Understanding the Basics

Question 1

Describe the operation of a liquid-in-glass thermometer.

Answer 1

A liquid-in-glass thermometer operates based on the principle of expansion. The liquid (usually mercury or alcohol) expands when heated and contracts when cooled, moving up or down the glass tube to indicate temperature.

Question 2

List and describe the significance of the Steady Flow Energy Equation

Answer 2

Energy In = Energy Out

Heat and Work across system boundaries are transitional energies.

Image of Equation: https://drive.google.com/file/d/1t-gj0xHsZHnYiP4eDkz9JpmoR8Z4Kc6q/view?usp=drive_link

Question 3

Name the two types of temperature detectors used in Naval applications. Give 2 examples of each.

Answer 3

Expansion Thermometers
* Liquid in glass
* Bimetallic
* Filled system/distant reading

Pyrometers
* Thermocouple
* Resistance
* Radiation and optical pyrometers

Question 4

List three examples of pressure measuring devices.

Answer 4

Manometers
Bourdon tube
Bellows gage

Question 5

State the 1st law of thermodynamics.

Answer 5

Energy can neither be created nor destroyed, only transformed

Question 6

Name and define the three mechanisms of heat transfer.

Answer 6

Conduction - Transfer of thermal energy when source and sink are in physical contact.

Convection - Transportation or movement of some portions of a fluid within a mass of fluid.

Radiation – Transfer of heat by electromagnetic wave phenomenon.

Question 7

Define Sensible Heat.

Answer 7

Heat absorbed or rejected with a corresponding change of temp, but no change in phase

Question 8

Define Latent Heat.

Answer 8

Heat absorbed or lost w/ a change in phase.

Question 9

Latent Heat of Fusion?

Answer 9

Heat absorbed or lost w/ a change in phase between a solid and a liquid.

Question 10

What is a subcooled liquid?

Answer 10

A liquid that is below the saturation temperature for a given pressure.

Question 11

What is a superheated vapor?

Answer 11

A vapor that is above the saturation temperature for a given pressure.

Question 12

What is a saturated liquid and how is it different from a saturated vapor in terms of heat absorbed?

Answer 12

A saturated liquid is at the saturation temperature for a given pressure. It differs from a saturated vapor in that it has slightly less latent heat.

Question 13

Define Enthalpy.

Answer 13

Enthalpy: the total energy of the fluid due to both internal energy & flow energies

Question 14

Define Entropy.

Answer 14

Entropy: theoretical measure of thermal energy that cannot be transformed into mech. Work in a thermodynamic system

Question 15

State the term used to describe a thermodynamic process in which there is no heat transferred into or out of the system.

Answer 15

Adiabatic

Question 16

Name and describe the five basic elements necessary for a thermodynamic cycle to work.

Answer 16

Working substance: transports energy within system

Heat source: supplies heat to the working medium

Engine: device that converts the thermal energy of the medium into work

Heat sink/receiver: absorbs heat from the working medium

Pump: moves the working medium from the low-pressure side to the high-pressure side of the cycle

Question 17

State the Carnot Principle.

Answer 17

The max thermal efficiency depends only on the difference between the source and sink temps.

Question 18

Define temperature.

Answer 18

An indication of the internal energy (Kinetic Energy) contained in a substance.

Question 19

How does a Bellow Pressure Gage work?

Answer 19

The medium being measured will either expand or compress a bellow which is attached to a gauge. ADD Picture

Question 20

Define Heat Transfer.

Answer 20

Heat flow from one body, region or substance to another.

Question 21

Draw a Temperature vs Entropy Graph and Label Subcooled Liquid, Vapor, Superheated Vapor

Answer 21

Image of Graph: https://drive.google.com/file/d/1lzZjv3Jndrwv0rA6VbwFNZyiDqJzZ0C_/view?usp=drive_link

Question 22

Draw a Basic Thermodynamic Cycle.

Answer 22

Image of Cycle: https://drive.google.com/file/d/1PFkZPzGaLQmBo35iLhX5wvrX1CQtKdJq/view?usp=drive_link

Question 23

How does a thermocouple work to measure temperature?

Answer 23

A thermocouple measures temperature by generating a voltage when there is a temperature difference between two different metals joined at two points. This voltage is proportional to the temperature difference.

Question 24

Explain how a Bourdon Tube pressure gauge works.

Answer 24

A Bourdon tube pressure gauge works by having a coiled tube that straightens when pressurized. This movement is transferred to a pointer on a dial to indicate the pressure.

Question 25

Describe one advantage and one limitation of an optical pyrometer.

Answer 25

Advantage: Physical contact with the temperature source is not required, allowing for high accuracy (+/- 5°C) at high temperatures.

Limitation: It cannot measure temperatures below 700°C as it requires illumination of the temperature source for measurement.

Question 26

What is kinetic energy and how is it different from potential energy?

