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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.
| 851. |
In a heat exchanger, floating head is provided to |
| A. | Facilitate cleaning of the exchanger |
| B. | Increase the heat transfer area |
| C. | Relieve stresses caused by thermal expansion |
| D. | Increase log mean temperature gradient |
| Answer» D. Increase log mean temperature gradient | |
| 852. |
According to Reynolds analogy, Stanton number is equal to (where, f = Fanning friction factor) |
| A. | 2f |
| B. | f |
| C. | f/2 |
| D. | f/4 |
| Answer» D. f/4 | |
| 853. |
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. | (D)0.2 |
| D. | (D)1.8 |
| Answer» C. (D)0.2 | |
| 854. |
Thermal conductivity of a gas at low density, __________ with increase in temperature. |
| A. | Decreases |
| B. | Increases |
| C. | Remains unchanged |
| D. | May increase or decrease; depends on the gas |
| Answer» C. Remains unchanged | |
| 855. |
Viscosity of gases __________ with increase in temperature. |
| A. | Increase very rapidly |
| B. | Increase slowly |
| C. | Decrease slowly |
| D. | Remain unaffected |
| Answer» C. Decrease slowly | |
| 856. |
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» C. Fick's law | |
| 857. |
The thermal radiation emitted by a body is proportional to Tn, where T is its absolute temperature. The value of 'n' is exactly 4 for |
| A. | Black painted bodies only |
| B. | All bodies |
| C. | Polished bodies only |
| D. | A black body |
| Answer» C. Polished bodies only | |
| 858. |
If a single tube pass heat exchanger is converted to two pass, then for the same flow rate, the pressure drop per unit length in tube side will |
| A. | Increase by 1.8 times |
| B. | Decrease by 22 |
| C. | Increase by 216 |
| D. | Remain unchanged |
| Answer» D. Remain unchanged | |
| 859. |
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 | |
| 860. |
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» D. Either more or less ; depends on the nature of vapor | |
| 861. |
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» B. Decreased economy | |
| 862. |
A diathermaneous substance __________ the thermal radiation completely. |
| A. | Absorbs |
| B. | Reflects |
| C. | Transmits |
| D. | None of these |
| Answer» D. None of these | |
| 863. |
With increase in temperature, the thermal conductivity of steel |
| A. | Increases |
| B. | Decreases |
| C. | Remains unchanged |
| D. | Increases exponentially |
| Answer» C. Remains unchanged | |
| 864. |
With increase in temperature, the thermal conductivity of a gas |
| A. | Increases |
| B. | Decreases |
| C. | Remains same |
| D. | May increase or decrease depending on the type of gas |
| Answer» B. Decreases | |
| 865. |
In a co-current double pipe heat exchanger used for condensing saturated steam over the inner tube, if the entrance and exit conditions of the coolant are interchanged, then the rate of condensation will |
| A. | Increase |
| B. | Decrease |
| C. | Remain unchanged |
| D. | Either increase or decrease; depends on the coolant flow rate |
| Answer» D. Either increase or decrease; depends on the coolant flow rate | |
| 866. |
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» C. Highest at the inlet of the last effect | |
| 867. |
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» C. < 0.50 | |
| 868. |
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 materialA 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 | |
| 869. |
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» B. Increase in liquor film co-efficient | |
| 870. |
Resistance to heat flow by conduction is proportional to (where, t & ρ are thickness & density of the material respectively and A = area normal to the direction of heat flow. ) |
| A. | T |
| B. | 1/ρ |
| C. | 1/A |
| D. | All of the above |
| Answer» E. | |
| 871. |
The type of liquor circulation system to be ' employed in evaporators (viz. natural or forced circulation) is determined mainly by the __________ of the liquid. |
| A. | Viscosity |
| B. | Density |
| C. | Thermal conductivity |
| D. | Corrosive nature |
| Answer» B. Density | |
| 872. |
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» B. Dynamic viscosity | |
| 873. |
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» E. | |
| 874. |
In a 1-1 cocurrent heat exchanger, if the tube side fluid outlet temperature is equal to the shell 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 | |
| 875. |
Overall heat transfer co-efficient of a particular tube is U₁. If the same tube with some dirt deposited on either side has coefficient U₂, then |
| A. | U₁ = U₂ |
| B. | U₂ > U₁ |
| C. | U₁ > U₂ |
| D. | U₁ = dirt factor - U₂ |
| Answer» B. U₂ > U₁ | |
| 876. |
Baffles in the shell side of a shell and tube heat exchanger |
| A. | Increase the cross-section of the shell side liquid |
| B. | Force the liquid to flow parallel to the bank |
| C. | Increase the shell side heat transfer co-efficient |
| D. | Decrease the shell side heat transfer co-efficient |
| Answer» D. Decrease the shell side heat transfer co-efficient | |
| 877. |
Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is |
| A. | Vertical heat exchanger with steam on tube side |
| B. | Vertical heat exchanger with steam on shell side |
| C. | Horizontal heat exchanger with steam on tube side |
| D. | Horizontal heat exchanger with steam on shell side |
