[PSUBS-MAILIST] thruster vacuum fill

[Jon Wallace via Personal_Submersibles]

Hank, another question on this procedure...with the cavity filled with 
oil don't you still run into the issue of fluid expansion due to 
temperature rise either through operation or sitting in the hot sun for 
a few hours?

Jon


On 3/23/2016 11:17 AM, Jon Wallace via Personal_Submersibles wrote:
>
> I assumed Hank was suggesting the vacuum simply as a means of 
> displacing air from the motor housing to achieve a complete filling of 
> the cavity with oil.  How would you seal the motor in this manner 
> after all the cavity is filled with oil and you want to remove it from 
> the vacuum chamber...a one way valve perhaps?
>
> Jon
>
>
> On 3/22/2016 8:35 PM, Stephen Fordyce via Personal_Submersibles wrote:
>> Hi guys,
>> I've got a reasonable working knowledge of vacuum from being involved 
>> with design and fabrication of vacuum-insulated pipes and vessels for 
>> cryogenic fluids, and have a couple of comments on this:
>>
>> 1. I'm missing how it will help having vacuum in a pod when you are 
>> at depth.  Ie. there is still a very large pressure on the outside 
>> trying to get in (in fact, even more than if the inside was at ambient).
>> 2. There's a potential benefit from vacuuming the pod before filling 
>> with oil (ie. pull a vacuum, then release the vacuum with oil) as it 
>> means there will be no possibility of condensation from any remaining 
>> air, and oil will fill all the spaces where air might otherwise get 
>> trapped.  Realistically, the amount of moisture you'd save from the 
>> air would be pretty negligible, possibly the removal of airspace will 
>> help with preventing water leaks from the outside.
>> 3. Vacuuming the pod with oil or water in it may have weird effects.  
>> Ie. water will boil (creating residue buildup from salt, tannins, or 
>> whatever else was dissolved in it).  Oil will also evaporate/boil, to 
>> a much lesser extent, but the thin oil typically used for 
>> compensating will probably evaporate quite significantly under vacuum 
>> for long periods.
>>
>> Cheers,
>> Steve
>>
>>
>
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