Pick out the wrong statement. (A) In case of heat transfer by purely forced convection, GR /Re 2 ≤ 1 (B) The equivalent diameter of heat transfer for a duct of square cross￾section (having each side as 'x') is equal to 4x (C) Distillation process is not the same as evaporation (D) The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are formed and detached from the heating surface

Pick out the wrong statement.

(A) In case of heat transfer by purely forced convection, GR

/Re

2 ≤ 1

(B) The equivalent diameter of heat transfer for a duct of square cross￾section (having each side as 'x') is equal to 4x

(C) Distillation process is not the same as evaporation

(D) The effectiveness of nucleate boiling depends basically on the ease with

which the bubbles are formed and detached from the heating surface

by

1 Answer

Answer :

(B) The equivalent diameter of heat transfer for a duct of square cross￾section (having each side as 'x') is equal to 4x

by

Related questions

Pick out the wrong statement. (A) 'Solvates' are chemical compounds formed by solute with their solvents. When water is the solvent, then it is called a 'hydrate' (B) In heat exchanger calculations (Δt) weighted is used in place of Δt, when it involves more than one sequence of heating or cooling i.e., desuperheating & condensation or condensation & sub-cooling (C) Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted (D) In case of short tube vertical evaporators, area of central downtake is about 50 to 100% of the total tube cross-sectional area

Description : Pick out the wrong statement. (A) 'Solvates' are chemical compounds formed by solute with their solvents. When water is the solvent, then it is called a 'hydrate' (B) In heat exchanger ... vertical evaporators, area of central downtake is about 50 to 100% of the total tube cross-sectional area

Last Answer : (C) Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted

In forced convection, the heat transfer depends on(A) Re, Pr (B) Re, Gr (C) Mainly Gr (D) Re only

Description : In forced convection, the heat transfer depends on (A) Re, Pr (B) Re, Gr (C) Mainly Gr (D) Re only

Last Answer : (A) Re, Pr

Pick out the wrong statement about nucleate boiling. (A) Bubble generation is by expansion of entrapped gas/vapour at small cavities in the surface (B) Surface temperature is greater than the saturation temperature of the liquid (C) Heat transfer from the surface of the liquid is less than that in film boiling (D) The temperature is less than that of film boiling

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Last Answer : (D) The temperature is less than that of film boiling

In case of __________ boiling, the bubbles formed on a submerged hot surface get absorbed in the mass of the liquid. (A) Nucleate (B) Pool (C) Low pressure (D) None of these

Description : In case of __________ boiling, the bubbles formed on a submerged hot surface get absorbed in the mass of the liquid. (A) Nucleate (B) Pool (C) Low pressure (D) None of these

Last Answer : (B) Pool

Pick out the wrong statement. (A) In drying a solid containing moisture above the critical moisture content the number of degrees of freedom is 2 (B) Sherwood number in mass transfer corresponds to Nusselt number in heat transfer and Schmidt number to Prandtl number (C) Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger (D) Hot gases at moderate pressure are usually in the shell side of shell and tube heat exchangers. At higher pressure, however, it is customary to put gas in the tube side

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Last Answer : (C) Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger

Pick out the wrong statement. (A) With decrease in feed temperature, the number of plates required for binary distillation decreases for a given ‘L/V’ ratio (B) The extraction per unit of total height for a short packed column is more effective than for a tall column, in case of liquid-liquid extraction(C) Natural draft cooling towers are made of ferroconcrete and its cross￾section is wider at the bottom(D) Vander wall adsorption is also called chemisorption

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Last Answer : (D) Vander wall adsorption is also called chemisorption

Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re 0.8 . Pr n , is not valid, if the value of (A) n = 0.4 is used for heating (B) n = 0.3 is used for cooling (C) Reynolds number for the flow involved is > 10000 (D) Reynolds number for the flow involved is < 2100

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Last Answer : (D) Reynolds number for the flow involved is < 2100

In forced convection, the Nusselt number is a function of (A) Re and Pr (B) Re and Gr (C) Pr and Gr (D) Re and Sc

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Last Answer : (A) Re and Pr

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 that of the damp material (C) Ratio of its capacity to economy equals the steam consumption in kg/hr in an evaporator (D) Vaporisation of organic substances in evaporator mostly causes foam formation

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Last Answer : (B) Thermal conductivity of a dry material is more than that of the damp material

Pick out the wrong statement. (A) Different solids have different equilibrium moisture curves (B) Total condenser or reboiler is considered equivalent to one theoretical plate in McCabe-Thiele method of theoretical plate calculation for distillation column (C) Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column (D) Even a forced draft cooling tower cannot cool water below the wet bulb temperature

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Last Answer : (C) Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column

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 temperature distribution, is the thermal conductivity (C) In unsteady state heat conduction, heat flows in the direction of temperature rise (D) In heat transfer by forced convection, Grashoff number is very important

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Last Answer : (B) In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity

The burnout heat flux in the nucleate boiling regime is not a function of the (A) Liquid density (B) Vapour density (C) Temperature difference (D) Heat of evaporation

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Last Answer : (B) Vapour density