| Answer» C. Horizontal heat exchanger with steam on tube side | |
| 878. |
The equivalent diameter for the annulus of a double pipe heat exchanger, whose inner pipe has fins on the outside is __________ compared to the same size pipes without fins. |
| A. | More |
| B. | Less |
| C. | Same |
| D. | Unpredictable |
| Answer» C. Same | |
| 879. |
Three material A, B and C of equal thick-nes and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface between B and C will be at a temperature of __________ °C. |
| A. | 40 |
| B. | 95 |
| C. | 70 |
| D. | 50 |
| Answer» D. 50 | |
| 880. |
In case of a multipass shell and tube heat exchanger, the temperature drop in the fluid |
| A. | Is inversely proportional to the resistance across which the drop occurs |
| B. | And the wall are proportional to individual resistances |
| C. | And the wall is not related |
| D. | None of these |
| Answer» C. And the wall is not related | |
| 881. |
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 | |
| 882. |
Temperature profile in steady state heat transfer is |
| A. | Asymptotic |
| B. | Hyperbolic |
| C. | Parabolic |
| D. | Linear |
| Answer» E. | |
| 883. |
If all the conditions and dimensions are same, then the ratio of velocity through the tubes of a double pass heat exchanger to that through the single pass heat exchanger is |
| A. | 1 |
| B. | 2 |
| C. | 1/2 |
| D. | 4 |
| Answer» C. 1/2 | |
| 884. |
A hot liquid is kept in a big room. The logorithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly a/an |
| A. | Ellipse |
| B. | Straight line |
| C. | Parabola |
| D. | Circular arc |
| Answer» C. Parabola | |
| 885. |
Loss of heat from untagged steam pipe to the ambient air is by |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | All of the above |
| Answer» E. | |
| 886. |
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» C. Because it occupies less floor area | |
| 887. |
Heat transfer by radiation between two bodies at T₁ & T₂ and in an ambient temperature of Ta°C depends on |
| A. | T₁ - T₂ |
| B. | T₁ - Ta |
| C. | T₂ - Ta |
| D. | None of these |
| Answer» E. | |
| 888. |
The Graetz number is concerned with the |
| A. | Mass transfer between a gas and a liquid |
| B. | Absorption with chemical reaction |
| C. | Heat transfer in turbulent flow |
| D. | Heat transfer in laminar flow |
| Answer» E. | |
| 889. |
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» E. | |
| 890. |
Which of the following situations can be approximated to a steady state heat transfer system? |
| A. | A red hot steel slab (having outside surface temperature as 1300°C) exposed to the atmosheric air at 35°C |
| B. | 10 kg of dry saturated steam at 8 kgf/cm² flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C |
| C. | Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C |
| D. | A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper pipe exposed to atmospheric air at 35°C |
| Answer» C. Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C | |
| 891. |
Which of the following forced convection heat transfer equation accounts for the liquid viscosity effect for viscous liquids? |
| A. | Dittus-Boeltier equation |
| B. | Sieder-Tate equation |
| C. | Nusselt equation |
| D. | None of these |
| Answer» C. Nusselt equation | |
| 892. |
Radiation heat losses from satisfactorily insulated high pressure boilar may be about __________ percent. |
| A. | 1 |
| B. | 7 |
| C. | 18 |
| D. | 26 |
| Answer» C. 18 | |
| 893. |
Vibrations in the tubes of a shell and tube heat exchanger is induced due to the |
| A. | Flow of fluid on the tube and shell sides |
| B. | Oscillations in the flow of shell/tube sides fluid |
| C. | Vibrations transmitted through piping and/or supports due to external reasons |
| D. | All of the above |
| Answer» E. | |
| 894. |
If heat transfer rate varies with the time, it is termed as |
| A. | Forced convection |
| B. | Steady state conduction |
| C. | Monochromatic radiation |
| D. | None of these |
| Answer» E. | |
| 895. |
Which one gives the monochromatic emissive power for black body radiation? |
| A. | Planck's law |
| B. | Kirchhoffs law |
| C. | Wien's law |
| D. | Stefan-Boltzman law |
| Answer» B. Kirchhoffs law | |
| 896. |
Water always boils when its |
| A. | Temperature reaches 100° C |
| B. | Vapour pressure equals 76 cm of Hg |
| C. | Saturated vapour pressure equals the external pressure on its surface |
| D. | Saturated vapour pressure is less than the atmospheric pressure |
| Answer» D. Saturated vapour pressure is less than the atmospheric pressure | |
| 897. |
The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is |
| A. | 2.36 |
| B. | 4.36 |
| C. | 120.36 |
| D. | Dependent on NRe only |
| Answer» C. 120.36 | |
| 898. |
The ratio of momentum diffusivity to thermal diffusivity is the __________ number. |
| A. | Prandtl |
| B. | Nusselt |
| C. | Stanton |
| D. | Grashoff |
| Answer» B. Nusselt | |
| 899. |
The advantage of backward feed multiple effect evaporators over forward feed units is that |
| A. | Heat sensitive material can be handled |
| B. | There is no additional cost of pumping |
| C. | Most concentrated liquid is at highest temperature |
| D. | Equal heat transfer co-efficients exist in various effects |
| Answer» D. Equal heat transfer co-efficients exist in various effects | |
| 900. |
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» D. None of these | |