Where is a refractory wall used to isolate the charge from the flame? Identify the furnace in which a refractory barrier separates the stock (work) from direct contact with the heat source.

Introduction / Context:
Many processes require heating without exposing the product to flame or combustion products. Furnaces that provide this separation use a refractory “muffle” or wall to isolate the charge from the burner flame while still transferring heat efficiently.

Given Data / Assumptions:

• The question asks for a furnace featuring a refractory wall between heat source and stock.
• Charge quality (avoid contamination/oxidation) is important in such applications.

Concept / Approach:
A muffle furnace places the work inside an enclosed refractory chamber (the muffle). Burners heat the outside of the muffle; heat reaches the stock by radiation and convection through the hot refractory surfaces. This design avoids direct flame impingement and combustion byproducts contacting the product, which is crucial for clean heating and precise treatments.

Step-by-Step Solution:

Verification / Alternative check:
Standard diagrams show a separate muffle box or tube heated externally by burners or elements.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming all indirect-fired units are called “continuous furnaces”—“continuous” describes operation mode, not isolation method.

Final Answer:
muffle furnace