The equivalent diameter for pressure drop calculation for a duct of square cross-section is given by (where, x = each side of the square duct). (A) x (B) √(πx) (C) √(2x) (D) √(x/2)

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Last Answer : (A) x

Even though heat transfer co-efficient in boiling liquids is large, use of fins is advantageous, when the entire surface is exposed to __________ boiling. (A) Film (B) Nucleate (C) Transition (D) All modes of

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Pick out the wrong statement pertaining to the cooling towers. (A) In case of induced draft cooling tower, the fan is placed at the top of the tower (B) Effectiveness of forced draft cooling tower is reduced by the recirculation of the humid and hot discharged air (C) A natural draft cooling tower is recommended to be used, when the air humidity is low and air temperature is also low (D) Effectiveness of a mechanical draft cooling tower is reduced with increase in air wet-bulb temperature

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Last Answer : (D) Effectiveness of a mechanical draft cooling tower is reduced with increase in air wet-bulb temperature

Pick out the wrong statement. (A) Fluid movement under the influence of buoyant forces resulting from change in density takes place in case of natural convection (B) The ratio NNu /NRe . Npr is called the Stanton number (C) The Peclet number is a measure of the ratio of energy transport by convection to that by conduction (D) The Colburn jH factor for heat transfer is given by Nst Npr

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Last Answer : (D) The Colburn jH factor for heat transfer is given by Nst Npr

In a furnace with heating element temperature at 1700°C, the dominant mechanism of heat transfer will be (A) Conduction (B) Radiation (C) Natural convection (D) Forced convection

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Last Answer : (B) Radiation

Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the (A) Existence of thermal boundary layer (B) Temperature gradient produced due to density difference (C) Buoyancy of the bubbles produced at active nucleation site (D) None of these

Description : Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the (A) Existence of thermal boundary layer (B) Temperature gradient produced ... difference (C) Buoyancy of the bubbles produced at active nucleation site (D) None of these

Last Answer : (D) None of these

When vaporisation takes place directly at the heating surface, it is called (A) Film boiling (B) Nucleate boiling (C) Vapour binding (D) None of these

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Last Answer : (B) Nucleate boiling

Pick out the wrong statement. (A) Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient (B) In a shell and tube heat exchanger, the shell pressure drop is maximum for orifice baffles (C) S.I. unit of fouling factor is Watt/m2 .°K (D) Longitudinal fins are used in extended surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube

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Last Answer : (C) S.I. unit of fouling factor is Watt/m2 .°K

The equivalent diameter for fluid flow through square cross section channel of side 'x', for pressure drop calculation purpose is given by (A) 4x (B) 2x (C) x (D) √x

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Last Answer : (C) x

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 conduction (developing thermal boundary layer) (C) Mixed convection (both free and forced) (D) Forced convection

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Last Answer : (C) Mixed convection (both free and forced)

Two footings, one circular and the other square, are founded on the surface of a purely cohesionless soil. The diameter of the circular footing is the same as that of the side of the square footing. The ratio between their ultimate bearing capacities will be : (a) 1.0 (b) 1.3 (c) 1.33 (d) 0.75

Description : Two footings, one circular and the other square, are founded on the surface of a purely cohesionless soil. The diameter of the circular footing is the same as that of the side of the square footing. The ratio between their ultimate bearing capacities will be : (a) 1.0 (b) 1.3 (c) 1.33 (d) 0.75

Last Answer : (d) 0.75

Pick out the wrong statement. (A) In process heat exchangers, saturated steam is preferred over the superheated steam (B) The maximum is the emissive power of a surface at a temperature T1 occurs at a wavelength of λ1 . If the surface temperature is halved, the maximum in the emissive power would occur at a wavelength of 0.5 λ1 (C) When a vertical plate is heated in infinite air environmental under natural convection conditions, the velocity profile in air, normal to the plate, exhibits a maximum

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Last Answer : (B) The maximum is the emissive power of a surface at a temperature T1 occurs at a wavelength of λ1 . If the surface temperature is halved, the maximum in the emissive power would occur at a wavelength of 0.5 λ1

Pick out the wrong statement. (A) Economy of a multiple effect evaporator is not influenced by the boiling point elevation (B) Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature (C) Double pipe heat exchangers are mostly used in the field of refrigeration (D) Finned tube heat exchangers are suitable for heating air by steam

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In case of __________ boiling, the liquid temperature is below the saturation temperature and the boiling takes place in the vicinity of the heated surface. (A) Nucleate (B) Local (C) Pool (D) Saturated

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Rate of heat transfer by vaporisation from pools of water is affected by the (A) Nature of heating surface and distribution of bubbles (B) Surface tension of water (C) Viscosity of water (D) All (A), (B) and (C)

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Last Answer : (D) All (A), (B) and (C)

Pick out the wrong statement. (A) Conversion of SO2 to SO3 in Monsanto-4 pass converter is about 98% (B) The chemical formula of oleum is H2S2O7 , which is formed by saturating sulphuric acid with sulphur trioxide (C) Vitriol oil is nothing but technical sulphuric acid (D) Decomposition of sulphuric acid on heating does not start before its boiling

