Need help designing a 194.0 °F bioreactor for cell culture.

stopfortheklopp · Oct 9, 2018

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 a 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.](**broken link removed**)

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.

dknguyen · Oct 9, 2018

An arduino and thermistor sound good to me. I assume you need modulated temperature control rather than bang-bang (full-on, full-off) temprature control.

Acryllic has a max operating temperature of 80C so you can't make it from acryllic.

Why would you put the electronics inside the box? It's already small enough and you have two enormous lightbulbs which will fill most of it already, and possibly a fan. Not to mention it'll also be hot which isn't good for the electronics. The only thing you need inside the box are the heating elements and sensors.

You may not even be able to find a fan small enough that can also withstand those high temperatures. But I would think that at such close proximity to the light bulb (it's could be a LOT hotter than 90C in operation especially if you bang-bang instead of modulate it) the temperature gradient might be too intense if the bulbs are real close to the sample so you really would need a fan in that case.

Typically, an NTC thermistor is used for temperature sensing because technical reasons (material characteristics I think). Not a PTC. Thermistors are probably your best choice since they have the highest sensitivity but are non-linear. But you have a narrow, known operating temperature range so you can linearize and optimize for that range. RTDs are much more linear, repeatable, and accurate, but not as sensitive and so take additional signal conditioning to work. You probably don't need thermocouples either since you aren't running so hot that they are required and they take some additional signal conditioning as well.

Or you could use thermopiles to have contactless temperature sensing of the surface of interest. It's up to you. I don't know the caveats of your bioculture stuff but I assume you'll be more interested in surface temperature than air temperature and I don't know if you want the thermistor to be in contact with the same surface the culture will be on. I'd use surface heater than lighbulbs to be honest but maybe that's not suitable for cultures. Seems like it would be more effective though.

Note that common PVC wiring is not suitable for 90C operation.

In theory, you can reach any temperature inside any enclosed space if it is insulated well enough since you just keep adding energy to the system and it has nowhere to go (or can't get out fast enough). Maybe first try measuring how hot a 20W light bulb is in normal operation.

Pommie · Oct 9, 2018

I would suggest using soldering iron elements for heating. Most suitable are probably**broken link removed** - note high temp cable. Not sure what you can use as a fan due to the high temp involved.

Mike.

dougy83 · Oct 9, 2018

You can get a ready-made PID temperature controller for <$20 IIRC. then you just need to add a thermocouple and heater (e.g. a lamp).

stopfortheklopp · Oct 9, 2018

dknguyen said:
An arduino and thermistor sound good to me. I assume you need modulated temperature control rather than bang-bang (full-on, full-off) temprature control.

Acryllic has a max operating temperature of 80C so you can't make it from acryllic.

Why would you put the electronics inside the box? It's already small enough and you have two enormous lightbulbs which will fill most of it already, and possibly a fan. Not to mention it'll also be hot which isn't good for the electronics. The only thing you need inside the box are the heating elements and sensors.

You may not even be able to find a fan small enough that can also withstand those high temperatures. But I would think that at such close proximity to the light bulb (it's could be a LOT hotter than 90C in operation especially if you bang-bang instead of modulate it) the temperature gradient might be too intense if the bulbs are real close to the sample so you really would need a fan in that case.

Typically, an NTC thermistor is used for temperature sensing because technical reasons (material characteristics I think). Not a PTC. Thermistors are probably your best choice since they have the highest sensitivity but are non-linear. But you have a narrow, known operating temperature range so you can linearize and optimize for that range. RTDs are much more linear, repeatable, and accurate, but not as sensitive and so take additional signal conditioning to work. You probably don't need thermocouples either since you aren't running so hot that they are required and they take some additional signal conditioning as well.

Or you could use thermopiles to have contactless temperature sensing of the surface of interest. It's up to you. I don't know the caveats of your bioculture stuff but I assume you'll be more interested in surface temperature than air temperature and I don't know if you want the thermistor to be in contact with the same surface the culture will be on. I'd use surface heater than lighbulbs to be honest but maybe that's not suitable for cultures. Seems like it would be more effective though.

Note that common PVC wiring is not suitable for 90C operation.

In theory, you can reach any temperature inside any enclosed space if it is insulated well enough since you just keep adding energy to the system and it has nowhere to go (or can't get out fast enough). Maybe first try measuring how hot a 20W light bulb is in normal operation.

Thank you so much for your input. The incubator would look like this (http://imgur.com/XTlqU2x) What would you use instead of acrylic? Also, which surface heater would you think could be useful for these conditions?

Thanks again

dknguyen · Oct 10, 2018

stopfortheklopp said:
Thank you so much for your input. The incubator would look like this (http://imgur.com/XTlqU2x) What would you use instead of acrylic? Also, which surface heater would you think could be useful for these conditions?

Thanks again

Polycarbonate would work.

What does the set up actually look like when you're using it? Like what sits in it and what does that look like? You can use any heating element you can get your hands on to be honest (like what Pommie said or torn from a hot plate or coffee warmer since you are using an arduino to modulate power through it so it never gets too hot.

ClydeCrashKop · Oct 11, 2018

You could use a large cooking pot. More likely round than square. Some come with a glass lid if you need to see inside. A fan motor can be outside the pot with the shaft going through the side of the pot and the fan blade inside. A bronze bushing could seal the shaft and stabilize it.

Need help designing a 194.0 °F bioreactor for cell culture.

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