The incorrect expression for plastic deformation of metallic materials is: When plastic deformation progresses sufficiently, then the negative contribution to the strain hardening of the metal due to local adiabatic heating starts the local plastic deformation.
Plastic deformation is a permanent deformation that occurs when the external forces acting on a metal exceeds the elastic limit of the material. In metallic materials, plastic deformation is the most common mode of deformation. When a metal undergoes plastic deformation, the metal changes its shape permanently, and the forces required to cause further deformation decreases. Here, we are going to indicate the incorrect expression for plastic deformation of metallic materials.
Incorrect expression:
"When plastic deformation progresses sufficiently, then the negative contribution to the strain hardening of the metal due to local adiabatic heating starts the local plastic deformation." This is an incorrect expression as the plastic deformation does not start due to the negative contribution to the strain hardening of the metal. Local adiabatic heating has no role in starting the plastic deformation process. Hence, this option is incorrect.
Other options are as follows:
- The level of the yield strength does not indicate if necking occurs after a small amount of homogeneous deformation or after a large amount (in other words, if the start of necking is delayed or not). This statement is correct as the yield strength only indicates the initial point of plastic deformation. It does not determine the amount of homogeneous deformation.
- Greater strain-hardening exponent means an earlier ‘necking’. This statement is correct as a higher value of strain-hardening exponent leads to early onset of necking. Necking is defined as the formation of a localized narrow band in a metallic material.
- If ‘n’ and ‘m’ parameters are greater the larger the homogeneous plastic deformation range. This statement is correct as a higher value of 'n' and 'm' leads to a larger range of homogeneous plastic deformation.
Thus, the incorrect expression for plastic deformation of metallic materials is "When plastic deformation progresses sufficiently, then the negative contribution to the strain hardening of the metal due to local adiabatic heating starts the local plastic deformation". This expression is not correct as local adiabatic heating has no role in starting the plastic deformation process.
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Question 5 (a) Draw the sketch that explain the changes occurs in the flow through oblique and normal shock waves? (5 marks) (b) The radial velocity component in an incompressible, two-dimensional flow (v, = 0) is: V, = 2r + 3r2 sin e Determine the corresponding tangential velocity component (ve) required to satisfy conservation of mass. (10 marks) (c) Air enters a square duct through a 1.0 ft opening as is shown in figure 5-c. Because the boundary layer displacement thickness increases in the direction of flow, it is necessary to increase the cross-sectional size of the duct if a constant U = 2.0 ft/s velocity is to be maintained outside the boundary layer. Plot a graph of the duct size, d, as a function of x for 0.0 SX S10 ft, if U is to remain constant. Assume laminar flow. The kinematic viscosity of air is v = 1.57 x 10-4 ft2/s. (10 marks) U= 2 ft/s 1 ft dux) 2 ft/s
Part a)The oblique shock wave occurs when a supersonic flow over a wedge or any angled surface. The normal shock wave occurs when a supersonic flow is blocked by a straight surface or an object.
The normal shock wave has a sharp pressure rise and velocity decrease downstream of the wave front, while the oblique shock wave has a gradual pressure rise and velocity decrease downstream of the wave front. The oblique shock wave can be calculated by the wedge angle and the Mach number of the upstream flow. The normal shock wave can be calculated by the Mach number of the upstream flow only. Part b)Given radial velocity component, V, = 2r + 3r2 sin e
Required tangential velocity component (v?) to satisfy conservation of mass. Here, u, = 0 and
v, = 2r + 3r2 sin e.
Conservation of mass is given by Continuity equation, in polar coordinates, as : r(∂u/∂r) + (1/r)(∂v/∂θ) = 0 Differentiating the given expression of u with respect to r we get, (∂u/∂r) = 0
Similarly, Differentiating the given expression of v with respect to θ, we get, (∂v/∂θ) = 6r sin θ
From continuity equation, we have r(∂u/∂r) + (1/r)(∂v/∂θ) = 0
Substituting the values of (∂u/∂r) and (∂v/∂θ), we get:r(0) + (1/r)(6r sin θ) = 0Or, 6 sin θ
= 0Or,
sin θ = 0
Thus, the required tangential velocity component (v?) to satisfy conservation of mass is ve = r(∂θ/∂t) = r(2) = 2r.
Part c)GivenU = 2.0 ft/s kinematic viscosity of air, v = 1.57 × 10-4 ft2/sAt x = 0
duct size, d1 = 1.0 ft
At x = 10 ft,
duct size, d2 = ?
Reynolds number for the laminar flow can be calculated as: Re = (ρUd/μ) Where, ρ = density of air = 0.0023769 slug/ft3μ = dynamic viscosity of air = 1.57 × 10-4 ft2/s
U = velocity of air
= 2.0 ft/s
d = diameter of duct
Re = (ρUd/μ)
= (0.0023769 × 2 × d/1.57 × 10-4)
For laminar flow, Reynolds number is less than 2300.
Thus, Re < 2300 => (0.0023769 × 2 × d/1.57 × 10-4) < 2300
=> d < 0.0726 ft or 0.871 inches or 22.15 mm
Assuming the thickness of the boundary layer to be negligible at x = 0, the velocity profile for the laminar flow in the duct at x = 0 is given by the Poiseuille’s equation:u = Umax(1 - (r/d1)2)
Here, Umax = U = 2 ft/s
Radius of the duct at x = 0 is r = d1/2 = 1/2 ft = 6 inches.
Thus, maximum velocity at x = 0 is given by:u = Umax(1 - (r/d1)2)
= 2 × (1 - (6/12)2)
= 0.5 ft/s
Let the velocity profile at x = 10 ft be given by u = Umax(1 - (r/d2)2)
The average velocity of the fluid at x = 10 ft should be U = 2 ft/s
As the boundary layer thickness increases in the direction of flow, it is necessary to increase the cross-sectional area of the duct for the same flow rate.Using the continuity equation,Q = A1 U1 = A2 U2
Where,Q = Flow rate of fluid
A1 = Area of duct at x
= 0A2
= Area of duct at x
= 10ftU1 = Velocity of fluid at x
= 0U2 = Velocity of fluid at x
= 10ft
Let d be the diameter of the duct at x = 10ft.
Then, A2 = πd2/4
Flow rate at x = 0 is given by,
Q = A1 U1 = π(1.0)2/4 × 0.5
= 0.3927 ft3/s
Flow rate at x = 10 ft should be the same as flow rate at x = 0.So,0.3927
= A2 U2
= πd2/4 × 2Or, d2
= 0.6283 ft = 7.54 inches
Thus, the diameter of the duct at x = 10 ft should be 7.54 inches or more to maintain a constant velocity of 2.0 ft/s.
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force (F) in the wrench above is 15.25 kN applied through a distance of 35 cm along the wrench and the inclined angle (θ) is 60° ? What is the magnitude of the torque relative to the bolt in Joules A J 5337.50 B J 266875 C J 4622.41 D J 533.75
The magnitude of the torque relative to the bolt in Joules is 4622.41J.Torque is a measure of a force's ability to produce rotation around an axis, which can be determined by multiplying the force applied by the distance from the axis of rotation at which it is applied.
As well as the sine of the angle between the force and the lever arm. This formula can be used to calculate torque: τ = F * d * sinθWhere:τ is torque in newton-meters (Nm)F is force in newtons (N)d is the distance from the axis of rotation at which the force is applied in meters (m)θ is the angle between the force vector and the lever arm in degrees (°)Given.
