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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.
| 901. |
Economy of an evaporator is influenced by the |
| A. | Steam pressure |
| B. | Feed temperature |
| C. | Number of effect |
| D. | Both B & C |
| Answer» E. | |
| 902. |
LMTD can't be used as such without a correction factor for the |
| A. | Multipass heat exchanger |
| B. | Baffled heat exchanger |
| C. | Condensation of mixed vapour in a condenser |
| D. | All of the above |
| Answer» E. | |
| 903. |
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» B. 0.5 D | |
| 904. |
What is the thermal conductivity of a perfect heat insulator? |
| A. | Zero |
| B. | One |
| C. | ∞ |
| D. | Between 0 and ∞ |
| Answer» B. One | |
| 905. |
With increase in temperature, the thermal conductivity of non-metallic amorphous solids |
| A. | Decreases |
| B. | Increases |
| C. | Remains constant |
| D. | First decreases upto certain temperature and then increases |
| Answer» C. Remains constant | |
| 906. |
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» D. Forced convection | |
| 907. |
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 |
| Answer» B. 970 | |
| 908. |
Latent heat absorbed by 1 lb of water at 212°F, when it is changed to steam at 212°F, may be around __________ BTU. |
| A. | 180 |
| B. | 970 |
| C. | 3.97 |
| D. | None of these |
| Answer» B. 970 | |
| 909. |
In forced convection, the Nusselt number is a function of |
| A. | Re and Pr |
| B. | Re and Gr |
| C. | Pr and Gr |
| D. | Re and Sc |
| Answer» B. Re and Gr | |
| 910. |
Heat flux through several resistances in series in analogous to the current flowing through several |
| A. | Resistances in parallel |
| B. | Capacitors in series |
| C. | Resistances in series |
| D. | None of these |
| Answer» D. None of these | |
| 911. |
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. | |
| 912. |
In a heat exchanger with steam outside the tubes, a liquid gets heated to 45°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be |
| A. | Less than 45°C |
| B. | More than 45°C |
| C. | Equal to 45°C |
| D. | Initially decreases and remains constant thereafter |
| Answer» C. Equal to 45°C | |
| 913. |
Nusselt number is a function of Prandtl number and __________ number of fluid in natural convection heat transfer. |
| A. | Grashoff |
| B. | Biot |
| C. | Stantan |
| D. | Reynolds |
| Answer» B. Biot | |
| 914. |
Terminal point temperature differences between fluids in case of a heat exchanger is termed as |
| A. | Approach |
| B. | Log mean temperature difference |
| C. | Arithmetic mean temperature difference |
| D. | Geometric mean temperature difference |
| Answer» B. Log mean temperature difference | |
| 915. |
In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to __________ the velocity head. |
| A. | Twice |
| B. | Four times |
| C. | Square root of |
| D. | Square of |
| Answer» C. Square root of | |
| 916. |
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» B. A lower capacity | |
| 917. |
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 x l0⁵ |
| B. | 6.12 x 10⁵ |
| C. | 7.24 x 10⁵ |
| D. | 9.08 x 10⁵ |
| Answer» B. 6.12 x 10⁵ | |
| 918. |
200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 x 10⁻³ kg/m².s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m²/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid) |
| A. | 0.5 |
| B. | 0.05 |
| C. | 0.1 |
| D. | 0.15 |
| Answer» D. 0.15 | |
| 919. |
If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of |
| A. | 3 |
| B. | 6 |
| C. | 9 |
| D. | 81 |
| Answer» E. | |
| 920. |
Planck's law holds good for |
| A. | black bodies |
| B. | polished bodies |
| C. | all coloured bodies |
| D. | all of the above |
| Answer» B. polished bodies | |
| 921. |
A perfect black body is one which |
| A. | is black in colour |
| B. | reflects all heat |
| C. | transmits all heat radiations |
| D. | abslprbs heat radiations of all wave lengths falling on it |
| Answer» E. | |
| 922. |
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by |
| A. | convection |
| B. | free convection |
| C. | forced convection |
| D. | radiation |
| Answer» E. | |
| 923. |
The emissive power of a body depends upon its |
| A. | temperature |
| B. | wave length |
| C. | physical nature |
| D. | all of the above |
| Answer» E. | |
| 924. |
The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit |
| A. | temperature |
| B. | thickness |
| C. | area |
| D. | time |
| Answer» E. | |
| 925. |
Depending on the radiating properties, a body will be opaque when |
| A. | p = 0, x = 0 and a = 1 |
| B. | p=l,x = 0anda = 0 |
| C. | p = 0, x = 1 and a = 0 |
| D. | x - 0, a + p = 1 |
| Answer» E. | |
| 926. |
According to Wien's law, the wavelength corresponding to maximum energy is proportion to |
| A. | absolute temperature (T) |
| B. | I2 |
| C. | f |
| D. | t |
| Answer» B. I2 | |
| 927. |
According to Stefan's law, the total radiation from a black body per second per unit area is proportional to |
| A. | absolute temperature |
| B. | T2 |
| C. | T5 |
| D. | t |
| Answer» E. | |
| 928. |
The thermal diffusivities for gases are generally |
| A. | more than those for liquids |
