Answer: Convective heat transfer is defined as the transfer of heat from a particular place to another with the help of fluid movements.
Explanation: Convective heat also knows as convection that is transfer of heat from one place to another place by the help of fluid movements around the area having different temperatures. This process has many examples in everyday life to understand the process better.
Ex.- the melting of ice from solid to liquid form as it comes in contact of high temperature as heat surrounds the ice in form of air.
If you add 10 J of heat to a system so that the final temperature of the system is 200K, what is the change in entropy of the system? a)-0.05 J/K b)-0.30 J/k c)-1 J/K d)-9 J/K e)-2000 J/K
Answer:
0.05 J/K
Explanation:
Given data in question
heat (Q) = 10 J
temperature (T) = 200 K
to find out
the change in entropy of the system
Solution
we will solve this by the entropy change equation
i.e ΔS = ΔQ/T ...................1
put the value of heat Q and Temperature T in equation 1
ΔS is the enthalpy change and T is the temperature
so ΔS = 10/200
ΔS = 0.05 J/K
A long homogeneous resistance wire of radius ro = 5 mm is being used to heat the air in a room by the passage of electric current. Heat is generated in the wire uniformly at a rate of g=5'107 W/m as a result of resistance heating. If the temperature of the outer surface of the wire remains at 180°C, determine the temperature at r = 2 mm after steady operation conditions are reached. Take the thermal conductivity of the wire to be k = 8 W/m x °C.
Answer:
T = 212.8125°C
Explanation:
Given
radius of the wire, [tex]r_{0}[/tex] = 5 mm 0.005 m
heat generated, g = 5 x [tex]10^{7}[/tex] W/[tex]m^{3}[/tex]
outer surface temperature, [tex]T_{S}[/tex] = 180°C
Thermal conductivity, k = 8 W / m-k
Now maximum temperature occurs at the center of the wire
that is at r=0,
Therefore, [tex]T_{o}=T_{S}+\frac{g\times r_{o}^{2}}{4\times k}[/tex]
[tex]T_{o}=180+\frac{5\times 10^{7}\times 0.005^{2}}{4\times 8}[/tex]
[tex]T_{o}=219.0625[/tex]°C
Therefore, temperature at r = 2 mm
[tex]\frac{T-T_{S}}{T_{O}-T_{S}}= 1-\left (\frac{r}{r_{O}} \right )^{2}[/tex]
[tex]\frac{T-180}{219.0625-180}= 1-\left (\frac{2}{5} \right )^{2}[/tex]
Therefore, T = 212.8125°C
Explain with schematics the operating principle of solid state lasers.
Explanation:
A solid state laser contains a cavity like structure fitted with spherical mirrors or plane mirrors at the end filled with a rigidly bonded crystal. It uses solid as the medium. It uses glass or crystalline materials.
It is known that active medium used for this type of laser is a solid material. This lasers are pumped optically by means of a light source which is used as a source of energy for the laser. The solid materials gets excited by absorbing energy in the form of light from the light source. Here the pumping source is light energy.
Radiation heat transfer occurs from any object that is above 0K. a) True b) False
Answer:
True, hope this helps but there no school right now its summer
Determine the work done by an engine shaft rotating at 2500 rpm delivering an output torque of 4.5 N.m over a period of 30 seconds.
Answer:
work done= 2.12 kJ
Explanation:
Given
N=2500 rpm
T=4.5 N.m
Period ,t= 30 s
[tex]torque =\frac{power}{2\pi N}[/tex]
[tex]power=2\pi N\times T[/tex]
P=[tex]2\times \pi \times2500 \times 4.5[/tex]
P=70,685W
P=70.685 KW
power=[tex]\frac{work done}{time}[/tex]
work done = power * time
= 70.685*30=2120.55J
= 2.12 kJ
Explain the reasons for abandoning a well.
Answer:
explained below
Explanation:
An Abandoned well is well no longer in use or in such a state of despair that ground water can no longer be pumped out of it in useable quantity.
Following are few reasons for abandoning wells:
1. When the level ground water level falls down the well becomes redundant. And in recent times the ground water level has fallen to appreciable magnitude.
2. Wells represent potential conduits or pathways for surface contaminants to reach ground water supply.The ground water contamination at your well is likely to show up in municipal water supply.
