Dittus-Boelter equation cannot be used for molten metals mainly due to
its very low
(A) Prandtl number
(B) Grashoff number
(C) Thermal conductivity
(D) Viscosity
Description : The Dittus-Boelter equation for convective heat transfer [(i.e. h = 0.023 (K/D) (Re) 0.8 (Pr) 0.4 ] cannot be used for (A) Low Reynold's number (B) Very low Grashoff number (C) Molten metals (D) All (A), (B) and (C)
Last Answer : (D) All (A), (B) and (C)
Description : Dittus-Boelter equation used for the determination of heat transfer coefficient is valid (A) For fluids in laminar flow (B) For fluids in turbulent flow (C) When Grashoff number is very important (D) For liquid metals
Last Answer : (B) For fluids in turbulent flow
Description : Which of the following forced convection heat transfer equation accounts for the liquid viscosity effect for viscous liquids? (A) Dittus-Boelter equation (B) Sieder-Tate equation (C) Nusselt equation (D) None of these
Last Answer : (B) Sieder-Tate equation
Description : For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of (A) 1 (B) 1.74 (C) 6.1 (D) 37
Last Answer : (C) 6.1
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 : Pick out the correct statement. (A) 1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F (B) In steady state heat conduction, the only property of the substance which determines the ... in the direction of temperature rise (D) In heat transfer by forced convection, Grashoff number is very important
Last Answer : (B) In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity
Description : Which of the following liquid metals has the highest thermal conductivity? (A) Molten sodium (B) Molten lead (C) Mercury (D) Molten potassium
Last Answer : (A) Molten sodium
Description : Highly porous refractory bricks are (A) Less susceptible to chemical attack by molten fluxes and gases etc (B) Very strong (C) Having very high thermal conductivity (D) None of these
Last Answer : (D) None of these
Description : The type of liquor circulation system to be ' employed in evaporators (viz. natural or forced circulation) is determined mainly by the __________ of the liquid. (A) Viscosity (B) Density (C) Thermal conductivity (D) Corrosive nature
Last Answer : (A) Viscosity
Description : Among liquids, water has a comparatively high value of thermal conductivity, due to its (A) Low density (B) High viscosity (C) Partial ionisation (D) Dense structure
Last Answer : (C) Partial ionisation
Description : Pick out the wrong statement pertaining to the analogy between equations of heat and mass transfer operations. (A) Sherwood number in mass transfer is analogous to Nusselt number in heat transfer ... heat transfer (D) Reynolds number remains the same in both heat and mass transfer
Last Answer : (C) Reynolds number in mass transfer is analogous to Grashoff number in heat transfer
Description : Which of the following is unimportant in forced convection? (A) Reynolds number (B) Prandtl number (C) Grashoff number (D) None of these
Last Answer : (C) Grashoff number
Description : Natural convection is characterised by (A) Grashoff number (B) Peclet number (C) Reynolds number (D) Prandtl number
Last Answer : (A) Grashoff number
Description : Nusselt number is a function of Prandtl number and __________ number of fluid in natural convection heat transfer. (A) Grashoff (B) Biot (C) Stanton
Last Answer : (A) Grashoff
Description : Cpµ/K is termed as the __________ number. (A) Grashoff (B) Nusselt (C) Prandtl (D) Stanton
Last Answer : (C) Prandtl
Description : Critical value of the __________ number governs the transition from laminar to turbulent flow in free convection heat transfer. (A) Grashoff (B) Reynolds (C) Both 'a' & 'b' (D) Prandtl & Grashoff
Last Answer : (D) Prandtl & Grashoff
Description : Transition from laminar to turbulent zone in free convection heat transfer is governed by the critical value of (A) Grashoff number (B) Grashoff number & Reynolds number (C) Reynolds number (D) Grashoff number & Prandtl number
Last Answer : Option D
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 : During the manufacture of sulphuric acid, the temperature of molten sulphur is not increased beyond 160°C, as (A) It is very corrosive at elevated temperature (B) Its viscosity is not reduced on ... be further reduced) (C) It decomposes on further increasing the temperature (D) None of these
Last Answer : (B) Its viscosity is not reduced on further heating (hence pressure drop on pumping it, cannot be further reduced)
Description : Velocity of liquid hydrocarbon fuels in a pipeline cannot be measured by magnetic flow-meters, because their __________ is very low/small. (A) Thermal conductivity (B) Electrical conductivity (C) Specific gravity
Last Answer : (C) Specific gravity
Description : ick out the undesirable property for a good refrigerant. (A) High thermal conductivity (B) Low freezing point (C) Large latent heat of vaporisation (D) High viscosity
Last Answer : (D) High viscosity
Description : Brass tubes are used in the manufacture of tubes of evaporators used in sugar and salt industries, mainly because of its (A) High co-efficient of thermal expansion (B) Low thermal conductivity (C) High corrosion resistance (D) All (A), (B) and (C)
Last Answer : (C) High corrosion resistance
Description : Which of the following has the lowest Prandtl number? (A) Molten sodium (a coolant used in fast breeder reactor) (B) Water (C) Transformer oil (D) Dilute H2SO4
Last Answer : (A) Molten sodium (a coolant used in fast breeder reactor)
Description : (3) reflection of light due to the presence of free electrons Explanation: Lustre (or luster) is the way light interacts with the surface of a crystal, rock, or mineral. The word ... conductivity, and high density. Typically they are malleable and ductile, deforming -under stress without cleaving.
