McqMate
| 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 | |
| 351. |
Crystal size in a continuous crystalliser depends upon the |
| A. | Rate of heat transfer |
| B. | Degree of turbulence |
| C. | Degree of super-saturation |
| D. | All (A), (B) and (C) |
| Answer» D. All (A), (B) and (C) | |
| 352. |
The critical radius 'r' of insulation on a pipe is given by |
| A. | r = 2k/h |
| B. | r = k/h |
| C. | r = k/2h |
| D. | r = h/k |
| Answer» B. r = k/h | |
| 353. |
Boiling of milk in an open vessel is an example of __________ boiling. |
| A. | Film |
| B. | Sub-cooled |
| C. | Saturated nucleate |
| D. | None of these |
| Answer» A. Film | |
| 354. |
In an extended surface heat exchanger, fluid having lower co-efficient |
| A. | Flows through the tube |
| B. | Flows outside the tubes |
| C. | Can flow either inside or outside the tubes |
| D. | Should not be used as it gives very high pressure drop |
| Answer» B. Flows outside the tubes | |
| 355. |
Black liquor generated during paper manufacture is concentrated in a |
| A. | Single effect evaporator |
| B. | Single effect evaporator followed by a crystalliser |
| C. | Multiple effect evaporator |
| D. | Multiple effect evaporators followed by a crystalliser |
| Answer» C. Multiple effect evaporator | |
| 356. |
What is Nusselt number? |
| A. | CP. µ/k |
| B. | hD/k |
| C. | h. CP/µ |
| D. | CP. µ/h |
| Answer» B. hD/k | |
| 357. |
If h1 = inner film co-efficient and /h2 = outer film co-efficient, then the overall heat transfer co-efficient is |
| A. | Always less than h1 |
| B. | Always between h1 and h2 |
| C. | Always higher than h2 |
| D. | Dependent on metal resistance |
| Answer» B. Always between h1 and h2 | |
| 358. |
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 |
| Answer» C. Logarithmic mean temperature difference | |
| 359. |
Convective heat transfer, in which heat is transferred by movement of warmed matter is described by |
| A. | Fourier's law |
| B. | Newton's law of cooling |
| C. | Fick's law |
| D. | None of these |
| Answer» B. Newton's law of cooling | |
| 360. |
For a cold dilute feed to produce thick viscous liquor, backward feeding as compared to forward feeding results in |
| A. | Increased economy |
| B. | Decreased economy |
| C. | Lower capacity |
| D. | No effect on economy |
| Answer» A. Increased economy | |
| 361. |
Which of the following has the minimum absorptivity? |
| A. | Aluminium foil |
| B. | Coal dust |
| C. | Refractory bricks |
| D. | Iron plates |
| Answer» A. Aluminium foil | |
| 362. |
Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m3 /min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately |
| A. | 32 |
| B. | 37 |
| C. | 45 |
| D. | 50 |
| Answer» A. 32 | |
| 363. |
In a forward feed multiple effect, the pressure build up will be |
| A. | Least at the inlet of the first effect |
| B. | Least at the outlet of the last effect |
| C. | Highest at the inlet of the last effect |
| D. | Highest at the outlet of the last effect |
| Answer» B. Least at the outlet of the last effect | |
| 364. |
Graetz number is given by |
| A. | mCp/kL |
| B. | kL/mCp |
| C. | mCp/kµ |
| D. | kµ/mCp |
| Answer» A. mCp/kL | |
| 365. |
Thermal diffusivity is given by |
| A. | k/ρCp |
| B. | ρCp/k |
| C. | µCp/a |
| D. | µ/hCp |
| Answer» A. k/ρCp | |
| 366. |
The rate of heat transfer is a product of overall heat transfer co-efficient, the difference in temperature and the |
| A. | Heating volume |
| B. | Heat transfer area |
| C. | Nusselt number |
| D. | None of these |
| Answer» B. Heat transfer area | |
| 367. |
Reynold's analogy states that |
| A. | Nst α f |
| B. | Nst α NRe |
| C. | NNu α f |
| D. | NRe α f |
| Answer» A. Nst α f | |
| 368. |
In case of a vertical tube evaporator, with increase in the liquor level, the |
| A. | Capacity of the evaporator is decreased |
| B. | Capacity of the evaporator is increased |
