Determinants of heating capacity in a continuous reheating furnace: Which combination of furnace and stock properties most strongly governs throughput capability?

Introduction / Context:
Throughput in a reheating furnace depends on how quickly heat can be delivered to and absorbed by the stock. Radiative heat transfer dominates at high temperature, but geometry and surface properties also strongly influence effective heat flux and uniformity.

Given Data / Assumptions:

• Continuous furnace with preheat, heating, and soak zones.
• Predominant radiative exchange between walls/flames and stock.
• Steel slabs or billets with known surface condition.

Concept / Approach:
Heat transfer rate scales with radiative exchange area and temperature difference (approx. proportional to T^4 in radiation correlations) and is modified by emissivity. The wall-to-stock surface ratio affects how much radiating surface is available per unit of charge surface; larger hearth area and higher furnace temperature raise potential heat input, while higher stock emissivity improves absorption.

Step-by-Step Solution:

Verification / Alternative check:
Furnace models and performance tests show capacity gains when emissivity coatings are used or when higher wall temperatures and improved view factors are achieved.

Why Other Options Are Wrong:

Common Pitfalls:
Ignoring emissivity changes due to scale or surface condition; these can measurably shift heating rates.

Final Answer:
all (a), (b) and (c).