Free Heat Transfer Operations MCQs with Answers

• A. Tubes to avoid the expansion of high pressure shell construction
• B. Shell side for smaller total pressure drop
• C. Shell side, if the flow is counter-current and tube side if the flow is co-current
• D. Shell side for large overall heat transfer co-efficient

Explanation: Routing the high-pressure fluid through the tubes reduces the required thickness and cost of the pressure-containing shell, while tube…

• A. It is unsuitable for concentrating those liquids, which form a scale or deposit salt
• B. It is suitable for process, in which the final product is a liquor instead of solid
• C. Liquor flows inside the tube, while the steam is outside submerging the tube
• D. height = 2.5-4 metres
• E. Its usual dimensions are: tube dia = 2-3 cms; evaporator body dia = 1-4 metres and evaporator

Explanation: In a horizontal-tube evaporator, steam generally flows inside the horizontal tubes and the liquor remains outside, where it is heated by…

• A. Electric immersion
• B. None of these
• C. Steam coil
• D. Pipestill

Explanation: A pipestill, or fired tubular heater, heats crude by passing it through tubes exposed to hot combustion gases before it enters the…

• A. Large latent heat
• B. Low viscosity
• C. Small latent heat
• D. None of these

Explanation: Water absorbs a large amount of heat during vaporisation because its latent heat of vaporisation is high.

• A. Forced
• B. Natural
• C. Induced
• D. None of these

Explanation: Natural-draft towers use the density difference between warm, moist tower air and cooler ambient air to establish airflow.

• A. Dew point
• B. Wet bulb
• C. Both A & B
• D. Neither A nor B

Explanation: For unsaturated air, the dry-bulb temperature is higher than the wet-bulb temperature, and the wet-bulb temperature is higher than the…

• A. Evaporation
• B. Blowdown
• C. Entrainment
• D. All A., B. & C.

Explanation: Cooling-tower water is lost through evaporation, drift or entrainment, and intentional blowdown used to control dissolved solids.

• A. Both A. & B.
• B. Is equal to the number of kg, of water circulated times the cooling range
• C. Means the amount of heat thrown away (KCal/hr.) by the cooling tower
• D. Neither A. nor B.

Explanation: Cooling-tower heat load is the heat rejected per hour, and for water it is calculated approximately as mass flow rate multiplied by the…

• A. Cold water leaving the tower and the wet bulb temperature of the surrounding air
• B. Hot water entering the tower and the wet bulb temperature of the surrounding air
• C. Hot water entering the tower and the cooled water leaving the tower
• D. None of these

Explanation: Cooling-tower range is the temperature drop of the circulating water, calculated as hot-water inlet temperature minus cooled-water outlet…

• A. High maintenance cost
• B. Non-uniform & low production rate
• C. High labour cost & low heat economy
• D. All 'a', 'b' & 'c'

Explanation: Batch tray dryers commonly give non-uniform drying and low production rates, while also requiring substantial labour and having poor heat…

• A. 7
• B. 70
• C. 0.7
• D. 150

Explanation: For water near 20°C, the Prandtl number is approximately 7. It is much greater than unity because momentum diffusivity is about seven…

• A. Diffusion
• B. Heat transfer
• C. Both A. and B.
• D. Neither A. nor B.

Explanation: In a drum dryer, the wet material contacts a heated rotating drum and drying is mainly governed by the rate at which heat passes through…

• A. Range is 15°F
• B. Approach is 10°F
• C. Both A. & B.
• D. Neither A. nor B.

Explanation: The range is the decrease in water temperature, 95 - 80 = 15°F. The approach is the cold-water outlet temperature minus the entering-air…

• A. Tray
• B. Vacuum
• C. Tunnel
• D. Rotary

Explanation: Calcium ammonium nitrate is commonly dried industrially in a rotary dryer, which provides continuous solids handling and good contact with…

• A. Falling film
• B. Short tube
• C. Vacuum
• D. Long tube

Explanation: Long-tube evaporators are suitable for foaming liquids because the liquid and vapour move rapidly through long vertical tubes, limiting…

• A. 50
• B. 100
• C. 78
• D. None of these

Explanation: At 100% saturation, the air is fully saturated and no further evaporation occurs from the wet bulb.

• A. Drum
• B. Cylinder
• C. Rotary
• D. Freeze

Explanation: Rotary dryers are well suited to free-flowing granular solids because the rotating shell continuously lifts and tumbles the material…

• A. None of these
• B. Partial pressure of water vapor
• C. Relative humidity
• D. Wet bulb temperature

Explanation: With recirculated water, ideal evaporative cooling is approximately adiabatic saturation, so the wet-bulb temperature remains constant.

• A. None of these
• B. Relative humidity
• C. Partial pressure of vapour
• D. Wet bulb temperature

Explanation: In adiabatic evaporative cooling, some water evaporates, so the air's humidity and water-vapour partial pressure increase while its…

• A. Humidity
• B. Both A. & B.
• C. Temperature
• D. Neither A. nor B.

Explanation: Natural-draft cooling towers depend on a strong density difference between warm, moist tower air and the cooler outside air.