Cork is a good insulator because

- a)It is flexible
- b)It can be powered
- c)Low density
- d)It is porous

Correct answer is option 'D'. Can you explain this answer?

Telecom Tuners answered • Mar 02, 2021

Even though cork is a solid material, but it’s thermal conductivity is extremely low because of air filled in it’s pores. Typical value of thermal conductivity is in the range of 0.035 to 0.043 W/m-k

A sphere, a cube and a disc all are of the same material, quality and volume, are heated to 900 K and left in air. Which of these will have the lowest rate of cooling

- a)Cube
- b)Disc
- c)Sphere
- d)All will have the same rate of cooling

Correct answer is option 'C'. Can you explain this answer?

Telecom Tuners answered • Mar 02, 2021

For a given volume, the sphere has a minimum surface area hence rate of heat transfer to air by convection or radiation is minimum.

What are the units of Stefan-Boltzmann constant

- a)
- b)
- c)
- d)

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

By Stefan-Boltzmann law

Consider the astronaut compartments inside a space shuttle orbiting the moon. Inside these compartments air is maintained at STP conditions for comfortable breathing of astronauts. The cooling system of electronic equipment inside these compartments is based on

- a)Conduction
- b)Forced convection
- c)Free convection
- d)Thermal radiation

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

Since the equipment is in air and surface temperature is generally not high, conduction and radiation heat loss is insignificant. Also in space there is no gravity. Thus buoyancy and therefore free convection is not at all possible in the compartment air. Hence the only suitable mode for cooling is forced convection.

The minimum number of view factors that need to be known to solve a 10-surface enclosure completely, is

- a)1
- b)10
- c)22
- d)45

Correct answer is option 'D'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

For n-surface enclosure if ^{n}C_{2} view factors are known directly, entire enclosure can be solved. Thus for 10 surfaces, number of view factors that need to be evaluated directly will be

The wavelength for which the blackbody emissive power is maximum for a temperature of 300 K is

- a)5.1μm
- b)9.7μm
- c)15.5μm
- d)38.0μm

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

By Wien’s displacement law,

∵ λmT = 2898 μm-k

λm ≃ 9.7μm

Sanidhya Chandola asked • 8 hours ago

Suspended solid present in the waste water generated in blast furnace gas cooling and cleaning plant is removed by

- a)biological oxygen pond.
- b)radial settling tank (thickener) using coagulant (lime & ferrous sulphate).
- c)lagoons.
- d)filtration.

Correct answer is option 'B'. Can you explain this answer?

For a given heat flow rate and for the same thickness, the temperature drop across the material will be maximum for

- a)Copper
- b)Steel
- c)Glass-wool
- d)Refractory brick

Correct answer is option 'C'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

From Fourier’s law,

I.e. T₁ - T₂ will be maximum when k is minimum. k is minimum for glass wool.

Consider a light bulb of 100 watts power. When switched on, what is the surface temperature of the tungsten filament in °C.

Consider the surface to be a black surface having value of area equal to

- a)2166
- b)1893
- c)800
- d)3786

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

By Stefan Boltzmann law

T = 2166 K (or) 1893 °C

For the composite slab shown in figure, find out when k represents thermal conductivity and L represents thickness.

- a)110
- b)70
- c)60
- d)90

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

The thermal circuit of the system can be represent as follows

By idea of circuits ratio of resistances is equal to ratio of temperature drops across them

150 - T_{i} = 2T_{i} - 60

210 = 3T_{i}

T_{i} = 70°C

The spectral distribution of surface irradiation is as follows

What is the total irradiation in kW/m^{2} ?

- a)10
- b)20
- c)30
- d)40

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

Total irradiation is given as

i.e. it is equal to area under the curve Gλ Vs λ Hence,

x (25-20) x 1000

∴ G = 20000 W/m^{2}

I.e. G = 20 kW/m^{2}

Sandhya Mannuru asked • 16 hours ago

Hot water (0.01 m^{3} /min) enters the tube side of a counter current shell and tube heat exchanger at 80�C and leaves at 50�C. Cold oil (0.05 m^{3}/min) of density 800 kg/m^{3} and specific heat of 2 kJ/kg.K enters at 20�C. The log mean temperature difference in �C is approximately

- a)32
- b)37
- c)45
- d)50

Correct answer is option 'A'. Can you explain this answer?

