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Explain the modes of heat transfer.
1) Conduction involves the transfer of heat by the interactions of atoms or molecules of a material through which the heat is being transferred. 2) Convection involves the transfer of heat by the mixing and motion of macroscopic portions of a fluid. 3) Radiation or radiant heat transfer, invoRead more
1) Conduction involves the transfer of heat by the interactions of atoms or molecules of a material through which the heat is being transferred.
2) Convection involves the transfer of heat by the mixing and motion of macroscopic portions of a fluid.
3) Radiation or radiant heat transfer, involves the transfer of heat by electromagnetic radiation that arises due to the temperature of a body.
1) Conduction
Conduction Is The Heat Transfer Between Two Substances By Direct Transferring Of Molecular Kinetic Energy . Conduction Occurs When A hot Substance Comes Into Contact With A cold Substance .
Heat Is transferred From Hotter Substance Has A higher Temperature Than The Colder Substance , The Substance With A higher Temperature Has Molecules With Higher Average Kinetic Energy Than The Substance With The Lower Temperature .
Heat transfer rate by conduction speed related to four factors :-
1) Thermal conductivity of the substance
2) The surface area over which the heat is applied
3) The thickness of the material subject to the heat transfer
4) The temperature difference across the materials
Fourier’s Law of Conduction Q = k A ∆T/L
2) Convection
Convection heat transfer involves fluids, either liquids or gases in motion
convection heat transfer occurs in two parts :
o1 Heat transfer into or out of a fluid by the process of conduction
o2 The movement of the fluid transports the heated fluid, as well as its thermal energy.
Newton’s Law Of Cooling ˙Q= h A ΔT
3) Radiation
The energy emitted by matter in the form of electromagnetic waves (or photons) as a result of the
changes in the electronic configurations of the atoms or molecules.
Unlike conduction and convection, the transfer of energy by radiation does not require the presence of
an intervening medium .
All bodies at a temperature above absolute zero emit thermal radiation.
Black Body Radiation
A body that emits the maximum amount of heat for its absolute temperature is called a black body.
See lessRadiant heat transfer rate from a black body to its surroundings can be expressed by the following
equation.
Stefan-Boltzman law ˙Q= ðAT4
Explain NPSH and how it can be calculated.
Net Positive Suction Head (NPSH) is a crucial concept in the operation of pumps, particularly centrifugal pumps. It represents the amount of energy available at the pump's suction side to prevent the fluid from vaporizing (cavitation) when entering the pump. If the NPSH is too low, cavitation can ocRead more
Net Positive Suction Head (NPSH) is a crucial concept in the operation of pumps, particularly centrifugal pumps. It represents the amount of energy available at the pump’s suction side to prevent the fluid from vaporizing (cavitation) when entering the pump. If the NPSH is too low, cavitation can occur, which may damage the pump and reduce its efficiency. There are two important terms related to NPSH:
1. NPSH Available (NPSHA)
NPSHA is the energy available at the pump’s inlet to push the fluid into the pump without causing vaporization. It is primarily determined by the system’s conditions, including the fluid’s pressure, temperature, and the height difference between the fluid’s surface and the pump’s inlet.
In summary, NPSHA is the difference between the available pressure energy at the pump’s inlet and the energy required to prevent the liquid from vaporizing.
2. NPSH Required (NPSHR)
NPSHR is the minimum suction head required by the pump to avoid cavitation. It is specified by the pump manufacturer and depends on the type of pump and its operating conditions, including the flow rate and the pump speed. NPSHR is determined experimentally and varies with factors such as:
Typically, NPSHR increases as the flow rate through the pump increases, since higher flow rates lead to greater friction losses and a greater likelihood of cavitation.
NOTE:- If anyone need derivation of how to calculate NPSH ask me personally.
See lessDefine Mach Number. Explain and give its significance.
Mach Number:- The Mach number (M) is a dimensionless quantity that represents the ratio of the speed of a fluid (usually air or any gas) to the speed of sound in that same fluid. Significance of Mach Number: Characterization of Flow Regimes: Mach number helps in determining the flow regime, which diRead more
Mach Number:-
The Mach number (M) is a dimensionless quantity that represents the ratio of the speed of a fluid (usually air or any gas) to the speed of sound in that same fluid.
Significance of Mach Number:
- Characterization of Flow Regimes:
- Subsonic flows: The flow is usually smooth, and pressure and density variations are minor.
- Supersonic flows: The flow becomes more complicated with the formation of shock waves, and properties such as pressure and temperature vary drastically in short distances.
