After a few days of project downtime due to a busy schedule, I finally had time today to run another airflow test on the dry box. This time, I added two centrifugal fans inside the sealed container: one positioned at the PTC outlet, configured to pull hot air upward, and another mounted at the top of the enclosure, used to push air downward.
The goal was to improve the internal air circulation and achieve more even temperature distribution across the enclosure. To verify the effect, I reused the previous monitoring layout: two SNZB-02LD sensors were placed inside – one near the PTC outlet to measure the hottest area, and one near the top of the filament spool to observe heat accumulation. Meanwhile, the bottom-right corner (farthest from the PTC outlet) was monitored by the temperature sensor attached to the SONOFF TH Elite.
Additionally, for this test I swapped out the previous 100W PTC heater and replaced it with a 50W version. The goal was to avoid excessive local heat buildup near the structural support – especially in case airflow isn’t able to dissipate the heat quickly enough. In previous tests, higher-wattage heating had already caused some minor deformation of nearby printed parts, so I’m now taking a more conservative approach to thermal output.
Once the test started, I immediately noticed that the temperature rise was much more balanced than before. As expected, the 50W PTC produced much less heat, causing the overall temperature in the sealed box to rise gradually and uniformly.
In the early phase, while temperatures were still under 50°C, the difference between the PTC outlet and the top sensor remained within 2–3°C. Interestingly, at the very beginning, the top sensor even reported a slightly higher reading than the area near the PTC outlet.
Once the outlet temperature reached around 50°C, the difference between the two SNZB-02LD sensors grew to about 5°C, and the TH Elite sensor at the bottom corner showed about 10°C lower than the PTC outlet.
This pattern held up until the outlet temperature approached 65°C, after which the overall temperature rise began to slow down, and the temperature gaps gradually widened. The maximum differences grew to about 10°C between top and bottom, and 15°C between PTC outlet and the far bottom corner, once the outlet temperature reached around 80°C.
It’s becoming clear that achieving perfectly uniform temperature throughout a sealed space is extremely difficult – if not impossible. Even in my earlier testing of the Bambu Lab AMS HT, I saw clear temperature differences inside the enclosure.
So in that context, I’m actually very happy with the improvements in this round.
Although there was still a temperature gap of around 15°C when the PTC outlet reached 80°C, the average difference around 65°C—the target drying zone – was consistently held within 5–8°C. That’s a significant improvement over my previous test, and for certain common materials, this level of performance is already sufficient. However, for high-temperature engineering filaments, I’ll still need to find a way to push the internal temperature higher – ideally reaching 90°C or more to meet the drying requirements.
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