Wednesday, October 26, 2011

Heat exchanger goes online!

What began as a pipe-dream (pardon the pun) more than two years ago has finally come to fruition. Five members of the University of Alabama team (Alex Huryn, Jon Benstead, Dan Nelson, Vija Pelekis and Philip Johnson) left on 19 October to install the heat exchanger at Hengill. Here we are unloading 750 lbs of gear at Birmingham airport. Those 14 bags came to $950 in excess baggage charges. Not bad for overnighting all that stuff to Iceland.

We were joined in Iceland by our stalwart postdoc Jim Hood and Ryan McClure, an undergraduate from Wyatt Cross's lab at Montana State University. With limited time, we had to hit the ground running. So the red-eye flight was followed only by a change of clothes, lots of coffee and obligatory hot-dogs. Then the rather groggy team headed out to Hengill for a long day's work, starting with some punishing sand-bag detail (Dr. Wyatt Cross's absence was more than conspicuous at this point :-) :). With the sandbags filled and carried to the site, we could begin constructing the heat exchanger. Here's a couple of shots of Alex Huryn and our intrepid engineer Philip Johnson joining the stainless steel pipes and starting to attach them to the PVC manifolds.

By mid-morning the next day, the heat exchanger was complete and the flexible 2" tubing for moving water through it was in place on the hillside. Here's a shot of the completed exchanger, with Alex, Philip and Gisli Gislason in the background.

It was soon lifted into place in the pool at the head of the warm stream and hooked up to the flexible tubing.

All that was left was to submerge the heat exchanger by damming the warm stream. Here's a shot of the completed set-up.

We could finally begin the warming manipulation, with immediate and impressive results! Here's a plot from four temperature loggers spaced along the experimental warming reach. All showed an increase of 3 degrees C (the upper logger [A] showed some variability as we adjusted the position of the diffuser at the outlet). This is good news, given that discharge in the cold stream is high at the moment, with only 40% of its flow going through the heat exchanger. Our potential warming will increase as discharge declines.

Here's a final shot from the opposite hillside, showing the position of all the components of the heat exchanger (including the vital engineer!). The whole set-up creates a ~30-m reach of the right-hand (cold) stream that will be warmed at 3 to 5 degrees C above ambient, hopefully for the next three years. We've already been studying this reach (and a reference cold stream) for a year. Every month we collect microbial, algal and invertebrate samples, as well as measuring nutrient uptake and whole-stream metabolism.

All in all, a fantastically successful trip and the result of many months of preparation by a large group of people. Special mention should go to our engineer, Dr. Philip Johnson, and Chau Tran, who helped Jon Benstead test the heat exchanger over the summer and then packed all of its components for shipping from Alabama.

Watch this space!