When is very high thermal conductivity not a priority? Identify the furnace/service where high thermal conductivity of the refractory is least important.

Introduction / Context:
Thermal conductivity of refractories governs heat flow through furnace walls and internal structures. In heat exchangers like regenerators and recuperators, high conductivity improves heat transfer. In contrast, in furnaces where containment and insulation are key, lower conductivity reduces heat losses and improves temperature uniformity.

Given Data / Assumptions:

• Comparison among regenerators/recuperators (heat-exchanging roles), blast furnaces (severe thermal and chemical loads), and muffle furnaces (isolated chamber).
• Goal: identify where high conductivity is not a prime requirement.

Concept / Approach:
Coke-oven regenerators and recuperators rely on refractories to temporarily store and transfer heat; higher conductivity aids this duty. Blast furnaces require robust linings; conductivity interacts with cooling and skull formation strategies but cannot be arbitrarily low. A muffle furnace uses a lined chamber to separate products from combustion gases; here the lining’s role is containment and insulation, so low conductivity (good insulation) is preferred, making high conductivity unimportant or even undesirable.

Step-by-Step Solution:

Verification / Alternative check:
Furnace design texts specify insulating refractories (low k) for muffle walls to minimize energy consumption and stabilize internal temperatures.

Why Other Options Are Wrong:

• Regenerators/recuperators: heat transfer function favors higher k.
• Blast furnace: complex duty; excessively low k can impair thermal management.
• Waste-heat boilers: metallic heat exchange dominates; refractory selection focuses on protection, not maximizing k in the lining.

Common Pitfalls:
Assuming one “best” conductivity fits all furnaces; neglecting that high-k linings increase heat loss in insulated chambers.

Final Answer:
Muffle furnace (product isolated from flame)