F = 15.25 kN = 15,250 Nd = 35 cm = 0.35 mθ = 60°To convert kN to N, we need to multiply by 1,000:15.25 kN = 15.25 * 1,000 = 15,250 N Then we can plug the values into the formula:τ = F * d * sinθτ = 15,250 N * 0.35 m * sin(60°)τ = 4622.41 J, the magnitude of the torque relative to the bolt in Joules is J 4622.41.
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A fluid in a fire hose with a 46.5 mm radius, has a velocity of 0.56 m/s. Solve for the power, hp, available in the jet at the nozzle attached at the end of the hose if its diameter is 15.73 mm. Express your answer in 4 decimal places.
Given data: Radius of hose
r = 46.5m
m = 0.0465m
Velocity of fluid `v = 0.56 m/s`
Diameter of the nozzle attached `d = 15.73 mm = 0.01573m`We are supposed to calculate the power, hp available in the jet at the nozzle attached to the hose.
Power is defined as the rate at which work is done or energy is transferred, that is, P = E/t, where E is the energy (J) and t is the time (s).Now, Energy E transferred by the fluid is given by the formula E = 1/2mv² where m is the mass of the fluid and v is its velocity.We can write m = (ρV) where ρ is the density of the fluid and V is the volume of the fluid. Volume of the fluid is given by `V = (πr²l)`, where l is the length of the hose through which fluid is coming out, which can be assumed to be equal to the diameter of the nozzle or `l=d/2`.
Thus, `V = (πr²d)/2`.Energy transferred E by the fluid can be expressed as Putting the value of V in the above equation, we get .Now, the power of the fluid P, can be written as `P = E/t`, where t is the time taken by the fluid to come out from the nozzle.`Putting the given values of r, d, and v, we get Thus, the power available in the jet at the nozzle attached to the hose is 0.3011 hp.
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Explain the following in brief: a. Stagnation temperature b. Dynamic temperature c. Choking of the nozzle d. External flow
Stagnation temperature is the temperature at a point in a moving fluid where the velocity of the fluid is reduced to zero. It is the maximum temperature that can be reached in a fluid when the fluid is brought to rest isentropically.
It is one of the important properties used in thermodynamics to study compressible flow.b) The temperature measured in a moving fluid when the fluid is brought to rest adiabatically is known as dynamic temperature. The dynamic temperature of a gas is the temperature that the gas would have if it were brought to rest isentropically. The choking of the nozzle occurs when the flow velocity reaches the local velocity of sound.
It refers to a critical point in a flow system beyond which the velocity of the fluid cannot increase. At this point, the fluid becomes a choke, and the mass flow rate remains constant. The choke point is where the Mach number is equal to 1. The condition is known as choking.d) The external flow is the flow around a body or an object. The flow may be laminar or turbulent, depending on the Reynolds number.
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The diffusivity of copper in a commercial brass alloy is 10-20 mº/s at 500 °C. The activation energy for diffusion of copper in this system is 200 kJ/mol. Calculate the diffusivity at 800 °C. Express your answer to three significant figures. IVO AEDT vec ? 20 The diffusivity at 800 °C is 1.0087·10 mº/s. Submit Previous Answers Request Answer X Incorrect; Try Again; 7 attempts remaining
Diffusivity is the property of materials that governs how quickly elements or molecules can move through them when subjected to a concentration gradient.
Diffusivity of copper in a commercial brass alloy is 10-20 mº/s at 500 °C, and the activation energy for diffusion of copper in this system is 200 kJ/mol. To find the diffusivity at 800°C, we can use the Arrhenius equation, which is:
[tex]$$D=D_0 e^{-E_a/RT}$$[/tex]
Where: D is the diffusivityD0 is the pre-exponential factor Ea is the activation energy R is the universal gas constant.
T is the absolute temperature. We are given the diffusivity, pre-exponential factor, and activation energy at 500°C, so we can use those to find the value of D0.
[tex]$$D=D_0 e^{-E_a/RT} $$$$D_0 = D/e^{-E_a/RT} $$$$D_0 = 10^{-20}/e^{-200000/(8.31*500)}= 1.204*10^{-14}$$[/tex]. Now that we have the pre-exponential factor.
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The Reynolds number, pvD/u, is a very important parameter in fluid mechanics. Verify that the Reynolds number is dimensionless, using the MLT system for basic dimensions, and determine its value for ethyl alcohol flowing at a velocity of 3 m/s through a 2-in- diameter pipe.
Reynolds number is a dimensionless quantity which represents the ratio of inertial forces (ρvD) to the viscous forces (u).Here,ρ is the density of the fluidv is the velocity of the fluidD is the diameter of the pipemu is the dynamic viscosity of the fluid.
If the Reynolds number is very less than 2300, then the flow is laminar and if it is greater than 4000, then the flow is turbulent.If the Reynolds number lies between 2300 and 4000, then the flow is transitional. Ethyl alcohol is flowing through a 2-inch diameter pipe at a velocity of 3 m/s.
We have to find the Reynolds number value.Let's put the values in the formula,Re = ρvd/µRe = (7850 kg/m³ x 3 m/s x 0.0508 m) / (1.2 x 10⁻³ N s/m²)Re = 9,34,890.67Reynolds number value is more than 100 words.
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A 6-cylinder, two-stroke, diesel engine produces 1200hp at 360rpm. The engine has an expansion ratio of 5.2, a percent clearance of 6.0%, and a mechanical efficiency of 82% when operating at 32∘C and 99.3kPa standard atmospheric conditions. It is then used as a generating unit by a plant at an elevation of 2846ft where it gave a brake heat rate of 18,530 kJ/kW-hr at k=1.37 using a fuel having a heating value of 42,566 kJ/kg. Determine at this elevation the Pressure in kPa. Use four (4) decimal places in your solution and answer.
a. Define the following quantities clearly; provide equations and units for all quantities: (i) weight (ii) density (iii) pressure [30\%] b. With the aid of a diagram, explain the operation of the Gear Pump. State its strengths and a common application. [40\%]
c. A hydraulic actuator has a piston area of 0.03 m² in contact with hydraulic fluid, and is required to lift a 10000 kg mass. What pressure must be supplied to the hydraulic fluid to do this? Calculate the volume of fluid that a pump would need to provide to move the actuator by 10 cm. [30\%]
Weight: The force of gravity acting on an object is referred to as weight. You may figure it out by using the equation: Weight = Mass × Gravity, Unit: Newtons (N).
The mass of a substance per unit volume is known as its density. You may figure it out by using the equation:
Density = Mass / Volume
Unit: Kilograms per cubic meter (kg/m³)
The force applied per unit area is referred to as pressure. You may figure it out by using the equation:
Pressure = Force / Area
Unit: Pascals (Pa)
How a Gear Pump Works: A Gear Pump is a form of Positive Displacement Pump that pumps fluids using meshing gears. The following describes how a gear pump works:
The pump has two gears: an input gear that is powered by an engine or motor and an output gear.A vacuum is created at the intake when the input gear spins, drawing fluid into the pump.As the gears revolve, the fluid is carried around the pump's housing because it becomes wedged between the gear teeth and the housing.As the gears mesh and the amount of the trapped fluid decreases, the fluid is subsequently driven out through the outlet.Hydraulic Actuator: To use a hydraulic actuator to raise a 10,000 kg mass, we must determine the necessary pressure.
Pressure = Force / Area
Force = Mass × Gravity
So,
Force = 10,000 kg × 9.8 m/s²
Pressure = (10,000 kg × 9.8 m/s²) / 0.03 m²
Now,
Volume = Area × Distance
Area = 0.03 m²
Distance = 10 cm = 0.1 m
Volume = 0.03 m² × 0.1 m
Thus, these are the definition asked.
