Heat-Up & Cool-Down Time

"How long until it is up to temperature?" — heat soak before a test, oven warm-up, quench time, electronics stabilising. It is an exponential, so the useful landmarks are 63% in one time constant, 95% in three, 99% in five, and the target is never quite reached. The Biot number decides whether any of this applies.

The lumped model treats the object as internally uniform, which is only true when Bi = hL/k < 0.1. Above that the surface races ahead of the core and this understates the time to bring the core up — the error is always in the unsafe direction for a soak test. Radiation is not included, and above roughly 200 °C it becomes significant, making real heat-up faster than shown. Get h from the Convection Coefficient tool rather than guessing, and material properties from the material reference. Defaults are a 10 kg aluminium block in a 200 °C oven.