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Re: [PSUBS-MAILIST] Introduction to the PSUBS group



John,
examining the air conditioning problem, we would like to remove heat from the interior of the sub both by lowering the temperature of the air and by removing humidity from the air.  If we want to reject that heat to the surrounding water we can do that, but if the temperature of the surrounding water is higher than the interior air we need to use a heat pump to move the heat in that direction. 

Two common ways of moving heat are the reverse Rankine cycle (vapor compression like in your home window shaker) and thermo-electric coolers.  The reverse Rankine cycle is far more efficient than the thermo electric coolers, but the equipment is bulky and the working fluids are not so great for enclosed spaces.  I wouldn't think about installing one in the cabin of a sub.  Thermo electric coolers (TECs) are self contained and can be scaled fairly easily.

We used TECs from TE tech http://www.tetech.com/ on a project I did recently.  Checking out the website I see they also offer air to liquid coolers, designed to move heat from the liquid to the ambient air.  This should be reversable by just reversing the polarity on the input power, making the hot side cold and the cold side hot.  I didn't see any specs on the liquid heat exchanger, but we would need to know the pressure specs on it.  The TEC option has the added benefit of being able to be used as a heater in cold weather, with an efficiency of greater than 100%.

The ice option will work too.  Here we aren't rejecting heat to the outside but letting the ice absorb it in a phase change process. 

Both the TEC and ice systems are using resources on the sub.  Mass and volume seem to be critical, limited resources on a sub so i think our cooler should be designed to conserve both.  The TEC uses power from a lead-acid battery so we need to consider how many joules of heat our TEC can remove from the sub per pound of battery, and compare that to how many joules of heat the ice system can remove per pound.

David Hoffman


From: John Hodorek <amsjohn@sbcglobal.net>
To: personal_submersibles@psubs.org
Sent: Wed, August 11, 2010 11:10:03 AM
Subject: Re: [PSUBS-MAILIST] Introduction to the PSUBS group

Welcome Aboard David,
 
  I am a former Hard Hat Diver the work is hard but, you are payed to blow bobbles there is on better job then one you enjoy.  Glad your on board it look as if we need you to help with this Air Conditioning problem.  Or is thermo the wrong way, on the A/C chart?
 
                                                           John Hodorek


From: David Hoffman <coupe413@yahoo.com>
To: personal_submersibles@psubs.org
Sent: Wed, August 11, 2010 12:08:07 AM
Subject: [PSUBS-MAILIST] Introduction to the PSUBS group

Hello all,
I figured I might as well introduce myself, as I have been reading the group emails for a few months and learning a lot.  My name is David Hoffman, I live near St. Paul, MN and I am a recent graduate in mechanical engineering from the university of minnesota.  I have a huge range of interests in science and engineering ranging from evolutionary biology to cosmology to jet turbines.  My focus in education is on thermodynamics, particularly computational thermodynamics, heat transfer and combustion.  I know my way around the shop and am a pretty good welder, machinist and fabricator.

I don't know what got me started on my interest in submarines but it seems to have started with reading a wikipedia article on the mid-ocean ridge in the Atlantic.  I think that might have gotten me onto Robert Ballard and the sinking of the Thresher and Scorpion.  Anyway, after doing a lot of reading I am considering a career in oceanography or deep water work.  I am still trying to figure out exactly where I want to take my career, whether I should go to dive school or go for an advanced degree in oceanography or get a desk job.  If anyone here has any advise I would love to hear it.  I likely won't be building my own sub any time soon but I am still interested in the goings-on of the community.

I am pretty impressed with most of the discussion and projects being built by the group, and hope that I can be of help through my thermodynamics education and fabrication experience.  You guys have some elegant ways to solve complex problems that I had no idea even existed prior to reading about them here. 

David Hoffman