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AE-JE (ME) || Heat Transfer Revision Quiz

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Question 1

Consider two infinitely long thin concentric tubes of circular cross section as shown in the figure. If D₁ and D₂ are the diameters of the inner and outer tubes respectively, then the view factor F₂₂ is given by

Question 2

A plate having 10 cm² area each side is hanging in the middle of a room of 100 m² total surface area. The plate temperature and emissivity are respectively 800 K and 0.6. the temperature and emissivity values for the surfaces of the room are 300K and 0.3 respectively. Boltzmann’s constant σ = 5.67 × 10^–8 W/m²K⁴. The total heat loss from the two surfaces of the plate is

Question 3

A coolant fluid at 30 °C flows over a heated flat plate maintained at a constant temperature of 110 °C. The boundary layer temperature distribution at a given location on the plate may be approximated as

where y (in m) is the distance normal to the plate and T is in °C. If thermal conductivity of the fluid is 1.0 W/m-K, the local convective heat transfer coefficient at that location will be ____________ W/m²-K.

Question 4

A smaller sphere (1) of radius 50 mm is inside a larger sphere (2) of radius 100 mm. What will be the value of the radiation shape factor F₂₂:

Question 5

A solid copper ball of mass 0.5 kg when quenched in a water bath at 30⁰C, cools from 530⁰C to 430⁰C in 10 seconds. What will be the temperature (⁰C) of the ball after the next 10 seconds?

Question 6

A steel ball l of radius 30 mm is initially in thermal equilibrium at 1000 ° C in furnace. It is then suddenly removed and cooled in ambient air at 30 ° C with convection heat transfer coefficient h = 20 W/m²K. find the time required in seconds to cool the steel ball in air from 1000 ° C to 450 ° C, (Take thermo physical properties of steel: density ρ = 7600 kg/m³, Conductivity k = 40 W/mK, specific heat Cp = 500 J/kg K.)

Question 7

Two large parallel plates having temperatures T₁ = 1500K and T₂ = 500K are kept in such a way that radiation leaving from each surface is completely reached the 2nd surface. Emissivity values for plates are 0.5 and 0.25 respectively. Then heat transfer between the plates __________ (in kW/m²).

Question 8

If the temperature of the sun is doubled, the rate of energy received on earth will be increased by a factor of

Question 9

Which one of the following have a highest thermal conductivity

Question 10

A wall of 0.5 m thickness is to be constructed from a material which has an average thermal conductivity of 1.4 W/m-K. The wall is to be insulated with a material having an average thermal conductivity of 0.35 W/m-K so that the heat loss per square metre will not exceed 1450 W. Assuming that the inner and outer surface temperature are 1200 °C and 15 °C respectively. The thickness of insulation required is ____ metre.

Question 11

Determine the heat transfer through a plane of length 4 m, height 3 m and thickness 0.2 m. The temperatures of innner and outer surfaces are

and

respectively. Thermal conductivity of the wall is 0.5 W/mK.

Question 12

A solid sphere of radius 10 cm with heat generation 8 × 10⁶ W/m³. The surface temperature is 50°C. The maximum temperature (in ° C) in sphere under steady state,1-D condition is {k = 10 W/m-deg}

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AE & JE Exams Mechanical Engineering

Dec 30AE & JE Exams