০২। "The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium". This is __________ law.
ক) Kirchoffs
খ) Planck's
গ) Wien's displacement
ঘ) Stefan-Boltzman
০৩। 'Duhring's plot' is of use in
ক) extractive distillation
খ) evaporation
গ) leaching
ঘ) absorption
০৪। 'Fouling factor' used in the design of a multipass shell and tube heat exchanger is a
ক) non-dimensional factor.
খ) factor of safety.
গ) conversion factor for individual film heat transfer co-efficient to overall heat transfer co-efficient.
ঘ) none of these.
০৫। (NGr x NPr) is called the __________ number.
ক) Graetz
খ) Reyleigh
গ) Nusselt
ঘ) Stanton
০৬। 1 BTU/hr.ft.°F is equal to __________ kcal/hr. m.°C.
ক) 1.49
খ) 1
গ) 4.88
ঘ) none of these
০৭। 1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the liquid is 1500 W/m2.°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be
ক) 15 min
খ) 22 min
গ) 44 min
ঘ) 51 min
০৮। 1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is
ক) 520
খ) 200
গ) 400
ঘ) 500
০৯। 200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 x 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)
ক) 0.5
খ) 0.05
গ) 0.1
ঘ) 0.15
১০। A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be
ক) greater than that for uninsulated steam pipe.
খ) less than that of the uninsulated steam pipe.
গ) equal to that of the uninsulated steam pipe.
ঘ) less than the steam pipe with 5 cms insulation.
১১। A 2-4 heat exchanger involves
ক) only counter-flow of fluids.
খ) only parallel-flow of fluids.
গ) both counter and parallel-flow of the fluids.
ঘ) smaller pressure drop compared to 1-2 exchanger.
১২। A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides
ক) higher economy
খ) lower capacity
গ) both (a) & (b)
ঘ) lower economy
১৩। A black body does not __________ radiation.
ক) absorb or emit
খ) refract
গ) reflect
ঘ) both(b) & (c)
১৪। A black body when hot, emits heat radiation of __________ wavelengths.
ক) small
খ) large
গ) all
ঘ) one fixed
১৫। A body cools down from 75°C to 70°C in 10 minutes. It will cool down from 70° C to 65° C in __________ minutes.
ক) 10
খ) >10
গ) <10
ঘ) either (b) or (c), depends on the mass of the body
১৬। A body is called grey if the monochromatic emissivity of the body is
ক) zero
খ) unity
গ) same for all wavelengths
ঘ) different for all wavelengths
১৭। A BTU/hr.ft.2 °F is equal to
ক) 1 kcal/hr. m2°C.
খ) 4.88 kcal/hr. m.2°C.
গ) 1 kcal/hr. m2.°K.
ঘ) none of these.
১৮। A composite flat wall of a furnace is made of two materials 'A' and 'B'. The thermal conductivity of 'A' is twice of that of material 'B', while the thickness of layer of 'A' is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material 'A' is
ক) 125
খ) 133
গ) 150
ঘ) 160
১৯। A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are kA and kB and the specific heat capacities are CPA and CPB for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when
is called the __________ number
is termed as the __________ number.