Free Heat Transfer Operations MCQs with Answers

• A. Should be as low as possible i.e., 1 : 2
• B. Should be 1:1 for a batch type furnace
• C. Is the ratio of maximum to minimum permissible heat input rates
• D. Is normally much more for a continuous furnace as compared to a batch furnace

Explanation: Burner turn-down ratio is defined as the maximum permissible heat-input rate divided by the minimum stable permissible heat-input rate.

• A. All A., B. and C.
• B. Vertical
• C. Tangential
• D. Horizontal

Explanation: Pulverised-fuel burners may be arranged for horizontal, vertical, or tangential firing, depending on furnace geometry and the required…

• A. Tunnel kiln
• B. Soaking pit
• C. Rotary kiln
• D. Reheating furnace

Explanation: A soaking pit is a periodic or batch furnace: ingots are charged, heated or soaked, and then discharged.

• A. Temperature control
• B. Measurement of flue gas volume
• C. Movement of gases
• D. Pressure adjustment

Explanation: Furnace aerodynamics concerns the flow and movement of combustion gases, including mixing, circulation, and residence time.

• A. Surface area & emissivity of the stock
• B. Properties of the muffle wall (temperature, area, and emissivity)
• C. Neither A. nor B.
• D. Both A. & B.

Explanation: A muffle furnace heats the charge indirectly, so heat transfer depends on both the charge surface and emissivity and the muffle wall's…

• A. Blast furnace
• B. Glass melting tank
• C. L.D. converter
• D. Soaking pit

Explanation: A blast furnace is a vertical shaft furnace in which solids descend through zones of preheating, reduction and melting while gases rise.

• A. Soaking pit
• B. Coke oven
• C. Steam boiler
• D. Reheating furnace

Explanation: A coke oven normally uses regenerative heating, in which checker-brick chambers store and return heat, rather than a recuperator that…

• A. 50
• B. 65
• C. 85
• D. 99

Explanation: Air or fuel-gas recuperators can achieve thermal efficiencies of roughly 85 percent under favourable operating conditions.

• A. None of these
• B. Reheating furnace
• C. Glass tank furnace
• D. Cupola

Explanation: A cupola is charged intermittently with alternate layers of coke, metal and flux, so it is commonly classified as a batch furnace even…

• A. 50
• B. 100
• C. 150
• D. 250

Explanation: A chimney outlet temperature of about 150°C is a practical compromise: lower temperatures risk condensation and poor draught, while much…

• A. Rate of firing and emissivity of flame
• B. All A., B. and C.
• C. Nature of process; whether batch, continuous or intermittent
• D. Thermal conductivity of the charge & structural materials of furnace

Explanation: Charge heating and furnace losses are governed by firing rate and flame emissivity, material thermal conductivities, and whether the…

• A. To increase heat transfer by convection
• B. To ensure uniform temperature
• C. All A., B. and C.
• D. In furnaces, operating below 750°C

Explanation: Forced gas circulation increases convective heat transfer and reduces temperature differences within the furnace.

• A. Rotary hearth
• B. Shaft
• C. Tunnel
• D. Walking beam

Explanation: A walking-beam furnace advances stock by lifting and walking it forward, reducing contact losses and improving movement and fuel economy…

• A. CO
• B. All A., B. & C.
• C. High CO/CO2
• D. H2

Explanation: Scaling is oxidation of hot stock, so it is reduced by a reducing furnace atmosphere supplied by CO or H2; a high CO-to-CO2 ratio also…

• A. Temperature of flue gas
• B. All A., B. and C.
• C. Thickness of heating stock
• D. Thermal conductivity of stock

Explanation: Furnace capacity depends on the available heat in the flue gas, the stock's ability to conduct heat inward, and the distance heat must…

• A. 50 kcal/hr
• B. 200 BTU/hr
• C. 200 BTU/minute
• D. 200 BTU/day

Explanation: One ton of refrigeration equals 12,000 BTU per hour. Dividing by 60 gives 200 BTU per minute, so option C is the equivalent rate.

• A. Expansion valve
• B. Condenser
• C. Refrigerator
• D. Compressor

Explanation: Vapour-compression systems use a mechanical compressor, whereas absorption systems replace it with an absorber, pump, generator and…

• A. Prandtl number is one
• B. Schmidt number tends to infinity
• C. Nusselt number tends to infinity
• D. Archimedes number is greater than 10000

Explanation: When Prandtl number is one, momentum diffusivity and thermal diffusivity are equal.

• A. Heat conduction to viscosity of a fluid
• B. Cp/Cv of a fluid
• C. Elastic force to pressure force in the fluid flow
• D. Inertial force to elastic force in the fluid flow

Explanation: The Prandtl number is Pr = mu Cp/k, the ratio of momentum diffusivity to thermal diffusivity, so it compares viscous transport with heat…

• A. Density
• B. Specific heat
• C. None of these
• D. Thermal conductivity

Explanation: Thermal diffusivity is given by α = k/(ρCp), so it increases with thermal conductivity when density and specific heat are fixed.