MCQOPTIONS
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MCQOPTIONS
This section includes 968 Mcqs, each offering curated multiple-choice questions to sharpen your GATE (Mechanical Engineering) knowledge and support exam preparation. Choose a topic below to get started.
| 201. |
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» B. √(A1 + A2) | |
| 202. |
For flow over a flat plate, the ratio of thermal boundary layer thickness, 'xt' andhydrodynamic boundary layer thickness 'x' is equal to (where, NPr = Prandtl number) |
| A. | NPr |
| B. | NPr 1/3 |
| C. | NPr -1 |
| D. | NPr -1/3 |
| Answer» C. NPr -1 | |
| 203. |
Convective heat transfer, in which heat is transferred by movement of warmed matter isdescribed by |
| A. | Fourier's law |
| B. | Newton's law of cooling |
| C. | Fick's law |
| D. | None of these |
| Answer» C. Fick's law | |
| 204. |
Dittus-Boelter equation cannot be used for molten metals mainly due to its very low |
| A. | Prandtl number |
| B. | Grashoff number |
| C. | Thermal conductivity |
| D. | Viscosity |
| Answer» B. Grashoff number | |
| 205. |
The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficientat inside of the pipe) |
| A. | K/h0 |
| B. | 2K/h0 |
| C. | hi/K |
| D. | 2hi/K |
| Answer» B. 2K/h0 | |
| 206. |
What is the logarithmic mean of r1 and r2? |
| A. | (r1 - r2)/ln(r1/r2) |
| B. | (r1 - r2)/ln(r2/r1) |
| C. | (r2 - r1)/ln(r1/r2) |
| D. | (r1 - r2)/-ln(r1/r2) |
| Answer» B. (r1 - r2)/ln(r2/r1) | |
| 207. |
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» D. 287 W/m2.K | |
| 208. |
A steam pipe is to be insulated by two insulating materials put over each other.For best results |
| A. | better insulation should be put over pipe and better one over it |
| B. | inferior insulation should be put over pipe and better one over it |
| C. | both may be put in any order |
| D. | whether to put inferior OIL over pipe or the better one would depend on steam temperature |
| E. | unpredictable. |
| Answer» B. inferior insulation should be put over pipe and better one over it | |
| 209. |
The overall resistance for heat transfer through a series of flat resistance, is the __________of the resistances. |
| A. | Average |
| B. | Geometric mean |
| C. | Product |
| D. | Sum |
| Answer» E. | |
| 210. |
Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipeis negligible, if the value of Prandtl number is |
| A. | 0.2 |
| B. | 0.4 |
| C. | 0.6 |
| D. | 0.8 |
| Answer» D. 0.8 | |
| 211. |
For a counter current heat exchanger with Ti h = 80°C, T°c = 60°C, T°h = 50°C and Ti c = 30°C, and the temperature difference between the two streams being the same everywhere along Z, the direction of flow of hot fluid. The temperature profile should satisfy |
| A. | d 2T/dZ2 > 0 |
| B. | d 2T/dZ2 = 0 |
| C. | d 2T/dZ2 < 0 |
| D. | dT/dZ = 0 |
| Answer» C. d 2T/dZ2 < 0 | |
| 212. |
Which of the following forced convection heat transfer equation accounts for the liquidviscosity effect for viscous liquids? |
| A. | Dittus-Boelter equation |
| B. | Sieder-Tate equation |
| C. | Nusselt equation |
| D. | None of these |
| Answer» C. Nusselt equation | |
| 213. |
In a 1-1 concurrent heat exchanger, if the tube side fluid outlet temperature is equal to theshell side fluid outlet temperature, then the LMTD is |
| A. | ∞ |
| B. | 0 |
| C. | Equal to the difference between hot and cold fluids inlet temperature |
| D. | Equal to the difference between hot fluid inlet temperature and cold fluid outlet temperature |
| Answer» C. Equal to the difference between hot and cold fluids inlet temperature | |
| 214. |
Heat transfer takes place as per – |
| A. | zeroth law of thermodynamics |
| B. | first law of thermodynamic |
| C. | second law of the thermodynamics |
| D. | Kirchoff’s law |
