Trying to recreate a human hand at 37 degrees celcius

Thread Starter

NikolaV

Joined Nov 14, 2019
6
I am doing some testing that requires the application of a human hand to foam. I want to create a constant test enviroment and so need to make a mock hand that is temperature controlled. I am planning on getting the hand 3D printed which should hold up fine at the required 37 degrees celcius. My issue is how do I make sure that the hand maintains a constant temperature. I was thinking of using some form of heating trace like nichrome and controlling the temperature using a cheap Thermostat controll like this one.
Is this possible? how closley do you guys think I will be able to maintain the temperature? Any ideas about how much current/voltage I would need to run through nichrome to achive such a slight temperature increase?

Any Advice would be greatly appreciated!!! Thanks in advance!!
 

Marley

Joined Apr 4, 2016
311
I agree, the warm fluid is the answer. I think you will find, if you hold a temperature sensor or thermometer, that you hands are slightly cooler than your core body temperature due to your blood having to travel some way to get there!
Also, are you going to make the 3D printed hands out of some sort of rubbery material that has a similar thermal conductivity to real flesh? Might be important for your simulation.
 

Thread Starter

NikolaV

Joined Nov 14, 2019
6
Since it is 3D printed, why not include channels and circulate a warming fluid (e.g., water or air) through it? That's pretty much is how your hands are kept warm.
I thought about that, but I feel like that might significantly complicate things in the build process. I would have to probably build a resevoir tank with some sort of immersion heater and temperature controll and then install a pump to circulate the liquid through the hand. Some how i thought an electric solution would be simpler but i might be wrong.

As for as the channels go, I doubt the 3D printed material would be water tight enough for that application, though thats not really an issue. Some rubber/silicon tubing and we're flying.
 

Thread Starter

NikolaV

Joined Nov 14, 2019
6
I agree, the warm fluid is the answer. I think you will find, if you hold a temperature sensor or thermometer, that you hands are slightly cooler than your core body temperature due to your blood having to travel some way to get there!
Also, are you going to make the 3D printed hands out of some sort of rubbery material that has a similar thermal conductivity to real flesh? Might be important for your simulation.
No I don't think I need to simmulate the thermal conductivity of real flesh. I would like to have the ability to control the temperature within a range in which case i can increase the temperature to whatever it needs to be to achieve the required temp on the "skin" side.

The test involves applying my hand with a constant force to a piece of material and monitoring the rate of heat loss from the material once the hand is removed. I have been doing this with my own hand, so far, but it has too many inconsistencies to be reliable. And if im being honest its not very fun to sit there and keep your hand on something for 15 minutes with out moving.

And as I mentioned in my reply to Jpanhalt, water might be a bit more complicated, expensive and space consuming
 

Tonyr1084

Joined Sep 24, 2015
3,913
The temperature of your hand will fluctuate naturally. Due to your core body temperature, the length of your arm and how much heat is lost, how active or sedentary you are. There are times my wife will put her hand on the back of my neck and it will feel cold. Other times warm. It all depends on what she's been doing. Or if she's been holding a hot coffee mug.

Currently my wife and I have been dealing with a cold. We have a warm mist humidifier in the room. The tank gets warm. I can put my hands on the tank for a few seconds then put my heated hands on her back. So body temperature is a rather dynamic thing to try and replicate. Besides, flesh will radiate temperature at a different rate than a fake hand. Assume you have a fake hand made of aluminum. Heat transfer is going to be a lot faster than if it were made of wool.

My question to you would be "Why do you want to perform this experiment? What information do you hope to glean?".
 

jpanhalt

Joined Jan 18, 2008
8,329
No I don't think I need to simmulate the thermal conductivity of real flesh. I would like to have the ability to control the temperature within a range in which case i can increase the temperature to whatever it needs to be to achieve the required temp on the "skin" side.
Then why do you need a "hand?" Take a surgical glove, fill it with warm water (or plaster of Paris) and you are good to go. I think you are grossly underestimating the difficulty of uniformly heating a piece of plastic shaped like a hand.

Maybe if you want to use electrical heating, you could make your printed hand hollow and only the bottom half. Wire that with heating elements (e.g., resistors) and sensors. Then bring all the wiring to a connector. Fill the voids with a resin and start empirically adjusting currents to get the temperatures you need. Of course, if you want the hand to have a top, then you could make one too.