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Stickman has built a rocket sled. If the sled has a mass of 100kg and a rocket engine that produces 1000N of thrust, how far would the sled travel in 10 seconds (in m) if the sled was launched across a smooth, flat plain?
The rocket sled, with a mass of 100kg and a thrust of 1000N, would travel 500 meters in 10 seconds across a smooth, flat plain.
To calculate the distance the sled would travel, we can use Newton’s second law of motion, which states that the net force acting on an object is equal to the product of its mass and acceleration. In this case, the net force is the thrust produced by the rocket engine, and the acceleration is the sled’s acceleration.
First, we need to determine the acceleration of the sled. We can use the formula:
Acceleration = Net Force / Mass
In this case, the net force is 1000N (thrust) and the mass is 100kg:
Acceleration = 1000N / 100kg = 10 m/s²
Now that we have the acceleration, we can use the kinematic equation to calculate the distance traveled:
Distance = Initial Velocity × Time + 0.5 × Acceleration × Time²
Since the sled starts from rest, the initial velocity is 0 m/s. Plugging in the values:
Distance = 0 × 10 + 0.5 × 10 × 10²
Distance = 0 + 0.5 × 10 × 100
Distance = 0 + 0.5 × 1000
Distance = 0 + 500
Distance = 500 meters
Therefore, the sled would travel a distance of 500 meters in 10 seconds across a smooth, flat plain.
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A plastic dry rubbing bearing runs over a 9 mm non-rotating steel axle. The radial wear rate of the bearing is approximately 0.086 mm/year. If the bearings are to be replaced when the diametral clearance reaches 555 μ m , calculate the minimum expected bearing life (in years). Give your answer to 2 decimal places. Hint: start by choosing a suitable hole basis fit . Then, calculate the maximum diametral clearance (using the fit you selected) and use this value to determine the bearing life.
The life expectancy of a plastic bearing running over a non-rotating steel axle can be calculated using the radial wear rate and the diametral clearance limit.
Firstly, we'll select a suitable hole basis fit. Given the conditions, a clearance fit seems suitable. However, without specific fit class information, it's hard to precisely determine the initial diametral clearance. Assuming zero initial clearance (or at least significantly less than the replacement limit), the maximum diametral clearance before replacement becomes 555 μm or 0.555 mm. This clearance will be twice the radial wear due to symmetry (diametral wear = 2*radial wear). The wear rate is given as 0.086 mm/year radially, which translates to 0.172 mm/year diametrically. Hence, the minimum expected life of the bearing will be the maximum diametral clearance divided by the diametral wear rate. This will provide the estimated bearing life in years, rounded to two decimal places.
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Determine the moment of this force about point B. Express your
answer in terms of the unit vectors i, j, and k.
The pipe assembly is subjected to the 80-NN force.
Given, The pipe assembly is subjected to the 80-NN force. We need to determine the moment of this force about point B using the unit vectors i, j, and k.In order to determine the moment of the force about point B, we need to determine the position vector and cross-product of the force.
The position vector of the force is given by AB. AB is the vector joining point A to point B. We can see that the coordinates of point A are (1, 1, 3) and the coordinates of point B are (4, 2, 2).Therefore, the position vector AB = (3i + j - k)We can also determine the cross-product of the force. Since the force is only in the y-direction, the vector of force can be represented as F = 80jN.Now, we can use the formula to determine the cross-product of F and AB.
The formula for cross-product is given as: A × B = |A| |B| sinθ nWhere, |A| |B| sinθ is the magnitude of the cross-product vector and n is the unit vector perpendicular to both A and B.Let's determine the cross-product of F and AB:F × AB = |F| |AB| sinθ n= (80 j) × (3 i + j - k)= 240 k - 80 iWe can see that the cross-product is a vector that is perpendicular to both F and AB. Therefore, it represents the moment of the force about point B. Thus, the main answer is 240k - 80i.
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Build the circuit in Figure 3 in Multisim using the values you have calculated and Measure the Q-point and compare with expected value. Connect and set the generator to a sinusoidal of 3 kHz (small-signal peak to peak voltage of 20 mV). Use 10 μF for the capacitor C. Make sure the capacitor is connected with the correct polarity. Adjust the input amplitude so that none of the waveforms is clipped. Observe and include in your report the following waveforms: - Input voltage v₁, collector voltage vc, emitter voltage VE, and collector-emitter voltage VCE. - Plot all those waveforms on a common time scale using 2 to 3 sinusoidal cycles.
The input voltage v1, collector voltage vc, emitter voltage VE, and collector-emitter voltage VCE waveforms are then observed and plotted on a common time scale using 2 to 3 sinusoidal cycles.
To build the circuit in Figure 3 in Multisim using the values calculated, the following steps can be followed:
Components R1 and R2 are calculated as follows: R1 = Vcc / Icq
= 12 V / 0.0008 A
= 15 kohm and R2 = Vbe / Ib
= 0.7 V / 0.000025 A = 28 kohm.
A resistor with the nearest higher standard value of 30 kohm was used for R2 instead of the calculated value of 28 kohm.
A 10μF capacitor is used for C.
The circuit is then simulated using Multisim software and the values of VCE and IC obtained are measured. These values are then used to calculate the Q-point.
The measured values are compared with the expected values. If there is any significant difference, the circuit may be adjusted or the values of R1 and R2 calculated again to ensure that they are within the tolerances of the resistors used. Once the Q-point is determined, the generator can be connected and set to a sinusoidal of 3 kHz (small-signal peak to peak voltage of 20 mV). The input amplitude is then adjusted so that none of the waveforms is clipped.
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Make use of a signal flow graph to find the transfer function X5/X1: X2 = a_12X_1 + a_32X_3 + a_42X_4+ a_52X_5 X_3 = a_23X_2 X_4a_34X_3+ a44X4 X_5 = a_35X_3 + a_45X_4 Where X1 is the input variable and Xs is the output variable. Show all steps clearly. (10)
A signal flow graph (SFG) provides an effective means of representing a system's control configuration. The graph depicts the cause-and-effect relationships between signals in the system in a compact and understandable way.
It is a graphical representation of the signals and the relationships between them.Using the SFG to find the transfer function X5/X1:
[tex]X2 = a_12X_1 + a_32X_3 + a_42X_4+ a_52X_5 X_3[/tex]
[tex]= a_23X_2 X_4a_34X_3+ a44X4 X_5[/tex]
[tex]= a_35X_3 + a_45X_4[/tex]
We need to locate all the paths that lead to the output signal. We can only locate one path that links X1 to X5. X1 is connected to X2. X2 is connected to X3, X3 is connected to X4, and X4 is connected to X5. Therefore, there is only one path from X1 to X5, and the transfer function of the entire system can be calculated by simply following the arrows' direction in the SFG. For the given system, we can write down the equations for each node based on the graph's structure:
[tex]X2 = a12X1 + a32X3 + a42X4 + a52X5X3[/tex]
[tex]= a23X2X4[/tex]
[tex]= a34X3 + a44X4X5[/tex]
[tex]= a35X3 + a45X4[/tex]
Therefore:
[tex]X5 = a35X3 + a45X4[/tex]
[tex]= (a35a23 + a45a44) X1 + (a35a32 + a45a34) X3 + (a35a42 + a45) X4[/tex]
To calculate the transfer function, we can see that the output signal X5 is related to X1.
