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.
| 1. |
When does the heat generated by fluid friction becomes appreciable compared to the heattransferred between the fluids? |
| A. | At high fluid velocity |
| B. | At low velocity |
| C. | When fluid flows past a smooth surface |
| D. | None of these |
| Answer» B. At low velocity | |
| 2. |
For heat flow through very thick walled cylinder, use _________mean radius. |
| A. | Arithmetic |
| B. | Logarithmic |
| C. | Geometric |
| D. | Either (A) or (C) |
| Answer» C. Geometric | |
| 3. |
Heat conducted througfi unit area and unit thick face per unit time whentemperature difference between opposite faces is unity,is called |
| A. | thermal resistance |
| B. | thermal coefficient |
| C. | temperature gradient |
| D. | thermal conductivity |
| E. | heat-transfer. |
| Answer» E. heat-transfer. | |
| 4. |
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heattransfer will take place mainly by |
| A. | convection |
| B. | free convection |
| C. | forced convection |
| D. | radiation |
| E. | radiation and convection. |
| Answer» E. radiation and convection. | |
| 5. |
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 |
| E. | none of the above. |
| Answer» E. none of the above. | |
| 6. |
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.°C1 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-2 is |
| A. | 165.4 |
| B. | 167.5 |
| C. | 172.5 |
| D. | 175 |
| Answer» B. 167.5 | |
| 7. |
Intermittent tube cleaning is possible to be done in case of a __________ evaporator. |
| A. | Basket type |
| B. | Horizontal tube |
| C. | Calandria |
| D. | None of these |
| Answer» B. Horizontal tube | |
| 8. |
The maximum heat transfer co-efficient from steam heating will be attained when thesteam is: |
| A. | Supersaturated |
| B. | Saturated |
| C. | Wet |
| D. | None of these |
| Answer» C. Wet | |
| 9. |
The average heat transfer co-efficient over the entire length of the plate (ha) and the localheat transfer co-efficient (hL), in case of heat transfer over a flat plate in laminar zone is related as |
| A. | ha = 0.8hL |
| B. | ha = 2hL |
| C. | ha = hL |
| D. | ha = 5hL |
| Answer» C. ha = hL | |
| 10. |
The heat transfer by radiation from a mild steel surface is to be reduced by reducing theemissivity of the surface. This can be best achieved by |
| A. | Painting the surface black |
| B. | Painting the surface white (with aluminium paint) |
| C. | Giving the surface a mirror finish |
| D. | Roughening the surface |
| Answer» C. Giving the surface a mirror finish | |
| 11. |
The total emissivity power is .defined as the total amount of radiation emitted bya black body per unit |
| A. | temperature |
| B. | thickness |
| C. | area |
| D. | time |
| E. | area and time. |
| Answer» E. area and time. | |
| 12. |
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 is maximum for perfectly black body |
| E. | ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body. |
| Answer» F. | |
| 13. |
Evaporation by thermo compression results in the |
| A. | Saving of steam |
| B. | Realisation of multiple effect economy in a single effect |
| C. | Both (A) and (B) |
| D. | None of these |
| Answer» D. None of these | |
| 14. |
LMTD in case of counter flow heat exchanger as compared-to parallel flow heatexchanger is |
| A. | higher |
| B. | lower |
| C. | same |
| D. | depends on the area of heat exchanger |
| E. | depends on temperature conditions. |
| Answer» B. lower | |
| 15. |
Forced circulation evaporators are useful for the concentration of viscous, salting and scaleforming liquors. Which of the following is a forced circulation evaporator? |
| A. | Long vertical evaporator |
| B. | Horizontal tube evaporator |
| C. | Agitated film evaporator |
| D. | Calandria vertical tube evaporator |
| Answer» D. Calandria vertical tube evaporator | |
| 16. |
