Free Bachelor of Mechanical Engineering Hydraulic Machines Questions and Answers — Questions and Answers
Question 1: The category of a hydraulic coupling is .
- Energy transfer machines (Correct answer)
- Power absorbing machines
- Energy generating machines
- Energy absorbing machines
Correct answer: Energy transfer machines
A hydraulic coupling is a device used to transmit rotational mechanical power. It functions by transferring kinetic energy from a rotating input shaft (impeller) to an output shaft (turbine) via a fluid, typically oil. Therefore, it falls under the category of energy transfer machines, as it facilitates the movement of energy from one component to another without generating or absorbing it in a net sense.
Question 2: The hydraulic energy that is converted into electricity is .
- Hydroelectric power (Correct answer)
- Thermal power
- Mechanical power
- Solar power
Correct answer: Hydroelectric power
Hydroelectric power is the specific term for electricity generated by harnessing the energy of moving water. In hydroelectric power plants, the potential energy of water stored at a height is converted into kinetic energy as it flows downwards, which then drives turbines connected to generators to produce electricity. This process directly converts hydraulic energy into electrical energy.
Question 3: What is currently the least expensive method of generating power?
- Electric Power
- Thermal power
- Nuclear power
- Hydroelectric power (Correct answer)
Correct answer: Hydroelectric power
While initial construction costs for hydroelectric power plants can be significant, their operational and maintenance costs are remarkably low compared to other power generation methods. Hydroelectric power utilizes a free and renewable fuel source (water), resulting in no fuel costs and minimal environmental emissions during operation. This makes it one of the most cost-effective methods for generating electricity over its long operational lifespan.
Question 4: A reaction turbine with inward radial flow is called .
- Propeller turbine
- Pelton turbine
- Kaplan turbine
- Francis turbine (Correct answer)
Correct answer: Francis turbine
The Francis turbine is a type of reaction turbine characterized by its inward radial flow design. Water enters the runner radially inward, flows through the blades, and exits axially. This design allows it to efficiently operate under a wide range of heads and flows, making it one of the most common types of hydraulic turbines used for medium-head applications.
Question 5: Axial flow reaction turbines of particular significance are .
- Propeller and Kaplan turbines (Correct answer)
- Propeller and Francis turbines
- Kaplan and Francis turbines
- Propeller and Pelton turbines
Correct answer: Propeller and Kaplan turbines
Propeller and Kaplan turbines are both classified as axial-flow reaction turbines, meaning water flows parallel to the axis of rotation through the runner. The Kaplan turbine is an advanced version of the propeller turbine, distinguished by its adjustable runner blades. This adjustability allows Kaplan turbines to maintain high efficiency over a broader range of flow rates and heads, making them particularly significant for variable load conditions.
Question 6: _____________ is an axial flow reaction turbine if the vanes are fastened to the turbine hub.
- Pelton turbine
- Kaplan turbine
- Francis turbine
- Propeller turbine (Correct answer)
Correct answer: Propeller turbine
A propeller turbine is an axial-flow reaction turbine where the runner blades are rigidly fixed to the hub. In this design, water flows axially through the runner, imparting energy to the fixed blades. The simplicity of its fixed-blade design makes it suitable for relatively constant flow and head conditions, distinguishing it from the adjustable-blade Kaplan turbine.
Question 7: Turbines with water flowing through them are known as radial flow reaction turbines.
- Axial direction
- Tangential direction
- Radial direction (Correct answer)
- All of the mentioned
Correct answer: Radial direction
As the name suggests, radial flow reaction turbines are designed such that water flows predominantly in a radial direction as it interacts with the runner blades. This means the water moves either inward towards the center or outward away from the center of the turbine's axis of rotation, transferring its energy to the runner.
Question 8: Radial flow reaction turbines' primary components are .
- Draft tube
- Casing
- Guide mechanism
- All of the mentioned (Correct answer)
Correct answer: All of the mentioned
Radial flow reaction turbines, like Francis turbines, require several key components for efficient operation. The casing (often a spiral or volute casing) directs water to the runner, the guide mechanism (guide vanes) controls the flow angle and quantity of water entering the runner, and the draft tube recovers kinetic energy from the water exiting the runner, all contributing to the turbine's overall performance.
Question 9: Discharge through a reaction turbine with radial flow is .
