HEAT TRA Flashcards
Crystal size in a continuous crystalliser depends upon the
-rate of heat transfer.
-degree of turbulence.
-degree of supersaturation.
-all (a), (b) and (c).
all (a), (b) and (c).
Heat waves
-can not pass through vacuum.
-travel in straight line.
-can be reflected by a mirror.
-both (b) and (c).
-both (b) and (c).
Air is best heated with steam in a heat exchanger of
-plate type.
-double pipe type with fin on steam side.
-double pipe type with fin on air side.
-shell and tube type.
-double pipe type with fin on air side.
Which of the following is generally considered as opaque surface towards radiations?
-Gases
-Solids
-Liquids
-Both (b) and (c)
Both (b) and (c)
Black liquor generated during paper manufacture is concentrated in a
-single effect evaporator.
-single effect evaporator followed by a crystalliser.
-multiple effect evaporator.
-multiple effect evaporators followed by a crystalliser.
-multiple effect evaporator.
When vaporisation takes place directly at the heating surface, it is called
-film boiling
-nucleate boiling
-vapour binding
-none of these
-nucleate boiling
Steam consumption in kg/hr in case of an evaporator is given by (where, C & E are capacity the economy of the evaporator respectively)
-C/E
-E/C
-CE
-1/CE
C/E
Reynold’s analogy states that
Nst α f
Nst α NRe
NNu α f
NRe α f
Nst α f
With increase in temperature, the thermal conductivity of non-metallic amorphous solids
-decreases
-increases
-remains constant
-first decreases upto certain temperature and then increases
increases
Fourier’s law applies to the heat transfer by
-convection
-radiation
-conduction
-all (a), (b) & (c)
conduction
Shell side pressure drop in a shell and tube heat exchanger does not depend upon the
-baffle spacing & shell diameter.
-tube diameter & pitch.
-viscosity, density & mass velocity of shell side fluid.
-none of these.
-none of these.
In the equation Q = UAΔt; Δt is
-geometric mean temperature difference.
-arithmetic mean temperature difference.
-logarithmic mean temperature difference.
-the difference of average bulk temperatures of hot and cold fluids.
-logarithmic mean temperature difference.
With increase in porosity, the thermal conductivity of a solid substance
-increases
-decreases
-remains unchanged
-may increase or decrease; depends on the solid
-decreases
For an ideal black body
absorptivity = 1
reflectivity = 1
emissivity = 0
transmissivity = 1
absorptivity = 1
In Joule’s experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms-2. Neglecting the heat capacity of agitator, the temperature of water (in °C) is
40.5
34.4
26.8
25
34.4
Fouling factor
-is a dimensionless quantity.
-does not provide a safety factor for design.
-accounts for additional resistances to heat flow.
-none of these.
accounts for additional resistances to heat flow.
In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient
-increases
-decreases
-is not affected
-may increase or decrease; depends on the feed
decreases
The steam ejector is used to
-remove condensate from the steam pipelines.
-create vacuum.
-superheat the steam.
-none of these.
-create vacuum.
For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area
-increases
-decreases
-remains constant
-passes through a maxima
-passes through a maxima
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
-(COP)R = (COP)HP = 0.6
-(COP)R = 2.5; (COP)HP = 1.5
-(COP)R = 1.5; (COP)HP = 2.5
-(COP)R = (COP)HP = 2.5
-(COP)R = 1.5; (COP)HP = 2.5
Hot water (0.01 m3 /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 m3/min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately
32
37
45
50
32
In a heat exchanger, floating head is provided to
-facilitate cleaning of the exchanger.
-increase the heat transfer area.
-relieve stresses caused by thermal expansion.
-increase log mean temperature gradient.
-relieve stresses caused by thermal expansion.
Leidenfrost point is a term concerned with the
-condensation of the saturated vapor on a cold surface.
-concentration of a corrosive solution by evaporation.
-heat transfer between two highly viscous liquids.
-boiling of a liquid on a hot surface.
-boiling of a liquid on a hot surface.
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
-counter flow with process stream on shell side.
-counter flow with process stream on tube side.
-parallel flow with process stream on shell side.
-parallel flow with process stream on tube side.
-counter flow with process stream on shell side.