Thus, we can write the transfer function X5/X1 as follows:
[tex]X5/X1 = (a35a23 + a45a44) + (a35a32 + a45a34) X3/X1 + (a35a42 + a45) X4/X1[/tex]
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Identify appropriate bearings for the following applications: (a) A single spool (shaft) gas turbine operating at 12 000 rpm with a shaft diameter of 40mm. (b) A turbocharger spinning at up to 150 000 rpm with a shaft diameter of 10mm. (c) A photocopier roller operating at 150 rpm with a spindle diameter of 10mm. (d) A ship’s propeller shaft operating at 1500 rpm.
Appropriate bearings for the following applications are:(a) A single spool (shaft) gas turbine operating at 12 000 rpm with a shaft diameter of 40mm:
The cylindrical roller bearings or deep groove ball bearings are most appropriate bearings for single spool gas turbines, which can operate at high speeds and reduce the overall frictional torque.
(b) A turbocharger spinning at up to 150 000 rpm with a shaft diameter of 10mm: For a turbocharger spinning at up to 150 000 rpm with a shaft diameter of 10mm, either ball bearings or fluid bearings can be used. However, ball bearings are best suited for this application due to their high speed and load capacity.
(c) A photocopier roller operating at 150 rpm with a spindle diameter of 10mm: The sintered bronze or porous metal bearings are ideal for this application. These bearings are ideal because of their self-lubricating and vibration damping characteristics, which are ideal for quiet operation.
(d) A ship’s propeller shaft operating at 1500 rpm: Tapered roller bearings or spherical roller bearings are the most appropriate for the ship's propeller shaft. These bearings are ideally suited for high axial and radial loads, as well as moments that are developed in a shaft due to external forces.
All of the above-given applications require bearings of different kinds. The spindle and shaft diameters, as well as the speed of rotation, are the key factors influencing the selection of appropriate bearings. Single spool gas turbines are widely used in energy generation, aviation, and oil and gas industries.
Cylindrical roller bearings or deep groove ball bearings are commonly used in such turbines due to their high speed and load-bearing capacity. Similarly, turbochargers require bearings that can withstand high speeds and loads. Ball bearings can provide smooth operation at speeds up to 150,000 rpm, making them ideal for turbochargers.
For photocopier rollers, which operate at low speeds but must operate quietly, sintered bronze or porous metal bearings are used. Finally, tapered roller bearings or spherical roller bearings are best suited for ship propellers, which must handle high loads, moments, and speeds.
Bearings must be selected based on the specific requirements of the application in which they will be used. Careful consideration of factors such as speed, load, and spindle or shaft diameter will help ensure that the appropriate bearing is selected.
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A 20-KV motor absorbs 81 MVA at 0.8 pf lagging at rated terminal voltage. Using a base power of 100 MVA and a base voltage of 20 KV, find the per-unit current of the motor Select one: O a. 0.81∠-36.87° (p.u) O b. 0.27∠-36.87° (p.u) O c None of these O d. 0.45∠-36.87° (p.u) O e 0.65∠-36.87° (p.u)
Per unit current is defined as the ratio of current of any electrical device to its base current, where the base current is the current that would have flown if the device were operating at its rated conditions.
We use per unit system to make calculations easy. So, given a 20-KV motor absorbs 81 MVA at 0.8 pf lagging at rated terminal voltage. Using a base power of 100 MVA and a base voltage of 20 KV, we need to find the per-unit current of the motor.
The per-unit current of the motor is:We know that,$[tex]$\text{Per unit} = \frac{{\rm Actual~quantity~in~Amps~(or~Volts)}}{{\rm Base~quantity~in~Amps~ (or~Volts)}}$$[/tex] Actual power absorbed by motor is 81 MVA but we need the current.
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An industrial plant absorbs 500 kW at a line voltage of 480 V with a lagging power factor of 0.8 from a three-phase utility line. The apparent power absorbed is most nearly O a. 625 KVA O b. 500 KVA O c. 400 KVA O d. 480 KVA
So, the most nearly apparent power absorbed is 625 KVA.Answer: The correct option is O a. 625 KVA.
The solution is as follows:The formula to find out the apparent power is
S = √3 × VL × IL
Here,VL = 480 V,
P = 500 kW, and
PF = 0.8.
For a lagging power factor, the apparent power is always greater than the real power; thus, the value of the apparent power will be greater than 500 kW.
Applying the above formula,
S = √3 × 480 × 625 A= 625 KVA.
So, the most nearly apparent power absorbed is 625 KVA.Answer: The correct option is O a. 625 KVA.
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E3: Air flows from a nozzle with a mass flow rate of 1.0 slugs /sec. If T 0=607 ∘F,p 0 = 120psia, and p exit =15psia, the Ma number at the exit is most nearly a. 2.55 b. 2.05 c. 3.15 d. 1.00 e. 1.60
The Mach number at the exit of the nozzle, given a mass flow rate of 1.0 slugs/sec, is option (a) 2.55, according to the provided parameters.
To determine the Mach number at the exit of the nozzle, we can use the isentropic flow equations and the given parameters.
Given:
Mass flow rate (ṁ) = 1.0 slugs/sec
Total temperature at the inlet (T₀) = 607 °F
Total pressure at the inlet (p₀) = 120 psia
Pressure at the exit (p_exit) = 15 psia
First, we need to convert the total temperature from Fahrenheit to Rankine:
T₀ = 607 °F + 459.67 °R = 1066.67 °R
Next, we can use the mass flow rate and the total pressure to find the exit velocity (V_exit):
V_exit = ṁ / (A_exit * ρ_exit)
To find the exit area (A_exit), we need to calculate the exit density (ρ_exit) using the ideal gas equation:
Ρ_exit = p_exit / (R * T_exit)
The gas constant R for air is approximately 1716.5 ft·lbf/(slug·°R).
Using the isentropic flow equations, we can find the exit temperature (T_exit) as follows:
(p_exit / p₀) = (T_exit / T₀) ^ (γ / (γ – 1))
Here, γ is the specific heat ratio for air, which is approximately 1.4.
Now, let’s calculate the exit temperature:
(T_exit / T₀) = (p_exit / p₀) ^ ((γ – 1) / γ)
(T_exit / 1066.67 °R) = (15 psia / 120 psia) ^ ((1.4 – 1) / 1.4)
(T_exit / 1066.67 °R) = 0.3272
T_exit = 0.3272 * 1066.67 °R = 349.96 °R
Now, we can calculate the exit density:
Ρ_exit = 15 psia / (1716.5 ft·lbf/(slug·°R) * 349.96 °R) ≈ 0.00624 slug/ft³
Next, let’s calculate the exit velocity:
V_exit = 1.0 slugs/sec / (A_exit * 0.00624 slug/ft³)
Now, we can use the mass flow rate equation to find the exit area (A_exit):
A_exit = 1.0 slugs/sec / (V_exit * 0.00624 slug/ft³)
Finally, we can calculate the Mach number at the exit:
M_exit = V_exit / (γ * R * T_exit)^0.5
Let’s plug in the values and calculate the Mach number:
A_exit = 1.0 slugs/sec / (V_exit * 0.00624 slug/ft³)
M_exit = V_exit / (1.4 * 1716.5 ft·lbf/(slug·°R) * 349.96 °R)^0.5
After performing the calculations, the most approximate Mach number at the exit is option (a) 2.55.