In case of a vertical tube evaporator, with increase in the liquor level, the __________ isincreased. |
| A. | Velocity of circulation |
| B. | Liquor-film co-efficient |
| C. | Both (A) and (B) |
| D. | Neither (A) and (B) |
| Answer» E. | |
| 17. |
The separation of liquid droplets from the vapor is done by a/an __________, in the evaporators. |
| A. | Steam ejector |
| B. | Entrainment separator |
| C. | Compressor |
| D. | Vacuum pump |
| Answer» C. Compressor | |
| 18. |
In case of __________ boiling, the liquid temperature is below the saturation temperatureand the boiling takes place in the vicinity of the heated surface. |
| A. | Nucleate |
| B. | Local |
| C. | Pool |
| D. | Saturated |
| Answer» C. Pool | |
| 19. |
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 | |
| 20. |
A cube, sphere & a thin circular plate (all having same mass and made of same material)are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest? |
| A. | Cube |
| B. | Plate |
| C. | Sphere |
| D. | All will cool at the same rate |
| Answer» D. All will cool at the same rate | |
| 21. |
A backward feed multiple effect evaporator is better than forward feed for concentratingcold feed, because it provides |
| A. | Higher economy |
| B. | Lower capacity |
| C. | Both (A) & (B) |
| D. | Lower economy |
| Answer» B. Lower capacity | |
| 22. |
Evaporation of 1kg of water from a solution in a single effect evaporator requires about__________ kg of steam. |
| A. | 0.4 - 0.6 |
| B. | 1-1.3 |
| C. | 1.8-2 |
| D. | 2 - 2.4 |
| Answer» C. 1.8-2 | |
| 23. |
The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body). |
| A. | αT |
| B. | α × 1/T |
| C. | α T4 |
| D. | Independent of T |
| Answer» C. α T4 | |
| 24. |
Which of the following property of air does not increase with rise in temperature |
| A. | thermal conductivity |
| B. | thermal diffusivity |
| C. | density |
| D. | dynamic viscosity |
| E. | kuiematic viscosity. |
| Answer» D. dynamic viscosity | |
| 25. |
Removal of __________ heat is involved in the condensation of a vapor under saturatedconditions. |
| A. | Super |
| B. | Sensible |
| C. | Latent |
| D. | Both (B) & (C) |
| Answer» C. Latent | |
| 26. |
Controlling heat transfer film co-efficient is the one, which offers __________ resistance toheat transfer. |
| A. | No |
| B. | The least |
| C. | The largest |
| D. | Lower |
| Answer» D. Lower | |
| 27. |
A body cools down from 75°C to 70°C in 10 minutes. It will cool down from 70° C to 65° Cin __________ minutes. |
| A. | 10 |
| B. | > 10 |
| C. | < 10 |
| D. | Either (B) or (C), depends on the mass of the body |
| Answer» C. < 10 | |
| 28. |
Heat is transferred by all three modes of transfer, viz, conduction, convectionand radiation in |
| A. | electric heater |
| B. | steam condenser |
| C. | melting of ice |
| D. | refrigerator condenser coils |
| E. | boiler. |
| Answer» F. | |
| 29. |
Fourier’s law of heat conduction is valid for |
| A. | one dimensional cases only |
| B. | two dimensional cases only |
| C. | three dimensional cases only |
| D. | regular surfaces having non-uniform temperature gradients |
| E. | irregular surfaces. |
| Answer» B. two dimensional cases only | |
| 30. |
One kilogram of water at 0°C is changed to superheated steam of one atm pressure and300° C. The major heat consumption in the process will be to |
| A. | Heat the water from 0°C to 100°C |
| B. | Evaporate the water |
| C. | To superheat the steam |
| D. | Data insufficient, can't be predicted |
| Answer» C. To superheat the steam | |
| 31. |
As the difference between the wall temperature and bulk temperature increases, the boilingheat transfer co-efficient |
| A. | Continues to increase |
| B. | Continues to decrease |
| C. | Goes through a minimum |
| D. | Goes through a maximum |
| Answer» D. Goes through a maximum | |
| 32. |
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 | |
| 33. |
