1. The exit diameter for a simple elbow draft tube should be________
a) Large
b) Small
c) Very small
d) Same
Explanation: The exit diameter for a simple elbow draft tube should be large as possible. It helps to cut down the cutdown the cost and recover the kinetic energy at the outlet of runner. The simple elbow draft tube is placed close to the tail race.
2. Properties that do not affect a draft tube is _______
a) Pressure
b) Temperature
c) Pressure velocity
d) Velocity
Explanation: Temperature does not affect the performance of the draft tube. With increase and decrease of temperature of fluid in a draft tube, the draft tube remains the same
3. The other name for elbow with varying cross section tube is called_____
a) Pressure tube
b) Bent draft tube
c) Velocity tube
d) Sink tube
Explanation: The other name for elbow with varying cross section tube is called bent draft tube. It is so called because only the bent part is of varying cross section. Thus, the answer is bent draft tube.
4. What is the efficiency of the simple elbow type draft tube?
a) 10
b) 30
c) 60
d) 90
Explanation: The efficiency of the simple elbow type draft tube is 60 percent. The exit diameter for a simple elbow draft tube should be large as possible. It helps to cut down the cutdown the cost and recover the kinetic energy at the outlet of runner. The simple elbow draft tube is placed close to the tail race.
5. The horizontal portion of the draft tube is usually bent to prevent entry of air from the exit end.
a) True
b) False
Explanation: The horizontal portion of the draft tube is usually bent to prevent entry of air from the exit end. This might lead to a mixing up of gases. In order to avoid this, it is important to avoid air entry from exit.
6. The efficiency of the draft tube is ratio of ________
a) Pressure energy by kinetic energy
b) Kinetic energy by Pressure energy
c) Kinetic energy into mechanical energy
d) Pressure into mechanical
Explanation: The efficiency of the draft tube is defined as the ratio of actual conversion of kinetic energy into the pressure energy. The pressure energy and kinetic energy is present at the inlet of the draft tube.
7. Draft tubes are not used in which of the following turbines?
a) Francis
b) Reaction
c) Kaplan
d) Pelton
Explanation: Turbine extracts energy and converts it into useful work. Turbine is a vortex related device. Draft tubes are not used in Pelton wheels. Draft tube is a tube that is installed in power turbines.
8. The draft tube at the exit of the nozzle increases the _______
a) Temperature
b) Pressure
c) Volume of the flow
d) Density of flow
Explanation: The draft tube at the exit of the nozzle increases the pressure in the fluid. It increases it at the expense of its velocity. This means that the turbine can reduce its pressure without fear of back flow to the tail race.
9. Efficiency of a draft tube gives __________
a) Temperature difference
b) Pressure difference
c) Kinetic energy difference
d) Density of flow
Explanation: The efficiency of the draft tube gives difference of the kinetic energy between the inlet and the outlet tube losses. The efficiency of the draft tube is defined as the ratio of actual conversion of kinetic energy into the pressure energy.
10. Cavitation in a draft tube occurs when _______
a) Temperature difference
b) Pressure drop
c) Kinetic energy difference
d) Density of flow
Explanation: Cavitation in a draft tube occurs when pressure drop takes place. The absolute pressure falls below the saturated vapour pressure of the water for the given temperature.