What are the relevant boundary conditions in case of heat transfer from a bar connected to two heat sources at different temperatures?
a) α = α 1 at x = 1 and α = α 2 at x = 2L
b) α = α 1 at x = 0 and α = α 2 at x = infinity
c) α = α 1 at x = 0 and α = α 2 at x = L
d) α = α 1 at x = infinity and α = α 2 at x = 1
Q.2.
Radiation heat transfer is characterized by
a) Movement of discrete packets of energy as electromagnetic waves
b) Due to bulk fluid motion, there is a transport of energy
c) There is the circulation of fluid by buoyancy effects
d) Thermal energy transfer as vibrational energy in the lattice structure of the material
Q.3.
A thin metal plate of 4 cm diameter is suspended in atmospheric air whose temperature isK. This plate attains a temperature ofK when one of its faces receives radiant energy from a heat source at the rate of 2 W. If heat transfer coefficient on both surfaces of the plate is stated to be 87.5 W/m 2 K, workout the reflectivity of the plate.
a) 0.15
b) 0.55
c) 0.25
d) 0.45
Q.4.
Which of the following is the unit of coefficient of radiant heat transfer?
a) W/m2
b) W/m K
c) W/m2 K
d) W/K
Q.5.
The radiant heat transfer from a plate of 2.5 cm2 area atK to a very cold enclosure is 5.0 W. Determine the emissivity of the plate at this temperature
a) 0.544
b) 0.144
c) 0.044
d) 0.244
Q.6.
The calculation of heat transmission by convection is based on the determination of a Nusselt number or convective film coefficient. To that goal, which of the following strategies have been proposed
a) ii and iii
b) i and iii
c) i, ii, and iii
d) i and ii
Q.7.
The non-dimensional parameter known as Stanton number is used in which of the following heat transfer?
a) Natural convection heat transfer
b) Unsteady state heat transfer
c) Condensation heat transfer
d) Forced convection heat transfer
Q.8.
The convective heat transfer coefficient in the laminar flow over a flat plate __________
a) Decreases with increase in free stream velocity
b) Increases if a denser fluid is used
c) Increases with distance
d) Increases if a higher viscosity fluid is used
Q.9.
Maximum heat transfer rate in a modern boiler is about
a) 4 * 10 5 W/m2
b) 5 * 10 5 W/m2
c) 3 * 10 5 W/m2
d) 2 * 10 5 W/m2
Q.10.
In spite of the large heat transfer coefficient in boiling liquids, fins are used advantageously when the entire surface is exposed to
a) Nucleate boiling
b) Film boiling
c) Transition boiling
d) All modes of boiling
Q.11.
The condensate film runs down a vertical flat surface where saturated steam is allowed to condense. Condensation’s local coefficient of heat transfer
a) Increases with increasing thickness of film
b) Increases with increasing temperature differential between the surface and vapour
c) Decreases with increasing distance from the top of the surface
d) Remains constant at all heights of the surface
Q.12.
A steam condenser is transferringk W of thermal energy at a condensing temperature ofdegree Celsius. The cooling water enters the condenser atdegree Celsius with a flow rate ofkg/hr. If overall heat transfer coefficient for the condenser surface isW/m2 K, what surface area is required to handle this load?
a) 7.08 m2
b) 5.08 m2
c) 4.08 m2
d) 1.08 m2
Q.13.
What is the value of overall heat transfer coefficient ammonia condensers?
a) 200-750 W/m2 K
b) 250-2500 W/m2 K
c) 1500-1750 W/m2 K
d) 800-1400 W/m2 K
Q.14.
Which of the following is having highest value of overall heat transfer coefficient?
a) Steam
b) Steam condensers
c) Feed water heaters
d) Alcohol condensers
Q.15.
For laminar film condensation on a vertical plate, the local heat transfer coefficient at the lower edge of the plate is given by
a) [k 3 p 2 g h f g /4 δ l (t sat – t s)] 0.125
b) [k 3 p 2 g h f g /4 δ l (t sat – t s)] 0.1
c) [k 3 p 2 g h f g /4 δ l (t sat – t s)] 0.25
d) [k 3 p 2 g h f g /4 δ l (t sat – t s)] 0.5
Q.16.
The outer surface of a vertical tube is 1.m long and outer diameter ismm is exposed to saturated steam at atmospheric pressure. If the tube surface is maintained atdegree Celsius by the flow of cooling water through it, determine the rate of heat transfer to the coolant
a) 32397 W
b) 19879 W
c) 48476 W
d) 25234 W
Q.17.
What is the value of the overall heat transfer coefficient for air to heavy tars and liquid?
a) As low as 25 W/m2 K
b) As low as 15 W/m2 K
c) As low as 45 W/m2 K
d) As low as 55 W/m2 K
Q.18.
Exhaust gases (c P = 1.k J/kg K) flowing through a tubular heat exchanger at the rate ofkg/hr are cooled fromdegree Celsius todegree Celsius. This cooling is affected by water (c P = 4.k J/kg K) that enters the system atdegree Celsius at the rate ofkg/hr. If the overall heat transfer coefficient isk J/m2 hr degree, what heat exchanger area is required to handle the load for counter flow arrangement?
a) 1.758 m2
b) 6.758 m2
c) 8.758 m2
d) 3.758 m2
Q.19.
What is the value of the overall heat transfer coefficient for air condensers?
a) 250-900 W/m2 K
b) 200-1950 W/m2 K
c) 350-780 W/m2 K
d) 200-350 W/m2 K
Q.20.
Heat transfer coefficients for natural convection across the surface of a vertical pipe and a vertical flat plate at the same height. What could be the cause(s) of this?
a) iii and iv
b) iv
c) i and ii
d) i
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