Answer 26

Kinetic energy is the energy that a body possesses by virtue of being in motion. It differs from potential energy, which is due to an object’s position or state.

Question 27

Explain the Ideal Gas Law and its components.

Answer 27

The Ideal Gas Law is PV=mRT
PV=mRT, where P is pressure, V is volume, m is mass, R is the gas constant, and T is temperature in absolute terms.

Question 28

What is thermal energy and how does it differ from mechanical energy?

Answer 28

Thermal energy, also known as heat, is a form of internal energy of a system due to the random movement of molecules. Mechanical energy is the ordered movement of molecules as a single unit. Thermal energy cannot be fully converted into mechanical energy.

Question 29

List the three mechanisms of heat transfer and provide an example for each.

Answer 29

conduction (e.g., heat transfer through a metal rod)
convection (e.g., boiling water where heat is radiation (e.g., heat from the sun)

Question 30

What is the difference between an open and a closed thermodynamic system?

Answer 30

An open system allows mass and energy to enter and leave, while a closed system does not allow mass to flow in or out, though energy can be exchanged.

Question 31

What is meant by ‘saturated conditions’ for a working substance?

Answer 31

Saturated conditions refer to the state where a working substance is at its boiling point for a given pressure, meaning any additional heat will result in phase change rather than temperature increase.

Question 32

What is the Steady Flow Energy Equation (SFEE)? (Describe in words)

Answer 32

The Steady Flow Energy Equation is used for open flowing systems where the properties and velocities of the fluid remain constant, ensuring that the energy in equals the energy out.

Question 33

What happens during an isobaric process?

Answer 33

During an isobaric process, the pressure remains constant, resulting in a change in enthalpy.

Question 34

Describe an adiabatic process.

Answer 34

An adiabatic process is one where there is no net transfer of heat to or from the medium during the process, often occurring in rapid processes or thermally insulated containers.

Question 35

What is the significance of the Second Law of Thermodynamics?

Answer 35

The Second Law of Thermodynamics states that no process is possible where the sole result is the removal of heat from a low-temperature reservoir and the absorption of an equal amount of heat by a high-temperature reservoir. It limits the direction of processes and the extent of heat-to-work conversions.

Question 36

Explain Pascal’s Principle.

Answer 36

Pascal’s Principle states that a pressure change at any point in a confined fluid is transmitted undiminished throughout the fluid and to the walls of its container.

Question 37

What are the two components of mass flow rate in the Continuity Equation?

Answer 37

The two components of mass flow rate are volumetric flow rate and density. Mathematically, it is expressed as m˙=ρ⋅Q where m˙ is the mass flow rate, ρ is the density, and Q is the volumetric flow rate.

Question 38

Describe the main difference between laminar and turbulent flow.

Answer 38

Laminar flow is characterized by smooth, parallel layers of fluid with a parabolic velocity profile, while turbulent flow is characterized by chaotic fluid motion with a flattened velocity profile and enhanced mixing, which increases heat transfer rates.

Question 39

List and describe the main components of a valve

Answer 39

The main components of a valve include the valve body, disc, seat, bonnet, valve stem, packing, packing gland, packing gland nut follower, and handwheel. These parts work together to control the flow and direction of fluids within a piping system.

Question 40

Compare and contrast a globe valve and a gate valve, focusing on their advantages and disadvantages.

Answer 40

Globe Valve:
Advantages: Good throttling (flow control) characteristics, excellent stop valve.
Disadvantages: High head loss (flow resistance), large pressure drop.

Gate Valve:
Advantages: Minimum pressure drop, excellent stop valve.
Disadvantages: Poor throttling, hard to open with large pressure difference or temperature.

Question 41

What is the purpose of a pressure reducing valve?

Answer 41

A pressure reducing valve automatically provides a steady lower pressure to a system from a higher pressure source, used in systems such as air, lube-oil, seawater, and others.

Question 42

How does a swing-check valve operate?

Answer 42

A swing-check valve operates by allowing fluid to flow in one direction. The disc swings on a hinge to either block reverse flow or allow forward flow. When fluid flows in the correct direction, the disc moves off the seat; when fluid attempts to flow backward, the disc swings back onto the seat to block the flow.

Question 42

Differentiate between positive displacement and variable displacement pumps.

Answer 42

Positive Displacement Pump: Delivers a fixed volume of fluid for each cycle regardless of pressure conditions, suitable for high-pressure, low-flow applications.

Variable Displacement Pump: The volume of fluid delivered varies with the pressure conditions. Common types include centrifugal and propeller pumps, which are used for low-pressure, high-flow applications.

Question 43

Define cavitation and explain why it is undesirable in pump operation.

Answer 43

Cavitation is the formation of vapor bubbles in a liquid due to a drop in pressure below the vapor pressure of the liquid. It is undesirable in pump operation because these bubbles collapse when they reach higher pressure areas, causing noise, vibration, and damage to the pump components.