I've been having trouble deciding how to design a 194.0 °F (90ºC) bioreactor for cell culture (not cell culture now but I do need to get to that temperature to take sample). Its supposed to be an incubator, basically a 3mm thick 5.5"x5.5"(14 cm) acrylic box, but I'm not sure If I can reach that temperature by only using 2 20W bulbs (how can I calculate the amount of bulbs needed?) or if I should use a PTC Resistor like [this one.](https://alexnld.com/product/ac-dc-5...MIhLnm4fn63QIVmbrACh1Hug5ZEAYYAiABEgIWtPD_BwE)


The objective is to regulate the temperature inside the box from 60º to 90º C and I'm planning on using a thermistor and an Arduino to regulate the temperature, but I'm convinced there must be an easier way.

Also, would you change the material from acrylic to something else? Would you use a small fan to regulate heat dispersion? And finally, how would you protect the electronics (PCB, Arduino, electrodes) inside the box?

Any help is greatly appreciated.

 

I would use a couple of 10 ohms resistors 50W each, or a soldering iron heating element, and use your Thermistor Arduino circuit to control the temperature, with pwm DC or pulsed on/off.

 

You box appears to be missing a dimension, unless the 3 mm is (inside?) height.

40 W may not be enough heat if there is no insulation. 90 °C is hot enough to generate considerable convection assuming your ambient is "room temperature." I would stick with a heater of relatively fixed resistance, otherwise your hormones will be fighting with your capillaries (old Bugs Bunny reference). Do you want to put the heater inside the box or on the outside? If outside, a flexible heater, typically made of a foil like material in a serpentine pattern or the like laminated with polyimide film might work well. Unless you use two temperature sensors, one for the heater itself and one for the air temperature of whatever you are actually measuring inside the box, you run the risk of the heater temperature rising well above the melting point of the acrylic. An aluminum heat spreader plate might be useful, especially with "lumped" heaters like resistors. A tiny fan might be helpful, but most probably will die at 90 °C, plus you might have issues with blowing contaminants into your culture vessels.

The temperature control circuit should live outside the box. Many electronic components in use these days have a maximum operating temp of 105 °C, but there are still lots that are rated for only 70-85 max. Things like Arduinos are probably made with the expectation of ambient less than 50 °C,

Some acrylic has a glass transition temperature as low as 85 °C but most is higher. Polycarbonate's glass transition temp is over 140 °C. It is very tough but very prone to scratching and I don't know anything about "gluing" it. You might actually find a suitable container off the self as a steam table dish from a food service supplies vendor. They come in an assortment of square and rectangular sizes and depths. I think Rubbermaid Commercial makes such things, but I'm not sure. Polymethylpentene is usable at over 200 °C, but again I know nothing of fab'ing methods. There are staining boxes in PMP available, but I don't know about sizes. It is also used for some food containers.

Omega Engineering is a good place to look for controllers and heaters. They won't be the cheapest, but it is one stop shopping for lots of things like this.