| C. | True temperature drop increases |
| D. | Both (B) and (C) |
| Answer» A. Capacity of the evaporator is decreased | |
| 369. |
Which of the following has the minimum thermal conductivity? |
| A. | Nitrogen |
| B. | Steel |
| C. | Carbon black |
| D. | Tar |
| Answer» A. Nitrogen | |
| 370. |
Low thermal conductivity of heat insulating materials is due to its |
| A. | Dense structure |
| B. | High proportion of air space |
| C. | High specific heat |
| D. | None of these |
| Answer» B. High proportion of air space | |
| 371. |
For an ideal black body |
| A. | Absorptivity = 1 |
| B. | Reflectivity = 1 |
| C. | Emissivity = 0 |
| D. | Transmissivity = 1 |
| Answer» A. Absorptivity = 1 | |
| 372. |
In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always |
| A. | < 1 |
| B. | > 1 |
| C. | 1 |
| D. | ∞ |
| Answer» A. < 1 | |
| 373. |
For concentrating an aqueous solution of a material like anhydrous Na2SO4, whose solubility decreases with rise in temperature, the most suitable evaporator is a __________ evaporator. |
| A. | High pressure |
| B. | Vacuum |
| C. | Backward feed |
| D. | None of these |
| Answer» B. Vacuum | |
| 374. |
Small scale evaporation is done in a |
| A. | Heat exchanger |
| B. | Condenser |
| C. | Multiple effect evaporator |
| D. | Steam jacketed kettle |
| Answer» D. Steam jacketed kettle | |
| 375. |
Leidenfrost point is a term concerned with the |
| A. | Condensation of the saturated vapor on a cold surface |
| B. | Concentration of a corrosive solution by evaporation |
| C. | Heat transfer between two highly viscous liquids |
| D. | Boiling of a liquid on a hot surface |
| Answer» D. Boiling of a liquid on a hot surface | |
| 376. |
In a single effect evaporator, the economy is |
| A. | 1 |
| B. | < 1 |
| C. | > 1 |
| D. | None of these |
| Answer» B. < 1 | |
| 377. |
At steady state the temperature variation in a plane wall, made of two different solids I & II is shown below: The thermal conductivity of material „I‟ |
| A. | Is smaller than that of II |
| B. | Is greater than that of II |
| C. | Is equal to that of II |
| D. | Can be greater than or smaller than that of II |
| Answer» A. Is smaller than that of II | |
| 378. |
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 |
| Answer» B. Natural convection | |
| 379. |
Which of the following is not used as a medium for high temperature heating ? |
| A. | Dowtherm |
| B. | Mercury |
| C. | Liquid metal (e.g. molten sodium) |
| D. | Fused salts (e.g., an eutectic mixture of 53% KNO3, 40% NaNO2and 7% NaNO3) |
| Answer» B. Mercury | |
| 380. |
In counter flow compared to parallel flow, |
| A. | LMTD is greater |
| B. | Less surface area is required for a given heat transfer rate |
| C. | Both (A) and (B) |
| D. | More surface area is required for a given heat transfer rate |
| Answer» C. Both (A) and (B) | |
| 381. |
The inside heat transfer co-efficient in case of turbulent flow of liquid in the tube side in a 1-2 shell and tube heat exchanger is increased by __________ times, when the number of tube passes is increased to 8. |
| A. | 20.8 |
| B. | 40.8 |
| C. | 40.4 |
| D. | 20.4 |
| Answer» B. 40.8 | |
| 382. |
Heat exchangers operating, when the asymptotic range is reached, |
| A. | Provide very large heat transfer co-efficient |
| B. | Results in making part of the heating surface inactive |
| C. | Results in abruptly increased velocity |
| D. | None of these |
| Answer» B. Results in making part of the heating surface inactive | |
| 383. |
In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred |
| A. | Through a metallic wall |
| B. | By direct contact of hot flue gas with air |
| C. | By heating an intermediate material (like chequor bricks) and then heating the air from this hot material |
| D. | None of these |
| Answer» C. By heating an intermediate material (like chequor bricks) and then heating the air from this hot material | |
| 384. |
