Description : Pick out the wrong statement. (A) The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are the same for NSc = NPr= 1 (B) 1 Nm3 of dry air is lighter ... ) The Lewis number of a mixture is unity, when the thermal diffusivity is equal to the mass diffusivity
Last Answer : (B) 1 Nm3 of dry air is lighter than 1Nm3 of humid air
Description : Lewis number, which is important in problems involving simultaneous heat and mass transfer, is the ratio of (A) Mass diffusivity to momentum diffusivity (B) Thermal diffusivity to mass diffusivity (C) Momentum diffusivity to thermal diffusivity (D) None of these
Last Answer : (B) Thermal diffusivity to mass diffusivity
Description : The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, NPr = NSc = __________ (A) 1 (B) 0.5 (C) 10 (D) 0
Last Answer : (A) 1
Description : . (NSh /NRe .NSc ) is termed in mass transfer operation as the (A) Stanton number (B) Peclet number (C) Thermal diffusivity (D) Momentum diffusivity
Last Answer : (A) Stanton number
Description : In physical terms, Schmidt number means (A) Thermal diffusivity/mass diffusivity (B) Thermal diffusivity/momentum diffusivity (C) Momentum diffusivity/mass diffusivity (D) Mass diffusivity/thermal diffusivity
Last Answer : (C) Momentum diffusivity/mass diffusivity
Description : The Schmidt number which is defined as, μ/ρ D, is the ratio of the (A) Momentum diffusivity to the mass diffusivity (B) Thermal diffusivity to the mass diffusivity (C) Momentum diffusivity to the thermal diffusivity (D) None of these
Last Answer : (A) Momentum diffusivity to the mass diffusivity
Description : Prandtl number is the ratio of (A) Mass diffusivity to thermal diffusivity (B) Momentum diffusivity to thermal diffusivity (C) Thermal diffusivity to mass diffusivity (D) Thermal diffusivity to momentum diffusivity
Last Answer : (B) Momentum diffusivity to thermal diffusivity
Description : Prandtl number is the ratio of (A) Momentum diffusivity to mass diffusivity (B) Momentum diffusivity to thermal diffusivity (C) Thermal diffusivity to mass diffusivity (D) Thermal diffusivity to momentum diffusivity
Description : Prandtl number is the reciprocal of (A) Thermal diffusivity/Momentum diffusivity (B) Thermal diffusivity × Momentum (C) Thermal diffusivity × Mass diffusivity (D) Mass diffusivity × Momentum diffusivity
Last Answer : (A) Thermal diffusivity/Momentum diffusivity
Description : Diffusion co-efficient generally depends upon the temperature, pressure & the nature of the components of the system. Its dimension is not the same as that of the (A) Mass transfer co-efficient (B) Thermal diffusivity (C) Kinematic viscosity (D) Volumetric diffusivity
Last Answer : (A) Mass transfer co-efficient
Description : Which of the following has the same dimension as mass diffusivity? (A) Momentum flux (B) Kinematic viscosity (C) Thermal diffusivity (D) Both (B) and (C)
Last Answer : (D) Both (B) and (C)
Description : In fluid flow, and heat and mass transfer, one encounters (i) kinematic velocity (μ), (ii) molecular diffusivity (θ) and thermal diffusivity (α). The units of these quantities are. (A) μ , α and θ all have units of m/ ... μ has unit of m/s (D) α and θ have units of m/s, while μ has unit of m2/s
Last Answer : Option C
Description : The diffusivity, DAB (for component A diffusing in B) is equal to the diffusivity DBA (for component B diffusing in A) for a binary mixture of (A) Newtonian liquids (B) Non-Newtonian liquids (C) Ideal gases (D) Real gases
Last Answer : (C) Ideal gases
Description : Pick out the wrong statement. (A) The Reynolds analogy for mass transfer is given by Lewis relation and is applicable, when Schmidt number is one (B) Sherwood number for flow in pipes can be expressed ... flux of a component A in binary mixture of A and B is given by - Dab'.dCA/dz