3. Moreover, if the well is unused it can cause physical hazard to people and animals living nearby. As these well grow vegetation around them thus hiding their hole.
Calculate the change of entropy of 2 kg of air when its temperature increases from 400 K to 500 K at constant pressure equal to 300 kPa.
Answer:
0.45516
Explanation:
ENTROPY : Entropy is a measure of molecular disorder it is denoted by S. Entropy is also measured in terms of thermal energy and temperature it is equal to thermal energy per unit temperature.
from the table S₁=1.99194 KJ/kg.k (at 400k)
from the table S₂=2.21952 KJ/kg.k (at 500k)
so total entropy change is given by =m (S₂-S₁)
=2(2.21952-1.99194)
=0.45516
A typical aircraft fuselage structure would be capable of carrying torsion moment. a)True b)- False
Answer:
True
Explanation:
An aircraft is subject to 3 primary rotations
1) About longitudinal axis known as rolling
2) About lateral axis known as known as pitching
3) About the vertical axis known as yawing
The rolling of the aircraft induces torsion in the body of the aircraft thus the fuselage structure should be capable of carrying torsion
In a vapour absorption refrigeration system, the compressor of the vapour compression system is replaced by a a)- absorber, generator and liquid pump. b)-absorber and generator. c)- liquid pump. d)-generator.
Answer:
a). absorber, generator and liquid pump
Explanation:
The Vapour absorption system consists of compression, expansion, condensation and evapouration processes. This system uses ammonia, lithium bromide or water as refrigerant.
An absorber, pump and generator is used in place of a compressor in the vapour compression refrigeration system. The operation is smooth in vapour absorption system since all the moving elements are in the pump only. This system make use of low energy like heat and can work on lower evapourator pressure. It has low Coefficient of performance.
The velocity of flow over a flat plate is doubled. Assuming the flow remains laminar over the entire plate, what is the ratio of the new thermal boundary layer thickness to the original boundary layer thickness?
Answer:
Given:
laminar flow
and since velocity of flow is doubled, we consider [tex]v_{n}[/tex] as new velocity and [tex]v_{o}[/tex] as original velocity
Explanation:
As per laminar flow, thickness, t is given by
t = [tex]\frac{4.91x}{\sqrt( R_{ex}) }[/tex]
t = [tex]\frac{4.91x}{\sqrt{\frac{\rho vx}{\mu }}}[/tex]
t = [tex]\frac{4.91x\mu }{\sqrt{\rho vx}}[/tex]
where,
[tex]R_{ex}[/tex] = Reynold's no.
therefore,
t ∝ [tex]\frac{1}{\sqrt{v} }[/tex]
Now,
[tex]\frac{t_{n} }{t_{o} }[/tex] = [tex]\sqrt{(\frac{v_{o} }{v_{n} })}[/tex]
[tex]\frac{t_{n} }{t_{o} }[/tex] = [tex]\sqrt{(\frac{v_{o} }{2v_{o} } )} =\frac{1}{\sqrt{2} }[/tex]
therefore,
[tex]t_{n}:t_{o} = 1:\sqrt{2}[/tex]
Shear strain can be expressed in units of either degrees or radians. a)True b)- False
Answer:
true
Explanation:
shear strain is define as the ratio of change in deformation to the original length perpendicular to the axes of member due to shear stress.
ε = deformation/original length
strain is a unit less quantity but shear stain is generally expressed in radians but it can also be expressed in degree.
Refectories are one of the types of ceramics that have low melting temperature. a)-True b)-False
Answer:
b). False
Explanation:
A refractory material is a type of material that can withstand high temperatures without loosing its strength. They are used in reactors, furnaces, kilns, etc.
Refractory materials are certain super alloys and ceramics materials.
Properties of refractory materials :
1. Refractory materials have high melting point.
2.They acts barriers between high heat zone and low heat zone.
3. The specific heat of refractory material is very low.
4. Refractories that have high bulk densities are better in quality.
Hence, Refractory materials have a very high melting temperature.
A closed system contains propane at 35°c. It produces 35 kW of work while absorbing 35 kW of heat. What is process? the temperature of the system after this process.
