The Light Green Machine Institute

23 Dec 15: Two phase pumps?
This is a bit whimsical, but I thought you might enjoy it here in the holiday season.  Well over three hundred people faithfully open this newsletter each week, and when the subject becomes a bit far-fetched (like this one), shall we say, even more do so. Thus, a treat for all you thinking engineers out there.
I have spent almost my entire adult life thinking about how to build a pump that can pump steam. What does this have to do with the Light Green Machine?  I'll admit not much, for in the paper industry, we have the ubiquitous dryer can to condense steam and make our total steam cycle efficient.  However, once in a while in our business, and certainly in lots of other industries, the ability to pump steam would come in mighty handy.  
Of course, it is not that we want to pump steam per se, that is a misnomer on my part.  What we really want to do is take lower pressure steam, convert it to water and then take that condensate back to the boiler.  Figure out how to do this and many a cooling tower (and the energy losses that go with them) will disappear.
Now, there are such devices as condensing turbines, and they play into what I am about to describe below.  It is also likely that what I am describing below has already been tried, but I have seen no literature on it.  So, dear reader, if you have heard of this, please share it with all of us.
Here is my idea.  What if we took two standard ANSI pumps and direct connected them to each other at their inlet flanges?  Then, at one of the normal outlet flanges we connected our steam supply (making this normal outlet an inlet) and to the other outlet flange we took away the condensate that was created in this mashed up machinery configuration.  
The steam comes into the one pump via the (former) outlet connection and discharges through the (former) inlet connection directly into the second pump which is operating in a normal fashion.
The trick of course, and it is a huge (maybe insurmountable) trick, is to get the steam to give up its energy in the form of mechanical energy (not heat) to spin the impeller in the first pump, thus being fully spent and changing phase to water before it enters the second pump.
As a thought experiment (just like imagining the perfect golf shot) it works fine.  But what is the practical reality?
A couple of things come to mind that need lots of work, perhaps cannot even be overcome.  
First, the pump turned into a steam turbine will have to have a specially designed impeller in order to do the best job it can to extract the energy mechanically and not waste it as heat.
Second, the motor hooked to the now steam turbine will have to be a regenerative motor, for it is through this motor acting as a generator that the energy given up by the condensing steam is saved and used as electricity.
Yet, there is another thought.  What if the turbine end of this machine could be designed so that it would spin at exactly the same speed as the pump end?  Then a common shaft could be used to directly deliver the mechanical energy from the turbine to the pump.  Further, the bearings on either end of this shaft could be placed inside the casing, making the entire unit a sealed unit with no packing, seals or other high maintenance connections.
Surely someone has thought this all through before and dismissed it as impractical... However, if you want to throw some calculations on it and show us all why it won't work, we would be delighted to hear from you. Just don't say "it won't work" without backing up your statement

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Think light!


Brian Brogdon, Ph.D.
Executive Director




Jim Thompson

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