Difficulty: Medium
Correct Answer: Type of fuel used (solid, liquid, or gaseous)
Explanation:
Introduction / Context:
In high-temperature furnaces, heat transfer to the charge is dominated by radiation from flames, hot gases, and refractory walls. While the choice of fuel affects combustion control, emissions, and convenience, the fundamental radiative/convective heat-transfer drivers are more directly tied to temperatures, emissivities, and geometry.
Given Data / Assumptions:
Concept / Approach:
Heat transfer rate q_rad ∝ ε_eff * σ * (T_hot^4 − T_stock^4) and depends on effective emissivity and view factors. Fuel type per se is not a primary variable; what matters is the achieved gas/wall temperatures and emissivity. Therefore, among the listed factors, “type of fuel” exerts the least direct influence when temperatures and excess air are properly controlled.
Step-by-Step Solution:
Identify dominant drivers: high flue-gas/wall temperatures, emissivities, geometry, and stock initial temperature.Compare to “fuel type”: indirect effect through achievable flames, but not a first-order variable when all else is equal.Select the least direct factor: type of fuel.
Verification / Alternative check:
Engineering practice shows comparable heat transfer can be achieved with gas, oil, or pulverized coal, provided temperature and atmosphere are controlled, supporting the choice.
Why Other Options Are Wrong:
Flue-gas temperature, emissivity, initial stock temperature, and geometry all explicitly enter the radiative/convective heat-transfer calculation.
Common Pitfalls:
Overemphasizing the inherent “quality” of a fuel rather than the achieved thermal field; process variables matter more than fuel identity.
Final Answer:
Type of fuel used (solid, liquid, or gaseous)
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