- Both P1*b1*Vf1 & P2*b2*Vf2 (Correct answer)
Correct answer: Both P1*b1*Vf1 & P2*b2*Vf2
The discharge (Q) through a reaction turbine, representing the volume of water flowing per unit time, must be constant throughout the turbine for steady flow conditions. It is calculated by multiplying the flow area (circumference * width, or P*b) by the radial component of velocity (Vf). Therefore, the discharge can be expressed as P1*b1*Vf1 at the inlet and P2*b2*Vf2 at the outlet, where P is the circumference, b is the width, and Vf is the velocity of flow.
Question 10: Spiral casing is seen in radial flow reaction turbines and it has the following area:
- Suddenly decreases
- Gradually increases
- Remains constant
- Gradually decreases (Correct answer)
Correct answer: Gradually decreases
The spiral casing, or volute casing, in radial flow reaction turbines is designed with a gradually decreasing cross-sectional area along its length. This design ensures that the water maintains a relatively constant velocity as it flows around the runner towards the guide vanes. By gradually decreasing the area, it helps to distribute the water uniformly around the runner periphery and convert pressure energy into kinetic energy efficiently before the water enters the guide vanes.
Question 11: Around the turbine runner, the ___________ is made up of stationary circular wheels.
- Drafting
- Runner
- Casing
- Guide mechanism (Correct answer)
Correct answer: Guide mechanism
The guide mechanism, composed of a series of stationary guide vanes or wicket gates, is positioned around the turbine runner. Its primary function is to control the quantity of water flowing into the runner and to direct the water at the optimal angle of attack to the runner blades. This ensures efficient energy transfer from the water to the turbine.
Question 12: The pressure at the reaction turbine's runner exit is often ______ than the atmospheric pressure
- Equal
- Constant
- Lesser (Correct answer)
- Greater
Correct answer: Lesser
For efficient operation and to maximize the head utilized by the turbine, the pressure at the exit of a reaction turbine's runner is often designed to be less than atmospheric pressure. This lower pressure allows for the effective use of a draft tube, which recovers kinetic energy from the exiting water and converts it back into pressure energy, thereby increasing the net head acting on the turbine and improving overall efficiency.
Question 13: A pipe with progressively larger surface area is utilized to transport water from the turbine's outlet to the tail race.
- Runner
- Casing
- Guide mechanism
- Draft tube (Correct answer)
Correct answer: Draft tube
The pipe with a progressively larger surface area used to transport water from the turbine's outlet to the tail race is known as a draft tube. Its diverging shape is crucial for recovering the kinetic energy of the water exiting the runner by gradually reducing its velocity. This conversion of kinetic energy into pressure energy increases the effective head across the turbine, thereby improving its overall efficiency.
Question 14: A turbine with an inward radial flow response is one in which water flows across the runner blades.
- Axial direction
- Radial direction
- Radially inward (Correct answer)
- Radially outward
Correct answer: Radially inward
In an inward radial flow reaction turbine, such as a Francis turbine, water enters the runner from the periphery and flows radially inward across the runner blades. As the water moves towards the center, it imparts its energy to the rotating runner. This inward flow path is characteristic of this turbine type, distinguishing it from outward radial flow designs.
Question 15: Vapour cavity creation is known as .
- Emulsion
- Static pressure drop
- Cavitation (Correct answer)
- Isentropic expansion
Correct answer: Cavitation
The creation of vapor cavities or bubbles in a liquid, typically due to a localized drop in pressure below the liquid's vapor pressure, is known as cavitation. In hydraulic machinery like turbines, these bubbles can form and then collapse violently as they move into higher pressure regions, causing noise, vibration, and significant damage to the turbine components.
Question 16: The degree of reaction in the case of gas turbines and compressors is .
- Static temperature drop in stage/ static temperature drop in rotor
- Static pressure drop in rotor/ static pressure drop in stage
- Static pressure drop in stage/ static pressure drop in rotor
- Isentropic enthalpy drop in rotor/ isentropic enthalpy drop in stage (Correct answer)
Correct answer: Isentropic enthalpy drop in rotor/ isentropic enthalpy drop in stage
The degree of reaction in gas turbines and compressors is a dimensionless parameter that quantifies the proportion of the total isentropic enthalpy drop (or static pressure drop) occurring in the rotor blades relative to the entire stage (rotor plus stator). Specifically, it is defined as the ratio of the isentropic enthalpy drop in the rotor to the isentropic enthalpy drop in the stage. This parameter helps characterize the design and performance of turbomachinery.
Free Bachelor of Mechanical Engineering Hydraulic Machines Questions and Answers
The category of a hydraulic coupling is .