4 ms·

I would like to understand why they are using helium at all instead of a several other plausible alternatives. The article offers the following rationale for us

I would like to understand why they are using helium at all instead of a several other plausible alternatives. The article offers the following rationale for using helium in this capacity; >>>At one-seventh the density of air, helium produces less drag on the moving components of a drive - the spinning disk platters and actuator arms -- which translates into less friction and lower operating temperatures.<<< This appears to be a slight misunderstanding as the density of any gas is variable and we have found that it is directly proportional to the unit weight of the substance, the pressure and inversely proportional to temperature. It is not fixed. They could have easily achieved the result in multiple ways. For instance, to reduce density it might have been easier to simply reduce pressure and then create a hermetically sealed chamber with a reasonably inert gas with low atomic or molecular mass such as nitrogen. This should have saved them a lot of trouble as helium is actually pretty hard to contain. An alternative nitrogen based solution would also have been good enough for a long enough period of time and it could have been achieved in a much less expensive manner. (they say in the article that successfully trapping helium for a long enough period of time required a decade of research. This is a relatively solved problem for gases such as nitrogen) I am sure that the people at Western Digital can see something that I don't - I'm just curious as to what that insight is. What makes helium worth all of the trouble?

adrianb 13y ago
I'm guessing the fact that it's an inert gas is important as it won't be a risk (in case of fire or toxicity) in case the enclosing is broken. Also I think the density was presumed to be at room temperature, reasonable pressure. Under these circumstances He might provide the least drag. Having a pressurized enclosure might make the drive more expensive as stronger materials need to be used, and it would also make it more dangerous in case of mishandling, so I think there was a limited range of pressure they could maintain in the enclosure.
- todayiamme 13y ago
  Nitrogen is also inert enough for such use, it's easily contained and it doesn't require such measures. >>>Having a pressurized enclosure might make the drive more expensive as stronger materials need to be used, and it would also make it more dangerous in case of mishandling<<< Actually containing He at all would require these measures anyway, as He diffuses through solids much faster than air and as such cannot be easily contained. To quote the wikipedia article; >>>One industrial application for helium is leak detection. Because helium diffuses through solids three times faster than air, it is used as a tracer gas to detect leaks in high-vacuum equipment (such as cryogenic tanks) and high-pressure containers. The tested object is placed in a chamber, which is then evacuated and filled with helium. The helium that escapes through the leaks is detected by a sensitive device (helium mass spectrometer), even at the leak rates as small as 10−9 mbar·L/s (10−10 Pa·m3/s). The measurement procedure is normally automatic and is called helium integral test. A simpler procedure is to fill the tested object with helium and to manually search for leaks with a hand-held device. Helium leaks through cracks should not be confused with gas permeation through a bulk material. While helium has documented permeation constants (thus a calculable permeation rate) through glasses, ceramics, and synthetic materials, inert gases such as helium will not permeate most bulk metals.<<< Further, high pressure containers are dangerous as they might have an outward failure. That is unlikely to be the case with a drive that is at say .5 atm as the pressure is directed inwards, so the worst case over is most probably a drive filled with air or a slightly crumpled drive. (as a thought experiment think about how submarines implode instead of exploding when the hull encounters pressures beyond what it can handle)
- crististm 13y ago
  For what is worth, we're breathing more N than O - so toxicity is not an issue when comparing He to N.
graycat 13y ago
The idea of using helium in a hard drive is old, goes back at least 20 years. As I recall, the main reason for using helium is that it conducts heat better. Heat? Yes, the spinning drive acts like a centrifugal pump which moves the gas and heats it.
jccooper 13y ago
Helium gets you low density at standard pressure. I am guessing that they prefer not to construct hard drives as pressure vessels. Probably that makes thermal conductivity, among other things, a problem.
tryp 13y ago
The density of helium is less than 1/7 of the density of nitrogen, which is a good approximation for air. Two ways that this is helpful come to mind: 1. Aerodynamic effects like drag and vorticity are largely governed by the Reynolds Number, which holding all else constant, varies linearly with density. Changing the density of the fluid can drastically change the aerodynamic situation. See http://www.grc.nasa.gov/WWW/k-12/airplane/dragsphere.html http://www.grc.nasa.gov/WWW/k-12/airplane/dragsphere.html for an interesting and accessible example. 2. "Flow-induced vibration" is caused by the swirling gases crashing like stormy seas, making platters vibrate and heads flutter. Switching to helium cuts the momentum in these turbulent flows to a seventh of what they would be with air.
Lagged2Death 13y ago
... to reduce density it might have been easier to simply reduce pressure and then create a hermetically sealed chamber... Disk heads "fly" above the surface of the disk on a cushion of gas that's pulled under the head by the spinning disk. If there isn't enough gas pressure inside the disk enclosure, this method of locating the heads won't work. Wikipedia actually says: If the air density is too low, then there is not enough lift for the flying head, so the head gets too close to the disk, and there is a risk of head crashes and data loss. Specially manufactured sealed and pressurized disks are needed for reliable high-altitude operation, above about 3,000 m (9,800 ft). http://en.wikipedia.org/wiki/Hard_disk_drive#Integrity_and_failure http://en.wikipedia.org/wiki/Hard_disk_drive#Integrity_and_f... Atmospheric pressure on the top and bottom faces of a 3.5" drive case (~22 square inches) is in the neighborhood of 300 pounds each, and there's still more on the front, back, and sides. A square box of thin aluminum is probably not a great starting point for building a pressure vessel. If the box is filled with a gas at close to atmospheric pressure, you don't have to worry about it. Helium's specific heat is five times that of air, so it probably offers better heat conduction than air at 1/7th atmospheric pressure would.
- hengheng 13y ago
  Shot in the dark, but might there be advantages simply because there are more molecules flying around than with air? 10nm ground effect flying probably isn't trivial.
- todayiamme 13y ago
  I'm sold, but I have an additional question though. Can you please explain why hard-drives follow a flying head approach? Why don't they just perpendicularly fix the reader above the disk, rotate the disk and then use a linear actuator to move the reader back and forth - exactly like optical drives? I'm guessing that the status quo exists and that my suggestion is inherently flawed because of the precision required to maintain the head at 10 nm above the surface and as such letting fluid dynamics wrestle with gravity might do the trick for you (given that you can make the spindles in a precise manner that the forces cancel out in a way that ensures that the head is exactly at the desired distance above the drive) That leads to another thought, would the following conjecture be in the realm of possibility? Imagine that you have coated the disk with mystery thing X - which is an etched semiconductor that does something very magical. When an incident beam of light strikes a point on the coating, it releases electrons, which are then controlled through magical mechanism Y etched on X to create a magnetic field that flips the bit. If you do this then you can remove all of this stuff and it might lead to some gains.
robomartin 13y ago
Helium is nearly 7 times better at conducting heat than both air and nitrogen [0], lower density [1] and about the same viscosity [2]. [0] http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html http://www.engineeringtoolbox.com/thermal-conductivity-d_429... [1] http://www.engineeringtoolbox.com/gas-density-d_158.html http://www.engineeringtoolbox.com/gas-density-d_158.html [2] http://hyperphysics.phy-astr.gsu.edu/hbase/tables/viscosity.html http://hyperphysics.phy-astr.gsu.edu/hbase/tables/viscosity....

