McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 151. |
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 |
| Answer» C. Mixed convection (both free and forced) | |
| 152. |
"The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium". This is __________ law. |
| A. | Kirchoff’s |
| B. | Planck's |
| C. | Wien's displacement |
| D. | Stefan-Boltzmann |
| Answer» A. Kirchoff’s | |
| 153. |
The units of resistance to heat transfer is |
| A. | J.m-2.K-1 |
| B. | J.m-1.K-1 |
| C. | W.m-2.K-1 |
| D. | W-1m2K |
| Answer» D. W-1m2K | |
| 154. |
For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is |
| A. | Nu = 0.023 Re0.8. Pr0.4 |
| B. | Nu = (π/2) Gz |
| C. | Nu = (2/π) Gz |
| D. | Nu = 2Gz0.5 |
| Answer» C. Nu = (2/π) Gz | |
| 155. |
For hot feed, forward feeding as compared to backward feeding results in __________ economy. |
| A. | Increased |
| B. | Decreased |
| C. | No effect on |
| D. | None of these |
| Answer» A. Increased | |
| 156. |
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 |
| Answer» D. The Colburn jH factor for heat transfer is given by Nst Npr | |
| 157. |
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 |
| Answer» B. Temperature of the heating surface is more than the boiling point of the liquid | |
| 158. |
Which is the best tube arrangement (in a shell and tube heat exchanger) if the fluids are clean and non-fouling? |
| A. | Square pitch |
| B. | Triangular pitch |
| C. | Diagonal square pitch |
| D. | None of these |
| Answer» B. Triangular pitch | |
| 159. |
Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer cannot take place |
| A. | Between two bodies in physical contact with each other |
| B. | Between two bodies not in physical contact with each other |
| C. | From one part of a body to the another part of the same body |
| D. | Both 'b' & 'c' |
| Answer» B. Between two bodies not in physical contact with each other | |
| 160. |
A multiple effect evaporator as compared to a single effect evaporator of the same capacity has |
| A. | Lower heat transfer area |
| B. | Lower steam economy |
| C. | Higher steam economy |
| D. | Higher solute concentration in the product |
| Answer» C. Higher steam economy | |
| 161. |
The thickness of condensate layer in filmwise condensation depends on the |
| A. | Condensation rate |
| B. | Surface configuration |
| C. | Liquid flow rate from the surface |
| D. | All (A), (B) and (C) |
| Answer» D. All (A), (B) and (C) | |
| 162. |
With increase in temperature, the total emissivity of conductors |
| A. | Increases |
| B. | Decreases |
| C. | Remain same |
| D. | Decreases linearly |
| Answer» A. Increases | |
| 163. |
Steam economy in case of a triple effect evaporator will be |
| A. | 1 |
| B. | < 1 |
| C. | > 1 |
| D. | Between 0 and 1 |
| Answer» C. > 1 | |
| 164. |
Dittus-Boelter equation used for the determination of heat transfer co-efficient 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 |
| Answer» B. For fluids in turbulent flow | |
| 165. |
In a forward feed multiple effect evaporator unit |
| A. | Viscosity of liquid is highest in first effect |
| B. | Transfer from effect to effect is done by pumps |
| C. | No pump is required to withdraw the product from the last effect |
| D. | None of these |
| Answer» D. None of these | |
| 166. |
In a shell and tube heat exchanger, floating head is used for |
| A. | Large temperature differentials |
| B. | High heat transfer co-efficient |
| C. | Low pressure drop |
| D. | Less corrosion of tubes |
| Answer» A. Large temperature differentials | |
| 167. |
The heat transfer co-efficient in film type condensation is __________ that for dropwise condensation. |
| A. | Greater than |
| B. | Lower than |
| C. | Is same as |
| D. | Half |
| Answer» B. Lower than | |
| 168. |
Resistance to heat flow by conduction is proportional to (where, t & ρ are thickness & density of the material respectively and A = area normal to the direction of heat flow.) |
| A. | t |
| B. | 1/ρ |
| C. | 1/A |
| D. | All (A), (B) & (C) |
| Answer» D. All (A), (B) & (C) | |
| 169. |
Dropwise condensation is promoted on a/an __________ surface. |
| A. | Glazed |
| B. | Oily |
| C. | Coated |
| D. | Smooth |
| Answer» B. Oily | |
| 170. |
Maximum heat transfer rate is obtained in __________ flow. |
| A. | Laminar |
| B. | Turbulent |
| C. | Creeping |
| D. | Transition region |
| Answer» B. Turbulent | |
| 171. |
Which of the following parameters of the fluid is not very important, while deciding its route in a shell and tube heat exchanger? |
| A. | Corrosiveness & fouling characteristics |
| B. | Pressure |
| C. | Viscosity |
| D. | Density |
| Answer» D. Density | |
| 172. |
In case of a super-cooled solution, which is on the verge of crystallisation, the free energy of the solution as compared to that of the solid is |
| A. | More |
| B. | Less |
| C. | Same |
| D. | More or less; depends on the nature of solution |
| Answer» A. More | |
| 173. |
It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is |
| A. | 3.06 × 105 |
| B. | 6.12 × 105 |
| C. | 7.24 × 105 |
| D. | 9.08 × 105 |
| Answer» A. 3.06 × 105 | |
| 174. |
In a single evaporator system, the steam economy __________ by creating vacuum in the evaporator. |
| A. | Increases |
| B. | Decreases |
| C. | Remain constant |
| D. | May increase or decrease, depends on the vacuum |
| Answer» A. Increases | |
| 175. |
Fqra cold viscous feed, backward feed gives __________ than forward feed. |
