Temperature Distribution
The incubator prototype underwent long-term testing to evaluate temperature and CO2 stability under room temperature conditions. Temperature regulation was tested continuously for 3 months at the IRNAS office, with no observed abnormalities. In addition, the incubator was tested in a controlled environment with lower external temperature (18°C) for 1 week. Using the primary regulatory algorithm, the average internal temperature settled at 36.7°C (target 37°C), however, this was resolved with adjustment of the regulatory algorithm. Heat distribution was tested extensively with trays at various positions in the incubator, as well as several configurations of heating and agitation. Temperature sensors were positioned into 4 liquid filled syringes (emulating medium reservoirs) and placed into the incubator as shown in Figure 3. Altogether, the following variables were tested:
tray positions (all 4 slots, 3 out of 4 slots in all possible combinations)
tray fan size (small fans, large fans or no fans at all)
heater openness (the heater has an internal fan which was kept open or closed)
A total of 30 experiments, examining all possible combinations were performed. The results are shown in the figure below. The bars show the average temperature of all temperature sensors in the incubator and are categorized by heater-fan status. All configurations showed temperature deviations at different positions in the incubator. As expected, the largest variation was measured with the heater closed and without active tray fans (σ = 0.79°C, with a difference between coolest and hottest position being equal to 2.1°C), while the smallest variation was measured with the open heater and active small fans (σ = 0.28°C, largest measured difference equal to 0.9°C). Conventional laboratory incubators typically exhibit a temperature variation of 0.2°C between the hottest and coolest position. To improve spatial temperature variation in the incubator, we propose adding heating regulation to individual trays.
On the left a schematic of the experimental set-up is shown – the incubator with 5 possible measurement positions, 4 possible trays with fans and heater. The door is shown for orientation. Measurements were logged at 4 positions simultaneously, with either all 4 trays in the incubator or with 3 trays (1 was removed) in the incubator. All possible positional combinations were measured. On the right measurement results are shown. Two variables were tested, 1) heater ventilation (heater open – ho, or heater closed – hc) and 2) fan configuration on individual trays (small fans – sf, large fans – lf or no fans – nf). Temperature was logged for at least 1 hour, or until it was stable.
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