Solar radiation is incident on a semitransparent body at a rate of . If of this incident radiation is reflected back and is transmitted across the body, the absorptivity of the body is

- a)0
- b)0.25
- c)0.30
- d)0.45

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

G = 500 W/m^{2} G_{r} = 150 W/m^{2}

G_{t} = 225 W/m^{2}

By energy conservation principle,

G_{a}+G_{e}+G_{t} = G

Where G_{a} = absorbed radiation

G_{r} = reflected radiation

G_{t} = transmitted radiation

G = incident radiation

= transmissivity

α = 1-0.3 - 0.45 = 0.25

What will be the view factor for the geometry as shown in the figure (sphere within a hollow cube)?

- a)
- b)
- c)
- d)

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

1 is a spherical surface

∴ F_{11} = 0

By summation rule,

F_{12} + F_{11} = 1

∴ F_{12} = 1

By Reciprocity theorem,

A_{1}F_{12} = A_{2}F_{21}

Consider monochromatic emissive power (E_{λ}) Vs Wavelength(λ) of a black and grey surface both at same temperature. The ratio AB/AC is given as

- a)Monochromatic emissivity (λ) of grey surface
- b)Total emissivity (ε) of grey surface
- c)Total emissive power of grey surface
- d)None of the above

Correct answer is option 'A'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

AB & AC are monochromatic emissive power of grey and black surfaces for same wavelength. Hence, ratio is

which is monochromatic emissivity of grey surface.

Find out the heat flux (in W/m²) between two fluids separated by a planar wall as shown in the figure.

- a)200
- b)200

Correct answer is between '200,200'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

Consider the thermal circuit for the system

Where nodes H, 1, 2 & C represent hot fluid, left surface of wall, right surface of wall and cold fluid respectively. Therefore,

Solar radiation of falls on a grey opaque surface at steady state. The surface has a temperature of and emissivity of 0.8. Find radiosity from the surface?

Correct answer is 'A'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

J = E+G_{r}

E = εσT4

E = 0.8 x 5.67 x 10-8 x (50 + 273)4

E = 493.72 W/m2

Given G = 1200 W/m2

But as surface is at steady state

α = ε = 0.8

∴ ρ = 1 -α = 0.2

∴ G_{r} = ρG

G_{r} = 0.2 x 1200 = 240 W/m^{2}

Therefore

J = E+G_{r}

J = 493.72 + 240

J = 733.72 W/m^{2}

Consider H gas, both at temperature of 30°C. The thermal conductivity of H is ________ than that of .

- a)greater
- b)equal
- c)lower
- d)depends upon pressure

Correct answer is option 'A'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

The thermal conductivity of a gaseous medium is dominantly based on diffusion rate, which depends on root mean square velocity.The root mean square velocity for molecules is given by

where M is the molecular mass of the gas & T is the temperature of the gas and ̅ is universal gas constant. Thus diffusion rate and therefore thermal conductivity is lower for gases with higher molecular masses because

Therefore H₂ gas has more thermal conductivity than O₂.

Two radiating surfaces A^{1}= 6m^{2} and A^{2}=4m^{2} have shape factor Then shape factor will be

- a)0.18
- b)0.15
- c)0.12
- d)0.10

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

By Reciprocity theorem

A_{1}F_{12} = A_{2}F_{21}

= 0.15

Consider a hemispherical furnace. The view factor of it’s roof (hemisphere) with respect to itself is __________.

- a)0
- b)0.25
- c)0.5
- d)1.0

Correct answer is option 'C'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

By reciprocity theorem

A_{1}F_{12} = A_{2}F_{12}

1 is a planar surface, i.e F^{11} = 0

∴ F^{12} = 1

Hence F^{21} = 0.5

F^{21} + F^{22} = 0.5

F^{22} + 1-0.5 = 0.5

With increase in pressure, the thermal conductivity of an ideal gas __________.

- a)increases
- b)remains constant
- c)decrease
- d)remains constant

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

For an ideal gas, thermal conductivity is given as

Where ⊽ is the mean travel velocity of molecules C_{v}, is the specific heat of gas at constant volume, L is the mean free path of molecules and is the density of the gas.

As pressure increases, density of gas increases but based on experiments it is observed that the mean free path diminishes in the same proportions. Thus the product remains constant.

Also ⊽ depends upon temperature only hence if temperature is constant, change in pressure does not bring any change in ⊽ Also for an ideal gas C_{v} is independent of pressure.

Shubham Kumar asked • 16 hours ago

If average heat transfer co-efficient is *h*_{a} and the local coefficient at the end of the plate is *h*_{l} then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length

- a)
*h*=_{a}*h*_{l} - b)
*h*= 2_{a}*h*_{l} - c)
*h*= 0.5_{a}*h*_{l} - d)
*h*= 0.75_{a}*h*_{l}

Correct answer is option 'B'. Can you explain this answer?