The Nusselt number for fully developed (both thermally and hydrodynamically) laminarflow 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» D. Dependent on NRe only | |
| 34. |
Depending on the radiating properties, a body will be opaque when (where a = absorptivity, p = reflectivity, X = transmissivity.) |
| 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 |
| E. | a=0,x + p= 1. |
| Answer» E. a=0,x + p= 1. | |
| 35. |
In case of heat flow by conduction for a cylindrical body with an internal heat source, thenature of temperature distribution is |
| A. | Linear |
| B. | Hyperbolic |
| C. | Parabolic |
| D. | None of these |
| Answer» D. None of these | |
| 36. |
Grashoff number is given by |
| A. | gD3.β.Δtρ2/μ2 |
| B. | gD2βΔtρ/μ2 |
| C. | gD2βΔtP2μ |
| D. | gD3βΔtP2/μ |
| Answer» B. gD2βΔtρ/μ2 | |
| 37. |
Heat flux through several resistances in series in analogous to the current flowing throughseveral |
| A. | Resistances in parallel |
| B. | Capacitors in series |
| C. | Resistances in series |
| D. | None of these |
| Answer» D. None of these | |
| 38. |
LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counter-flow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface area required is the least in the __________ flow. |
| A. | Parallel |
| B. | Mixed |
| C. | Counter flow |
| D. | Same in either 'a', b' or 'c' |
| Answer» E. | |
| 39. |
Stefan-Boltzmann 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 | |
| 40. |
Boiling point of a solution according to Duhring's rule is a linear function of the__________ of water. |
| A. | Boiling point (at the same pressure) |
| B. | Viscosity |
| C. | Density |
| D. | Thermal conductivity |
| Answer» B. Viscosity | |
| 41. |
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. | D0.2 |
| D. | D1.8 |
| Answer» C. D0.2 | |
| 42. |
Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100°C and the inside heat transfer coefficient is „3k/l’. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade? |
| A. | 35.5 |
| B. | 43.75 |
| C. | 81.25 |
| D. | 48.25 |
| Answer» D. 48.25 | |
| 43. |
Overall thermal resistance for conductive heat transfer through a series of flat resistancesis equal to the |
| A. | Maximum resistance in the series |
| B. | Sum of all resistances |
| C. | Average of all resistances |
| D. | Minimum resistance presents in the series |
| Answer» C. Average of all resistances | |
| 44. |
Fluid motion in the natural convection heat transfer between a solid surface and a fluid incontact with it, results from the |
| A. | Existence of thermal boundary layer |
| B. | Temperature gradient produced due to density difference |
| C. | Buoyancy of the bubbles produced at active nucleation site |
| D. | None of these |
| Answer» E. | |
| 45. |
Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowingin it, is |
| A. | In the central core of the fluid |
| B. | Uniformly distributed throughout the fluid |
| C. | Mainly confined to a thin film of fluid near the surface |
| D. | None of these |
| Answer» D. None of these | |
| 46. |
The thermal radiation emitted by a body is proportional to T n, 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 | |
| 47. |
The absorptivity of a grey body at a given temperature __________ with increasingwavelength of radiation. |
| A. | Increases |
| B. | Decreases |
| C. | Remain constant |
| D. | May increase or decrease; depends on the material |
| Answer» E. | |
| 48. |
In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) dividedby |
| A. | hr (time) |
| B. | sqm (area) |
| C. | °C (temperature) |
| D. | cm (thickness) |
| E. | kcal (heat). |
| Answer» E. kcal (heat). | |
| 49. |
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» C. Equal to that of the un-insulated steam pipe | |
| 50. |
In heat exchangers, degree of approach is defined as the difference betweentemperatures 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 |
| E. | none of the above. |
| Answer» E. none of the above. | |