Last Answer : Cloud is a colloidal dispersion of – (1) Air in a dispersion medium of water (2) Fog in a dispersion medium of water (3) Mist in a dispersion medium of air (4) Water drops in a dispersion medium of air
Description : Refractory metals are known for which of the following properties: w) lack of chemical reactivity x) low density y) high melting point z) high thermal conductivity
Last Answer : ANSWER: Y -- HIGH MELTING POINT
Description : Pick out the wrong statement. (A) Bubble size increases with the dynamic viscosity of the liquid in case of nucleate pool boiling (B) Thermal conductivity of a dry material is more than ... in kg/hr in an evaporator (D) Vaporisation of organic substances in evaporator mostly causes foam formation
Last Answer : (B) Thermal conductivity of a dry material is more than that of the damp material
Description : Power consumption during turbulent flow in agitation tank is proportional to the __________ of the liquid. (A) Viscosity (B) Thermal conductivity (C) Surface tension (D) Density
Last Answer : (D) Density
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 : Heat transfer occurs by natural convection because change in temperature causes difference in (A) Viscosity (B) Density (C) Thermal conductivity (D) Heat capacity
Last Answer : (B) Density
Description : Boiling point of a solution according to Duhring's rule is a linear function of the __________ of water. (A) Boiling point (at the same pressure) (B) Viscosity (C) Density (D) Thermal conductivity
Last Answer : (A) Boiling point (at the same pressure)
Description : The ratio of thermal & electrical conductivity is same for all the metals at the same temperature; and at around room temperature, this ratio is proportional to(where, T = absolute temperature, °K) (A) T (B) 1/T (C) T2 (D) 1/T2
Last Answer : A) T
Description : Copper has very low (A) Malleability (B) Ductility (C) Tensile strength (D) Thermal & electrical conductivity
Last Answer : (C) Tensile strength
Description : Finned tube heat exchangers (A) Give larger area per tube (B) Use metal fins of low thermal conductivity (C) Facilitate very large temperature drop through tube wall (D) Are used for smaller heat load
Last Answer : (A) Give larger area per tube
Description : When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is: (A) Free convection (B) Entry length problem in laminar forced ... (developing thermal boundary layer) (C) Mixed convection (both free and forced) (D) Forced convection
Last Answer : (C) Mixed convection (both free and forced)
Description : Low thermal conductivity of heat insulating materials is due to its (A) Dense structure (B) High proportion of air space (C) High specific heat (D) None of these
Last Answer : (B) High proportion of air space
Description : Superconductors are those elements – (1) Whose conductivity is intermediate between metals and insulators (2) Whose resistance falls almost to zero at very low temperature (3) Which conduct electricity only at super-high temperature (4) Which conduct electricity only, at super-high temperatures
Last Answer : (2) Whose resistance falls almost to zero at very low temperature Explanation: Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in ... lines from the interior of the superconductor as it transitions into the superconducting state.
Description : Superconductors are those elements (1) Whose conductivity is intermediate between metals and insulators (2) Whose resistance falls almost to zero at very low temperatures (3) which turn into insulators at very low temperatures (4) which conduct electricity only at super-high temperatures
Last Answer : Whose resistance falls almost to zero at very low temperatures
Description : On a cold day when the room temperature is 15°C, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15°C, because - (1) metals ... metals (3) metals are good conductors of heat (4) plastics have a higher thermal conductivity than metals
Last Answer : (3) metals are good conductors of heat Explanation: On a chilly day, the room temperature is lower than our body temperature. Since metals have a higher coefficient of thermal conductivity than plastic, they ... from our fingers will flow to the metal cap much more quickly than to the plastic body.
Description : On a cold day when the room temperature is 15°C, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15°C, because : (1) metals ... metals (3) metals are good conductors of heat (4) plastics have a higher thermal conductivity than metals
Last Answer : metals are good conductors of heat
Description : The equation, (h.D/K) is called the __________ number. (A) Nusselt (B) Peclet (C) Rayleigh (D) Grashoff
Last Answer : (A) Nusselt
Description : Which °fine metals has the maximum thermal conductivity? (1) Iron (2) Aluminium (3) Silver (4) Copper
Last Answer : (3) Silver Explanation: Silver has the best thermal conductivity of 429 W/mK at RT (295K). It is followed by copper, gold and aluminium. Metals generally have very good electrical conductivity, that leads to high thermal conductivity.
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 : Which of the metals has the maximum thermal conductivity? (1) Iron (2) Aluminium (3) Silver (4) Copper
Last Answer : Silver
Description : __________ equation relates the thermal conductivity of a solid to its temperature. (A) Antoine (B) Kopp's (C) Lee's (D) Kistyakowsky
Last Answer : (C) Lee's
Description : Plate towers are preferred to packed towers, when large temperature changes are involved, because of the reason that the (A) Packing may be crushed due to thermal expansion/contraction of the ... C) Viscosity variation of the fluids may cause channelling/flooding (D) None of these
Last Answer : (A) Packing may be crushed due to thermal expansion/contraction of the components of the equipments
Description : Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is (A) 1 (B) < 1 (C) > 1 (D) > 5
Last Answer : (B) < 1
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 : At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical? (A) 1 (B) < 1 (C) > 1 (D) None of these
Last Answer : (A) 1
Description : . If Prandtl number is greater than the Schmidt number, then the (A) Thermal boundary layer lies inside the concentration boundary layer (B) Concentration boundary layer lies inside the thermal boundary ... (D) Hydrodynamic (i.e., momentum) boundary layer is thicker than the other two
Last Answer : (A) Thermal boundary layer lies inside the concentration boundary layer
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