Consider a composite slab as shown in the figure.

If the left most and right most surfaces are maintained at temperatures of 100°C & 40°C respectively, find out the interface temperature in in °C

Correct answer is 'Range: 66 to 67'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

The slab can be represented by the following thermal circuit.

Considering the width of slab to plane of paper to be equal to W,

R₂ and R₃ are arranged in parallel and can be shown by single equivalent resistance Rₑ

By idea of series circuit, that ratio of temperature drops across resistances is equal to ratio of respective thermal resistances.

I.e.,

Which of the following events represents thermal radiation?

- a)Microwave heating
- b)Nuclear reaction in a sun
- c)Light bulb
- d)None of the above

Correct answer is option 'C'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

In microwave ovens, the radiation emitted is a result of excitation of crystals like magnetrons and klystrons and in microwave wavelength band which is not in the range of thermal radiation. Also during nuclear reactions like those inside sun, -rays are produced which is actually not considered as thermal radiation. Once these -rays get absorbed by the matter in the sun then temperature rises and thermal radiation is emitted. Thus nuclear reaction does not directly emit thermal radiation.

But during lighting of bulb energy is emitted mainly in form of light and IR due to temperature of tungsten filament. Thus this event is termed as thermal radiation.

Which of the following is used to measure the temperature inside a furnace?

- a)Gas thermometer
- b)Optical pyrometer
- c)Alcohol thermometer
- d)Mercury thermometer

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Mar 01, 2021

In a furnace heat transfer is a result of thermal radiation due to high temperature values and contribution of conduction and convection to the phenomenon is insignificant. Hence optical pyrometers are best suited devices to measure temperature inside the furnace. These devices detect wavelength corresponding to maximum monochromatic emissive power in the infrared radiation and using Wien’s law, i... more

Karan Gohil asked • 21 hours ago

The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)_{R} and the co-efficient of performance as a heat pump (COP)_{HP} are

- a)(COP)
_{R}= (COP)_{HP}= 0.6 - b)(COP)
_{R}= 2.5; (COP)_{HP}= 1.5 - c)(COP)
_{R}= 1.5; (COP)_{HP}= 2.5 - d)(COP)
_{R}= (COP)_{HP}= 2.5

Correct answer is option 'C'. Can you explain this answer?

Consider two infinitely long blackbody concentric cylinders with a diameter ratio . The shape factor of the inner surface of outer cylinder with respect to itself will be

- a)0
- b)1/3
- c)2/3
- d)1

Correct answer is option 'C'. Can you explain this answer?

Telecom Tuners answered • Feb 28, 2021

By Energy conservation

F_{12} + F_{22 }=1

∴ F_{22} = 1-F_{21} ….①

By Reciprocity theorem

A_{1}F_{12} = A_{2}F_{21}

πD_{1}L x F_{12} = πD_{2}L x F_{21}

If the temperature of a solid surface changes from then its emissive power will increases in the ratio of

- a)3
- b)9
- c)27
- d)81

Correct answer is option 'D'. Can you explain this answer?

Telecom Tuners answered • Feb 28, 2021

By Stefan Boltzmann law

E ∝ T^{4}

For an opaque plane surface at steady state the irradiation, radiosity and emissive power are respectively 20, 12 and . What is the emissivity of the surface?

- a)0.9
- b)0.4
- c)0.8
- d)1.0

Correct answer is option 'A'. Can you explain this answer?

Telecom Tuners answered • Feb 28, 2021

J = _{p}G + εE_{b}

For an opaque body

∵ α + ρ = 1

ρ = 1- α

∴ J = (1-α)G + εE_{b}

By kirchoff’s law, α = ε

∴ J = (1-α)G + εE_{b}

12 = (1- ε)20 + 10

ε = 0.9

Navya Rajulapati asked • yesterday

Choose the wrong statement with respect to Nusselt number and convective heat transfer coefficient

- a)Nusselt number represents the ratio of temperature gradient at the surface, to an overall or reference temperature gradient
- b)Nusselt number represents the dimensionless slope of the temperature distribution curve at the surface
- c)The convective coefficient can be evaluated from a knowledge of fluid temperature distribution in the neighbourhood of the surface
- d)For a given Nusselt number, the convective coefficient is inversely proportional to thermal conductivity of the fluid.

Correct answer is option 'D'. Can you explain this answer?

