McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 301. |
Economy of a multiple effect evaporator depends upon the |
| A. | Heat balance consideration |
| B. | Rate of heat transfer |
| C. | Both (A) and (B) |
| D. | Neither (A) nor (B) |
| Answer» A. Heat balance consideration | |
| 302. |
The main purpose of providing fins on heat transfer surface is to increase the |
| A. | Temperature gradient |
| B. | Mechanical strength of the equipment |
| C. | Heat transfer area |
| D. | Heat transfer co-efficient |
| Answer» C. Heat transfer area | |
| 303. |
Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is __________ law. |
| A. | Stefan's |
| B. | Dalton's |
| C. | Wien's |
| D. | Kirchoff’s |
| Answer» C. Wien's | |
| 304. |
Trap is used to remove __________ from steam pipe lines. |
| A. | Steam |
| B. | Condensate |
| C. | Non-condensable |
| D. | None of these |
| Answer» B. Condensate | |
| 305. |
Prandtl number is given by |
| A. | CP µ/a |
| B. | hD/k |
| C. | CP µ/k |
| D. | µ/h CP |
| Answer» C. CP µ/k | |
| 306. |
Pick out the wrong statement: |
| A. | With change in temperature, the radiant energy emitted by a black body remains unchanged |
| B. | Absorptivity of a body approaches unity in case of diffuse reflection |
| C. | Absorptivity of a perfectly black body is unity |
| D. | Value of Stefan-Boltzmann constant is 4.876 × 10-8 KCal/m2 .hr.°K4 |
| Answer» A. With change in temperature, the radiant energy emitted by a black body remains unchanged | |
| 307. |
Prandtl number is the ratio of |
| A. | Momentum diffusivity to mass diffusivity |
| B. | Momentum diffusivity to thermal diffusivity |
| C. | Thermal diffusivity to mass diffusivity |
| D. | Thermal diffusivity to momentum diffusivity |
| Answer» B. Momentum diffusivity to thermal diffusivity | |
| 308. |
In the free convection regime of pool boiling, the heat flux is proportional to |
| A. | Δt1/2 |
| B. | Δt2 |
| C. | Δt5/4 |
| D. | Δt |
| Answer» C. Δt5/4 | |
| 309. |
Radiation heat losses from satisfactorily insulated high pressure boiler may be about __________ percent. |
| A. | 1 |
| B. | 7 |
| C. | 18 |
| D. | 26 |
| Answer» B. 7 | |
| 310. |
When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling. |
| A. | Pool |
| B. | Nucleate |
| C. | Transition |
| D. | Film |
| Answer» D. Film | |
| 311. |
In SI units, fouling factor is expressed in |
| A. | m2°K/W |
| B. | W/m2°K |
| C. | m2°K |
| D. | m°K/W |
| Answer» A. m2°K/W | |
| 312. |
Kg of liquid evaporated per hour in an evaporator is defined as its |
| A. | Capacity |
| B. | Economy |
| C. | Steam load |
| D. | None of these |
| Answer» A. Capacity | |
| 313. |
The left face of a one dimensional slab of thickness 0.2 m is maintained at 80°C and the right face is exposed to air at 30°C. The thermal conductivity of the slab is 1.2 W/m.K and the heat transfer co-efficient from the right face is 10 W/m2 .K. At steady state, the temperature of the right face in °C is |
| A. | 77.2 |
| B. | 71.2 |
| C. | 63.8 |
| D. | 48.7 |
| Answer» D. 48.7 | |
| 314. |
In forced convection, the heat transfer depends on |
| A. | Re, Pr |
| B. | Re, Gr |
| C. | Mainly Gr |
| D. | Re only |
| Answer» A. Re, Pr | |
| 315. |
Agitated film evaporator is suitable for concentrating __________ liquids. |
| A. | Foaming |
| B. | Viscous |
| C. | Very thin |
| D. | Corrosive |
| Answer» B. Viscous | |
| 316. |
A composite flat wall of a furnace is made of two materials 'A' and 'B'. The thermal conductivity of 'A' is twice of that of material 'B', while the thickness of layer of 'A' is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material 'A' is |
| A. | 125 |
| B. | 133 |
| C. | 150 |
| D. | 160 |
| Answer» D. 160 | |
| 317. |
Kirchoff's law is applicable to |
| A. | Monochromatic radiation only |
| B. | Total radiation only |
| C. | Both (A) and (B) |
| D. | Only volumes and not to surfaces |
| Answer» C. Both (A) and (B) | |
| 318. |
The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is 8 kW/m2 . The flux, when the element temperature is increased to 1000°C for the same furnace temperature is |
