As you can see to make DP happen (let's say if RH~40%-50%) delta between metal temp and air temp inside HDD should be very high (~10C or 18F) which is only possible when we cooling drive extremely fast
RH 40% can be easily achieved with silica gel

PS: Don't forget even IF DP happen when air gets cooled down vaporizing sucks all ice/dew back in air

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Hi Doomer, that's a great little RH chart you posted earlier, but your interpretation is not quite right.
The difference between to two temps is not the gradient [delta] that must be achieved, but simply the temp that the air must be brought down to for precipitation [dew] to form.
e.g From the table, if the RH is 50% @ 20c, it shows us that the dew point is 9.3c
i.e if 20c air @ 50% RH is cooled to 9.3c then dew will form. The air no longer has enough heat energy to hold this amount of water as vapor.
This will happen regardless of whether the air or the container [hdd case] is quickly or slowly cooled to 9.3c

The temp gradient between the air that is in contact with the metal and the air that is in the middle will yield different phenomena.
If cooling of the container and air is very slow such that all the contained air is at the same temp, then all of the air reaches dew point at the same time and fog will form.
If the container is cooled quickly, then because air is a poor conductor of heat [good convector], the air that is in contact with the container will reach dew point first and dew droplets will form on the surface of the container. Convection of the air will bring the warmer air into contact with the surface, it will be cooled to dew point and more droplets will be formed on the container surface.
With this in mind, then perhaps it is better to cool the drive as quickly as possible so any dew will be deposited on the case and cover surfaces and not on other parts.

If a very high RH hard drive is cooled slowly, then maybe a thunderstorm will form in your drive!! [kidding!!]

I would disagree (but you already proven yourself wrong)
If you cool down slowly fog will form but not dew. Forming actual dew on platters is much worse than fog inside
There is a possibility that platters would cool down faster than air through screws and the spindle if you freeze drive very fast

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Nice discussion

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SAN, NAS, RAID, Server, and HDD Data Recovery.

Hi Doomer, I'm not sure which part you are referring to here?


Very true!


This could be, but bear in mind that the thermal path to the platter surface is rather restricted as compared to the inner surface of the case.
The bearing is made of steel which is not as good a conductor as aluminium, the bearing is in two pieces with lubricant between the pieces, then there is substantial heatsinking effect of the aluminium rotor [spindle], then maybe even more thermal resistance if the platters are ceramic or glass?...non-metal anyway.

This has however, lead me to consider the reverse situation, when the drive is removed from the freezer.
There is a case to argue that it should not be left in the freezer for too long, as the platters will eventually attain the same temp as everything else.
Then when the drive is removed from the freezer, the dew drops which have long been frozen to ice will thaw and vaporize into the air as it warms, be carried by convection to the still very cold platters which now can't warm as quickly as the rest of the drive, and be deposited back onto the platters as dew again.

But seriously, I think we're shooting peas at the moon here. I'd still argue that there's not enough air/moisture available inside a drive for there to be any significant dew to form.
Especially when also considering that just because dew point is reached, it does not mean that all of the available water vapor becomes dew, only that excess vapor that the cooler air can no longer hold.
To validate this we would need to start delving into specific humidity.......stuff it, I'll just wait for guru and BlackST's results....mmmmm....steamed hard drive for dinner!!

My idea : a common dew sensor used in VCRs , put inside a scrap HDD chassis. The sensor connection comes out from the top lid, closed, as there is a gasket ...
These sensors change their resistance according to RH (there are more precise, but these sensor are a small square, 1 mm. thick. and I have a lot....).
I can put a K thermocouple inside the chassis too.
I'll put everything on my freezer , only the wires go outside to an ohmmeter with logger and thermometer. Then we will see.

I only need a few hours.

ok nice idea

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" что случилось в России - останется в России "
" Россия еще раз"

sorry was very busy... Any other ideas for me to try?

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All went well until I plugged the drive in.

I think a "Wet-Bulb Temperature" test would be interesting

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All went well until I plugged the drive in.

I found an hygrometer, but I have to use an empty HDD chassis to fit the test probe.... remove headstack, platters etc. Would the test be real then ?

dont think so. Platters play an important role i think.
They can obstruct convection, they can play the role of a heatsink etc...

Dobre

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I bought a small Peltier-driven refrigerator for mild cooling of drives, and the minimum temperature that is achieved is about 37oF inside of the refrigerator - or a bit higher with a drive throwing off BTUs. There are some cases where a good fan makes a difference with imaging speed, so I wanted to see what the results would be cooling a drive below ambient as well.

We had an another, older portable refrigerator containing a decent-sized Peltier-effect device. The AC/DC power supply was cheap and blew up, so I took the refrigerator apart and removed the device.

My 12 year old son was looking for a science fair project, so I bought a lab type variable DC power supply and suggested that he test the performance of the Peltier device at different voltages and current levels and then graph it.

What he "discovered" is that the Peltier effect is strongest initially upon application of energy. The delta T between the hot and cold sides tends to decrease after it reaches a maximum, to an equilibrium point.

The "problem" with Peltier effect devices is that you really have to have good forced airflow to keep the "condenser" side as cool as possible. Another limitation is the surface and surface area of the "evaporator" side. This limits its application a bit when placed directly on hard drive.

My conclusion is that Peltier-effect devices have limited (but potentially useful) applications for hard drive recovery.

In any event, the kid won his school and county fairs with the project, and placed 3rd in the State, so I guess the experiment was "successful."

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