In case of evaporators, liquid entrainment results primarily due to |
| A. | High vacuum in the evaporator |
| B. | High evaporation rate |
| C. | Foaming of the solution |
| D. | High heat transfer rate |
| Answer» C. Foaming of the solution | |
| 385. |
A multiple effect evaporator has a capacity to process 4000 kg of solid caustic soda per day, when it is concentrating from 10% to 25% solids. The water evaporated in kg per day is |
| A. | 6000 |
| B. | 24000 |
| C. | 60000 |
| D. | 48000 |
| Answer» B. 24000 | |
| 386. |
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 |
| Answer» C. Exit fluid temperature = wall temperature | |
| 387. |
The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is |
| A. | 1.66 |
| B. | 88.66 |
| C. | 3.66 |
| D. | Dependent on NRe only |
| Answer» C. 3.66 | |
| 388. |
Economy of a multiple effect evaporator is not influenced much by the |
| A. | Boiling point elevations |
| B. | Temperature of the feed |
| C. | Rate of heat transfer |
| D. | Ratio of the weight of the thin liquor to thick liquor |
| Answer» A. Boiling point elevations | |
| 389. |
For evaporation of viscous solution in a multiple effect evaporator, the preferred feeding scheme is |
| A. | Forward |
| B. | Backward |
| C. | Parallel |
| D. | None of these |
| Answer» B. Backward | |
| 390. |
What is the absorptivity of a black body? |
| A. | 1 |
| B. | 0 |
| C. | 0.78 |
| D. | 0.95 |
| Answer» A. 1 | |
| 391. |
Multiple effect evaporators ar used to |
| A. | Increase the steam economy & decrease the capacity |
| B. | Increase the steam economy & the capacity |
| C. | Decrease the steam economy & the capacity |
| D. | Decrease the steam economy & increase the capacity |
| Answer» B. Increase the steam economy & the capacity | |
| 392. |
The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, ΔT = Temperature drop across condensate film) |
| A. | (ΔT)2 |
| B. | √(ΔT) |
| C. | (ΔT)1/4 |
| D. | (ΔT)3/2 |
| Answer» C. (ΔT)1/4 | |
| 393. |
Heat transfer co-efficient (h1) for liquids increases with |
| A. | Increasing temperature |
| B. | Decreasing temperature |
| C. | Decreasing Reynolds number |
| D. | None of these |
| Answer» A. Increasing temperature | |
| 394. |
Which characteristic of a fluid is not important in deciding its route in a shell and tube heat exchanger? |
| A. | Corrosiveness |
| B. | Fouling characteristic |
| C. | Viscosity |
| D. | None of these |
| Answer» D. None of these | |
| 395. |
Steady state one dimensional heat flow by conduction as given by Fourier's low does not assume that |
| A. | There is no internal heat generation |
| B. | Boundary surfaces are isothermal |
| C. | Material is anisotropic |
| D. | Constant temperature gradient exists |
| Answer» C. Material is anisotropic | |
| 396. |
An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates 30000 kg of water. The amount of solids handled by the system in kg is |
| A. | 4000 |
| B. | 9000 |
| C. | 4600 |
| D. | 3000 |
| Answer» A. 4000 | |
| 397. |
A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides |
| A. | Higher economy |
| B. | Lower capacity |
| C. | Both (A) & (B) |
| D. | Lower economy |
| Answer» A. Higher economy | |
| 398. |
Analogy between mass and heat transfer is not applicable in case of |
| A. | Same velocity profile or equal eddy diffusivities |
| B. | Thermal or pressure mass diffusion |
| C. | Viscous heating or chemical reaction |
| D. | Both (B) and (C) |
| Answer» D. Both (B) and (C) | |
| 399. |
1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the liquid is 1500 W/m2.°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be |
| A. | 15 min |
| B. | 22 min |
| C. | 44 min |
| D. | 51 min |
| Answer» D. 51 min | |
| 400. |
The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface) |
| A. | K/h0 |
| B. | 2K/h0 |
| C. | h0/K |
| D. | h0/2K |
| Answer» B. 2K/h0 | |
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