| A. | A higher capacity |
| B. | A lower capacity |
| C. | Lower economy |
| D. | None of these |
| Answer» A. A higher capacity | |
| 176. |
Cpµ/K is termed as the __________ number. |
| A. | Grashoff |
| B. | Nusselt |
| C. | Prandtl |
| D. | Stanton |
| Answer» C. Prandtl | |
| 177. |
The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m2.K. The fouling factor after one year of operation is found to be hd0 = 2000W/m2.K. The overall heat transfer co-efficient at this time is |
| A. | 1200 W/m2.K |
| B. | 894 W/m2.K |
| C. | 333 W/m2.K |
| D. | 287 W/m2.K |
| Answer» C. 333 W/m2.K | |
| 178. |
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 |
| Answer» D. Heat transfer in laminar flow | |
| 179. |
At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe? |
| A. | 0.5 |
| B. | < 0.5 |
| C. | > 0.6 |
| D. | < 0.1 |
| Answer» C. > 0.6 | |
| 180. |
The unit of conductance in SI unit is |
| A. | W/m |
| B. | W/m2 |
| C. | W/°K |
| D. | W/m°K |
| Answer» C. W/°K | |
| 181. |
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 |
| Answer» B. Thermal conductivity of a dry material is more than that of the damp material | |
| 182. |
Pick out the correct statement. |
| A. | Higher is the temperature of the radiating body, higher is the wavelength of radiation |
| B. | Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder |
| C. | The wavelength corresponding to maximum mono-chromatic emissive power increases with rise in temperature |
| D. | Solid angle subtended by the finite surface at the radiating element is called the angle of incidence |
| Answer» B. Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder | |
| 183. |
Nucleate boiling is promoted |
| A. | On polished surfaces |
| B. | On rough surfaces |
| C. | In the absence of agitation |
| D. | None of these |
| Answer» B. On rough surfaces | |
| 184. |
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 |
| Answer» A. Molten sodium (a coolant used in fast breeder reactor) | |
| 185. |
The thermal boundary layer at NPr > 1 |
| A. | Is thicker than hydrodynamic boundary layer |
| B. | Is thinner than hydrodynamic boundary layer |
| C. | And the hydrodynamic boundary layers are identical |
| D. | Disappears |
| Answer» B. Is thinner than hydrodynamic boundary layer | |
| 186. |
In case of a multipass shell and tube heat exchanger, the temperature drop in the fluid |
| A. | Is inversely proportional to the resistance across which the drop occurs |
| B. | And the wall are proportional to individual resistances |
| C. | And the wall is not related |
| D. | None of these |
| Answer» B. And the wall are proportional to individual resistances | |
| 187. |
Which of the following is directly concerned with the heat transfer? |
| A. | Strouhal number |
| B. | Sherwood number |
| C. | Euler number |
| D. | Grashoff number |
| Answer» D. Grashoff number | |
| 188. |
The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the |
| A. | Solution has an elevation of boiling point |
| B. | Evaporators operate under vacuum |
| C. | Evaporators operate at atmospheric pressure |
| D. | None of these |
| Answer» A. Solution has an elevation of boiling point | |
| 189. |
The equation, Nst = f/2, is the __________ analogy. |
| A. | Colburn |
| B. | Reynolds |
| C. | Prandtl |
| D. | None of these |
| Answer» B. Reynolds | |
| 190. |
Nusselt number is a function of Prandtl number and __________ number of fluid in natural convection heat transfer. |
| A. | Grashoff |
| B. | Biot |
| C. | Stanton |
| D. | Reynolds |
| Answer» A. Grashoff | |
| 191. |
Forced circulation evaporators are normally used for concentrating liquids having |
| A. | Scaling characteristics |
| B. | High viscosity |
| C. | Both (A) & (B) |
| D. | Neither (A) nor (B) |
| Answer» C. Both (A) & (B) | |
| 192. |
Radiation energy is emitted by all the substances, which are above |
| A. | 0°K |
| B. | 0°C |
| C. | 100°C |
| D. | Room temperature |
| Answer» A. 0°K | |
| 193. |
View factor is important in heat transfer by |
| A. | Steady state conduction |
| B. | Natural convection |
| C. | Forced convection |
| D. | Radiation |
| Answer» D. Radiation | |
| 194. |
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 |
| Answer» B. Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature | |
| 195. |
'Duhring's plot' is of use in |
| A. | Extractive distillation |
| B. | Evaporation |
| C. | Leaching |
| D. | Absorption |
| Answer» B. Evaporation | |
| 196. |
The dimensionless group in mass transfer that is equivalent to Prandtl number in heat transfer is |
| A. | Nusselt number |
| B. | Sherwood number |
| C. | Schmidt number |
| D. | Stanton number |
| Answer» C. Schmidt number | |
| 197. |
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 |
| Answer» C. Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger | |
| 198. |
Loss of heat from untagged steam pipe to the ambient air is by |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | All (A), (B) & (C) |
| Answer» D. All (A), (B) & (C) | |
| 199. |
In Biot number, the characteristic length used is the ratio of the __________ of the solid. |
| A. | Volume to surface area |
| B. | Perimeter to surface area |
| C. | Surface area to volume |
| D. | Surface area to perimeter |
| Answer» A. Volume to surface area | |
| 200. |
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 |
| Answer» C. Radiation becomes important | |
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