Free Heat Transfer Operations MCQs with Answers

• A. 200 BTU/minute
• B. 50 kcal/minute
• C. 50 kJ/sec
• D. 3.5 KW

Explanation: One ton of refrigeration is approximately 200 Btu/min, 50 kcal/min or 3.5 kW.

• A. Both specific humidity & dry bulb temperature increases
• B. Both specific humidity & dry bulb temperature decreases
• C. Specific humidity decreases & dry bulb temperature increases
• D. Specific humidity increases & dry bulb temperature decreases

Explanation: Chemical dehumidification uses a hygroscopic absorbent to remove water vapour from air, reducing specific humidity.

• A. (r2 - r1)/r1. r2
• B. r1. r2/(r2 - r1)
• C. (r2 + r1)/r1. r2
• D. r1. r2/(r2 + r1)

Explanation: For steady radial conduction through a hollow sphere, heat flow is proportional to the spherical conductance factor r1r2/(r2 − r1).

• A. Feed water pump
• B. Feed check valve
• C. Blow off cock
• D. Stop valve

Explanation: A feed-water pump supplies water to the boiler and is therefore an accessory.

• A. Compared to the mass flow rate of cooling water, the rate of condensation of steam is
• B. invariably smaller
• C. Maintaining vacuum on tube side is more difficult than that on the shell side
• D. Condenser can act as a storage unit for condensed steam
• E. because of its lower specific volume compared to steam
• F. Water velocity can be increased conveniently to increase the overall heat transfer co-efficient

Explanation: Cooling water is placed inside the tubes because its velocity can be increased conveniently, which raises the tube-side heat-transfer…

• A. Saturation
• B. Dry bulb
• C. Wet bulb
• D. Dew point

Explanation: In an ideal evaporative cooling tower, water can theoretically approach the entering air's wet-bulb temperature.

• A. Conduction
• B. Convection
• C. Both A. & B.
• D. Radiation

Explanation: In a high-pressure boiler furnace, the flame and hot combustion gases transfer most of their energy to the water-wall tubes by radiation.

• A. Sensible heat is removed and the latent heat is added
• B. Sensible heat is added
• C. Latent heat is removed
• D. Sensible heat is added and latent heat is removed

Explanation: During evaporative cooling, sensible heat is removed from the air while water evaporates and adds latent heat to it.

• A. 10
• B. 30
• C. 50
• D. 80

Explanation: Boilers generating steam above about 80 kg/cm2 are commonly classified as high-pressure boilers.

• A. Soap solution
• B. Using chemical reagents
• C. Its smell
• D. Sulphur stick, which on detection gives white smoke

Explanation: A sulfur stick produces sulfur dioxide, which reacts with leaking ammonia to form visible white ammonium-salt fumes.

• A. None of these
• B. Diameter & length of the pipe
• C. Temperature of hot pipe surface & that of air in the room
• D. Emissivity of pipe surface

Explanation: Radiation and natural-convection heat loss depend on surface emissivity, pipe geometry, and the temperature difference between the pipe…

• A. Grashoff number
• B. Grashoff number & Prandtl number
• C. Reynolds number
• D. Grashoff number & Reynolds number

Explanation: The transition criterion in free convection is expressed through the Rayleigh number, Ra = Gr·Pr, so both the Grashof and Prandtl numbers…

• A. None of these
• B. Tube carrying hot flue gases are immersed in a pool of water
• C. Tubes are placed in vertical position
• D. Water passes through tubes and flue gases around it
• E. Answer: Option A

Explanation: In a water-tube boiler, water circulates inside the tubes while hot flue gases flow around their outer surfaces.

• A. All 'A', 'B' & 'C'
• B. Area
• C. Nature
• D. Temperature

Explanation: For thermal radiation, the wavelength of maximum emission is fixed by the surface temperature according to Wien's displacement law.

• A. Conduction in air
• B. Forced convection in air
• C. Free convection in air
• D. Boiling

Explanation: Still air has very low thermal conductivity, so conduction through air provides less heat transfer than either natural or forced…

• A. (ε1 + ε2)/ε1.ε2
• B. ε1.ε2
• C. ε1.ε2/(ε1 + ε2 - ε1.ε2)
• D. ε1 + ε2

Explanation: For two infinite facing gray surfaces, the radiation exchange factor is the reciprocal of the two surface resistances and the space…

• A. More
• B. Less
• C. Much more
• D. Equal

Explanation: For fixed terminal temperature differences, the LMTD calculation uses the same two end differences for both flow arrangements.

• A. Density
• B. Thermal diffusivity
• C. Viscosity
• D. Thermal conductivity

Explanation: As temperature rises at approximately constant pressure, air expands and its density decreases.

• A. High temperature heating medium (a petroleum product)
• B. Product of coal tar distillation
• C. Very heat sensitive material
• D. None of these

Explanation: Dowtherm is a high-temperature heat-transfer fluid used where water or steam cannot provide the required operating temperature.

• A. Convection heat transfer by stirring the fluid and cleaning the heating surface
• B. Radiation heat transfer by increasing the temperature and reducing the emissivity
• C. conductivity
• D. Conduction heat transfer by reduction in the material thickness and increase in the thermal
• E. None of these

Explanation: For radiation, lowering emissivity lowers the radiation heat-transfer coefficient and increases thermal resistance, so it does not produce…