Help needed with the temperature sensor

Thread Starter

tresbien

Joined Mar 25, 2020
3
Hi,

I'm a high school student who is doing a physics research project on the Mpemba Effect and various circumstances that may permit it to occur. My current concern is with the apparatus that I will have to use in the experimental part of the project. In view of that, I would like you to give me any insight and advice that you may have on how to go about this.

As for the premise of the experiment, I have so far considered using a temperature sensor to mark the data of various water samples (Various with respect to their density, temperature or solute within them). Along with that, I would be using a standard refrigerator so as to slowly cool down the samples.

Unfortunately, I haven't been able to find a suitable sensor as most of them lack the waterproof quality. I would once again appreciate your input here, especially if you happen to know certain brands/models that I should check out.
Thank you in advance.

P.S: Also, considering the wires that would go through the refirigirator - I think I will need to isolate them in order to minimize the error, however, I'm really unsure what is the best way to do so.
 

atferrari

Joined Jan 6, 2004
4,095
I recall using in my ver y first complete project, a small aluminum jacket containing an LM35 driven with a constant current in the micro amperes range (well below the mA). The jacket accommodated the sensor tight enough, immersed in silicon grease.

Later, trying to detect quick variations I got the advice of using instead of grease, a liquid product (memory is dubious here) called propilenglicol or similar (Not even sure how you translate it either). Tagging @jpanhalt who is qualified to give a master class here. Not even sure if it is conductive; I never used it.
 

jpanhalt

Joined Jan 18, 2008
10,251
Thank you for the compliment, Agustin.

The liquid you were thinking of was probably propylene glycol, which is like ethylene glycol with an additional methyl group attached to the end (https://en.wikipedia.org/wiki/Propylene_glycol).

As for temperature measurement, I suspect a thermistor (NTC) bead or thermocouple (Type K) would have adequate resistance to water. As for experimental advice, you will need to define the endpoint such that it can be determined reproducibly. That is, will the endpoint be "freezing" or reaching 0°?

You might also consider tests using the same volumes of hot and cold water set with different surface areas. That is, if you observe the effect in tall narrow containers versus wider containers.
 

Thread Starter

tresbien

Joined Mar 25, 2020
3
Thank you for the compliment, Agustin.

The liquid you were thinking of was probably propylene glycol, which is like ethylene glycol with an additional methyl group attached to the end (https://en.wikipedia.org/wiki/Propylene_glycol).

As for temperature measurement, I suspect a thermistor (NTC) bead or thermocouple (Type K) would have adequate resistance to water. As for experimental advice, you will need to define the endpoint such that it can be determined reproducibly. That is, will the endpoint be "freezing" or reaching 0°?

You might also consider tests using the same volumes of hot and cold water set with different surface areas. That is, if you observe the effect in tall narrow containers versus wider containers.
Thank you for your reply.

I consider taking the endpoint to be the moment defined by latent heat, that is when the temperature continues declining after being constant for a while. I appreciate your input about changing the surface area while keeping the volume constant - will definitely give that a thought.

However, as noted above I'm a high school student and I don't really have much experience with electronics. I would really appreciate if you could go a bit more into detail when it comes to the process of constructing such a sensor. In addition, one important thing about this temperature sensor is that I should somehow be able to obtain data, preferably in real-time. I've thought about getting a USB temperature sensor - as it allows me to track the data in real-time - however, they seem not to be waterproof.

Again, thank you for taking the time to read this.
 

jpanhalt

Joined Jan 18, 2008
10,251
Maxim makes some thermocouple amplifiers that are easy to use. Both are offered on breaskout boards, so soldering the small surface mount deivces is not an issue. The MAX31855 is analog and probably the easiest to use. The MAX31856 is digital and still easy to use, if you can use a microprocessor. Usual hobby sources have them, including Digikey and Adafruit :https://www.adafruit.com/?q=themocouple . Mouser, Sparkfun and Parallax (https://www.parallax.com/ )are other sources.

I am sure there are similar resources for thermistors.
 

MrChips

Joined Oct 2, 2009
21,889
You can buy glass encapsulated thermistors. If it is to be immersed in water I would insulate the leads with teflon insulation stripped off from hook-up wire and dip the entire end with the thermistor in epoxy.

You can then run long wires outside of the refrigerator door. The electronics and conversion to temperature will be discussed in another post,
 
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