What is net radiation heat exchange per square meter per unit time for two very large plates at temperature values of 800 K and 500 K? Emissivities of hot and cold plates are 0.8 and 0.6 respectively. Stefan-Boltzmann constant is - 5.67x10^{-8}W/m^{2}K^{4}

- a)1026 kW/m
^{2} - b)10.26 kW/m
^{2} - c)102.6 kW/m
^{2} - d)1.026 kW/m
^{2}

Correct answer is option 'B'. Can you explain this answer?

Telecom Tuners answered • Feb 28, 2021

For two very large parallel plates, the net radiation heat exchange (using thermal circuit) is given by,

= 10.26 kW/m^{2}

Sandeep Agrawal asked • yesterday

Pick out the wrong statement.

- a)Orifice baffles are never used in a shell and tube heat exchanger.
- b)Pressure drop on the shell side of a heat exchanger depends upon tube pitch also.
- c)In a horizontal tube evaporator, surface blanketing by air is avoided.
- d)Split ring type and pull through type floating heads are two commonly used floating heads is heat exchangers.

Correct answer is option 'A'. Can you explain this answer?

For the radiation between two infinite parallel planes of emissivity respectively, which one of the following is the expression for emissivity factor or equivalent emissivity?

- a)ε
_{1}ε_{2} - b)
- c)
- d)

Correct answer is option 'D'. Can you explain this answer?

Telecom Tuners answered • Feb 28, 2021

The equivalent thermal resistance between two gray bodies is given by

R_{th} = 1-ε_{1}/A_{1}ε_{1}+1/A_{1}F_{12}+1-ε_{2}/A_{2}ε_{2}

Now for infinite parallel panes, F_{12} =1

A_{1} = A_{2} = A

For unit area, A = 1 m^{2}

R_{th} = 1/ε_{1}+1/ε_{2}-1

Hence equivalent emissivity

Ε_{e} = 1/R_{th}

A metal storage tank with planar surfaces of external area contains water at and is located inside a large enclosure with walls at 65^{o}C . The tank is initially painted black on the outside and its emissivity is approximated to 0.95. How much percentage reduction in heat loss would occur if the outside surface of tank is coated with aluminium paint (instead of black) of emissivity 0.55? Take radiation constant

σb = 5.67 x 10^{-8} W/m^{2}K^{4}

- a)58
- b)42
- c)29
- d)21

Correct answer is option 'A'. Can you explain this answer?

Telecom Tuners answered • Feb 28, 2021

Consider outer surface of metal tank to be 1 & inner surface of enclosure to be surface 2.

By concept of thermal circuits

As the surfaces of 1 are planar, F_{11} = 0

∴ F_{21} = 1

Also ,

A_{2} >> A_{1}

∴ (Q_{1➝2})_{net} = σA_{1}ε_{1}(T_{1}^{4} - T_{2}^{4})

∴ Q ∝ ε_{1}

Q0.55/Q0.95 = 0.55/0.95 = 0.4211

Thus heat exchange rate decreases by 57.89 %, by painting the tank with aluminium paint.

Radha Ganji asked • yesterday

Air initially at 101. 3 kPa and 40^{o}C and with a relative humidity of 50%, is cooled at constant pressure to 30^{o}C. The cooled air has a

- a)higher dew point.
- b)higher absolute (specific) humidity.
- c)higher relative humidity
- d)higher wet bulb temperature.

Correct answer is option 'C'. Can you explain this answer?

Sajan Kumar asked • 2 days ago

Phenolic water generated in coke ovens & by-product plant attached to an integrated steel plant containing phenol in concentration of less than 100 mg/litre can be removed by

- a)chlorination
- b)treating in biological oxygen pond
- c)chemical coagulation
- d)none of these

Correct answer is option 'B'. Can you explain this answer?

Kk Vi asked • 2 days ago

For flow over a flat plate, the ratio of thermal boundary layer thickness, 'xt' and hydrodynamic boundary layer thickness 'x' is equal to (where, *N*_{Pr} = Prandtl number)

- a)
*N*_{Pr} - b)
*N*_{Pr}^{1/3} - c)
*N*_{Pr}^{-1} - d)
*N*_{Pr}^{-1/3}

Correct answer is option 'B'. Can you explain this answer?

Shamaim Malik asked • 3 days ago

In the equation *Q* = *UA*Δ*t*; Δ*t* is

- a)geometric mean temperature difference.
- b)arithmetic mean temperature difference.
- c)logarithmic mean temperature difference.
- d)the difference of average bulk temperatures of hot and cold fluids.

Correct answer is option 'C'. Can you explain this answer?

Manish Swaraj asked • 3 days ago

Relative humidity is the ratio of the

- a)partial pressure of the vapour to the vapour pressure of the liquid at room temperature.
- b)partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
- c)actual humidity to saturation humidity.
- d)none of these

Correct answer is option 'B'. Can you explain this answer?