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The output of a thermistor is highly nonlinear with temperature, and there is often a benefit to linearizing the output through appropriate circuit, whether active or passive. In this example, we examine the output of an initially balanced bridge circuit in which one of the arms contains a thermistor. Consider a Wheatstone bridge as shown in Figure 8.8, but replace the RTD with a thermistor having a value of R = 10,000 22 with B = 3680 K. Here, we examine the output of the circuit over two temperature ranges: (a) 25–325°C and (b) 25–75°C. KNOWN A Wheatstone bridge where R2 = R3 = R4 = 10,000 22 and where R, is a thermistor. FIND The output of the bridge circuit as a function of temperature.
Step 1: Let RT be the resistance of the thermistor at temperature T°C.RT = R₀exp(B/T)where R₀ = 10,000 Ω, B = 3680 K and T is the temperature in °C.
Step 2: Calculate the equivalent resistance of the bridge.The equivalent resistance of the bridge is given by the formula: Req = R₂ + R₄/[R₁ + R₃]The value of the resistors R2 = R3 = R4 = 10,000 Ω.Thus, Req = 10,000 Ω + 10,000 Ω/[10,000 Ω + RT].
Step 3: Calculate the current through the bridge.Using the bridge balance equation, we have:R₂R₄ = R₁R₃exp(β (T - 25))where β = 3680 K, T is the temperature in °C and R1 = RT.
Rearranging the above equation, we have:RT = R₃R₂exp(β (T - 25))/R₁The current flowing through the bridge is given by:I = [Vcc × R₂R₄]/[R₂ + R₄][R₁ + R₃]Where Vcc is the voltage supply.
Step 4: Find the output voltage of the bridge circuit.The output voltage of the bridge is given by:Vout = Vcc [R₄/(R₂ + R₄)] - Vcc [R₁/(R₁ + R₃)]This can be simplified as:Vout = Vcc [R₄/(R₂ + R₄)][R₁ + R₃]/[R₁ + R₃] - Vcc R₁/[R₁ + R₃]Vout = Vcc[R₄(R₁ + R₃) - R₁(R₂ + R₄)]/[(R₁ + R₃)(R₂ + R₄)].
For the range 25°C to 325°C, we can vary the temperature T from 25°C to 325°C in steps of 1°C and repeat steps 1 to 4 to obtain the output voltage of the bridge circuit at each temperature.
Similarly, we can obtain the output voltage of the bridge circuit for the range 25°C to 75°C as well.
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The actual Rankine cycle has an 89.07% turbine isentropic efficiency and 75.22% pump isentropic efficiency. If in the ideal Rankine cycle, the heat input in the boiler = 924 kW, the turbine work output = 398 kW, and pump work input = 20 kW, what is the actual cycle thermal efficiency if the heat input in the boiler is the same for the actual cycle? Express your answer in percent.
The actual cycle thermal efficiency is 31.83%. The thermal efficiency of the ideal Rankine cycle is given by:
η = (W_net / Q_in) x 100%
where:
W_net = turbine work output - pump work input
Q_in = heat input in the boiler
Given:
Heat input in the boiler (Q_in) = 924 kW
Turbine work output = 398 kW
Pump work input = 20 kW
Using the above values and the ideal Rankine efficiency formula, we can calculate the ideal Rankine cycle thermal efficiency:
W_net = Turbine work output - Pump work input
W_net = 398 kW - 20 kW
W_net = 378 kW
η_ideal = (W_net / Q_in) x 100%
η_ideal = (378 kW / 924 kW) x 100%
η_ideal = 40.98%
The thermal efficiency of the actual Rankine cycle is given by:
η_actual = (W_net_actual / Q_in) x 100%
where:
W_net_actual = turbine work output - pump work input losses
The pump and turbine isentropic efficiency values can be used to calculate pump and turbine work input losses as follows:
Pump work input losses = pump work input / pump isentropic efficiency
Pump work input losses = 20 kW / 0.7522
Pump work input losses = 26.57 kW
Turbine work output losses = turbine work output - actual turbine work output
Turbine work output losses = turbine work output - (turbine isentropic efficiency x turbine work output)
Turbine work output losses = 398 kW - (0.8907 x 398 kW)
Turbine work output losses = 398 kW - 354.6 kW
Turbine work output losses = 43.4 kW
Therefore,
W_net_actual = W_net - pump work input losses - turbine work output losses
W_net_actual = 378 kW - 26.57 kW - 43.4 kW
W_net_actual = 308.03 kW
η_actual = (W_net_actual / Q_in) x 100%
η_actual = (308.03 kW / 924 kW) x 100%
η_actual = 31.83%
The actual cycle thermal efficiency of the Rankine cycle is 31.83% given the ideal Rankine cycle parameters, 89.07% turbine isentropic efficiency, and 75.22% pump isentropic efficiency.
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Prove that the transfer function is as follows using the block diagram reduction. 160K₁/s²+(32+160K₁K₂)s + 160K₁
The given transfer function is:
[tex]$$\frac{160K_1}{s^2+(32+160K_1K_2)s + 160K_1}$$[/tex]
We can represent the above transfer function in a block diagram form as follows: Block diagram The first block represents the gain of 160K₁, the second block represents the summing point, the third block represents the gain of K₂ and the fourth block represents the plant with a transfer function of
[tex]$$\frac{1}{s^2+32s+160K_1}$$[/tex]
Now, we will perform the block diagram reduction process. First, we will merge the second and third blocks using the summing point reduction technique. Summing point reduction technique Applying summing point reduction technique, we get a new transfer function:
[tex]$$\frac{160K_1}{s^2+(32+160K_1K_2)s + 160K_1} = \frac{K_2}{1+sT_1}\left(\frac{160K_1}{s^2+2\xi\omegas+\omega_n^2}\right)$$[/tex]
where[tex]$$\omega_n = 4\sqrt{10K_1}$$$$\xi = \frac{1}{8\sqrt{10K_1}}$$$$T_1 = \frac{1}{8\sqrt{10K_1}K_2}$$[/tex]
Hence, we have proved that the given transfer function can be represented using the block diagram reduction and we got a new transfer function.
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Mention the name and function of ten (10) components/instruments are involved in a power system.
A power system involves several components and instruments that work together to provide a reliable and efficient supply of power. These components can be broadly categorized into four main categories: generation, transmission, distribution, and consumption.
1. Generators - they convert mechanical energy into electrical energy.
2. Transformers - they step up or step down the voltage levels to facilitate transmission and distribution of power.
3. Circuit Breakers - they are used to protect the system from overloads and short circuits by interrupting the flow of electricity when necessary.
4. Capacitors - they store electrical energy and are used to improve the power factor of the system.
5. Switches - they are used to control the flow of electricity in the system.
6. Meters - they measure the electrical parameters such as voltage, current, power, and energy consumption.
7. Protective Relays - they are used to detect abnormal conditions in the system and trigger the appropriate response to protect the system from damage.
8. Transmission Lines - they are used to transport electricity from the power generation station to the distribution substations.
9. Distribution Transformers - they are used to step down the voltage levels for distribution to consumers.
10. Loads - they are the electrical devices that consume power, such as light bulbs, motors, and electronic appliances.
These components and instruments are crucial in a power system, and their proper functioning ensures a reliable and efficient supply of power.