| E. | Stefan’s law. |
| Answer» D. Kirchoff’s law | |
| 215. |
Grashoff number, which is defined as g . β (Ts - T∞) ρ2. L3/μ2, is proportional to the ratio of buoyancy force to __________ force. |
| A. | Viscous |
| B. | Elastic |
| C. | Inertial |
| D. | None of these |
| Answer» B. Elastic | |
| 216. |
Thermal conductivity of glass-wool varies from sample to sample because ofvariation in |
| A. | composition |
| B. | density |
| C. | porosity |
| D. | structure |
| E. | all of the above. |
| Answer» F. | |
| 217. |
Stefan-Boltzmann law applies to __________ body. |
| A. | Black |
| B. | White |
| C. | Grey |
| D. | Any colour |
| Answer» B. White | |
| 218. |
Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re 0.8. Prn, 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 |
| Answer» E. | |
| 219. |
Log mean temperature difference in case of counter flow compared to parallelflow will be |
| A. | same |
| B. | more |
| C. | less |
| D. | depends on other factors |
| E. | none of the above. |
| Answer» C. less | |
| 220. |
Depending on the radiating properties, a body will be white when (where a = absorptivity, p = reflectivity, x = transmissivity) |
| A. | p = 0, x = 0 and a = 1 |
| B. | p=l,T = 0anda = 0 |
| C. | p = 0, x = 1 and a = 0 |
| D. | x = 0, a + p = 1 |
| E. | a = 0, x + p = 1. |
| Answer» C. p = 0, x = 1 and a = 0 | |
| 221. |
Thermal conductivity of air at room temperature in kcal/m hr °C is of the orderof |
| A. | 0.002 |
| B. | 0.02 |
| C. | 0.01 |
| D. | 0.1 |
| E. | 0.5. |
| Answer» C. 0.01 | |
| 222. |
Mode of heat transfer in which the fluid moves under the influence of changes in fluidpressure produced by external work is called |
| A. | Radiation |
| B. | Natural convection |
| C. | Forced convection |
| D. | Conduction |
| Answer» D. Conduction | |
| 223. |
The concept of overall coefficient of heat transfer is used in heat transferproblems of |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | all the three combined |
| E. | conduction and comte_ction. |
| Answer» F. | |
| 224. |
If the temperature of a solid surface changes form 27°C to 627°C, then itsemissive power changes in the ratio of |
| A. | 3 |
| B. | 6 |
| C. | 9 |
| D. | 27 |
| E. | 81. |
| Answer» F. | |
| 225. |
Which characteristic of a fluid is not important in deciding its route in a shell and tube heatexchanger? |
| A. | Corrosiveness |
| B. | Fouling characteristic |
| C. | Viscosity |
| D. | None of these |
| Answer» E. | |
| 226. |
Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only whenPrandtl number is |
| A. | 0.1 |
| B. | > 1 |
| C. | < 1 |
| D. | 1 |
| Answer» B. > 1 | |
| 227. |
A sphere of radius 'R1' is enclosed in a sphere of radius 'R2'. The view (or shape) factor forradiative 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» C. 1 | |
| 228. |
For gases, the thermal conductivity increases with temperature rise. For liquids, withincrease in concentration, its thermal conductivity generally |
| A. | Decreases |
| B. | Increases |
| C. | Remains unchanged |
| D. | Increases exponentially |
| Answer» B. Increases | |
| 229. |
Thermal diffusivity of a substance is . |
| A. | proportional of thermal conductivity |
| B. | inversely proportional to k |
| C. | proportional to (k) |
| D. | inversely proportional to k2 |
| E. | none of the above. |
| Answer» B. inversely proportional to k | |
| 230. |
A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of material A is twice that of B. Under the equilibrium, the temperature difference across the wall is 36°C. The temperature difference across the layer A is __________ °C. |
| A. | 6 |
| B. | 12 |
| C. | 18 |
| D. | 24 |
| Answer» C. 18 | |
| 231. |
In a shell and tube heat exchanger, the shell side fluid velocity can‟t be changed bychanging the |