Answer:
35°c
Explanation:
Given data in question
heat = 35 kw
work = 35 kw
temperature = 35°c
To find out
temperature of the system after this process
Solution
we know that first law of thermodynamics is Law of Conservation of Energy
i.e energy can neither be created nor destroyed and it can be transferred from one form to another form
first law of thermodynamics is energy (∆E) is sum of heat (q) and work (w)
here we know
35 = 35 + m Cv ( T - t )
35-35 = m Cv ( T-t )
T = t
here T = final temperature
t = initial temperature
it show final temp is equal to initial temp
so we can say temp after process is 35°c
Takt time is the rate at which a factory must produce to satisfy the customer's demand. a)- True b)- False
Answer: a)True
Explanation: Takt time is defined as the average time difference between the production of the two consecutive unit of goods by the manufacturer and this rate is matched with the demand of the customer. This is the time which is calculated to find the acceptable time for which the goods unit must be produced by the factory to meet the needs of the customer. Therefore , the statement is true that takt time is the rate at which a factory must produce to satisfy the customer's demand.
In a photonic material, signal transmission occurs by which of the following? a)- Electrons b)- Photons
B. Photons.
In a photonic material, signal transmission occurs by photons which are light particles.
Describe the slip mechanism that enables a metal to be plastically deformed without fracture.
Answer and explanation:
Deformation means change in position plastic deformation mainly cause due to motion of dislocation
THERE ARE MAINLY TWO MECHANISM BY WHICH PLASTIC DEFORMATION TAKES PLACE
SLIPTWINNINGSLIP : slip is a process of sliding of blocks over one another along the planes these planes are called slip planes slip takes place when the shear stress exceeds than the critical value of stress distance between the slip planes are called slip lines the resistance for slip plane is very less as compared to any other planes the slip plane is the plane has very high density
It is true about polymers: a)-They are light-weight materials b)-There are three general classes: thermosets, thermoplastics and thermoset c)-They present long term instability under load d)-All the above
Answer: d) All of the above
Explanation: Polymers are the substances that have molecular structure with having same bonds in the entire molecule together.There are light weight substance which occur natural as well as artificially. They are also categorized as thermoplastics ,thermosets, and elastomers. They also have the property of being stretching and bending under the pressure or load they are also instable. Therefore, all the options are correct statement about polymers.
A slider of mass 0.25 kg on a string, 0.5 m long is rotating around a pivot on a frictionless table. The velocity of the slider is initially 0.05 m/s. When the string is pulled into a radius of 0.125 m how fast is the mass spinning?
Answer:
0.025 m/sec
Explanation:
we have given m =0.25 kg
velocity=0.05 m/sec
radius =0.5 meter
the centrifugal force produced due to rotational motion
[tex]F_c=\frac{mv^2}{r}=\frac{0.25\times 0.05^2}{0.5}=0.00125 N[/tex]
now again using this equation for finding the final velocity
[tex]0.00125=\frac{mv_{final}^2}{r}=\frac{0.25v_{final}^2}{0.125}[/tex]
[tex]v_{final}=\sqrt{\frac{0.00125\times 0.125}{0.25}}=0.025\ m/sec[/tex]
so the final speed of mass spring will be 0.025 m/sec
Which of the following is/are FALSE about refining aluminum from the ore state (mark all that apply) a)- A blast furnace is used b)-The ore is called bauxite c)-The process uses a lot of electricity d)-Coke is used to produce the heat
Answer:
The options a)- A blast furnace is used and d)-Coke is used to produce the heat are FALSE.
Explanation:
Aluminium is a chemical element and the most abundant metal present in the Earth's crust. An aluminium ore is called bauxite. Aluminium is extracted from its ore by the process of electrolysis, called the Hall–Héroult process. The extraction of aluminium is an expensive process as it requires large amount of electricity. The bauxite is purified to produce aluminium oxide. Then, aluminium is extracted from the aluminium oxide.
Therefore, the refining of aluminum from its ore does not involve the use of a blast furnace and coke to produce heat.
A compressed-air drill requires an air supply of 0.25 kg/s at gauge pressure of 650 kPa at the drill. The hose from the air compressor to the drill has a 40 mm diameter and is smooth. The maximum compressor discharge gauge pressure is 690 kPa. Neglect changes in air density and any effects of hose curvature. Air leaves the compressor at 40° C. What is the longest hose that can be used?