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A single stage reciprocating compressor takes 1m of air per minute and 1.013 bar and 15°C and delivers at 7 bar. Assuming Adiabatic law (n=1.35) and no clearance. Calculate: 1.1. Mass flow rate (1.226 kg/min) 1.2. Delivery Temperature (475.4 K) 1.3. Indicated power (4.238 kW) This same compressor is now driven at 300 rpm, has a stroke to bore ratio of (1,5:1), it has a mechanical efficiency for the compressor of 85% and motor transmission efficiency of 90%. Calculate: 1.4. Volume per cycle (0.00333 m²/cycle) 1.5. Cylinder bore diameter (141.4 mm) 1.6. Power to the compressor (4.99 kW) 1.7. Motor power needed (5.54 kW) 1.8. The isothermal power (3.265 kW) 1.9. The isothermal efficiency (77%)
Therefore, the delivery temperature is 475.4 K.1.3. Calculation of Indicated Power The indicated power of the compressor can be calculated using the formula, Power = P * Q * n Where P is the pressure, Q is the flow rate, and n is the polytropic index.
Motor power = Power to compressor / η_tHere,
Power to compressor = 4.99 kW and
η_t = 0.90
So, the motor power needed is 5.54 kW.1.8. Calculation of Isothermal Power Isothermal Power can be calculated using the formula, P1V1/T1 = P2V2/T2 So, the isothermal power is 3.265 kW.1.9.
Calculation of Isothermal Efficiency The isothermal efficiency can be calculated using the formula, Isothermal efficiency = (Isothermal power / Indicated power) * 100 Substituting the values, we get,
Isothermal efficiency = (3.265 / 4.238) * 100 = 77%
Therefore, the isothermal efficiency is 77%.
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Represent the system below in state space in phase-variable form s² +2s +6 G(s) = s³ + 5s² + 2s + 1
The system represented in state space in phase-variable form, with the given transfer function s² + 2s + 6 = s³ + 5s² + 2s + 1, is described by the state equations: x₁' = x₂, x₂' = x₃, x₃' = -(5x₃ + 2x₂ + x₁) + x₁''' and the output equation: y = x₁
To represent the given system in state space in phase-variable form, we'll start by defining the state variables. Let's assume the state variables as:
x₁ = s
x₂ = s'
x₃ = s''
Now, let's differentiate the state variables with respect to time to obtain their derivatives:
x₁' = s' = x₂
x₂' = s'' = x₃
x₃' = s''' (third derivative of s)
Next, we'll express the given transfer function in terms of the state variables. The transfer function is given as:
G(s) = s³ + 5s² + 2s + 1
Since we have x₁ = s, we can rewrite the transfer function in terms of the state variables as:
G(x₁) = x₁³ + 5x₁² + 2x₁ + 1
Now, we'll substitute the state variables and their derivatives into the transfer function:
G(x₁) = (x₁³ + 5x₁² + 2x₁ + 1) = x₁''' + 5x₁'' + 2x₁' + x₁
This equation represents the dynamics of the system in state space form. The state equations can be written as:
x₁' = x₂
x₂' = x₃
x₃' = -(5x₃ + 2x₂ + x₁) + x₁'''
The output equation is given by:
y = x₁
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Explain four characteristics that the SCR and the Triac have in common. Question#8: What is the purpose of the resistor in the snubbing circuit? Question#9: Design a snubbing network for the S4006LS SCR driving a 200 W light bulb from a 120 Vrms line voltage. Determine the: a. Capacitor's capacitance and peak voltage. b. Minimum resistor. c. Diode's peak current. d. Inductor's inductance
The SCR (Silicon Controlled Rectifier) and the Triac are two of the most frequently used types of thyristors (a type of semiconductor device).
The four characteristics that the SCR and the Triac have in common are as follows:
Characteristics that the SCR and the Triac have in common: Both devices are unidirectional switching devices. These devices are triggered by a gate current, and once they are triggered, they remain on until the anode-cathode current is reduced to a level below the holding current. These devices do not require continuous gate current to remain turned on. They can be turned on with a gate current, and once turned on, they remain on until the anode-cathode current falls below a particular level. Both devices are ideal for controlling the output power to a load from a variable voltage source in the phase-control application. Their primary applications are in power switching, motor control, and lighting applications.
8: The purpose of the resistor in the snubbing circuit is to limit the rate of rise of the voltage at the anode of the SCR (or TRIAC) when it switches from its ON to OFF state. The voltage across the capacitor rises slowly in a snubbing circuit due to the resistor, preventing voltage spikes from damaging the device. It also aids in the dissipation of stored energy by the capacitor and the inductor.
9: Snubbers are used to protect the SCR and load against overvoltage transients and/or to reduce electromagnetic interference. The Snubbing network for the S4006LS SCR driving a 200 W light bulb from a 120 Vrms line voltage is given below:
Snubbing Network Capacitor's Capacitance: The value of the capacitor is calculated using the following formula:
C=I×t/V
Where I is the current that flows through the load, t is the pulse width of the voltage across the load, and V is the maximum voltage that the capacitor should be able to withstand.
Here, I = P/Vrms
= 200/120 = 1.66 A,
t = 5 μs (Assuming), and V = 1.414 × 120 = 170.8 V.
Substituting the values, C = (1.66) × (5 × 10-6)/170.8 = 48.6 nF Peak Voltage Across Capacitor: The peak voltage across the capacitor can be determined using the following formula:
Vp = Vrms × √2 = 120 × 1.414 = 170.8 V Minimum Resistor: The minimum resistance of the resistor is calculated using the following formula:
R = Vp/I
Where I is the current that flows through the load, and Vp is the peak voltage across the capacitor.
Here, I = 1.66 A and Vp = 170.8 V.
Substituting the values, R = 102.8 Ω (Round off to the nearest standard value of 100 Ω).
Peak Current of Diode: The peak current of the diode can be determined using the following formula:
Ip = Vp/[(L × t) + R]
Where L is the value of the inductance. Here, L = 0.01 H,
t = 5 μs, and R = 102.8 Ω.
Substituting the values, Ip = 835 mA (Round off to the nearest standard value of 1 A).
Inductance of Inductor: The value of the inductance is calculated using the following formula:
L = [(Vp/I) - R] × t/2
Where I is the current that flows through the load, and Vp is the peak voltage across the capacitor.
Here, I = 1.66 A, Vp = 170.8 V,
t = 5 μs, and R = 102.8 Ω.
Substituting the values, L = 0.01 H.
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A baseband 8-level PCM system is used to transmit a single analogue signal of maximum bandwidth 150 kHz. The signal is uniformly distributed in amplitude and has a dynamic range of 65 dB. The sample rate is 20% larger than the Nyquist rate. Determine the following: (i) the sampling rate; (ii) the number of bits per sample; the number of bits per symbol; (iii) (iv) the symbol rate; (v) the raised-cosine filter roll-off factor, a, which would limit the bandwidth to 1 MHz.
The parameters for the baseband 8-level PCM system are:
(i) Sampling rate: 360 kHz.
(ii) Number of bits per sample: 11 bits/sample.
(iii) Number of bits per symbol: 3 bits/symbol.
(iv) Symbol rate: 120 kSymbols/s.
(v) Raised-cosine filter roll-off factor: a = 7.33.
To determine the parameters for a baseband 8-level PCM system transmitting a single analog signal, we can follow these steps:
(i) Calculate the sampling rate:
The Nyquist rate for the maximum bandwidth of 150 kHz is twice that, i.e., 2 * 150 kHz = 300 kHz. The sample rate is given to be 20% larger than the Nyquist rate, so the sampling rate is 1.2 times the Nyquist rate:
Sampling rate = 1.2 * 300 kHz = 360 kHz.
(ii) Calculate the number of bits per sample:
The dynamic range is given as 65 dB. We know that the number of bits per sample is related to the dynamic range by the formula:
Number of bits per sample = dynamic range (in dB) / 6.02.
