Salt bath furnace heat-transfer mechanism: When a workpiece is immersed in a molten salt bath for heating, which mode of heat transfer to the charge dominates?

Introduction / Context:
Salt bath furnaces heat parts by immersing them in molten salts. These units are valued in heat treatment for rapid, uniform heating and minimal oxidation compared to direct-fired or gaseous atmospheres.

Given Data / Assumptions:

• Part is submerged in molten salt at controlled temperature.
• Bath is agitated naturally (buoyancy) or mechanically.
• Surface oxide formation is limited by exclusion of air at the metal surface.

Concept / Approach:
Heat transfer from the salt to the part occurs primarily via convection in the liquid boundary layer coupled with some conduction within the part. Because the surrounding medium is a liquid with high heat capacity and good thermal contact, convective heat transfer coefficients are significantly higher than for gases, and radiation is comparatively less important at typical salt bath temperatures.

Step-by-Step Solution:

Verification / Alternative check:
Empirical heat-up times correlate with liquid-side convection coefficients rather than radiative exchange equations.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing overall heating (including in-part conduction) with the primary surface mechanism from bath to part.

Final Answer:
convection