| B. | less than those for liquids |
| C. | more than those for solids |
| D. | dependent on the viscosity |
| Answer» B. less than those for liquids | |
| 929. |
Stefan Boltzmann law is applicable for heat transfer by |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and radiation combined |
| Answer» D. conduction and radiation combined | |
| 930. |
According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to |
| A. | absolute temperature |
| B. | square of temperature |
| C. | fourth power of absolute temperature |
| D. | fourth power of temperature |
| Answer» D. fourth power of temperature | |
| 931. |
Total emissivity of polished silver compared to black body is |
| A. | same |
| B. | higher |
| C. | more or less same |
| D. | very much lower |
| Answer» E. | |
| 932. |
The value of Prandtl number for air is about |
| A. | 0.1 |
| B. | 0.3 |
| C. | 0.7 |
| D. | 1.7 |
| Answer» D. 1.7 | |
| 933. |
Joule sec is the unit of |
| A. | universal gas constant |
| B. | kinematic viscosity |
| C. | thermal conductivity |
| D. | Plancks constant |
| Answer» E. | |
| 934. |
According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a |
| A. | grey body |
| B. | brilliant white polished body |
| C. | red hot body |
| D. | black body |
| Answer» E. | |
| 935. |
All radiations in a black body are |
| A. | reflected |
| B. | refracted |
| C. | transmitted |
| D. | absorbed |
| Answer» E. | |
| 936. |
According of Kirchhoff's law, |
| A. | radiant heat is proportional to fourth power of absolute temperature |
| B. | emissive power depends on temperature |
| C. | emissive power and absorptivity are constant for all bodies |
| D. | ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power |
| Answer» E. | |
| 937. |
In counter flow heat exchangers |
| A. | both the fluids at inlet (of heat ex¬changer where hot fluid enters) are in their coldest state |
| B. | both the fluids at inlet are in their hot¬test state |
| C. | both the fluids .at exit are in their hottest state |
| D. | one fluid is in hottest state and other in coldest state at inlet |
| Answer» C. both the fluids .at exit are in their hottest state | |
| 938. |
In heat exchangers, degree of approach is defined as the difference between temperatures of |
| A. | cold water inlet and outlet |
| B. | hot medium inlet and outlet |
| C. | hot medium outlet and cold water inlet |
| D. | hot medium outlet and cold water outlet |
| Answer» E. | |
| 939. |
LMTD in case of counter flow heat exchanger as compared-to parallel flow heat exchanger is |
| A. | higher |
| B. | lower |
| C. | same |
| D. | depends on the area of heat exchanger |
| Answer» B. lower | |
| 940. |
Two balls of same material and finish have their diameters in the ratio of 2 : 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of |
| A. | 1 :1 |
| B. | 2 :1 |
| C. | 1 :2 |
| D. | 4 :1 |
| Answer» D. 4 :1 | |
| 941. |
A grey body is one whose absorptivity |
| A. | varies with temperature |
| B. | varies with wavelength of the incident ray |
| C. | is equal to its emissivity |
| D. | does not vary with temperature and. wavelength of the incident ray |
| Answer» D. does not vary with temperature and. wavelength of the incident ray | |
| 942. |
Emissivity of a white polished body in comparison to a black body is |
| A. | higher |
| B. | lower |
| C. | same |
| D. | depends upon the shape of body |
| Answer» C. same | |
| 943. |
Film coefficient is defined as Inside diameter of tube |
| A. | Equivalent thickness of film |
| B. | Thermal conductivity Equivalent thickness of film Specific heat x Viscocity |
| C. | Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity |
| D. | Film coefficient x Inside diameter Thermalconductivity |
| Answer» C. Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity | |
| 944. |
In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by |
| A. | convection |
| B. | radiation |
| C. | conduction |
| D. | both convection and conduction |
| Answer» D. both convection and conduction | |
| 945. |
Thermal conductivity of wood depends on |
| A. | moisture |
| B. | density |
| C. | temperature |
| D. | all of the above |
| Answer» E. | |
| 946. |
Thermal diffusivity is |
| A. | a dimensionless parameter |
| B. | function of temperature |
| C. | used as mathematical model |
| D. | a physical property of the material |
| Answer» E. | |
| 947. |
Heat transfer by radiation mainly depends upon |
| A. | its temperature |
| B. | nature of the body |
| C. | kind and extent of its surface |
| D. | all of the above |
| Answer» E. | |
| 948. |
Heat is transferred by all three modes of transfer, viz, conduction, convection and radiation in |
| A. | electric heater |
| B. | steam condenser |
| C. | melting of ice |
| D. | boiler |
| Answer» E. | |
| 949. |
Moisture would find its way into insulation by vapour pressure unless it is prevented by |
| A. | high thickness of insulation |
| B. | high vapour pressure |
| C. | less thermal conductivity insulator |
| D. | a vapour seal |
| Answer» E. | |
| 950. |
Which of the following has maximum value of thermal conductivity |
| A. | aluminium |
| B. | steel |
| C. | brass |
| D. | copper |
| Answer» B. steel | |