Description : 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
Last Answer : (B) Vapour density
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 flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because (A) Convection becomes important (B) Conduction becomes important (C) Radiation becomes important (D) Sub-cooled boiling occurs
Last Answer : (C) Radiation becomes important
Description : For small temperature difference, the heat transfer rate as per Newton's law of cooling is proportional to (where, Δt = excess temperature) (A) Δt (B) Δt 2 (C) Δt 3 (D) √(Δt)
Last Answer : (A) Δt
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
Description : Upto the critical radius of insulation, added insulation, will (A) Increase the heat loss (B) Decrease heat loss and will have no effect beyond that (C) Decrease heat flux (D) Reduce convection heat loss compared to conduction heat less
Last Answer : Option B
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 convection heat transfer, if heat flux intensity is doubled then temperature difference between solid surface and fluid will ?
Last Answer : Get doubled.
Description : The concrete roof of a house is 10 m by 8 m and 10 cm thick (4"). Estimate the total heat the roof would absorb over the 12 day? a. 1.3 x 108 J b 2.3 x 108 J c. 3.3 x 108 J d. 4.3 x 108 J formula: ΔQ = ΔQ/Δtx Δt
Last Answer : 1.3 x 108 J
Description : Utilizing the answer to the previous problem, estimate the overall or average increase in temperature ( ΔT) of the concrete roof from the energy absorbed from the sun during a12hour day. Assume that all of the radiation absorbed goes into ... °C b. 8.9°C c. 9.9°C d. 10.9°C formula: ΔQ = m c ΔT
Last Answer : 7.9 °C
Description : In a boiling curve, the peak heat flux is called the __________ point. (A) Nusselt (B) Leidenfrost (C) Boiling (D) Burnout
Last Answer : (D) Burnout
Description : In the equation Q = UAΔt; Δt is (A) Geometric mean temperature difference (B) Arithmetic mean temperature difference (C) Logarithmic mean temperature difference (D) The difference of average bulk temperatures of hot and cold fluids
Last Answer : (C) Logarithmic mean temperature difference
Description : In pipe flow, heat is transferred from hot wall to the liquid by(A) Conduction only (B) Forced convection only (C) Forced convection and conduction (D) Free and forced convection
Last Answer : (C) Forced convection and conduction
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 : 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 : 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
Description : When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling. (A) Pool (B) Nucleate (C) Transition (D) Film
Last Answer : (D) Film
Description : 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
Last Answer : (B) Local
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 : Magnitude of induced e.m.f is proportional to A. rate of change of current B. rate of change of voltage C. rate of change of magnetic flux linkage D. rate of change of resistance
Last Answer : rate of change of magnetic flux linkage
Description : Hall voltage is directly proportional to A. current B. electric field C. magnetic flux density D. all of above
Last Answer : magnetic flux density
Description : The inductance is proportional to the ratio of flux to current. State True/False. a) True b) False
Last Answer : a) True
Description : The magnetic flux density is directly proportional to the magnetic field intensity. State True/False. a) True b) False
Description : 27] In a transformer, the leakage flux of each winding is proportional to the current in that winding because A. Ohm's law applies to magnetic circuits B. Leakage paths do no saturate C. the two windings are electrically isolated D. mutual flux is confined to the core
Last Answer : B. Leakage path do not saturate
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
Description : The terminal velocity of a particle moving through a fluid varies as dp n . What is the value of n' for Newton's law regime? (A) 0.5 (B) 1 (C) 1.5 (D) 3
Last Answer : (A) 0.5
Description : The terminal velocity of a particle moving through a fluid varies as dp n . The value of n is equal to __________ in Stoke's law regime. (A) 1 (B) 0.5 (C) 2 (D) 1.5
Last Answer : (C) 2
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 : 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 : 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 : 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 : 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 : 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 : 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 : In natural convection heat transfer, the correlating parameter is the (A) Graetz number (B) Eckert number (C) Grashoff number (D) Bond number
Last Answer : (C) Grashoff number
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
Last Answer : (D) None of these
Description : Loss of heat from untagged steam pipe to the ambient air is by (A) Conduction (B) Convection (C) Radiation (D) All (A), (B) & (C)
Last Answer : (D) All (A), (B) & (C)
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 : 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 : 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 : 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 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 : 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
Description : Heat transfer by __________ may not necessarily require the presence of a medium. (A) Conduction (B) Natural convection (C) Forced convection (D) Radiation