Last Answer : (C) According to film theory for equimolar counter diffusion, the mass transfer coefficient is given by DAB(B)P - 3, Q - 2
Description : The diffusivity (D) in a binary gas mixture is related to the temperature (T) as (A) D ∝ T (B) D ∝ T 0.5 (C) D ∝ T 1.5 (D) D ∝ T
Last Answer : (C) D ∝ T 1.5
Description : “The fugacity of a gas in a mixture is equal to the product of its mole fraction and its fugacity in the pure state at the total pressure of the mixture". This is (A) The statement as per Gibbs-Helmholtz (B) Called Lewis-Randall rule (C) Henry's law (D) None of these
Last Answer : (B) Called Lewis-Randall rule
Description : The ratio of momentum diffusivity to thermal diffusivity is the __________ number. (A) Prandtl (B) Nusselt (C) Stanton (D) Grashoff
Last Answer : (A) Prandtl
Description : The ratio of kinematic viscosity to thermal diffusivity is called the __________ number. (A) Peclet (B) Prandtl (C) Stanton (D) Nusselt
Last Answer : (B) Prandtl
Description : With increase in temperature, the rate of leaching increases, because the (A) Diffusivity of solute increases (B) Viscosity of solvent decreases (C) Thermal conductivity of solute increases (D) None of these
Last Answer : (A) Diffusivity of solute increases
Description : Thermal diffusivity is the most important in heat transfer by (A) Conduction (B) Radiation
Last Answer : (A) Conduction
Description : Heat transfer rate per unit area is called (A) Thermal conductivity (B) Heat flux (C) Heat transfer co-efficient (D) Thermal diffusivity
Last Answer : (B) Heat flux
Description : Thermal diffusivity of a material (A) Has the unit m2 /sec (B) Is defined as K/ρ . Cp (C) Is the ratio of thermal conductivity to thermal capacity (D) All (A), (B) and (C)
Last Answer : (D) All (A), (B) and (C)
Description : In Fourier's law, the proportionality constant is called the (A) Heat transfer co-efficient (B) Thermal diffusivity (C) Thermal conductivity (D) Stefan-Boltzmann constant
Last Answer : (C) Thermal conductivity
Description : Thermal diffusivity of a substance is proportional to (where, k = Thermal conductivity) (A) 1/k (B) k (C) k2 (D) 1/k2
Last Answer : (B) k
Description : 1. __________ of air does not increase with increase in temperature. (A) Density (B) Thermal diffusivity (C) Viscosity (D) Thermal conductivi
Last Answer : Option A
Description : What does thermal diffusivity of metals signify.
Last Answer : Thermal diffusivity is associated with the speed of propagation of heat into solids during changes in temperature with time.
Description : A bimetallic strip commonly found in home furnace thermostats works because of the difference in this property of the two metals. Is it: w) thermal shock x) thermal conductivity y) thermal expansion z) thermal diffusivity
Last Answer : ANSWER: Y -- THERMAL EXPANSION
Description : The mass transfer co-efficient for a solid sphere of radius 'a' dissolving in a large volume of quiescent liquid, in which ‘D’ is the diffusivity of solute, is (A) D/a (B) D/2a (C) Proportional to √D (D) Dependent on the Reynolds number
Last Answer : (D) Dependent on the Reynolds number
Description : Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as (A) K ∝ D (B) K ∝√D (C) K ∝ D1.5 (D) K ∝ D
Last Answer : (A) K ∝ D
Description : Wetted wall tower experiment determines the (A) Molal diffusivity (B) Volumetric co-efficient (C) Mass transfer co-efficient (D) None of these
Last Answer : (C) Mass transfer co-efficient
Description : According to the film theory of mass transfer, the mass transfer coefficient is proportional to (where, D = molecular diffusivity). (A) D (B) D2 (C) D0.5 (D) 1/D
Last Answer : (A) D
Description : Mass transfer co-efficient 'K' according to penetration theory varies with mass diffusivity as (A) D0.5 (B) D (C) 1/D (D) D1.5
Last Answer : (A) D0.5
Description : Dimension of mass diffusivity is the same as that of (A) Kinematic viscosity (B) Dynamic viscosity (C) Surface tension (D) Pressure
