Refrigeration using Peltier device 1

[WallaWalla]

Hello everyone,

I'm carrying out a project which provides the cooling of a fluid inside a tube. In particular I should cool water or a glycolytic solution from a temperature of 25 °C to about 0 °C. I thought to do this through the use of the thermoelectric effect, then the Peltier cells.

I have two ideas. The first involves the use of a fluid reservoir and the cold face of the Peltier cells is in contact with the bottom of the container (figure). I thought I could get at the bottom not just one but multiple cells .

The second one is to use a system which is a kind of enclosure of the tube in which the fluid flows (figure).

I can give you some more information:

Case 1) deltaT = 25 °C -> 25 °C to about 0 °C
         fluid volume / container -> 1 liter
         container size -> might be 10 cm x 10 cm x10 cm
         thick container -> 1mm steel

Calculating the heat subtracted from the volume of water: Q = 4186 * 1 * 25 = 104kJ. So if I want that the refrigeration is about 10 minutes I have to subtract cooling power of 104kJ/600s = 174W. Because of the dispersion may well need more than enough, say 200W (but it is a random number, I have not done any calculation).

With cells taken, for example, I run the following calculations: I took that model because one side is 47mm and the bottom of the container there are 4.

Their power is 72W and the maximum temperature difference of 74K, which means that for each kelvin of difference between the temperatures of the two faces is lost approximately 1W.

The thermal resistance of the steel wall is negligible.

4-cell 72W make 288W, 200W serve to us, means that we have 88W for the internal conduction of the cells, which means 22W per cell; then the maximum temperature difference between the two faces must be of approximately 22K.

Since the bottom of the container is at about 0C, the other face of the cells at the maximum can go to 22C. If the air is at 20C, I have a temperature difference of 2K to dissipate from the area to 1dm^2 a power equal to 4x (13.1Ax8.8V +50 W) = 660W.

Then I need a heatsink with thermal resistance of 2K/165W = 12mK / W for each cell. Or a single heatsink of 2K/660W = 3mK / W.

CALCULATION ARE RIGHT?

Case 2) flow -> 1l/min
         deltaT = 25 ° C -> 25 ° C to about 0 ° C
         wall thickness -> 0.1mm

In this case I would understand if it is possible and if the cooling depends on the length of the tube and such other factors.

I know that in the market there are some chillers that use the traditional refrigeration cycle but also the thermoelectric effect.
Also, if someone knew other methods to achieve my goal can tell me please.

Thank you to all, Emanuel

 

[WallaWalla]

This is the other figure.

 

[IRstuff]

Is this homework? As shown, your design will work poorly, at best. Time of contact is extremely low, so cooling will be absurdly inefficient. TECs are already extremely inefficient.

TTFN
faq731-376

 

[WallaWalla]

This is not my homework, but it is my project and before to realize my project I would understand if it is feasible. What do you mean by Time of contact?

 

[EnergyMix]

To expand on IRStuff's question: Is this a project for school?

 

[IRstuff]

Just because your fluid passes by a Peltier cooler doesn't guarantee cooling. If the flow rate is, say, 1 in/s, where 1 inch looks to be about the length of your cooler, then you're only applying 1 second's worth of cooling on the entire mass of fluid that just passed by. You need to do the math. Moreover, you're dumping a truckload of heat in a tiny volume, which further degrades the efficiency of the system.

TTFN
faq731-376

 

[EdStainless]

You need to take small diameter Cu tube and form a serpentine pattern, then solder this to a Cu plate.
Keep the plate as thin as is reasonable, maybe 1/4". (this is about 2 ft/sec)
Then mount the TEC's to this plate. The surface that they mount to will need to be very flat and smooth.
If you arrange this right you could have each TEC cooling a different temp range, they would each need to be on separate plates for this to work.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[WallaWalla]

Thanks,

EnergyMix - I started the project at the university but now I will made it myself.
IRstuff - Ok, I know that just because my fluid passes by a Peltier cooler doesn't guarantee cooling. But in the first case I have a reservoir and I do the math but I don't know in it is feasible in terms of voltage, supply, power, etc..

