Free Heat Transfer Operations MCQs with Answers

• A. Preheating the fuel gas
• B. Increasing the draft in the furnace
• C. Oxygen enrichment of combustion air
• D. Preheating the combustion air

Explanation: Increasing furnace draft usually admits more excess air, which dilutes the fuel gas and lowers the adiabatic flame temperature.

• A. 10-15
• B. 45-50
• C. 25-30
• D. 65-70

Explanation: Lumpy-coal furnaces lose substantial heat through hot flue gases, radiation, incomplete combustion, and furnace-wall losses, so their…

• A. None of these
• B. Open hearth furnace
• C. Coke ovens
• D. Soaking pit

Explanation: A soaking pit can recover heat from outgoing furnace gases to preheat the combustion air, making it a recuperative furnace.

• A. Positive pressure exists in the furnace
• B. The fan operates hot and hence blades are liable to corrosion and erosion
• C. Air is sucked in, so air leaks are more and hence the furnace efficiency is reduced
• D. None of these

Explanation: A forced-draught fan pushes combustion air into the furnace, producing pressure above atmospheric pressure.

• A. Coke oven heating chamber
• B. Both A. and B.
• C. Open hearth furnace
• D. Neither A. nor B.

Explanation: Both coke-oven heating chambers and open-hearth furnaces use regenerative arrangements, storing heat from waste gases and returning it to…

• A. More of CO2 in flue gas
• B. Less of excess air
• C. More of CO in flue gas
• D. More of excess air

Explanation: An oxidising furnace atmosphere requires oxygen in excess of the stoichiometric combustion requirement, so excess air must be increased.

• A. Use of waste heat recovery equipments
• B. Size of the furnace
• C. Emissivity of the refractory walls
• D. Thickness of the stock

Explanation: Heat transfer to the stock is governed by factors such as furnace geometry, refractory emissivity and stock thickness.

• A. Protect the charge from the effects of the products of combustion
• B. Both A. & B.
• C. Smooth out temperature inequalities on the combustion side of the muffle wall
• D. Neither A. nor B.

Explanation: A muffle separates the charge from direct contact with combustion gases and also helps distribute heat more uniformly through its wall.

• A. Solid fuels
• B. Hydrocarbon containing fuel gases (e.g. coke oven gas, refinery gas etc.)
• C. Both A. and B.
• D. Neither A. nor B.

Explanation: Solid fuel cannot be conveniently preheated before firing, and hydrocarbon-rich fuel gases are generally not preheated because heating can…

• A. Pulverised coal
• B. Furnace oil
• C. Coke oven gas
• D. Blast furnace gas/mixed gas

Explanation: Blast-furnace stoves burn blast-furnace gas, often supplemented by mixed gas, to heat the refractory checkerwork.

• A. Roasting/reduction of ores
• B. Annealing steel coil
• C. Heating air
• D. Steel melting

Explanation: A reverberatory furnace transfers heat mainly by radiation from the flame and hot roof to the charge, making it suitable for roasting and…

• A. Coke oven
• B. High pressure boiler
• C. Beehive coke oven
• D. Blast furnace stoves

Explanation: A high-pressure boiler commonly uses an induced-draught fan to draw flue gases through the furnace and boiler passes before discharge.

• A. Natural draft furnace
• B. Tunnel Kiln
• C. Rotary Kiln
• D. Batch furnace

Explanation: Cement manufacture uses a rotary kiln, in which the inclined rotating shell continuously moves and mixes the raw meal through drying…

• A. Low reactivity of carbonised residue containing high proportion of iron & sulphur
• B. Low forced draft & fuel bed temperature
• C. Thick firebed and preheated primary air
• D. All A., B. and C.

Explanation: Poorly reactive residue, inadequate draught, unsuitable bed conditions, a thick firebed and preheated primary air can create local…

• A. < 2
• B. < 5
• C. < 8
• D. < 10

Explanation: A well-adjusted gaseous-fuel furnace aims for only a small excess of air, commonly keeping flue-gas oxygen below about 2%.

• A. Fans
• B. Arrangement of heating stock in the furnaces
• C. Location of outlet ports and heating & combustion devices
• D. All A., B. and C.

Explanation: Gas circulation in a furnace is controlled by fan action, the arrangement of the stock, and the positions of outlets and heating or…

• A. Thermal efficiency of the process
• B. Sources of heat losses
• C. Scope of reduction of heat losses
• D. All A., B. and C.

Explanation: A furnace heat balance accounts for heat supplied and heat used or lost, so it can give efficiency, identify loss sources, and show where…

• A. Reverberatory furnace
• B. Walking beam reheating furnace
• C. Tower furnace
• D. Tunnel kiln

Explanation: A reverberatory furnace is directly fired because combustion gases transfer heat directly to the charge, usually by radiation from the…

• A. Hood annealing furnace
• B. Both A. and B.
• C. Muffle furnace
• D. Neither A. nor B.

Explanation: A muffle furnace heats the charge through a surrounding hot wall rather than exposing it directly to combustion gases.

• A. Higher calorific value
• B. Smokeless burning
• C. Better combustion
• D. Less erosion on furnace wall

Explanation: Pulverising coal greatly increases its surface area, allowing rapid and more complete mixing with air and therefore better combustion.