McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 201. |
Boiling point elevation for a strong and concentrated solution is found by Duhring's rule, which states that at the same pressure, the boiling point of a solution is a linear function of the __________ of pure water. |
| A. | Boiling point |
| B. | Dynamic viscosity |
| C. | Kinematic viscosity |
| D. | Density |
| Answer» A. Boiling point | |
| 202. |
In case of heat flow by conduction for a cylindrical body with an internal heat source, the nature of temperature distribution is |
| A. | Linear |
| B. | Hyperbolic |
| C. | Parabolic |
| D. | None of these |
| Answer» C. Parabolic | |
| 203. |
The average heat transfer co-efficient over the entire length of the plate (ha) and the local heat transfer co-efficient (hL), in case of heat transfer over a flat plate in laminar zone is related as |
| A. | ha = 0.8hL |
| B. | ha = 2hL |
| C. | ha = hL |
| D. | ha = 5hL |
| Answer» B. ha = 2hL | |
| 204. |
Which has the lowest Prandtl number? |
| A. | Liquid metal |
| B. | Aqueous solution |
| C. | Water |
| D. | Lube oil |
| Answer» A. Liquid metal | |
| 205. |
Stefan-Boltzmann law which describes the radiation heat transfer states that, it is proportional to (where, t = temperature in °C T = absolute temperature in ° K) |
| A. | t4 |
| B. | T4 |
| C. | 1/t4 |
| D. | 1/T4 |
| Answer» B. T4 | |
| 206. |
The ratio of velocity head to tube side return loss in case of a multipass shell and tube heat exchanger is |
| A. | 2 |
| B. | 1/2 |
| C. | 4 |
| D. | 1/4 |
| Answer» D. 1/4 | |
| 207. |
The equation, (NSt × N 2/3 Pr) = f/2, is the __________ analogy. |
| A. | Colburn |
| B. | Reynolds |
| C. | Prandtl |
| D. | None of these |
| Answer» A. Colburn | |
| 208. |
What is the geometric mean of two heat transfer areas A1 and A2? |
| A. | √(A1 . A2) |
| B. | √(A1 + A2) |
| C. | ½ √(A1 . A2) |
| D. | 2 √(A1 . A2) |
| Answer» A. √(A1 . A2) | |
| 209. |
The range of electromagnetic spectrum important in heat transfer by radiation is __________ microns. |
| A. | 0.38-0.78 |
| B. | 0.5-50 |
| C. | 100-1000 |
| D. | 5-50 |
| Answer» B. 0.5-50 | |
| 210. |
Stefan's block body radiation law can also be derived from __________ law. |
| A. | Kirchoff’s |
| B. | Planck's |
| C. | Fourier's |
| D. | None of these |
| Answer» B. Planck's | |
| 211. |
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 |
| Answer» A. Boiling point (at the same pressure) | |
| 212. |
Sensible heat absorbed by 1 lb of water when it is heated from 32 to 212°F may be around __________ BTU. |
| A. | 180 |
| B. | 970 |
| C. | 3.97 |
| D. | Data insufficient, can't be predicted |
| Answer» A. 180 | |
| 213. |
Prandtl number for most of dry gases is about |
| A. | 0.001 |
| B. | 0.72 |
| C. | 70 |
| D. | 150 |
| Answer» B. 0.72 | |
| 214. |
Pick out the wrong statement. |
| A. | The emissivity of a surface decreases, if it gets corroded by atmospheric environment |
| B. | The emissivity of a surface increases with increase in surface roughness |
| C. | The emissivity of a polished surface is quite low |
| D. | The emissivity of a non-metallic surface decreases with increase in the temperature |
| Answer» A. The emissivity of a surface decreases, if it gets corroded by atmospheric environment | |
| 215. |
Extremely large or small volumes of fluids are generally best routed through the shell side of a shell and tube heat exchanger, because of the |
| A. | Less corrosion problems |
| B. | Flexibility possible in the baffle arrangement |
| C. | Low pressure drop |
| D. | High heat transfer co-efficient |
| Answer» B. Flexibility possible in the baffle arrangement | |
| 216. |
Fresh orange juice contains 12% (by weight) solids and the rest water 90% of the fresh juice is sent to an evaporator to remove water and subsequently mixed with the remaining 10% of fresh juice. The resultant product contains 40% solids. The kg of water removed from 1 kg fresh juice is |
| A. | 0.4 |
| B. | 0.5 |
| C. | 0.6 |
| D. | 0.7 |
| Answer» D. 0.7 | |
| 217. |
The purpose of providing expansion bellows in the shell of tubular exchanger is to |
