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RVUNL || Heat-Transfer Revision Quiz

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Question 1

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 2

Match List-I (process) with List-II (predominant parameter associated with the process) and select the correct answer using the codes given below:
List-I:
(A). Mass transfer
(B). Forced convection
(C). Free convection
(D). Transient conduction
List-II:
(1). Reynolds number
(2). Sherwood number
(3). Mach number
(4). Biot number
(5). Grashoff number

Question 3

A heat exchanger is used to heat cold water (C_p=4.18kJ/kg-K) entering at 12⁰C at a rate of 1.2 kg/s by hot air (C_p=1.005 kJ/kg-K) entering at 90⁰C at rate of 2.5 kg/s. The highest rate of heat transfer in the heat exchanger is

Question 4

Heat is loss from a 200 mm diameter steam pipe placed horizontally in ambient at 30 °C if the nusselt number of air is 50 and thermal conductivity of air is 0.03 W/mk, then the heat transfer coefficient will be

Question 5

Air flows over a heated plate at a velocity of 40 m/s. The local skin friction co efficient at a point on the plate 0.004. Determine the local heat transfer coefficient ( in W/m²K) at this point using Reynold’s Colburn analogy
Following are property of air

0.88 kg/m³, Cp =1001 J/kg °K, k = 0.035 W/mK,

Kg/ms

Question 6

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 7

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 8

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 9

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 10

In a heat exchanger, the hot liquid enters with a temperature of 200 °C and leaves at 180 °C. The cooling fluid enters at 50 °C and leaves at 130 °C. The capacity ratio of the heat exchanger is __________.

Question 11

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 12

Which one of the following have a highest thermal conductivity

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AE & JE Exams Mechanical Engineering

May 27AE & JE Exams