its dew point temperature
c. at critical temperature
d. below its dew point temperature
d. below its dew point temperature
- The relative humidity of saturated air is:
a. 0%
b. 75%
c. 25%
d. 100%
d. 100%
- The process of treating air so as to control simultaneously its temperature, humidity, cleanliness and distribution to meet the requirements of the conditioned space.
a. Refrigeration
b. air conditioning
c. ducting system
d. air mixing
b. air conditioning
- A mechanical device used in refrigeration system for purpose of increasing the pressure upon the refrigerant.
a. Pump
b. compressor
c. expansion valve
d. drier
b. compressor
- The process of supplying or removing air by natural or mechanical means to or from
any space.
a. ventilation
b. evaporation
c. air supply
d. natural convection
a. ventilation
- An evaporator constructed of pipe or tubing.
a. expansion coil
b. condenser coil
c. evaporative condenser
d. cooling tower
a. expansion coil
- Two pumps are connected in parallel, if Q1 is the discharge of Pump 1 and Q2 is the discharge of Pump 2 where Q2
b. Q1 + Q2
- In a refrigeration system, the heat absorbed in the evaporator per kg mass of refrigerant passing through:
a. equals the increase in enthalpy
b. is decreased if pre-cooler is used
c. does not depend on the refrigerant used
d. equals the increase in volume
a. equals the increase in enthalpy