| A. | Tube layout |
| B. | Tube diameter |
| C. | Tube pitch |
| D. | Number of baffles |
| Answer» C. Tube pitch | |
| 232. |
As per Kirchoff‟s law, the ratio of the total radiating power to the absorptivity of a body depends on the |
| A. | Temperature of the body only |
| B. | Wavelength of monochromatic radiation |
| C. | Both (A) and (B) |
| D. | Nature of material of body |
| Answer» B. Wavelength of monochromatic radiation | |
| 233. |
In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2 .s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2 /kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is |
| A. | 2000 |
| B. | 4000 |
| C. | 5000 |
| D. | 6000 |
| Answer» D. 6000 | |
| 234. |
Which of the following parameters is increased by use of finned tube in a multipass shelland tube heat exchanger? |
| A. | Tube side pressure drop and the heat transfer rate |
| B. | Convective heat transfer co-efficient |
| C. | Effective tube surface area for convective heat transfer |
| D. | All (A) (B) and (C) |
| Answer» E. | |
| 235. |
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» C. 26.8 | |
| 236. |
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» B. 37 | |
| 237. |
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» B. counter flow with process stream on tube side. | |
| 238. |
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» E. | |
| 239. |
A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is |
| A. | 555 |
| B. | 55.5 |
| C. | 0.55 |
| D. | 0.15 |
| Answer» E. | |
| 240. |
The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C-1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m-2.°C-1. The rate of heat loss from the outer surface in W.m-2is |
| A. | 165.4 |
| B. | 167.5 |
| C. | 172.5 |
| D. | 175 |
| Answer» B. 167.5 | |
| 241. |
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 uninsulated steam pipe. |
| B. | less than that of the uninsulated steam pipe. |
| C. | equal to that of the uninsulated steam pipe. |
| D. | less than the steam pipe with 5 cms insulation. |
| Answer» C. equal to that of the uninsulated steam pipe. | |
| 242. |
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» E. | |
| 243. |
The rate of heat transfer through a pipe wall is given by, . For cylinder of very thin wall, q can be approximated by |
| A. | [A]. |
| B. | [B]. |
| C. | [C]. |
| D. | [D]. |
| Answer» E. | |
| 244. |
The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K= 0.04 W/m.°K and thickness 0.16m is 10 W/m2. The temperature of the inside wall is - 5°C. The outside wall temperature is |
| A. | 25°C |
| B. | 30°C |
| C. | 35°C |
| D. | 40°C |
| Answer» D. 40°C | |
| 245. |
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» E. | |
| 246. |
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» D. none, 'a' is just a number | |
| 247. |
Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m2 .°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the |
| A. | higher condensing film co-efficient is desired. |
| B. | condensate is corrosive in nature. |
| C. | lower pressure drop through the exchanger is desired. |
| D. | temperature of the incoming vapor is very high. |
| Answer» C. lower pressure drop through the exchanger is desired. | |
| 248. |
Grashoff number, which is defined as g . β(Ts - T∞) ρ2. L3/μ2, is proportional to the ratio of buoyancy force to __________ force. |
| A. | viscous |
| B. | elastic |
| C. | inertial |
| D. | none of these |
| Answer» B. elastic | |
| 249. |
Stefan-Boltzman 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» C. 1/t4 | |
| 250. |
Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m2°C. |
| A. | 10-50 |
| B. | 100-500 |
| C. | 1000-1500 |
| D. | 5000-15000 |
| Answer» E. | |