Kiln heat simulator

Each kiln runs an independent exploratory vertical slice of a round electric kiln. The default is 25 kW available element power and an approximately 71 × 69 cm inner chamber. In AB Comparison, shared playback advances both kilns; in Single kiln mode, only the selected kiln advances and the other stays hidden. Loads, programmes, available power and manual probes belong to each kiln. Previous and Next align both models at the same programme segment's target or hold end in comparison mode, even when they reach that event at different elapsed times. This 2D slice cannot reproduce all airflow and radiation paths.

How the model works

The grid gives air, brick, shelves, pots and elements different heat capacities. Neighbouring cells exchange heat. Early in the firing, warm air rises strongly through open vertical passages, while two closed circulation paths carry it up the sides, across the top and back towards the lower chamber. An additional side bypass represents rising air travelling around shelves in front of and behind this vertical slice. These transfers conserve energy and weaken as radiation becomes dominant.

Element radiation heats the exposed surfaces of pots and shelves. Hot brick, furniture and ware then exchange radiation across visible air paths. A pot also has a separate interior-clay temperature for each wall cell: its surface first receives heat from the chamber, then conducts it into the body and along connected clay cells of the same pot. This internal heat store slows the ware and can continue to warm during a thermocouple-controlled hold. Shelves and posts store heat and conduct it along the solid. Heat in the wall passes through inner refractory and outer insulation before reaching surfaces exposed to the room. A hold can reduce the spread without making every place identical.

The ramp/hold controller reads a simulated thermocouple near the side wall. It requests a duty cycle, while the element relays switch on and off in 40-second cycles. Each ramp's requested temperature advances at its programmed rate, but its hold and the next segment begin only after the thermocouple actually reaches the target. A 9999°C/h heating ramp requests full available power; it does not impose that rate on the kiln. Programmed cooling segments likewise wait for the measured drop. After the final row, the controller switches off the elements and the simulation continues cooling naturally until the kiln thermocouple reaches 200°C. This final cooling is separate from the programme and is included in the graph and timeline. Available power is an editable kW value that changes element energy only: it does not change heat transfer, losses or controller settings. Low power can lengthen a firing or prevent it reaching a target.

Reading the heat map

Absolute temperature uses the same 0–1300°C colour scale throughout the firing, so colours at different times can be compared directly. Spatial difference rescales to the current chamber range, excluding the coils from its endpoints, to reveal smaller gradients at a chosen moment. Change in last 30 min shows the actual change in each cell over the preceding thirty simulated minutes: blue cooled, orange warmed and pale cells changed little. In the first thirty minutes it compares with the start. It displays calculated temperature changes, not animated airflow.

Pot interiors are coloured by their modelled body temperatures; the thin coloured edges indicate exposed surface temperature. Click a pot to inspect its current surface and interior-clay temperatures below the graph.

The central chamber spread is the difference between the 10th and 90th percentile temperatures of central air, shelves and pot interiors. It excludes element pixels and the brick shell. Its dotted graph line uses the right-hand °C axis; the kiln and manual TC lines use the left. Shared graph zoom changes both temperature axes together and gently zooms toward the right end of each firing timeline. A faint dotted guide shows 100°C below each programme’s highest target; it is a reference temperature, not a cone or heatwork calculation. Its readout compares the current spread with the start of a hold, and the event log records the spread at each hold's end. A faster firing can widen this spread while a hold narrows it. The top and floor can still remain cooler as the elements cycle.

What to expect

The capacities, view factors, two-layer clay approximation, wall losses and control gains are illustrative and have not been calibrated against your kiln logs or cone packs. A real mug's wall thickness, clay body and stacking geometry would change its lag.

Background: Orton's explanation of convection, radiation and conduction through ware.