Radha Ganji asked • 3 days ago

A process stream of dilute aqueous solution flowing at the rate of10 Kg.s^{-1} is to be heated. Steam condensate at 95�C is available for heating purpose, also at a rate of 10 Kg.s^{-1}. A 1 - 1 shell and tube heat exchanger is available. The best arrangement is

- a)counter flow with process stream on shell side.
- b)counter flow with process stream on tube side.
- c)parallel flow with process stream on shell side.
- d)parallel flow with process stream on tube side.

Correct answer is option 'A'. Can you explain this answer?

Radha Ganji asked • 3 days ago

Overall efficiency of the distillation column is

- a)the ratio of number of ideal plates to actual plates.
- b)the ratio of number of actual plates to ideal plates.
- c)same as the Murphree efficiency.
- d)always more than the point efficiency.

Correct answer is option 'A'. Can you explain this answer?

Anshul Rasyotra asked • 4 days ago

200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, *N*_{c} = 0.5 x 10^{-3} kg/m^{2}.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m^{2}/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)

- a)0.5
- b)0.05
- c)0.1
- d)0.15

Correct answer is option 'C'. Can you explain this answer?

Shafi Shaik asked • 4 days ago

Compound A is extracted from a solution of A + B into a pure solvent S. A Co-current unit is used for the liquid-liquid extraction. The inlet rate of the solution containing A is 200 moles of B/hr.m^{2} and the solvent flow, rate is 400 moles of S/m^{2}. hr. The equilibrium data is represented by Y = 3X^{2} , where Y is in moles of a A/moles of B and X is in moles A/moles of S. The maximum percentage extraction achieved in the unit is

- a)25%
- b)50%
- c)70%
- d)90%

Correct answer is option 'B'. Can you explain this answer?

Sana Shakoor asked • 4 days ago

Which is the best and the most effective method for the removal of organic contaminant present in the polluted water in very small quantity (say < 200 mg/litre)?

- a)Lagooning
- b)Activated carbon adsorption
- c)Biological oxidation pond
- d)Chemical coagulation

Correct answer is option 'B'. Can you explain this answer?

CHAMELI DEVI asked • 2 weeks ago

An oil cooler in a high performance engine has an outside surface area 0.12 m^{2} and a surface temperature of 65 degree Celsius. At any intermediate time air moves over the surface of the cooler at a temperature of 30 degree Celsius and gives rise to a surface coefficient equal to 45.4 W/ m 2 K. Find out the heat transfer rate?

- a)238.43 W
- b)190.68 W
- c)543.67 W
- d)675.98 W

Correct answer is option 'B'. Can you explain this answer?

Krish Jat asked • 2 weeks ago

SHUBHAM SINGH asked • Apr 11, 2021

For an air(A)-water vapour(B) mixture, the partial pressure of the air is 5 pa and the total pressure of the system is 15 pa. The absolute humidity in mass of air/mass of water vapour is

- a)0.805
- b)0.311
- c)0.705
- d)0.411

Correct answer is option 'A'. Can you explain this answer?

ADITYA LAMBA asked • Mar 30, 2021

Of the radiant energy 350W/m2 incident upon a surface 250W/m^{2} is absorbed, 60W/m^{2} is reflected and the remainder is transmitted through the surface. Workout the value for absorptivity for the surface material

- a)0.113
- b)0.114
- c)0.115
- d)0.116

Correct answer is option 'C'. Can you explain this answer?

KANISHK DESHWAL asked • Mar 26, 2021

A gas mixture containing 21% O_{2} and 79% N_{2} flows through a pipe of circular cross-section of diameter 2cm at atmospheric pressure. The velocity of O_{2} is 0.04m/s and N_{2} is 0.035m/s.

- a)0.981
- b)0.891
- c)0.985
- d)0.857

Correct answer is option 'A'. Can you explain this answer?

TAMANNA RAVINDER asked • Mar 26, 2021

For a component A of a mixture, concentration as a function of x is given:

C_{A}=5e^{-10x} (x is in cm and C_{A} in mol/liter)

Calculate the value of diffusion velocity (m/s)of the component A at the point x=0, if diffusivity of A in the mixture is 2.567*10^{-5}m^{2}/s.

C

Calculate the value of diffusion velocity (m/s)of the component A at the point x=0, if diffusivity of A in the mixture is 2.567*10

- a)0.2567
- b)2.567
- c)0.0025
- d)3.541

Correct answer is option 'A'. Can you explain this answer?

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