adrianb 13y ago

I'm guessing the fact that it's an inert gas is important as it won't be a risk (in case of fire or toxicity) in case the enclosing is broken. Also I think the density was presumed to be at room temperature, reasonable pressure. Under these circumstances He might provide the least drag. Having a pressurized enclosure might make the drive more expensive as stronger materials need to be used, and it would also make it more dangerous in case of mishandling, so I think there was a limited range of pressure they could maintain in the enclosure.

todayiamme 13y ago
Nitrogen is also inert enough for such use, it's easily contained and it doesn't require such measures. >>>Having a pressurized enclosure might make the drive more expensive as stronger materials need to be used, and it would also make it more dangerous in case of mishandling<<< Actually containing He at all would require these measures anyway, as He diffuses through solids much faster than air and as such cannot be easily contained. To quote the wikipedia article; >>>One industrial application for helium is leak detection. Because helium diffuses through solids three times faster than air, it is used as a tracer gas to detect leaks in high-vacuum equipment (such as cryogenic tanks) and high-pressure containers. The tested object is placed in a chamber, which is then evacuated and filled with helium. The helium that escapes through the leaks is detected by a sensitive device (helium mass spectrometer), even at the leak rates as small as 10−9 mbar·L/s (10−10 Pa·m3/s). The measurement procedure is normally automatic and is called helium integral test. A simpler procedure is to fill the tested object with helium and to manually search for leaks with a hand-held device. Helium leaks through cracks should not be confused with gas permeation through a bulk material. While helium has documented permeation constants (thus a calculable permeation rate) through glasses, ceramics, and synthetic materials, inert gases such as helium will not permeate most bulk metals.<<< Further, high pressure containers are dangerous as they might have an outward failure. That is unlikely to be the case with a drive that is at say .5 atm as the pressure is directed inwards, so the worst case over is most probably a drive filled with air or a slightly crumpled drive. (as a thought experiment think about how submarines implode instead of exploding when the hull encounters pressures beyond what it can handle)
crististm 13y ago
For what is worth, we're breathing more N than O - so toxicity is not an issue when comparing He to N.