- Shock Waves and Wave Formation:
- Aerodynamic Design:
- Subsonic aircraft: Designed with curved, smooth shapes to maintain steady airflow at low speeds.
- Supersonic aircraft: Require sharp nosecones and delta wings to minimize drag and manage shockwaves at high speeds.
- Hypersonic vehicles: Require special designs to handle extremely high temperatures and pressures due to the high-speed flow.
- Compressibility Effects:
- Efficiency of Propulsion Systems:
- In subsonic jet engines, the engine works efficiently at lower Mach numbers.
- Supersonic and hypersonic aircraft require engines designed for high-speed intake and exhaust systems, such as ramjets or scramjets.
- Weather and Meteorology:
See lessMach number helps in determining the flow regime, which dictates how the fluid will behave. For example:
When an object or fluid flows at a Mach number greater than 1 (supersonic flow), shock waves form. These are abrupt changes in pressure, temperature, and density that can have significant effects on the object’s design, performance, and stability (e.g., in aircraft or rockets). For example, as the Mach number increases, the shock waves become stronger and can cause a dramatic rise in drag.
In aerodynamics, Mach number is used to design vehicles like airplanes, missiles, and rockets. The flow characteristics around the vehicle will differ greatly depending on whether it is subsonic, transonic, supersonic, or hypersonic.
At higher Mach numbers, the fluid (especially gases) becomes compressible, meaning that changes in pressure and temperature can cause significant variations in density. For example, in supersonic and hypersonic flows, the density of the fluid may not be constant, unlike in subsonic flows where density changes are relatively negligible.
In jet engines and rocket propulsion, the Mach number affects the performance and efficiency of engines. For instance:
In meteorology, the Mach number is used to analyze winds at different altitudes and understand the formation of sonic booms or atmospheric shock waves. For example, the flow of winds around mountain ranges or large atmospheric disturbances can sometimes reach supersonic speeds, influencing the weather patterns.
Describe different properties of fluids.
Different properties of fluids are as follows:- 1. Density (ρ) Definition: Density is the mass per unit volume of a fluid. Formula: ρ=mV\rho = \frac{m}{V}ρ=Vm Where mmm is mass and VVV is volume. Units: kg/m³ (in SI units). Importance: Density determines the buoyancy of a fluid and affects the flowRead more
Different properties of fluids are as follows:-
1. Density (ρ)
2. Viscosity (μ)
3. Surface Tension (σ)
4. Compressibility (β)
5. Specific Volume (v)
6. Pressure (P)
7. Temperature (T)
8. Specific Gravity (SG)
- Definition: Specific gravity is the ratio of the density of a fluid to the density of water at a specified temperature (usually 4°C for water).
- Formula:
- Importance: Specific gravity provides a quick comparison of fluid densities and is often used to determine whether a fluid will float or sink in water.
See lessExplain the construction and working of Orifice meter and Venturi meter.
Orifice Meter Construction: An Orifice Meter is a device used to measure the flow rate of a fluid in a pipe. It consists of the following components: Orifice Plate: A thin plate with a precisely sized hole (orifice) in the center, which is installed perpendicular to the flow direction of the fluid.Read more
Orifice Meter
Construction:
An Orifice Meter is a device used to measure the flow rate of a fluid in a pipe. It consists of the following components:
Working:
When a fluid flows through the pipe, it is forced through the small hole in the orifice plate. According to Bernoulli’s principle, the velocity of the fluid increases as it passes through the orifice, causing a drop in pressure. This pressure drop can be measured by the differential pressure gauge. The relationship between the flow rate and the pressure drop is given by the continuity equation and Bernoulli’s equation
Venturi Meter
Construction:
A Venturi Meter is another device used for measuring fluid flow, but it operates on the principle of gradual changes in pipe diameter. Its key components include:
Working:
The fluid flows into the converging section of the Venturi meter, where its velocity increases and pressure decreases due to the reduced cross-sectional area. At the throat, the velocity is at a maximum, and pressure is at a minimum. As the fluid exits the throat into the diverging section, the velocity decreases and pressure increases.
The flow rate is determined by measuring the pressure difference between the inlet and the throat.
See lessExplain Priming and Cavitation.
Priming: Priming refers to the process of filling a pump or pumping system with liquid to remove air or vapor before the pump can operate effectively. Priming is necessary for certain types of pumps, especially positive displacement pumps or centrifugal pumps, which rely on the fluid to create suctiRead more
Priming:
Priming refers to the process of filling a pump or pumping system with liquid to remove air or vapor before the pump can operate effectively. Priming is necessary for certain types of pumps, especially positive displacement pumps or centrifugal pumps, which rely on the fluid to create suction and generate flow. If a pump is not primed properly, it cannot generate the required suction, leading to failure in operation.