Answer:
L = 46.35 m
Explanation:
GIVEN DATA
\dot m = 0.25 kg/s
D = 40 mm
P_1 = 690 kPa
P_2 = 650 kPa
T_1 = 40° = 313 K
head loss equation
[tex][\frac{P_1}{\rho} +\alpha \frac{v_1^2}{2} +gz_1] -[\frac{P_2}{\rho} +\alpha \frac{v_2^2}{2} +gz_2] = h_l +h_m[/tex]
where[tex] h_l = \frac{ flv^2}{2D}[/tex]
[tex]h_m minor loss [/tex]
density is constant
[tex]v_1 = v_2[/tex]
head is same so,[tex] z_1 = z_2 [/tex]
curvature is constant so[tex] \alpha = constant[/tex]
neglecting minor losses
[tex]\frac{P_1}{\rho} -\frac{P_2}{\rho} = \frac{ flv^2}{2D}[/tex]
we know[tex] \dot m[/tex] is given as[tex] = \rho VA[/tex]
[tex]\rho =\frac{P_1}{RT_1}[/tex]
[tex]\rho =\frac{690 *10^3}{287*313} = 7.68 kg/m3[/tex]
therefore
[tex]v = \frac{\dot m}{\rho A}[/tex]
[tex]V =\frac{0.25}{7.68 \frac{\pi}{4} *(40*10^{-3})^2}[/tex]
V = 25.90 m/s
[tex]Re = \frac{\rho VD}{\mu}[/tex]
for T = 40 Degree, [tex]\mu = 1.91*10^{-5}[/tex]
[tex]Re =\frac{7.68*25.90*40*10^{-3}}{1.91*10^{-5}}[/tex]
Re = 4.16*10^5 > 2300 therefore turbulent flow
for Re =4.16*10^5 , f = 0.0134
Therefore
[tex]\frac{P_1}{\rho} -\frac{P_2}{\rho} = \frac{ flv^2}{2D}[/tex]
[tex]L = \frac{(P_1-P_2) 2D}{\rho f v^2}[/tex]
[tex]L =\frac{(690-650)*`10^3* 2*40*10^{-3}}{7.68*0.0134*25.90^2}[/tex]
L = 46.35 m
In a flow over a flat plate, the Stanton number is 0.005: What is the approximate friction factor for this flow a)- 0.01 b)- 0.02 c)- 0.001 d)- 0.1
Answer:
(a) .01
Explanation:
stanton number is a dimensionless quantity stanton is expressed as [tex]\frac{heat transer}{thermal capacity}[/tex]stanton number is discovered by Thomas edward stantonthere is relation between friction factor and stanton number and friction factor that is stanton number is half of friction factor
stanton number =[tex]\frac{friction factor}{2}[/tex]
.005=[tex]\frac{friction factor}{2}[/tex]
friction factor =2×.005
friction factor=.01
A strip ofmetal is originally 1.2m long. Itis stretched in three steps: first to a length of 1.6m, then to 2.2 m, and finally to 2.5 m. Compute the true strain after each step, and the true strain for the entire process (i.e. for stretching from 1.2 m to 2.5 m).
Answer:
strains for the respective cases are
0.287
0.318
0.127
and for the entire process 0.733
Explanation:
The formula for the true strain is given as:
[tex]\epsilon =\ln \frac{l}{l_{o}}[/tex]
Where
[tex]\epsilon =[/tex] True strain
l= length of the member after deformation
[tex]l_{o} = [/tex] original length of the member
Now for the first case we have
l= 1.6m
[tex]l_{o} = 1.2m[/tex]
thus,
[tex]\epsilon =\ln \frac{1.6}{1.2}[/tex]
[tex]\epsilon =0.287[/tex]
similarly for the second case we have
l= 2.2m
[tex]l_{o} = 1.6m[/tex] (as the length is changing from 1.6m in this case)
thus,
[tex]\epsilon =\ln \frac{2.2}{1.6}[/tex]
[tex]\epsilon =0.318[/tex]
Now for the third case
l= 2.5m
[tex]l_{o} = 2.2m[/tex]
thus,
[tex]\epsilon =\ln \frac{2.5}{2.2}[/tex]
[tex]\epsilon =0.127[/tex]
Now the true strain for the entire process
l=2.5m
[tex]l_{o} = 1.2m[/tex]
thus,
[tex]\epsilon =\ln \frac{2.5}{1.2}[/tex]
[tex]\epsilon =0.733[/tex]
0il with a relative density of 0,8 flows in a pipe of diameter 60 mm. A venturi meter having a throat diameter of 35 mm is installed in the pipeline. The pressure difference is measured with a mercury manometer. The levels of the manometer differ by 22 mm. The venturi meter has a discharge coefficient of 0,98. Calculate the flow rate of the oil.
