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 : 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 : 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 : 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 : 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 : Natural convection is characterised by (A) Grashoff number (B) Peclet number (C) Reynolds number (D) Prandtl number
Last Answer : (A) Grashoff number
Description : The Graetz number is concerned with the (A) Mass transfer between a gas and a liquid (B) Absorption with chemical reaction (C) Heat transfer in turbulent flow (D) Heat transfer in laminar flow
Last Answer : (D) Heat transfer in laminar flow
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 : Nusselt number is related to Grashoff number (Gr) in turbulent & laminar flow respectively, in respect of free convection over a vertical flat plate as (A) Gr0.25, Gr (B) Gr0.25, Gr0.33 (C) Gr, Gr0.25 (D) Gr0.33, Gr0.25
Last Answer : Option A
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 : 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 : jH factor for heat transfer is not a function of the __________ number. (A) Reynolds (B) Nusselt (C) Grashoff (D) Both (B) & (C)
Last Answer : (D) Both (B) & (C)
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 : Which of the following is directly concerned with the heat transfer? (A) Strouhal number (B) Sherwood number (C) Euler number (D) Grashoff number
Last Answer : (D) Grashoff number
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 : 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
Last Answer : (C) Transient conduction
Description : In which mode of heat transfer, the Biot number is important? (A) Transient heat conduction (B) Natural convection (C) Forced convection (D) Radiation
Last Answer : (A) Transient heat conduction
Description : 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 ... convection to that by conduction (D) The Colburn jH factor for heat transfer is given by Nst Npr
Last Answer : (D) The Colburn jH factor for heat transfer is given by Nst Npr
Description : Heat transfer by natural convection is enhanced in system with (A) High viscosity (B) High co-efficient of thermal expansio
Last Answer : (B) High co-efficient of thermal expansion
Description : The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as (A) (ΔT) 1/4 (B) (ΔT) 1/2 (C) (ΔT) 5/4 (D) (ΔT) 3/4
Last Answer : (D) (ΔT) 3/4
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 : Mode of heat transfer in which the fluid moves under the influence of changes in fluid pressure produced by external work is called (A) Radiation (B) Natural convection (C) Forced convection (D) Conduction
Last Answer : (C) Forced convection
Description : Mode of heat transfer involved in the cooling of air cooled internal combustion engine is (A) Conduction (B) Natural convection (C) Forced convection (D) None of these
Last Answer : (B) Natural convection
Description : View factor is important in heat transfer by (A) Steady state conduction (B) Natural convection (C) Forced convection (D) Radiation
Last Answer : (D) Radiation
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
Description : Heat transfer by __________ may not necessarily require the presence of a medium. (A) Conduction (B) Natural convection (C) Forced convection (D) Radiation
Description : 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
Last Answer : (B) Radiation
Description : 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)
Last Answer : (C) Both (A) & (B)
Description : 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 ... tube heat exchangers. At higher pressure, however, it is customary to put gas in the tube side
Last Answer : (C) Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger
Description : 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
Last Answer : (D) Reynolds number for the flow involved is < 2100
Description : A measure of the extent to which viscous heating is important relative to the heat flow resulting from the impressed temperature difference is represented by the __________ number. (A) Condensation (B) Grashoff (C) Stanton (D) Brinkman
Last Answer : (D) Brinkman
Description : NRe . NPr ) (D/L) is called the __________ number (A) Peclet (B) Stanton (C) Graetz (D) None of these
Last Answer : (C) Graetz
Description : Asymptotic conditions is reached, when for a fluid flowing in laminar flow through a long tube (A) Exit-fluid temperature > wall temperature (B) Exit fluid temperature < wall temperature (C) Exit fluid temperature = wall temperature (D) Graetz number > 100
Last Answer : (C) Exit fluid temperature = wall temperature
Description : Graetz number is given by (A) mCp /kL (B) kL/mCp (C) mCp /kµ (D) kµ/mC
Last Answer : (A) mCp /kL
Description : NGr × NPr ) is called the __________ number. (A) Graetz (B) Rayleigh (C) Nusselt (D) Stanton
Last Answer : (B) Rayleigh
Description : Heat transfer in the laminar sub-layer in case of a liquid flowing through a pipe, is mostly by (A) Eddies current (B) Conduction (C) Convection (D) None of these
Last Answer : (B) Conduction
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 : Fourier's law applies to the heat transfer by (A) Convection (B) Radiation (C) Conduction (D) All (A), (B) & (C)
Last Answer : (C) Conduction
Description : 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 ... nucleate boiling depends basically on the ease with which the bubbles are formed and detached from the heating surface
Last Answer : (B) The equivalent diameter of heat transfer for a duct of square crosssection (having each side as 'x') is equal to 4x
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
Description : When warm and cold liquids are mixed, the heat transfer is mainly by (A) Conduction (B) Convection (C) Radiation (D) Both (A) & (C
Last Answer : (B) Convection
Description : 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
Description : In furnaces operating at very high temperature (say) 1250°C, e.g. soaking pit), the maximum heat transfer takes place by (A) Conduction (B) Convection (C) Radiation (D) Cannot be predicted
Last Answer : (C) Radiation
Description : Maximum heat transfer in high temperature furnaces is by (A) Conduction (B) Convection (C) Radiation (D) Either (A), (B) or (C); depends on the type of furnace
Description : Forced recirculation of furnace gases is practised (A) To increase heat transfer by convection (B) To ensure uniform temperature (C) In furnaces, operating below 750°C (D) All (A), (B) and (C)
Description : Gibbs phase rule finds application, when heat transfer occurs by (A) Conduction (B) Convection (C) Radiation (D) Condensation
Last Answer : (D) Condensation
Description : Heat transfer by __________ is almost absent in case of fluidised bed drying operation. (A) Radiation (B) Conduction (C) Convection (D) Both (B) & (C)
Last Answer : A) Radiation
Description : Heat transfer to the water wall in a high pressure water wall type boiler furnace is mainly by (A) Conduction (B) Convection (C) Radiation (D) Both 'a' & 'b'
Last Answer : Option C
Description : 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 ... Radiation heat transfer by increasing the temperature and reducing the emissivity (D) None of these
Description : 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 ... under natural convection conditions, the velocity profile in air, normal to the plate, exhibits a maximum
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