| A. | Increase the heating load |
| B. | Impart structural strength |
| C. | Account for the uneven expansion of shell and tube bundles |
| D. | Facilitate increase of shell length, if needed |
| Answer» C. Account for the uneven expansion of shell and tube bundles | |
| 218. |
An equipment which converts the latent or sensible heat of one fluid into the latent heat of vaporisation of another, is called a |
| A. | Boiler |
| B. | Heat exchanger |
| C. | Recuperator |
| D. | Regenerator |
| Answer» B. Heat exchanger | |
| 219. |
Multipass heat exchangers are used |
| A. | Because of simplicity of fabrication |
| B. | For low heat load |
| C. | To obtain higher heat transfer co-efficient and shorter tube |
| D. | To reduce the pressure drop |
| Answer» C. To obtain higher heat transfer co-efficient and shorter tube | |
| 220. |
A black body does not __________ radiation. |
| A. | Absorb or emit |
| B. | Refract |
| C. | Reflect |
| D. | Both (B) & (C) |
| Answer» D. Both (B) & (C) | |
| 221. |
It is not recommended to use a 1-2 shell and tube heat exchanger for a particular heat duty, whenever the LMTD correction factor is |
| A. | > 0.75 |
| B. | < 0.75 |
| C. | < 0.50 |
| D. | < 0.25 |
| Answer» B. < 0.75 | |
| 222. |
Multiple effect evaporation accounts for |
| A. | Steam economy |
| B. | Lower operating costs |
| C. | Investment economy |
| D. | None of these |
| Answer» A. Steam economy | |
| 223. |
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 |
| Answer» A. Give larger area per tube | |
| 224. |
Tube expansion allowances exist in __________ heat exchanger. |
| A. | Multipass fixed tube sheet |
| B. | U-tube |
| C. | Single pass fixed tube sheet |
| D. | None of these |
| Answer» B. U-tube | |
| 225. |
Fruit juice (a heat sensitive material) can be concentrated in a __________ evaporator. |
| A. | Long tube |
| B. | Falling film |
| C. | High pressure |
| D. | None of these |
| Answer» B. Falling film | |
| 226. |
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 |
| D. | A body at 925 K emits an energy of 1.42 x 1011ζW/m2 (ζ is the Stefan-Boltzmann constant) in the wavelength band between 3 μm to 4 μm. The fraction of this energy in the total energy emitted over the entire wavelength range is equal to emissivity |
| 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 | |
| 227. |
The Sieder-Tate correlation for heat transfer in turbulent flow in pipe gives Nu α Re0.8 , where, Nu is the Nusselt number and Re is the Reynolds number for the flow. Assuming that this relation is valid, the heat transfer co-efficient varies with the pipe diameter (D) as |
| A. | D-1.8 |
| B. | D-0.2 |
| C. | D0.2 |
| D. | D1.8 |
| Answer» B. D-0.2 | |
| 228. |
Minimum recommended baffle spacing in a shell and tube heat exchanger is about (where, D = shell diameter). |
| A. | 0.2 D |
| B. | 0.5 D |
| C. | 0.66 D |
| D. | 0.80 D |
| Answer» A. 0.2 D | |
| 229. |
For heat flow through very thick walled cylinder, use _________mean radius. |
| A. | Arithmetic |
| B. | Logarithmic |
| C. | Geometric |
| D. | Either (A) or (C) |
| Answer» B. Logarithmic | |
| 230. |
Corrosiveness of steam condensate is due to the presence of |
| A. | CO2 |
| B. | Dissolved O2 |
| C. | Both (A) & (B) |
| D. | Neither (A) nor (B) |
| Answer» C. Both (A) & (B) | |
| 231. |
In a shell and tube heat exchanger, the shell side fluid velocity can‟t be changed by changing the |
| A. | Tube layout |
| B. | Tube diameter |
| C. | Tube pitch |
| D. | Number of baffles |
| Answer» B. Tube diameter | |
| 232. |
Solid angle subtended by the finite surface at the radiating element is |
| A. | Called the view factor |
| B. | Called the angle of vision |
| C. | Proportional to the square of the distance between surfaces |
| D. | Expressed in terms of radians |
| Answer» B. Called the angle of vision | |
| 233. |
LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counter-flow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface area required is the least in the __________ flow. |
| A. | Parallel |
| B. | Mixed |
| C. | Counter flow |
| D. | Same in either 'a', b' or 'c' |
