Monday, June 03, 2019

reader project 6

Project description from Matt Janssen:
[click any pic to enlarge]


Here is a 3/16" laser-cut steel-framed parabolic trough array based on your design.

There are a lot of things I really like about your design and there is no way I could have learned so much about parabolic trough technology that would have not taken more time and more money than building your design and experimenting with it. I believe your geometry with the fixed absorber tube is key for small trough construction. I have fought rotary joints on steam projects before and they are just too finicky and expensive.

One improvement I made after my first trough using your CAD files is to add a countersunk angle iron under the sheet at the longitudinal rim edge of the trough which assists with clamping the edge and avoiding corrugation caused by bending stress around fasteners.

We re-drew the ribs and added this countersunk notch as well as an offset for the reflector sheet thickness. The troughs have 68" T316 24 gauge Super 8 SS sheets which have about a 63% reflectivity. I am using one of the bottom holes for a 1/4" through stay rod. The troughs are powdercoated.

I started out with (9) 3/8" black pipe return bend elements slid in the borosilicate vacuum tubes running forced-flow in series and at no flow could make 200F. The geometric concentration ratio of this setup is about 22. While the array could make significant hot water with flow, I did not test it further as the max temperature was too low. I then installed 1/4" sch 40 pipe bare absorber tubes and reconfigured the pipes to parallel flow. In 40F with high insolation I could make 265F steam with no flow. This is about the limit of concentration ratio that a thin sheet reflector compressed to a rib frame will support - about 35.

I think even more performance could be achieved with these troughs by using silvered mirror film and encasing the tubes in glass. I have decided to start over and this array is now available.

I have about $15K in parts in it and a reasonable offer with timely removal takes it. There is one spare trough like these, my first trough, an aluminum trough, the other absorber elements, a bunch of borosilicate tubes, and a welding fixture.

The array was stored inside all winter and was just hauled-out 05/30/2019.


Matt Janssen
Sandpoint, ID

If you like, you can email Matt directly.

Thank you for your interest

George Plhak
Lions Head, Ontario, Canada

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