Free Heat Transfer Operations MCQs with Answers

• A. Economiser
• B. Steam superheater
• C. Air preheater
• D. All A., B. and C.

Explanation: Flue-gas heat can be recovered successively in an economiser for feedwater, a superheater for steam, and an air preheater for combustion…

• A. Regenerator
• B. Economiser
• C. Ceramic recuperator
• D. Waste heat boiler

Explanation: A regenerator stores heat in a solid matrix during one part of the cycle and gives it back during another, so its operation is periodic.

• A. Reduction in scale losses
• B. Increase in flame temperature
• C. Increase in calorific value of the fuel
• D. Saving in fuel consumption

Explanation: Preheated air raises flame temperature, reduces scale formation and saves fuel by improving heat transfer and combustion.

• A. Rotary kilns
• B. Blast furnace
• C. Coke oven heating chamber
• D. Blast furnace stoves

Explanation: Blast-furnace stoves are regenerative heaters operated in alternating heating and air-heating cycles, so they are periodic furnaces.

• A. None of these
• B. Gas velocity in furnace
• C. Ratio of wall surface to surface of stock
• D. Size of the furnace

Explanation: Furnace capacity depends on furnace size, gas velocity and the relative wall-to-stock surface area because these affect heat-transfer rate…

• A. Change in volume during a change of temperature
• B. All A., B. and C.
• C. Furnace pressure in conjunction with draft in flues
• D. Difference in density between hot and cold gases

Explanation: Gas circulation may result from thermal expansion, density differences between hot and cold gases, and pressure differences produced by…

• A. Elimination of cold spot at the bottom of the charge
• B. Increase in heating capacity/m2 of floor space
• C. Reduction in the temperature of furnace gases
• D. Protection of the periphery of the charge from excessive radiation

Explanation: Underfiring is used to remove the cold region near the bottom, shield the charge edges from excessive radiation and lower the furnace-gas…

• A. Store smaller quantity of waste heat
• B. Are lighter & compact
• C. Involve higher initial cost
• D. All A., B. & C.

Explanation: A regenerator uses refractory checkerwork to store heat cyclically and generally needs a heavier, more expensive arrangement than a…

• A. Before the I.D fan
• B. After the I.D. fan
• C. Near the top of the chimney
• D. Anywhere after the I.D. fan

Explanation: The damper is placed on the furnace side of the induced-draught fan so it can regulate flue-gas flow and furnace pressure before the fan…

• A. Electric arc struck between electrodes and the charge
• B. Flow of current through a heating element
• C. Combination of induced current and skin effect
• D. None of these

Explanation: In a resistance furnace, electrical resistance converts the current flowing through a heating element into heat, which is then transferred…

• A. Low emissivity
• B. High thermal conductivity
• C. Both A. and B.
• D. Neither A. nor B.

Explanation: High thermal conductivity allows heat to penetrate the stock rapidly, while low emissivity reduces the importance of radiative surface…

• A. Soaking pit
• B. None of these
• C. Reheating furnace
• D. Muffle furnace

Explanation: A muffle furnace heats the charge indirectly through a separate refractory chamber, so combustion gases or the heating elements do not…

• A. Cold rolled steel coil annealing
• B. Open hearth
• C. Soaking pit
• D. Walking beam reheating

Explanation: Cold-rolled steel coils are annealed in a controlled neutral atmosphere to prevent oxidation and preserve the required surface finish.

• A. 15
• B. 40
• C. 70
• D. 85

Explanation: A walking-beam slab-reheating furnace typically has a thermal efficiency near 40 percent, with the remainder lost through exhaust gases…

• A. Combination of induced current and skin effect
• B. Induction and resistance
• C. Current flow through a heating element
• D. None of these

Explanation: In a low- or standard-frequency induction furnace, the alternating magnetic field induces currents in the charge, and the electrical…

• A. Radiation
• B. Convection
• C. Conduction
• D. Cannot be predicted

Explanation: At about 1250°C, the radiative heat-transfer rate is dominant because it varies approximately with the fourth power of absolute…

• A. Waste heat recovery from flue gas
• B. Minimising heat losses from furnace walls
• C. Maintaining proper draught
• D. All A., B. and C.

Explanation: Furnace efficiency increases when useful heat is recovered from flue gases, wall losses are reduced by insulation, and draught is properly…

• A. Ostwald chart
• B. Cox chart
• C. Sankey diagram
• D. None of these

Explanation: A Sankey diagram represents the quantities in a heat or energy balance by bands whose widths are proportional to the quantities.

• A. Coke ovens
• B. Open hearth furnace
• C. Neither A. nor B.
• D. Both A. & B.

Explanation: Regenerators store heat from outgoing hot gases and return it to incoming combustion air or gas.

• A. All A., B. and C.
• B. Calcining
• C. Roasting
• D. Smelting

Explanation: A shaft furnace is a vertical furnace used for processes in which solids move downward through a hot gas stream, including smelting…