| A. | 11.2 kW/m2 |
| B. | 12.0 kW/m2 |
| C. | 14.6 kW/m2 |
| D. | 16.5 kW/m2 |
| Answer» D. 16.5 kW/m2 | |
| 319. |
With increase in temperature, the thermal conductivity of non-metallic amorphous solids |
| A. | Decreases |
| B. | Increases |
| C. | Remain constant |
| D. | First decreases upto certain temperature and then increases |
| Answer» B. Increases | |
| 320. |
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) |
| Answer» D. All (A), (B) and (C) | |
| 321. |
A black body when hot, emits heat radiation of __________ wavelengths. |
| A. | Small |
| B. | Large |
| C. | All |
| D. | One fixed |
| Answer» C. All | |
| 322. |
Tube pitch is the __________ of tube diameters and the clearances. |
| A. | Sum |
| B. | Difference |
| C. | Ratio |
| D. | None of these |
| Answer» A. Sum | |
| 323. |
In Joule's experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms-2 . Neglecting the heat capacity of agitator, the temperature of water (in °C) is |
| A. | 40.5 |
| B. | 34.4 |
| C. | 26.8 |
| D. | 25 |
| Answer» B. 34.4 | |
| 324. |
Heat transfer rate per unit area is called |
| A. | Thermal conductivity |
| B. | Heat flux |
| C. | Heat transfer co-efficient |
| D. | Thermal diffusivity |
| Answer» B. Heat flux | |
| 325. |
The unit of heat transfer co-efficient is |
| A. | BTU/hr. ft2°F |
| B. | BTU/hr. °F. ft |
| C. | BTU/hr. °F |
| D. | BTU/hr. ft |
| Answer» A. BTU/hr. ft2°F | |
| 326. |
The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are |
| A. | (COP)R = (COP)HP = 0.6 |
| B. | (COP)R = 2.5; (COP)HP = 1.5 |
| C. | (COP)R = 1.5; (COP)HP = 2.5 |
| D. | (COP)R = (COP)HP = 2.5 |
| Answer» C. (COP)R = 1.5; (COP)HP = 2.5 | |
| 327. |
For what value of Prandtl number, the Col-burn analogy is valid? |
| A. | 0.06 to 120 |
| B. | 0.6 to 120 |
| C. | 1 to 103 |
| D. | 1 to 50 |
| Answer» B. 0.6 to 120 | |
| 328. |
Natural convection is characterised by |
| A. | Grashoff number |
| B. | Peclet number |
| C. | Reynolds number |
| D. | Prandtl number |
| Answer» A. Grashoff number | |
| 329. |
Colburn analogy is applicable for the value of Prandtl number from |
| A. | 0.001 to 1 |
| B. | 0.6 to 120 |
| C. | 0.5 to 5 |
| D. | 120 to 400 |
| Answer» B. 0.6 to 120 | |
| 330. |
A process stream of dilute aqueous solution flowing at the rate of10 Kg.s-1 is to be heated. Steam condensate at 95°C is available for heating purpose, also at a rate of 10 Kg.s-1 . A 1 - 1 shell and tube heat exchanger is available. The best arrangement is |
| A. | Counter flow with process stream on shell side |
| B. | Counter flow with process stream on tube side |
| C. | Parallel flow with process stream on shell side |
| D. | Parallel flow with process stream on tube side |
| Answer» A. Counter flow with process stream on shell side | |
| 331. |
The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of 'a' in SI system will be |
| A. | W/m.k |
| B. | W/m |
| C. | W/m.k2 |
| D. | None, 'a' is just a number |
| Answer» C. W/m.k2 | |
| 332. |
Heat exchanger tubes are never made of |
| A. | Plain carbon steel |
| B. | Stainless steel |
| C. | Lead |
| D. | Copper |
| Answer» C. Lead | |
| 333. |
Presence of a non-condensing gas in a condensing vapour |
| A. | Increases the rate of condensation |
| B. | Decreases thermal resistance |
| C. | Is desirable to increase the film co-efficient |
| D. | None of these |
| Answer» D. None of these | |
| 334. |
The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient at inside of the pipe) |
| A. | K/h0 |
| B. | 2K/h0 |
| C. | hi/K |
| D. | 2hi/K |
| Answer» A. K/h0 | |
| 335. |
Multiple effect evaporators are commonly used in the manufacture of P. Paper Q. Superphosphate R. Sugar S. Fats |
| A. | P and Q |
| B. | P and R |
| C. | P and S |
| D. | R and S |
| Answer» C. P and S | |
| 336. |
In natural convection heat transfer, the correlating parameter is the |
| A. | Graetz number |
| B. | Eckert number |
| C. | Grashoff number |
| D. | Bond number |
| Answer» C. Grashoff number | |
| 337. |
Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is |
| A. | Finned tube heat exchanger with air inside and steam outside |
| B. | Finned tube heat exchanger with air outside and steam inside |
| C. | Shell and tube heat exchanger with air inside tubes and steam on shell side |
| D. | Shell and tube heat exchanger with air on shell side and steam inside tubes |
| Answer» B. Finned tube heat exchanger with air outside and steam inside | |
| 338. |
In a multiple effect evaporator, the effect of boiling point elevation is to |
| A. | Reduce the capacity |
| B. | Reduce the economy |
| C. | Increase the economy |
| D. | None of these |
| Answer» A. Reduce the capacity | |
| 339. |
Correction is applied to LMTD for __________ flow. |
| A. | Parallel |
| B. | Counter |
| C. | Cross |
| D. | None of these |
| Answer» C. Cross | |
| 340. |
The heat flux in the nucleate boiling regimes is proportional to (where, ΔT = excess temperature) |
| A. | (ΔT)2 |
| B. | (ΔT)4 |
| C. | (ΔT)3 |
| D. | √(ΔT) |
| Answer» C. (ΔT)3 | |
| 341. |
Increasing the liquor level in the evaporator results in the |
| A. | Decreased capacity |
| B. | Increase in liquor film co-efficient |
| C. | Decreased effect of hydrostatic head |
| D. | Increased true temperature drop |
| Answer» A. Decreased capacity | |
| 342. |
In case of a vertical tube evaporator, with increase in the liquor level, the __________ is increased. |
| A. | Velocity of circulation |
| B. | Liquor-film co-efficient |
| C. | Both (A) and (B) |
| D. | Neither (A) and (B) |
| Answer» D. Neither (A) and (B) | |
| 343. |
In case of a shell and tube heat exchanger, the minimum and maximum baffle spacing is respectively (where, D = inside diameter of the shell) |
| A. | D/5 and D |
| B. | D/2 and 2 D |
| C. | D/4 and 2 D |
| D. | D and 2 D |
| Answer» A. D/5 and D | |
| 344. |
Pick out the wrong statement. |
| A. | The controlling resistance in case of heating of air by condensing steam is in the air film |
| B. | The log mean temperature difference (LMTD) for counter flow and parallel flow can be theoretically same when any one of the fluids (hot or cold fluid) passes through the heat exchanger at constant temperature |
| C. | In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs |
| D. | Phase change in case of a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature |
| Answer» C. In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs | |
| 345. |
Double pipe heat exchangers are used |
| A. | When heat transfer area required is very high |
| B. | When heat transfer area required is very low, i.e. (100-200 ft2). |
| C. | Because it occupies less floor area |
| D. | Because it is less costly |
| Answer» B. When heat transfer area required is very low, i.e. (100-200 ft2). | |
| 346. |
Sensible heat of hot industrial flue gases cannot be recovered by a/an |
| A. | Economiser |
| B. | Regenerator |
| C. | Ceramic recuperator |
| D. | None of these |
| Answer» D. None of these | |
| 347. |
A body is called grey if the monochromatic emissivity of the body is |
| A. | Zero |
| B. | Unity |
| C. | Same for all wavelengths |
| D. | Different for all wavelengths |
| Answer» C. Same for all wavelengths | |
| 348. |
A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2 .°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be |
| A. | Greater than that for un-insulated steam pipe |
| B. | Less than that of the un-insulated steam pipe |
| C. | Equal to that of the un-insulated steam pipe |
| D. | Less than the steam pipe with 5 cms insulation |
| Answer» B. Less than that of the un-insulated steam pipe | |
| 349. |
While the total emissivity of a perfect black body is unity, the same for a real body is |
| A. | 0 |
| B. | 1 |
| C. | > 1 |
| D. | Between 0 and 1 |
| Answer» D. Between 0 and 1 | |
| 350. |
In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of |
| A. | Concentrations |
| B. | Chemical potentials |
| C. | Activity co-efficients |
| D. | Mass transfer co-efficients |
| Answer» A. Concentrations | |
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