 

[macmet]

I did a similar project a few years ago with a buddy. I milled a heat sink out of aluminum for the cold side of the TEC and made an aluminum radiator block for the hot side of the TEC. We also bought some expensive thermal paste to minimize surface resistance between the TECs and aluminum.

To dissipate the heat generated, we took an oil radiator (I think) off of an old car from the local wreckers and hooked up some large computer fans to it.

I was working at a department store at the time and a couple "accidents" happened, leaving a couple decorative fountains destroyed, and I kept the pumps, which we used on the cold side to circulate the fluid.

What we found worked well was putting the radiator in a chest freezer. Then we discovered it worked even better if we used sub-zero temperature glycol on the "hot side".

And finally we came full circle and just kept a bucket of glycol in the freezer with the fountain pumps and when we wanted a cold beer, we put the beer in the bucket, turned on the pumps, and two minutes later the beer was cold.

It was a very impressive looking device, but it took a long time to cool the glycol. Once you got it up and running it was pretty cool, but it was not very efficient. It just took a long time to get the temperatures we needed. It was definitely a lot of fun though.

 

[IRstuff]

If you've done the math, the how did the thermal conductivity of the water enter into your calculations?

TTFN
faq731-376

 

[EdStainless]

Macmet, I have used TEC's to cool computer CPUs.
We used to stack them (cascade).
We could get -50C or so under full CPU power. The TECs drew twice as much power as the computer, but we could really overclock processors.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[macmet]

They take a lot of power. The buddy I was working with was into electronics and he took apart three computer power supplies and wired them in series to power four TECs. It sure looked impressive.

 

[WallaWalla]

IRstuff - For the first case (reservoir with fluid inside) I don't think that I have to use the thermal conductivity but the specific heat of the water.

macmet - Thank you to describe your experience! I saw (on the web) that exist some water chillers for marine aquariums that uses thermoelectric module to cool water; but in this case the deltaT is lower than mine.

 

[IRstuff]

" I don't think that I have to use the thermal conductivity but the specific heat of the water"

Think again, and consult a heat transfer book, or at least, read this:

http://en.wikipedia.org/wiki/Biot_number

TTFN
faq731-376

 

[macmet]

Walla,

May I ask what your actual application is? Just curious.

 

[berkshire]

wallawalla
we looked at peltier diodes for a medical device and finaly came to the conclusion that they were not efficient enough for our purpose.
we ended up using a miniature refridgeration compressor.
B.E.

http://www.aspencompressor.com/Application.htm

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[IRstuff]

TECs are used in polymerase chain reaction (PCR) machines to heat and cool the reaction ampules. Of course, the ampules generally hold much less than a milliliter of fluid, but thermal cycles can be as short as a few seconds. Here, time is king, so absurdly short process times require the ability to slew the temperature extremely quickly, which TECs can excel at.

TTFN
faq731-376

 

[WallaWalla]

macmet
My study is about an endovascular device used to induce hypothermia. It is composed by a cvc catheter (central venous catheter) and an external device used to cool the fluid which will flow inside the catheter.
Inserting the catheter in a vein (femoral, subclavian or jugular), we can do an heat exchange between it and the blood which flow through the vessel and which is in contact with the external surface of the catehter (countercurrent heat exchanger).
I have already do some thermodinamical, geometrical and other analizes on the catheter and now I would to know how I can realize the external device.
In the marke there are 2 device, but they are expensive and also enough cumbersome; I though the use of TECs because of they are relatively cheap and less cumbersome.

berkshire
thak you!

 

[IRstuff]

No one is saying that can't be done, but it's woefully unclear whether you have done the math correctly, since you've shown nothing in that realm, and your thermal assertions don't appear to be valid.

TTFN
faq731-376

 

[WallaWalla]

Ok, then what are the math that I need to do correctly?
For the Biot number I read some information in your link. I had consider a stirrer for uniform the temperature inside the reservoir.