How Priming Works:
Cavitation:
Cavitation is a phenomenon that occurs when the local pressure in a fluid falls below its vapor pressure, leading to the formation of vapor bubbles. These bubbles then collapse violently when they encounter higher pressure areas, causing damage to the surface of pump components, pipes, or other parts of the system.
How Cavitation Occurs:
- Pressure Drop: Cavitation typically happens when the pressure in the pump inlet drops too low, causing the fluid to vaporize and form bubbles.
- Vapor Bubble Formation: When the pressure falls below the vapor pressure of the fluid (the pressure at which the fluid turns into vapor), small vapor bubbles form.
- Bubble Collapse: As the fluid moves into regions of higher pressure, the vapor bubbles collapse or implode. The rapid collapse generates shock waves, which can cause pitting, erosion, and vibration, ultimately damaging the pump or other components.
See lessExplain the different types of flows in detail.
Types of flows:- 1. Laminar Flow: Definition: In laminar flow, fluid particles move in parallel layers or streamlines with minimal mixing between the layers. The flow is smooth and orderly. Characteristics: The fluid velocity is low, and the Reynolds number (Re) is less than 2000. The flow is typicaRead more
Types of flows:-
1. Laminar Flow:
2. Turbulent Flow:
3. Transitional Flow:
4. Steady Flow:
5. Unsteady Flow:
6. Uniform Flow:
7. Non-Uniform Flow:
8. Compressible Flow:
9. Incompressible Flow:
10. Rotational Flow:
11. Irrotational Flow:
- Definition: In irrotational flow, the fluid particles do not exhibit any rotational motion, meaning the vorticity (rate of rotation) is zero at every point.
- Characteristics:
- Fluid elements move without any spinning around their axes.
- Often used in idealized conditions to simplify calculations, especially in potential flow theory.
- Example: Idealized flow in a frictionless fluid, such as airflow around a streamlined object in aerodynamics.
See lessWrite the difference between Orifice meter and Venturi meter?
Difference between orificemeter and venturimeter:- 1. Design and Construction:- Orifice Meter: Consists of a flat plate with a hole (orifice) in the center, installed perpendicular to the flow. The pressure difference is measured across the orifice. Venturi Meter: Has a gradually narrowing section (Read more
Difference between orificemeter and venturimeter:-
1. Design and Construction:-
2. Flow Characteristics:
3. Pressure Drop:
4. Accuracy:
5. Cost:
6. Applications:
7. Maintenance:
- Orifice Meter: May require more frequent cleaning and maintenance due to erosion and fouling at the orifice.
- Venturi Meter: Requires less frequent maintenance as the design is less prone to clogging or erosion.
See lessExplain the limitations of Bernoulli’s equation.
The limitations of Bernoulli’s equation are as:- 1. Incompressible Fluids Only:- Bernoulli's equation assumes that the fluid is incompressible, meaning its density remains constant throughout the flow. This is generally valid for liquids like water but not for gases, especially at high velocities orRead more
The limitations of Bernoulli’s equation are as:-
1. Incompressible Fluids Only:-
2. Non-Viscous Fluid:-
3. Steady Flow:-
4. Flow Along a Streamline:-
5. No Energy Losses:-
6. Neglecting Gravitational Effects in Some Cases:-
7. Requires Ideal Flow Assumptions:-
8. No Boundary Layer Considerations:-
- The equation assumes no boundary layer effects, which are important near solid surfaces (e.g., walls of pipes or ducts). In real flow near boundaries, the velocity gradient due to viscous effects can be significant, and Bernoulli’s equation does not capture this effect.
See lessGive the classification of pressure measuring devices.
Pressure measuring devices can be classified based on various factors such as their working principle, measurement range, accuracy, and the type of pressure they measure. But we are classified on the basis of mechanical pressure gauges:- 1) Bourdon Tube Pressure Gauges: Utilize a curved tubeRead more
Pressure measuring devices can be classified based on various factors such as their working principle, measurement range, accuracy, and the type of pressure they measure. But we are classified on the basis of mechanical pressure gauges:-
1) Bourdon Tube Pressure Gauges: Utilize a curved tube that straightens when pressure is applied.
2) Diaphragm Pressure Gauges: Use a flexible diaphragm that deforms under pressure.
3) Bellows Pressure Gauges: Utilize a metal bellows that expands or contracts with pressure changes.
4) Manometer (U-Tube): A simple device that measures pressure by balancing a column of liquid (e.g., mercury or water) against the pressure.
See less