Revised design of channels for recirculating air flowThe prototype Airflow reactors rely on the recirculation of heated air during heating phases, as air is passed from fan heater, past the sample tubes, then drawn back to the entry port of the heater. During the cooling phase, cool external air is drawn into the vessel, and heated air expelled by the concerted action of two blower fans.
In order to facilitate the efficient return flow of heated air in the vessel, the two blower fans were repositioned to a vertical orientation, and the two return channels were expanded to take up the entire width of the vessel (rather than two narrower side channels), and the mixing chamber beneath the fan heater was made larger. In addition, the heating column and return channel were printed in two pieces that stacked on top of each other.
Comparison of first (left) and revised (right) designs
The revised design produced a more compact vessel with wider return flow channels. The design was printed in heat-resistant Extruder GreenTEc Pro filament, fans and heater were installed, then the vessel was tested under control of the Arduino-based test-rig with touchscreen.
1 / 5 • Rendering of design
Printed and wired prototype
The prototype reactor was operated with "mock" PCR conditions (95ºC 30sec; 55ºC 30sec; 72ºC 1 min) under two conditions. (i) With the unmodified car fan heater with the supplied 15mmx60mmx60mm axial fan, and (ii) after replacement of the heater fan with a SanAce60 25mmx60mmx60mm higher power server fan.
These plots are worth expanding to look at in more detail. The revised vessel produced the fastest temperature cycling times that I have seen so far. The speed of cycling increased even further when the heater fan was upgraded to the 25mm San Ace 60 model. In addition, some uneven heating was seen with the slower 15mm fan. (The outer position on the sample rack heated more slowly than the central position). However, this difference was largely eliminated after installation of the hoigher powered 25mm fan. One possibility is that the higher velocity of air propelled by the 25mm fan may have promoted better dispersion and mixing after collision of the airstream with the baffle in the manifold, and more even distribution of heated air to the samples.
Design of console to house control electronicsThe heating/cooling column was designed to attach to a consolde with space for mounting a control touchscreen and internal electronics - again, printed in GreenTEC Pro for heat resistance, with space for mounting cable attachments and circuit boards. The front panel is printed to hold a 3.2" 4D Systems touchscreen.
1 / 9 • Airflow reactor with mini-console
Printed chassis:
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