Free Heat Transfer Operations MCQs with Answers

• A. Natural draft
• B. Forced draft
• C. Induced draft
• D. Atmospheric

Explanation: An induced-draft tower places the fan at the outlet, pulling air uniformly through the packing and reducing air recirculation.

• A. Increasing the air velocity over the wet surfaces
• B. Reducing the humidity of entering air
• C. Lowering the barometric pressure
• D. None of these

Explanation: All three changes can enhance cooling: higher air velocity improves contact, drier entering air increases evaporation potential, and lower…

• A. Less than the wet bulb
• B. More than the wet bulb
• C. Equal to the wet bulb
• D. Equal to the dry bulb

Explanation: A cooling tower cannot normally cool water below the entering-air wet-bulb temperature because that temperature represents the evaporative…

• A. Spray
• B. Rotary
• C. Cylinder
• D. Fluidised bed

Explanation: Paper is dried continuously by passing it over heated rotating cylinders, which transfer heat through the paper and evaporate its…

• A. Dry-bulb
• B. Adiabatic saturation
• C. Dew point
• D. Wet-bulb

Explanation: When liquid evaporates into a large unsaturated gas stream, the liquid cools until evaporation and sensible heat transfer reach…

• A. Both A. and B.
• B. Wet bulb temperature < dry bulb temperature
• C. Dew point < wet bulb temperature
• D. Neither A. not B.

Explanation: For unsaturated air, moisture can still evaporate, so the wet-bulb temperature is below the dry-bulb temperature.

• A. Means discarding a small fraction of circulating water to prevent and limit the concentration
• B. of salt and impurities
• C. Increases the scale forming tendencies of water
• D. Is undesirable
• E. All A., B. & C.

Explanation: Blowdown is the controlled discharge of a small portion of circulating cooling water to remove concentrated salts and impurities.

• A. Vapor load
• B. Blow down
• C. Drift
• D. None of these

Explanation: Drift is the liquid water carried out of a cooling tower by the moving air as entrained droplets.

• A. Both B. and C.
• B. Relative humidity
• C. Partial pressure of vapour
• D. Wet bulb temperature

Explanation: Evaporation adds water vapour to the circulating air, increasing both its relative humidity and water-vapour partial pressure.

• A. Long tube vertical evaporator
• B. Agitated film evaporator
• C. Short tube evaporator
• D. Calandria

Explanation: An agitated film evaporator is suitable for concentrating rubber latex because agitation handles viscous material and the thin film gives…

• A. Increasing the air velocity and area of exposed wet surface
• B. All A., B. and C.
• C. Reducing the humidity of the air
• D. Reducing the barometric pressure

Explanation: Evaporation in a cooling tower is enhanced by faster air movement, more exposed wet area, lower air humidity, and lower barometric…

• A. Solar evaporation
• B. Freeze drying
• C. Vacuum evaporation
• D. Electrolysis

Explanation: Vacuum evaporation removes water from brine at reduced pressure, giving better control and producing purer salt than solar evaporation…

• A. L.D. converter
• B. Blast furnace
• C. Rotary kiln
• D. Recuperator

Explanation: A recuperator transfers heat from hot exhaust gases to incoming air or gas, so high thermal conductivity reduces the resistance to heat…

• A. Cost benefit analysis
• B. Floor area availability
• C. Terminal parameters
• D. Evaporation capacity required

Explanation: Adding effects saves steam but increases equipment and operating complexity, so the optimum is found by comparing the economic benefit…

• A. Parallel flow with equal heat capacities
• B. Counter flow with unequal heat capacities
• C. Counter flow with equal heat capacities
• D. Parallel flow with unequal heat capacities

Explanation: For counterflow with equal heat-capacity rates, both temperature profiles have the same slope, so they appear as parallel straight lines…

• A. Steel
• B. Lignite
• C. Lime stone
• D. Water

Explanation: Heat stored for the same mass and temperature rise is mC_pΔT, so the material with the greatest specific heat stores the most heat.

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

Explanation: In a fluidised bed dryer, vigorous particle movement makes convection the dominant heat-transfer mode, while radiation contributes very…

• A. Steel
• B. Glass wood
• C. Copper
• D. Fireclay bricks

Explanation: For the same heat flow, area, and thickness, the temperature drop varies inversely with thermal conductivity.

• A. Remain same
• B. Increases
• C. Decreases
• D. May increase or decrease; depends on the altitude where snow melts

Explanation: Melting snow requires latent heat, which is drawn from the surrounding atmosphere and lowers its temperature locally.

• A. Refrigerant cooling
• B. Evaporator
• C. Throttling
• D. Condenser

Explanation: The tubes at the back release heat to the surroundings and condense the high-pressure refrigerant vapour into liquid.