Number of bits per sample = 65 dB / 6.02 = 10.80 bits/sample.
Since we can't have a fractional number of bits, we round it up to the nearest integer:
Number of bits per sample = 11 bits/sample.
(iii) Calculate the number of bits per symbol:
In an 8-level PCM system, each symbol represents 8 possible amplitude levels. The number of bits per symbol is given by the formula:
Number of bits per symbol = log2(Number of amplitude levels).
Number of bits per symbol = log2(8) = 3 bits/symbol.
(iv) Calculate the symbol rate:
The symbol rate can be calculated by dividing the sampling rate by the number of bits per symbol:
Symbol rate = Sampling rate / Number of bits per symbol.
Symbol rate = 360 kHz / 3 bits/symbol = 120 kSymbols/s.
(v) Calculate the raised-cosine filter roll-off factor (a):
The raised-cosine filter roll-off factor (a) determines the bandwidth of the system. We are given that the desired bandwidth is 1 MHz. The formula for calculating the bandwidth is:
Bandwidth = Symbol rate * (1 + a).
Rearranging the formula to solve for a:
a = (Bandwidth / Symbol rate) - 1.
a = (1 MHz / 120 kSymbols/s) - 1 = 7.33.
Therefore, the parameters for the baseband 8-level PCM system are:
(i) Sampling rate: 360 kHz.
(ii) Number of bits per sample: 11 bits/sample.
(iii) Number of bits per symbol: 3 bits/symbol.
(iv) Symbol rate: 120 kSymbols/s.
(v) Raised-cosine filter roll-off factor: a = 7.33.
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a) Interpret how stability can be determined through Bode Diagram. Provide necessary sketch. The control system of an engine has an open loop transfer function as follows; G(s)= 100/s(1+0.1s)(1+0.2s)
(i) Determine the gain margin and phase margin. (ii) Plot the Bode Diagram on a semi-log paper. (iii) Evaluate the system's stability.
To determine stability using a Bode diagram, we analyze the gain margin and phase margin of the system.
(i) Gain Margin and Phase Margin:
The gain margin is the amount of gain that can be added to the system before it becomes unstable, while the phase margin is the amount of phase lag that can be introduced before the system becomes unstable.
To calculate the gain margin and phase margin, we need to plot the Bode diagram of the given open-loop transfer function.
(ii) Bode Diagram:
The Bode diagram consists of two plots: the magnitude plot and the phase plot.
For the given transfer function G(s) = 100/(s(1+0.1s)(1+0.2s)), we can rewrite it in the form G(s) = K/(s(s+a)(s+b)), where K = 100, a = 0.1, and b = 0.2.
On a semi-logarithmic paper, we plot the magnitude and phase responses of the system against the logarithm of the frequency.
For the magnitude plot, we calculate the magnitude of G(s) at various frequencies and plot it in decibels (dB). The magnitude is given by 20log₁₀(|G(jω)|), where ω is the frequency.
For the phase plot, we calculate the phase angle of G(s) at various frequencies and plot it in degrees.
(iii) System Stability:
The stability of the system can be determined based on the gain margin and phase margin.
If the gain margin is positive, the system is stable.
If the phase margin is positive, the system is stable.
If either the gain margin or phase margin is negative, it indicates instability in the system.
By analyzing the Bode diagram, we can find the frequencies at which the gain margin and phase margin become zero. These frequencies indicate potential points of instability.
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Project report about developed the fidget spinner concept
designs and followed the steps to eventually build a fully
assembled and functional fidget spinner. ( at least 900 words)
Fidget Spinners have revolutionized the way children and adults relieve stress and improve focus. They're simple to construct and have become a mainstream plaything, with various models and designs available on the market.
Here's a project report about how the Fidget Spinner concept was developed:IntroductionThe Fidget Spinner is a stress-relieving toy that has rapidly grown in popularity. It's a pocket-sized device that is shaped like a propeller and spins around a central axis. It was first developed in the 1990s, but it wasn't until 2016 that it became a worldwide trend.
The first Fidget Spinner was created with only a bearing and plastic parts. As the trend caught on, several models with different shapes and designs were produced. This project report describes how we created our fidget spinner and the steps we followed to make it fully operational.
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For water at 3 MPa and 507 K, van der Waals equation of state predicts the following compressibility factors: 0.9231 0.0336 0.0650 Z= (a) (10 points) Using the Z values obtained from van der Waals equation, is water at saturation conditions? plain briefly
The compressibility factor, Z is utilized to account for the deviations from the ideal gas behavior that exist in real gases. The compressibility factor varies with pressure and temperature and is a function of the molar volume of a gas. The Van der Waals equation of state is one of the most commonly utilized equations of state that model real gases.
It is more accurate than the ideal gas law since it accounts for the volume occupied by the gas molecules and the attraction forces that exist between them. When the compressibility factor is equal to 1, the gas behaves ideally. If Z > 1, the gas behaves as if the attractive forces between the gas molecules are more powerful than those predicted by the ideal gas law.
If Z < 1, the gas behaves as if the attractive forces between the gas molecules are less powerful than those predicted by the ideal gas law. The compressibility factor, Z can be determined using the following equation:
Z = PV/RT where P is the pressure of the gas, V is its volume, R is the gas constant, and T is the temperature of the gas.
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Efficiency of home furnace can be improved by preheating combustion air using hot flue gas. The flue gas has temperature of Tg = 1000°C, specific heat of c = 1.1 kJ/kg°C and is available at the rate of 12 kg/sec. The combustion air needs to be delivered at the rate of 15 kg/sec, its specific heat is ca 1.01 kJ/kg°C and its temperature is equal to the room temperature, i.e. Tair,in = 20°C. The overall heat transfer coefficient for the heat exchanger is estimated to be U = 80 W/m2°C. (i) Determine size of the heat exchanger (heat transfer surface area A) required to heat the air to Tair,out 600°C assuming that a single pass, cross-flow, unmixed heat exchanger is used. (ii) Determine temperature of flue gases leaving heat exchanger under these conditions. (iii) Will a parallel flow heat exchanger deliver the required performance and if yes, will it reduce/increase its size, i.e. reduce/increase the heat transfer area A? (iv) Will use of a counterflow heat exchanger deliver the required performance and, if yes, will it reduce/increase its size, i.e. reduce/increase the heat transfer area A?
i) The size of the heat exchanger required is approximately 13.5 m².
ii) The temperature of the flue gases leaving the heat exchanger T_flue,out ≈ 311.36°C.
iii) To achieve the desired outlet temperature of 600°C for the combustion air, a counterflow heat exchanger is needed.
iv) The required surface area A remains the same for a counterflow heat exchanger, so the size of the heat exchanger does not change.
To solve this problem, we can use the energy balance equation for the heat exchanger.
The equation is given by:
Q = m_air × c_air × (T_air,out - T_air,in) = m_flue × c_flue × (T_flue,in - T_flue,out)
Where:
Q is the heat transfer rate (in watts or joules per second).
m_air is the mass flow rate of combustion air (in kg/s).
c_air is the specific heat of combustion air (in kJ/kg°C).
T_air,in is the inlet temperature of combustion air (in °C).
T_air,out is the desired outlet temperature of combustion air (in °C).
m_flue is the mass flow rate of flue gas (in kg/s).
c_flue is the specific heat of flue gas (in kJ/kg°C).
T_flue,in is the inlet temperature of flue gas (in °C).
T_flue,out is the outlet temperature of flue gas (in °C).
