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Heat Transfer Refrigeration and Air Conditioning
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Heat Transfer Refrigeration and Air Conditioning
mcqs by everyone
Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange betweenthem.
It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on bothsides.
The number of shields should be
Two
three
One
Four
In case of sensible heating of air, the coil efficiency is given by (where
B.P.F. = By-pass factor)
1 + B.RF.
P.F. - 1
1 - B.P.F.
The critical thickness of insulation for a sphere is
k/h0
2k/h0
h0/k
h0/2k
For air conditioning the operation theatre in a hospital, the percentage of outside air in the air supplied is
100
Zero
50
20
In a shell and tube heat exchanger, baffles are provided on the shell side to
improve heat transfer
prevent stagnation of shell side fluid
provide support for tubes
All of These
Thermal diffusivity is a
physical property of a substance
All of These
function of temperature
dimensionless parameter
Bell-Coleman cycle is a
reversed Carnot cycle
reversed Otto cycle
reversed Joule cycle
reversed Rankine cycle
The by-pass factor for a cooling coil
decreases with increase in velocity of air passing through it
increases with increase in velocity of air passing through it
remains unchanged with increase in velocity of air passing through it
A heat pump working on a reversed Carnot cycle has a
C.O.P. of 5. It works as a refrigerator taking 1 kW of workinput.
The refrigerating effect will be
2 kW
1 kW
4 kW
3 kW
Carbon dioxide is
odourless
colourless
All of These
non-flammable
The freezing point of sulphur dioxide is
-135.8°C
-56.6°C
-75.2°C
-77.7°C
The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is
less than one
equal to Nusselt number
greater than one
equal to one
Air conditioning means
dehumidifying
All of These
Cooling
heating
The pressure at the outlet of a refrigerant compressor is called
critical pressure
discharge pressure
suction pressure
back pressure
The subcooling in a refrigeration cycle
decreases C.O.P.
NONE OF THESE
does not alter C.O.P.
increases C.O.P.
In a saturated air-water vapour mixture, the
dry bulb, wet bulb and dew point temperature are same
dry bulb temperature is higher than dew point temperature
dew point temperature is lower than wet bulb temperature
dry bulb temperature is higher than wet bulb temperature
The super-heating in a refrigeration cycle
NONE OF THESE
decreases C.O.P.
increases C.O.P.
does not alter C.O.P.
In order to collect liquid refrigerant and to prevent it from going to a __________ , a device known as accumulator is used at the suction of compressor
compressor
Condenser
expansion valve
evaporator
The expression Q = ρ AT4 is called
Joseph-Stefan equation
Newton-Rikhmann equation
Fourier equation
Stefan-Boltzmann equation
Most thermostatic expansion valves are set for a superheat of
20°C
10°C
5°C
15°C
The undesireable property of a refrigerant is
non-flammable
non-explosive
high boiling point
non-toxic
The difference between dry bulb temperature and dew point temperature, is called
dry bulb depression
degree of saturation
dew point depression
wet bulb depression
When α is absorptivity, ρ is reflectivity and τ is transmittivity, then for a diathermanous body,
α = 1, ρ = 0 and τ = 0
α = 0, ρ = 0 and τ = 1
α = 0, ρ = 1 and τ = 0
α + ρ = 1 and τ = 0
The unit of thermal diffusivity is
m2/h
m/h
m2/hK
m/hK
The optimum effective temperature for human comfort is
higher in winter than in summer
lower in winter than in summer
same in winter and summer
not dependent on season
The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to
Grashoff number
Peclet number
Stanton number
Biot number
The relative humidity lines on a psychrometric chart are
horizontal and non-uniformly spaced
vertical and uniformly spaced
horizontal and uniformly spaced
curved lines
In larger industrial and commercial reciprocating compression systems, refrigerent widely used is
Ammonia
Carbon dioxide
Sulphur dioxide
R-12
In case ofsensible cooling of air, the coil efficiency is given by
1 + B.P.F.
1 - B.P.F.
P.F. - 1
The horizontal and non-uniformly spaced lines on a psychrometric chart indicates
wet bulb temperature
specific humidity
dew point temperature
dry bulb temperature
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