| Answer» D. Same in either 'a', b' or 'c' | |
| 234. |
A sphere of radius 'R1' is enclosed in a sphere of radius 'R2'. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is |
| A. | 0 |
| B. | R2/(R1+R2) |
| C. | 1 |
| D. | (R1/R2) 2 |
| Answer» B. R2/(R1+R2) | |
| 235. |
The maximum heat transfer co-efficient from steam heating will be attained when the steam is: |
| A. | Supersaturated |
| B. | Saturated |
| C. | Wet |
| D. | None of these |
| Answer» B. Saturated | |
| 236. |
One kilogram of water at 0°C is changed to superheated steam of one atm pressure and 300° C. The major heat consumption in the process will be to |
| A. | Heat the water from 0°C to 100°C |
| B. | Evaporate the water |
| C. | To superheat the steam |
| D. | Data insufficient, can't be predicted |
| Answer» B. Evaporate the water | |
| 237. |
The film co-efficient is decreased due to the presence of non-condensing gases in the vapors. The film co-efficient of superheated vapor as compared to that of saturated vapor is |
| A. | More |
| B. | Less |
| C. | Some |
| D. | Either more or less; depends on the nature of vapor |
| Answer» C. Some | |
| 238. |
The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are |
| A. | Re.Gz |
| B. | Nu, Pr |
| C. | Nu, Pr, Re |
| D. | Nu, Gz |
| Answer» D. Nu, Gz | |
| 239. |
Which of the following has maximum thermal conductivity? |
| A. | Iron |
| B. | Coal |
| C. | Nitrogen |
| D. | Tar |
| Answer» A. Iron | |
| 240. |
In case of heat transfer by conduction in a hollow cylinder, __________ mean area is used to calculate the heat transfer rate. |
| A. | Geometric |
| B. | Arithmetic |
| C. | Logarithmic |
| D. | Either (A), (B) or (C) |
| Answer» C. Logarithmic | |
| 241. |
The absorptivity of a grey body at a given temperature __________ with increasing wavelength of radiation. |
| A. | Increases |
| B. | Decreases |
| C. | Remain constant |
| D. | May increase or decrease; depends on the material |
| Answer» D. May increase or decrease; depends on the material | |
| 242. |
Thermal diffusivity of a material |
| A. | Has the unit m2/sec |
| B. | Is defined as K/ρ . Cp |
| C. | Is the ratio of thermal conductivity to thermal capacity |
| D. | All (A), (B) and (C) |
| Answer» D. All (A), (B) and (C) | |
| 243. |
Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator? |
| A. | Long vertical evaporator |
| B. | Horizontal tube evaporator |
| C. | Agitated film evaporator |
| D. | Calandria vertical tube evaporator |
| Answer» C. Agitated film evaporator | |
| 244. |
Nusselt number is the ratio of the temperature gradient at the wall to |
| A. | Temperature difference |
| B. | Heat flux |
| C. | That across the entire pipe |
| D. | None of these |
| Answer» C. That across the entire pipe | |
| 245. |
Which of the following has the lowest overall heat transfer co-efficient? |
| A. | Dowtherm |
| B. | Molten sodium |
| C. | Water |
| D. | Air |
| Answer» D. Air | |
| 246. |
What is the unit of thermal conductivity? |
| A. | Kcal/hr. m2°C |
| B. | Kcal/hr.m.°C |
| C. | Kcal/hr.m |
| D. | Kcal/hr. °C |
| Answer» B. Kcal/hr.m.°C | |
| 247. |
Indirect contact heat exchangers are preferred over direct contact heat exchangers, because |
| A. | Heat transfer co-efficient are high |
| B. | There is no risk of contamination |
| C. | There is no mist formation |
| D. | Cost of equipment is lower |
| Answer» B. There is no risk of contamination | |
| 248. |
Tubes are held between top and bottom tube sheets in Calandria type evaporator by keeping |
| A. | Both the tube sheets fixed |
| B. | Both the tube sheets floating |
| C. | The top tube sheet floating and bottom tube sheet fixed |
| D. | The top tube sheet fixed and the bottom tube-sheet floating |
| Answer» A. Both the tube sheets fixed | |
| 249. |
Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipe is negligible, if the value of Prandtl number is |
| A. | 0.2 |
| B. | 0.4 |
| C. | 0.6 |
| D. | 0.8 |
| Answer» C. 0.6 | |
| 250. |
What is the emissivity of a black body? |
| A. | 0 |
| B. | 1 |
| C. | 0.5 |
| D. | 0.90 |
| Answer» B. 1 | |
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