That all sounds very complicated compared to using a fluid. If the fluid is air, who cares if there is leakage? If water, you could simply flush the channels with a sealant after printing, or put the entire hand in a surgical glove. Temperature regulated water baths with circulators or air circulators are easy to make and readily available commercially. A light bulb with a muffin fan/circulator and thermostat can make a nice incubator and is not at all complicated

And as I mentioned in my reply to Jpanhalt, water might be a bit more complicated, expensive and space consuming
"Complicated, expensive, and cumbersome" are criticisms I have often heard from people who have never tried. What are your more suitable solutions?
 

jpanhalt

Joined Jan 18, 2008
8,329
Here's another approach. Get a high heat capacity gel (e.g., http://elitefoam.com/products/thermaphase/). Fill a rubber glove with it, and warm uniformly to your desired temperature ( more likely 32°C). That should keep it warm for just 15 minutes. By comparision, the heat capacity of water is just 4.2 J/g°C. That particular gel is 3x that and is reusable. A temperature probe in the glove could monitor the temperature in the gel during the experiment.

It's temperature is relatively constant as it depends on a phase change, just as the temperature of an ice-water mixture has a fairly constant temperature.
 

Thread Starter

NikolaV

Joined Nov 14, 2019
6
The temperature of your hand will fluctuate naturally. Due to your core body temperature, the length of your arm and how much heat is lost, how active or sedentary you are. There are times my wife will put her hand on the back of my neck and it will feel cold. Other times warm. It all depends on what she's been doing. Or if she's been holding a hot coffee mug.

Currently my wife and I have been dealing with a cold. We have a warm mist humidifier in the room. The tank gets warm. I can put my hands on the tank for a few seconds then put my heated hands on her back. So body temperature is a rather dynamic thing to try and replicate. Besides, flesh will radiate temperature at a different rate than a fake hand. Assume you have a fake hand made of aluminum. Heat transfer is going to be a lot faster than if it were made of wool.

My question to you would be "Why do you want to perform this experiment? What information do you hope to glean?".
The point of the experiment is to see the rate of heat loss of our material(Foam). So the requirment of having an accurate representation of human body temperature is not strict. All we need is a constant temperature and a compressive force on our material. After a specified period of time the pressure and heat will be removed and the rate of temperature loss in the material will be measured.

We are considering using a square metal plate instead of a hand too, as far as results go, they should be the same(more or less). The point of using a hand shaped device to apply pressure and temperature is mostly for marketing. People respond better when they see a thermal hand print rather then a square.

In essence I am looking for any device that can be used for surface temperature control within that range of 20 - 40 degrees celcius.
 

jpanhalt

Joined Jan 18, 2008
8,329
Re-read my post #11. A slurry of something, of which there is an almost infinite selection, will keep the temperature constant. If you don't like gels, look at waxes.
 

Thread Starter

NikolaV

Joined Nov 14, 2019
6
Here's another approach. Get a high heat capacity gel (e.g., http://elitefoam.com/products/thermaphase/). Fill a rubber glove with it, and warm uniformly to your desired temperature ( more likely 32°C). That should keep it warm for just 15 minutes. By comparision, the heat capacity of water is just 4.2 J/g°C. That particular gel is 3x that and is reusable. A temperature probe in the glove could monitor the temperature in the gel during the experiment.

It's temperature is relatively constant as it depends on a phase change, just as the temperature of an ice-water mixture has a fairly constant temperature.
Its Ironic because the therma phase gel you mention is pretty much exactly what we will be testing in our foam products. In your post #10 you mention how you would do it using elctricity. That is almost exactly how I magined this project would go. That still seems like the best way for me.
Some of my testing might need to simulate overnight pressure on a mattress, which is why I cant just warm up a specimen and hope it maintains its heat long enough. This means it will need to be continuosly heated which leaves me with either elecctric heating or water heating. We use both methods of heating on a larger scale for controlling the temperature of our moulds at around 50 degrees celcius and using water has consistently proven to be more of a headache and less consistent to boot.

I do appreciate all the input btw!
 

djsfantasi

Joined Apr 11, 2010
5,838
So for marketing purposes, any hand-shaped object can be used you don’t really believe the pizza’s in a Pizza Hut commercial was baked there or is even edible, do you?
 
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