Fridge salami Experiment

[Oddley]

markh interesting concept.

The temperature sensor on the beer chiller, is actually surrounded by the cooling element.

You are right as the air temp drops, the air has less ability to hold water. That is why all fridges are like dehumidifiers.

Obviously as the pump pushes the refrigerants through the cooler element, the cooler element will have a lower temp than the surrounding air therefore condensing the water from lower temperature air on it. As cold air drops below the warmer air and falls into the well of the chiller would this not act as an air circulating event. I believe it does.

I was thinking about using a peltier device but as they normally will only give a temp of about 20 degrees below ambient. I thought this unacceptable especially in the really hot weather.

I look forward to hearing the results of your experiments. I would also be happy to hear if you disagree with my logic in this post.

[Hobbitfeet]

Markh
You are referring to matters on the limits of my knowledge but am I not right in assuming that Peltier elements have very low efficiency. They will consume more power than they transport! Actual Peltier elements may consume twice as much energy (in the form of electricity) as they transport (in the form of heat). Since the device is inefficient, the total amount of heat energy that has to be removed is significant. To remove the energy from the inside of the fridge here, there needs to be some sort of convection and a fin heat-sink system to provide enough surface area to transfer the heat across. Is it not correct that the heat-sink it is used with must be much more powerful than a heat-sink used for cooling a heat source without a Peltier element. It may be better to combine Peltier elements with watercooling.

On the other hand car 'fridges use Peltier elements don't they? Probably too small for these purposes though.

I wish you luck in your research!

Have just found this...


http://store.securehosting.com/stores/s ... cd=sws117l

[aris]

Air circulation shouldn't be difficult with a couple of 12v PC fans.

[markh]

Oddley, agreed there is a convection effect, the reverse of a standard convection heater. However with forced air circulation the element will be better coupled to the environment - offer a lower thermal resistance - typically by a factor of around 3-4.

Presumably the refrigerant will be as cold but at least when coolant is not actually circulating any ice that has formed should melt and allow the humidity to rise again.

Hobbitfeet, the efficiency of peltier devices as far as I understand depends on the temperature difference between the hot and cold sides.
It is a true heat pump and at low temperature differences can actually pump more energy through it than supplied electrically - but as you point out, the electrical energy also appears at the Hot side and as such requires a big heatsink. Water-cooled would indeed be best!

The maximum no-load temperature difference at the module is typically greater than 60 deg. C, but efficiency reduces below 1 at around 30 deg. and then it depends on the quality of the insulation. The other thing is basically have as low a thermal resistance heatsink on the hot side as you can!

RS part number 238-3010 has some interesting Application Notes but you need to register on rswww.com to access them, afraid I dont know if I can upload them.

Aris, only problem might be the additional heat from the fan motors - I originally intended to use a 'mini' heatsink with an integrated small fan on the cold side - but it got hot which rather defeated the object!
Ideally you could do with the motor part outside the fridge coupled to the fan with a shaft.

If you could advise how to load pictures to the forum I will try and show the setup I was going to use.

[aris]

I would not have thought that a 12v brushless fan motor would create any heat at all - particularly if the power supply was outside the fridge (which it would be).

[Oddley]

markh, I will certainly give a fan a try, I have to go down to maplin next month to buy the components to make a timer for the fogger humidifier. You sound like you do a bit of electronics. So I'll tell you that I'm going to use a NE556N dual timer to control a relay which in turn controls the supply to the fogger.

[markh]

aris, I must admit I was surprised myself - the tiny fan I was using ( a 5V job only 40 x 40mm) was taking about 1watt and the bigger 12V one on a CPU cooler (used as the hot side sink) pulls 2.7 watts - not a great deal I admit but could be significant - particularly as the Peltier modules I was using were 50W max and as people have said, the cold side power drops sharply as the temperature difference increases. Having said which I have seen some rated up to 300W on ebay so maybe they would be better suited.

oddley, I am unsure of your intent with the fogger and am not sure of its mode of operation (incidently I am glad you included the link to the unit, I never would have thought to look there! ). Am I right in assuming that
a) It is submerged in the water and generates the mist presumably mechanically by a vibrating membrane?
b) You wish it to operate with a settable duty cycle, On for a while then Off again. presumably determining the ratio by trial and error
c) You intend to switch the 12V line - do you have a power rating for the unit? If it is reasonably low I would recommend a mosfet switch rather than a relay - especially if its in earshot!