Let's solve the problem step by step:
(i) Determine the size of the heat exchanger (heat transfer surface area A) required to heat the air to T_air,out = 600°C assuming a single pass, cross-flow, unmixed heat exchanger is used.
We can rearrange the energy balance equation to solve for A:
A = Q / (U × ΔT_lm)
Where ΔT_lm is the logarithmic mean temperature difference given by:
ΔT_lm = (ΔT1 - ΔT2) / ln(ΔT1 / ΔT2)
ΔT1 = T_flue,in - T_air,out
ΔT2 = T_flue,out - T_air,in
Plugging in the values:
ΔT1 = 1000°C - 600°C = 400°C
ΔT2 = T_flue,out - 20°C (unknown)
We need to solve for ΔT2 by substituting the values into the energy balance equation:
Q = m_air × c_air × (T_air,out - T_air,in) = m_flue × c_flue × (T_flue,in - T_flue,out)
15 kg/s × 1.01 kJ/kg°C × (600°C - 20°C) = 12 kg/s × 1.1 kJ/kg°C × (1000°C - T_flue,out)
Simplifying:
9090 kJ/s = 13200 kJ/s - 13.2 kJ/s * T_flue,out
13.2 kJ/s × T_flue,out = 4110 kJ/s
T_flue,out = 311.36°C
Now we can calculate ΔT2:
ΔT2 = T_flue,out - 20°C
ΔT2 = 311.36°C - 20°C
ΔT2 = 291.36°C
Now we can calculate ΔT_lm:
ΔT_lm = (ΔT1 - ΔT2) / ln(ΔT1 / ΔT2)
ΔT_lm = (400°C - 291.36°C) / ln(400°C / 291.36°C)
ΔT_lm ≈ 84.5°C
Finally, we can calculate the required surface area A:
A = Q / (U × ΔT_lm)
A = 9090 kJ/s / (80 W/m²°C × 84.5°C)
A ≈ 13.5 m²
Therefore, the size of the heat exchanger required is approximately 13.5 m².
(ii) Determine the temperature of flue gases leaving the heat exchanger under these conditions.
We already determined the temperature of the flue gases leaving the heat exchanger in part (i): T_flue,out ≈ 311.36°C.
(iii) In a parallel flow heat exchanger, the hot and cold fluids flow in the same direction. The temperature difference between the two fluids decreases along the length of the heat exchanger. In this case, a parallel flow heat exchanger will not deliver the required performance because the outlet temperature of the flue gases is significantly higher than the desired outlet temperature of the combustion air.
To achieve the desired outlet temperature of 600°C for the combustion air, a counterflow heat exchanger is needed.
(iv) In a counterflow heat exchanger, the hot and cold fluids flow in opposite directions. This arrangement allows for better heat transfer and can achieve a higher temperature difference between the two fluids. A counterflow heat exchanger can deliver the required performance in this case.
To determine if the size of the heat exchanger will be reduced or increased, we need to recalculate the required surface area A using the new ΔT1 and ΔT2 values for a counterflow heat exchanger.
ΔT1 = 1000°C - 600°C = 400°C
ΔT2 = T_flue,out - T_air,in = 311.36°C - 20°C = 291.36°C
ΔT_lm = (ΔT1 - ΔT2) / ln(ΔT1 / ΔT2)
ΔT_lm = (400°C - 291.36°C) / ln(400°C / 291.36°C)
ΔT_lm ≈ 84.5°C
A = Q / (U × ΔT_lm)
A = 9090 kJ/s / (80 W/m²°C * 84.5°C)
A ≈ 13.5 m²
The required surface area A remains the same for a counterflow heat exchanger, so the size of the heat exchanger does not change.
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3y+2x=z+1 3x+2z=8−5y
3z−1=x−2y
Determine the value of y by using Cramer's rule. 2.1.1 Sketch the graph of y= −2/ x
2.1.2 Is the graph of y= -2/ x continuous or discontinuous? 2.1.3 State any one line to which the graph is symmetrical to.
The value of y is 1 using Cramer's rule. The graph of y = -2/x is discontinuous because it has asymptotes at x = 0 and y = 0.
To determine the value of y using Cramer's rule, we need to solve the system of equations:
3y + 2x = z + 1
3x + 2z = 8 - 5y
3z - 1 = x - 2y
First, let's find the determinant of the coefficient matrix, D:
D = | 3 2 -1 |
| 2 0 2 |
| -2 -2 3 |
D = (3 * 0 * 3) + (2 * 2 * -2) + (-1 * 2 * -2) - (-1 * 0 * -2) - (3 * 2 * 2) - (2 * -2 * 3)
D = 0 + (-8) + 4 - 0 - 12 - (-12)
D = -4
Next, let's find the determinant of the matrix obtained by replacing the y-column with the constant terms:
Dy = | 3 2 -1 |
| 2 0 2 |
| -2 -2 3 |
Dy = (3 * 0 * 3) + (2 * 2 * -2) + (-1 * 2 * -2) - (-1 * 0 * -2) - (3 * 2 * 2) - (2 * -2 * 3)
Dy = -4
Now, let's find the determinant of the matrix obtained by replacing the x-column with the constant terms:
Dx = | 3 2 -1 |
| 8 0 2 |
| -2 -2 3 |
Dx = (3 * 0 * 3) + (2 * 2 * -2) + (-1 * 2 * -2) - (8 * 0 * 3) - (-2 * 2 * 3) - (2 * -2 * 3)
Dx = -4
Finally, let's find the determinant of the matrix obtained by replacing the z-column with the constant terms:
Dz = | 3 2 1 |
| 2 0 8 |
| -2 -2 -1 |
Dz = (3 * 0 * -1) + (2 * 8 * -2) + (1 * 2 * -2) - (-2 * 0 * -1) - (3 * 8 * -2) - (2 * -2 * -2)
Dz = -2
Now, we can calculate the value of y using Cramer's rule:
y = Dy / D
y = -4 / -4
y = 1
2.1.1 To sketch the graph of y = -2/x, we can plot some points and connect them. As x approaches infinity or negative infinity, y approaches 0. As x approaches 0, y approaches negative infinity. As x decreases, y increases, and as x increases, y decreases. The graph is a hyperbola that passes through the points (1, -2), (-1, 2), (2, -1), and (-2, 1), with asymptotes at y = 0 and x = 0.
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Q5
Question 5 What is the Australian standard number for tensile testing (i.e.) "metallic materials - tensile testing at ambient temperatures"?
An Australian standard number refers to a unique identification number assigned to a specific standard published by Standards Australia. The Australian standard number for tensile testing of metallic materials at ambient temperatures is AS 1391.
AS 1391 is the Australian standard that specifically addresses the tensile testing of metallic materials at ambient temperatures. This standard provides guidelines and requirements for conducting tensile tests on metallic materials to determine their mechanical properties.
Tensile testing is a widely used method for evaluating the mechanical behavior and performance of metallic materials under tensile forces. It involves subjecting a specimen of the material to a gradually increasing axial load until it reaches failure.
AS 1391 outlines the test procedures, specimen preparation methods, and reporting requirements for tensile testing at ambient temperatures. It ensures consistency and standardization in conducting these tests, allowing for accurate and reliable comparison of material properties across different laboratories and industries in Australia.
The Australian standard number for tensile testing of metallic materials at ambient temperatures is AS 1391. This standard provides guidelines and requirements for conducting tensile tests to evaluate the mechanical properties of metallic materials. Adhering to this standard ensures consistency and reliability in conducting tensile tests in Australia
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