Last Answer : (A) Kinematic viscosity
Description : Penetration theory relates the average mass transfer co-efficient (K) with diffusivity (D) as (A) K ∝D (B) K ∝√D (C) K ∝D1.5 (D) K ∝D
Last Answer : (B) K ∝√D
Description : In case of non-ideal gases and liquids, the molal diffusivity (A) Varies inversely as the pressure (B) Varies directly as the pressure (C) Is independent of pressure (D) Is equal to the volumetric diffusivity
Last Answer : (C) Is independent of pressure
Description : Which of the following plays an important role in problems of simultaneous heat and mass transfer (A) Lewis number (B) Schmidt number (C) Prandtl number (D) Sherwood number
Last Answer : (A) Lewis number
Description : __________ number indicates the ratio of the rates of the heat and mass transfer incase of a cooling tower. (A) Sherwood (B) Stanton (C) Lewis (D) Peclet
Last Answer : (C) Lewis
Description : Which is not concerned directly with mass transfer? (A) Schmidt number (B) Sherwood number (C) Lewis relationship (D) Froude number
Last Answer : (D) Froude number
Description : In case of cooling towers, the ratio of the rates of heat and mass transfer is indicated by the __________ number. (A) Lewis (B) Grashoff (C) Sherwood
Last Answer : (A) Lewis
Description : Which of the following is concerned with both heat and mass transfer? (A) Lewis relationship (B) Nusselt number (C) Kutateladze number (D) Froude number
Last Answer : (A) Lewis relationship
Description : "The rate at which a substance reacts is proportional to its active mass and the rate of a chemical reaction is proportional to the product of active masses of the reacting substances". This is the (A) Lewis- ... (B) Statement of Van't Hoff Equation (C) Le-Chatelier's principle (D) None of these
Last Answer : (D) None of these
Description : For the air water system under ambient conditions, the adiabatic saturation temperature and the wet bulb temperature are nearly equal, because (A) Water has a high latent heat of evaporation (B) Lewis number is close to unity (C) They are always equal under all circumstances
Last Answer : (A) Water has a high latent heat of evaporation
Description : Liquid diffusivity is of the order of __________ cm2 /second. (A) 0.01 (B) 0.1 (C) 10 -5 to 10 -6 (D) > 1
Last Answer : (C) 10 -5 to 10
Description : The eddy diffusivity for a liquid in plug flow must be (A) 1 (B) 0 (C) ∞ (D) Between 0 and 1
Last Answer : (B) 0
Description : For a first order isothermal chemical reaction in a porous catalyst, the effectiveness factor is 0.3. The effectiveness factor will increase if the (A) Catalyst size is reduced or the ... the catalyst diffusivity is reduced (D) Catalyst size is increased or the catalyst diffusivity is increased
Last Answer : (B) Catalyst size is reduced or the catalyst diffusivity is increased
Description : In a mixer, the quantity, (v. L/D) is termed as __________ number (where, v = longitudinal velocity of material, L = length of the mixer, D = diffusivity in axial mixing). (A) Weber (B) Peclet (C) Brinkman (D) Schmidt
Last Answer : (B) Peclet
Description : Analogy between mass and heat transfer is not applicable in case of (A) Same velocity profile or equal eddy diffusivities (B) Thermal or pressure mass diffusion (C) Viscous heating or chemical reaction (D) Both (B) and (C)
Description : Schmidt number and Lewis number for pure air at atmospheric conditions are respectively (A) < 1 and ≈ 1 (B) 1 and 0 (C) > 1 and ≈ 1 (D) 0 and ≈ 1
Last Answer : (A) < 1 and ≈ 1
Description : The value of Lewis number (Le = Sc/Pr) for air-water vapour system is around (A) 1 (B) 0.24
Description : The binary diffusivity in gases at atmospheric conditions is about (A) 10 -9 cm/sec (B) 10 -1 cm2 /sec (C) 10 -3 sec/cm (D) 10 -4 cm2 /sec
Last Answer : (B) 10 -1 cm2 /sec