Do you intend to run the 556 as two monostables with the output of one triggering the other?

As I recall (afraid I haven't used one for some time) the only problems with the 556 is the limited maximum R values, requiring large capacitance for long delays, and the noisy totem pole output stage requiring really good decoupling otherwise you can get retriggering problems.

By the way, which is the Temp/Humidity meter you are using and would you reccomend it? (I was going to put a link to the one I thought it was but it looks like the websites down!)

[Oddley]

markh This is the wireless temp/ humidity meter I'm using seems to do what it say's on the box.

http://www.maplin.co.uk/module.aspx?Mod ... 3&doy=16m8

You are right about the fogger and timer. I love relays easy to use no probs with heat dissipation, as long as the circuit is not frequency dependant.

Just a matter of the right capacitance for decoupling. I don't forsee too long delays hopefully so no probs there I hope. If there is, there are other but more complicated ways of doing it. I have home built 9/12V supplies laying about so that will save time/effort.

And now I know you know a bit I can always contact you,
if I get in trouble...

[markh]

Oddley, thanks for the link, may have to invest in one - I got the 4-in-one meter
http://www.maplin.co.uk/Module.aspx?ModuleNo=34518&doy=16m8
when it was on offer but it does have the problem that you have to see it

Best of luck on the project, anything I can do, just holler.

[Paul Kribs]

I hope this thread will culminate with some information that some of us menials can relate to... I was getting quite interested but although I am trying to follow it, it is somewhat over my head.

Regards, Paul Kribs

[Oddley]

Paul sorry mate. All we are talking about is turning the fogger on and off. The fogger is just a device that vibrates in a tub of water and causes a mist thereby humidifying the air.



Also having a fan in the fridge just to move the air about so the cold transfers from the cooler element to the air more efficiently. Hopefully stopping the icing up.

[markh]

My apologies also, I am afraid I am a bit of a Techie at heart and sometimes get carried away - its the food that counts.

The reason I was wanting to try using two devices was that in a wet/dry bulb hygrometer (the old fashioned method of measuring humidity), the wet bulb is normally lower in temperature than the dry bulb - water is evaporating and cooling it - the lower the humidity, the bigger the difference in temperature because it 'boils off' faster... But if its evaporating it must be increasing the humidty unless it is being condensed at an equal (or faster) rate by the dry bit. The higher the 'wet' temperature the faster it will evaporate, and vice versa.

The upshot is that in theory you have two power controls to the unit - both help control the temperature, and the difference controls the humidity.. effectively once its calibrated you should be able to 'dial up' the required combination.

The beauty of using the peltier devices is that you can reverse the heat flow - what used to cool can heat - so you can also use it for the initial incubation stage in the depths of winter (or for keeping the bottles of red warm )

At least that is the theory - I hopefully I will be able to post some results shortly - such a shame work keeps getting in the way...

[Oddley]

I would be interested to see some diagrams/images of your setup. Also be interested to see the results when you have them.

[Platypus]

I have been following this thread with great interest as I have been looking at the possibilities of building an all-in-one unit that is capable of maintaining:
High(ish) temperature high humidity - for incubation
Low temperature high humidity - for curing
High temperature low humidity - for drying biltong etc

I had come to the conclusion that peltier was the way to go along with fans and misters.

I am really pleased that others are looking into similar methods and the fact that you have already started experimenting will spur me on.

Any images or info that you can post is eagerly awaited.

[aris]

I would imagine that an enterprising refridgeration firm would sell a fair few units that could do what Platypus described.