Answer:
the flow rate of the oil is 2.5 m³/s
Explanation:
Given data
relative density (S) = 0.8
diameter (d1) = 60 mm = 0.06 m
diameter (d2) = 35 mm = 0.035 m
height (h) = 22 mm = 0.022 m
discharge coefficient (Cd) = 0.98
To find out
the flow rate of the oil
solution
we know the formula for rate of flow i.e.
flow rate = Cd a1 a2 [tex]\sqrt{2 g n }[/tex] / [tex]\sqrt{a1^{2} a2^{2} }[/tex] ...............1
here first we find area a1 and a2 i.e.
a1 = ( [tex]\pi[/tex] /4 ) × d² = ( [tex]\pi[/tex] /4 ) × 0.06² = 0.002827 m²
a2 = ( [tex]\pi[/tex] /4 ) × d² = ( [tex]\pi[/tex] /4 ) × 0.035² = 0.000962 m²
and now we find n = (density of mercury / density of oil) - 1 × h
n = ((13.56 / 0.8) - 1) × 0.022 = 0.3509
put all these value in equation 1
flow rate = Cd a1 a2 [tex]\sqrt{2 g n }[/tex] / [tex]\sqrt{a1^{2} a2^{2} }[/tex]
flow rate = 0.98× 0.002827× 0.000962 [tex]\sqrt{2*9.81*0.3509}[/tex] / [tex]\sqrt{0.002827^{2} 0.000962^{2} }[/tex]
flow rate = 2.571386 m³/s
Which of the following is a correct formula of Ohm s Law (a) E= R/I (b) E=1+R (c)E=I/R (d) E= IR
Answer: The correct answer is Option d.
Explanation:
Ohm's law is defined as the law which gives us the relationship between voltage and current.
In electronics, the equation used to represent this law is:
[tex]E=IR[/tex]
where,
E = voltage of the circuit. The unit for this is Volts.
I = current of the circuit. The unit for this is Amperes
R = resistance of the circuit. The unit for this is Ohms.
Hence, the correct answer is Option d.
Describe how the Rotary Engine works.
Answer:
Rotary engine was early known by the name of internal combustion engine. It convert heat from a high pressure of combustion. The main advantage of rotary engine is that it can be operate with less number of vibration. It works on the principle of converting pressure into rotating motion. In rotary engine the expansion pressure is applied on the flank rotor.
Answer: The rotary engine works on the same basic principle as the piston engine: combustion in the power plant releases energy to power the vehicle. However, the delivery system in the rotary engine is wholly unique. The piston engine performs four key operations: intake, compression, combustion, and exhaust.
Explanation:
What different between 'flow analysis using control volume method' and 'flow analysis using differential method'?
Answer:
control volume
control volume is used to determine the flow characteristics of complex shape like turbine and compressorsdifferential approach
it is carried out by considering infintely small region for fluid analysis.Explanation:
control volume:
control volume is used to determine the flow characteristics of complex shape like turbine and compressorsit is used to determine the flow velocity within in the boundaries of control volume. it can also used for force analysis for flow. one main disadvantage of control volume is that it doesn't provide detail information about stress and pressure variation.differential approach:
it is carried out by considering infintely small region for fluid analysis.solution of the fluid analysis is in the form of differential equationit provide detail information about the flow.Saturated water vapor at 140°C is compressed in a reversible, steady-flow device to 895 kPa while its specific volume remains constant. Determine the work required.
Answer:
The work required to compress the saturated water vapor to 895 kPa pressure is 130.9540 k J/Kg
Explanation:
Given data in question
temperature = 140°C
pressure (P2) = 895 kPa
To find out
work required for compress saturated water
Solution
We know the equation for reversible work for compress saturated water vapor
i.e.