graycat 13y ago

The idea of using helium in a hard drive is old, goes back at least 20 years. As I recall, the main reason for using helium is that it conducts heat better. Heat? Yes, the spinning drive acts like a centrifugal pump which moves the gas and heats it.

jccooper 13y ago

Helium gets you low density at standard pressure. I am guessing that they prefer not to construct hard drives as pressure vessels. Probably that makes thermal conductivity, among other things, a problem.

tryp 13y ago

The density of helium is less than 1/7 of the density of nitrogen, which is a good approximation for air. Two ways that this is helpful come to mind: 1. Aerodynamic effects like drag and vorticity are largely governed by the Reynolds Number, which holding all else constant, varies linearly with density. Changing the density of the fluid can drastically change the aerodynamic situation. See http://www.grc.nasa.gov/WWW/k-12/airplane/dragsphere.html http://www.grc.nasa.gov/WWW/k-12/airplane/dragsphere.html for an interesting and accessible example. 2. "Flow-induced vibration" is caused by the swirling gases crashing like stormy seas, making platters vibrate and heads flutter. Switching to helium cuts the momentum in these turbulent flows to a seventh of what they would be with air.

Lagged2Death 13y ago

... to reduce density it might have been easier to simply reduce pressure and then create a hermetically sealed chamber... Disk heads "fly" above the surface of the disk on a cushion of gas that's pulled under the head by the spinning disk. If there isn't enough gas pressure inside the disk enclosure, this method of locating the heads won't work. Wikipedia actually says: If the air density is too low, then there is not enough lift for the flying head, so the head gets too close to the disk, and there is a risk of head crashes and data loss. Specially manufactured sealed and pressurized disks are needed for reliable high-altitude operation, above about 3,000 m (9,800 ft). http://en.wikipedia.org/wiki/Hard_disk_drive#Integrity_and_failure http://en.wikipedia.org/wiki/Hard_disk_drive#Integrity_and_f... Atmospheric pressure on the top and bottom faces of a 3.5" drive case (~22 square inches) is in the neighborhood of 300 pounds each, and there's still more on the front, back, and sides. A square box of thin aluminum is probably not a great starting point for building a pressure vessel. If the box is filled with a gas at close to atmospheric pressure, you don't have to worry about it. Helium's specific heat is five times that of air, so it probably offers better heat conduction than air at 1/7th atmospheric pressure would.

hengheng 13y ago
Shot in the dark, but might there be advantages simply because there are more molecules flying around than with air? 10nm ground effect flying probably isn't trivial.
todayiamme 13y ago
I'm sold, but I have an additional question though. Can you please explain why hard-drives follow a flying head approach? Why don't they just perpendicularly fix the reader above the disk, rotate the disk and then use a linear actuator to move the reader back and forth - exactly like optical drives? I'm guessing that the status quo exists and that my suggestion is inherently flawed because of the precision required to maintain the head at 10 nm above the surface and as such letting fluid dynamics wrestle with gravity might do the trick for you (given that you can make the spindles in a precise manner that the forces cancel out in a way that ensures that the head is exactly at the desired distance above the drive) That leads to another thought, would the following conjecture be in the realm of possibility? Imagine that you have coated the disk with mystery thing X - which is an etched semiconductor that does something very magical. When an incident beam of light strikes a point on the coating, it releases electrons, which are then controlled through magical mechanism Y etched on X to create a magnetic field that flips the bit. If you do this then you can remove all of this stuff and it might lead to some gains.

robomartin 13y ago

Helium is nearly 7 times better at conducting heat than both air and nitrogen [0], lower density [1] and about the same viscosity [2]. [0] http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html http://www.engineeringtoolbox.com/thermal-conductivity-d_429... [1] http://www.engineeringtoolbox.com/gas-density-d_158.html http://www.engineeringtoolbox.com/gas-density-d_158.html [2] http://hyperphysics.phy-astr.gsu.edu/hbase/tables/viscosity.html http://hyperphysics.phy-astr.gsu.edu/hbase/tables/viscosity....