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Last Answer : (D) Decomposition of sulphuric acid on heating does not start before its boiling

The equivalent diameter of channel of a constant non-circular cross￾section of 3 cm by 6 cm will be __________ cms. (A) 20 (B) 12 (C) 8 (D) 2

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Last Answer : (D) 2

Pick out the wrong statement. (A) Heat transfer by radiation cannot occur across an absolute volume (B) In case of a shell and tube heat exchanger, the pressure drop through the shell is proportional to the number of times the fluid crosses the bundle between baffles (C) Propagation velocity for travel of heat radiation through vacuum is equal to the velocity of the light (D) The amount of heat involved in the condensation or vaporisation of 1 kg of a fluid is the same

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Last Answer : (A) Heat transfer by radiation cannot occur across an absolute volume

In sub-cooled boiling, (A) Temperature of the heating surface is less than the boiling point of the liquid (B) Temperature of the heating surface is more than the boiling point of the liquid (C) Bubbles from heating surface are absorbed by the mass of the liquid (D) Very large vapour space is necessary

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Last Answer : (B) Temperature of the heating surface is more than the boiling point of the liquid

Leidenfrost point is a term concerned with the (A) Condensation of the saturated vapor on a cold surface (B) Concentration of a corrosive solution by evaporation (C) Heat transfer between two highly viscous liquids (D) Boiling of a liquid on a hot surface

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Last Answer : (D) Boiling of a liquid on a hot surface

Pick out the wrong statement. (A) In the McCabe-Thiele diagram for binary distillation, vertical feed line represents saturated liquid feed and horizontal feed line represents saturated vapour feed (B) In small columns, local efficiency is larger than Murphree efficiency; in large columns local efficiency is smaller than Murphree efficiency (C) For Laminar flow over a plate of length L, the local mass transfer co￾efficient at a distance L from the leading edge is 1.5 × 10 -2m/s. Then the average mass transfer co-efficient for the plate is 2 × 10 -2m/s (D) The concentration and hydrodynamic boundary layers over a flat plate are of equal thickness, if Schmidt number is equal to unity

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Last Answer : (C) For Laminar flow over a plate of length L, the local mass transfer co￾efficient at a distance L from the leading edge is 1.5 × 10 -2m/s. Then the average mass transfer co-efficient for the plate is 2 × 10 -2m/s

reduction in thermal resistance during heat transfer does not occur in the (A) Convection heat transfer by stirring the fluid and cleaning the heating surface (B) Conduction heat transfer by reduction in the material thickness and increase in the thermal conductivity (C) Radiation heat transfer by increasing the temperature and reducing the emissivity (D) None of these

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Last Answer : Option C

Pick out the wrong statement. (A) The value of hydrostatic head increases with increase in vacuum in the effect in a multiple effect evaporator system (B) Entering velocity of the liquid in the tubes of natural circulation evaporators is in the range of 0.3 to 0.9 metre/second (C) Duhring's plot is used for calculating the concentration of solution (D) In a multiple effect evaporation system, the number of effects is limited by the total boiling point rise

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Pick out the wrong statement. (A) Heat transfer from a hot body to cold body by the emission of heat waves is called radiation (B) Filmwise condensation takes place on non-wettable surfaces (C) The boiling point of a solution is affected by liquid head as well as boiling point elevation (D) None of these

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Last Answer : (B) Filmwise condensation takes place on non-wettable surfaces

Nusselt number (for forced convection heat transfer) is a function of the __________ number. (A) Prandtl (B) Reynolds (C) Both (A) & (B) (D) Neither (A) nor (B)

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Last Answer : (C) Both (A) & (B)

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

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The Fourier number (defined as a.t/L 2 ) is used in the analysis of problem involving heat transfer by (A) Forced convection (B) Natural convection(C) Transient conduction(D) Steady state conduction

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Last Answer : (A) Transient heat conduction

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Last Answer : (C) Forced convection

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Last Answer : (B) Natural convection

If heat transfer rate varies with the time, it is termed as (A) Forced convection (B) Steady state conduction (C) Monochromatic radiation (D) None of these

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View factor is important in heat transfer by (A) Steady state conduction (B) Natural convection (C) Forced convection (D) Radiation

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Heat transfer by __________ may not necessarily require the presence of a medium. (A) Conduction (B) Natural convection (C) Forced convection (D) Radiation

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Last Answer : (D) Radiation

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Pick out the wrong statement. (A) The equivalent stiffness of two springs (of equal stiffness 'S') in series is S/2 while in parallel is 2S (B) For a helical spring, deflection is proportional to D3(D = mean coil diameter) or d4(d = wire diameter) (C) Crushing load or columns is less than the buckling load (D) Modulus of resilience is proportional to (stress at elastic limit)2

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Which of the following are methods of heat transfer? (1) Convection (2) Evaporation (3) Revolution (4) Thermal Expansion

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Which of the following are methods of heat transfer? (1) Convection (2) Evaporation (3) Revolution (4) Thermal Expansion

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Last Answer : Convection