W = [tex]-\int_{1}^{2}vdP-\Delta ke - \Delta pe[/tex]
w is reversible work, v is specific volume, P is water vapor pressure and
ke is kinetic energy and pe is potential energy
and in question we have given v is constant so ke and pe will be zero
so
W = [tex]-\int_{1}^{2}vdP[/tex]
W = -v( P2 - P1 )
we can given in question temperature = 140°C and use steam table "A-4 saturated water - temperature table"
at this water property P1 will be 361.53 kPa and v will be 0.50850 m³/kg
so put these value in above equation
W = -0.50850( 104 - 361.53 )
W = 130.9540 kJ/Kg
The product second moment of area Ixy is found by multiplying Ix and Iy. a)True b)- False
Answer:
(b)False
Explanation:
[tex]I_{xy}[/tex] defined as
[tex]I_{xy}[/tex] =[tex]\int \left (x\cdot y\right )dA[/tex]
Where x is the distance from centroidal x-axis
y is the distance from centroidal y-axis
dA is the elemental area.
The product of x and y can be positive or negative ,so the value of [tex]I_{xy}[/tex] can be positive as well as negative .
So from the above expressions we can say that the product of [tex]I_{x},I_y[/tex] is different from [tex]I_{xy}[/tex] .
What is the thermal efficiency of this reheat cycle in terms of enthalpies?
Answer:
[tex]\eta =\dfrac{\left (h_3-h_4\right )+(h_5-h_6)-(h_2-h_1)}{(h_3-h_2)+(h_5-h_4)}[/tex]
Explanation:
For close gas turbine:
Gas turbine works on Brayton cycle.Gas turbine have lots of applications like ,it is use in aircraft,in land applications etc.
Reheating is the method to improve the efficiency of the gas turbine.In reheating gas is expanding in two turbine instead of one turbine alone.Two turbine like high pressure turbine and low pressure turbine are used for expansion.
In the above diagram 1-2 is a compressor,2-3 heat addition,3-4 high pressure turbine,4-5 reheating of cycle 5-6 low pressure turbine,6-1 heat rejection,
We know that [tex]\eta =\frac{W_{net}}{Q_{s}}[/tex]
Now take [tex]h_{1},h_{2},,h_{3},h_{4},h_{5},h_{6}[/tex] represent the enthalpy of point 1,2,3,4,5,6 in the cycle respectively.
So total heat supplied [tex]Q_S[/tex]=
[tex]\left (h_3-h_2\right )+\left (h_5-h_4\right )[/tex]
Net work out put
[tex]W_{net}[/tex]=[tex]\left (h_5-h_6\right )-\left (h_2-h_1\right )[/tex]
So efficiency [tex]\eta =\frac{W_{net}}{Q_{s}}[/tex]
[tex]\eta =\dfrac{\left (h_3-h_4\right )+(h_5-h_6)-(h_2-h_1)}{(h_3-h_2)+(h_5-h_4)}[/tex]
A pipe which is on a slope, transports water downwards. A doubling of cross sectional area takes place 6 above the reference level. The pressure in the smaller pipe, just before the enlargement, is 860 kPa. The flow velocity in the large pipe is 2,4 m/s. Determine the pressure in kPa at a point 1,5 m above the reference level. Ignore friction losses.
Answer:
P₂ = 830.75 kPa
Explanation:
Given:
Pressure in the smaller pipe,P₁ = 860 kPa
Velocity in the larger pipe, v₂ = 2.4 m/s
Therefore velocity in the smaller pipe, v₁ = 4.8 m/s ( velocity gets doubled since area is reduced to half )
Height at section where the area is doubled, z₁ = 6 m
Height at the section where pressure is to be calculated, z₂ = 1.5 m
Now apply Bernouli Equation between the section of enlargement and at section where pressure is to be calculated,
[tex]\frac{P_{1}}{\rho .g}+\frac{v_{1}^{2}}{2.g}+z_{1} = \frac{P_{2}}{\rho .g}+\frac{v_{2}^{2}}{2.g}+z_{2}[/tex]
[tex]\frac{860}{1000 \times 9.81}+\frac{4.8^{2}}{2\times 9.81}+6 = \frac{P_{2}}{1000 \times 9.81}+\frac{2.4^{2}}{2\times 9.81}+1.5[/tex]
P₂ = 830.75 kPa
Therefore, pressure at the section 1.5 m above datum is 830.75 kPa