Solar Cookers World Network

Georgia Tech Spiral Solar Cooker

1,765pages on
this wiki
Add New Page
Add New Page Comments0
Last updated: 15 February 2015      
GA Tech SC

Suntwist Company (no longer in business) promotional sheet.

Richard A . Steenblick and Dar-Veig Ho invented this design while Steenblick was a student at the Georgia Institute of Technology, circa 1980. He started The Suntwist Company, which published and sold instructions and a large paper pattern to allow construction of the novel fresnel-type reflector, from a single flat sheet of reflective material. It was intended to be both effective and affordable, though ultimately the design has not found a large following. He and his associate were granted a US patent regarding the Suntwist design, and many other variations of spiral concentrators, with both positive and negative focal lengths. The Suntwist Company ceased operations after a time, and Steenblick went on to pursue a distinguished career as a professor at GA Tech, in the field of optics.

After cutting the spiral from a 4-foot (1.2m) square sheet, pairs of holes were drilled at four points along each turn of the spiral. The holes were plotted in a special pattern, so that if the spiral were "wound up" somewhat like a torsion spring, the holes could be aligned, and wire passed through them to tie the spiral to a supporting X-frame. The winding set up spring tension in the turns of the spiral with the result that the continuous strip tilted inward toward the center, to varying degrees. The resulting geometry constituted a fresnel-type reflector, of depth less than 2" (5cm), yet approximating the effect of a paraboloid shape.

For low cost, The Suntwist Company recommended using fiberboard substrate and a glued-on aluminum foil reflective surface. While these materials satisfied the performance requirements of the concentrator, the practical issue of material durability was amplified in significance by the design. In particular the anchor holes, necessarily located quite near the inner edges of the spiral's turns, were at risk of breaking through to the edge under stress from the wire, during construction and with handling/use. This would result in de-alignment of the spiral and degradation of the focus. Construction using sheet metal could overcome the issue, but increased cost and tooling needed for construction.

Suntwist Paper Pattern

Paper Pattern/template for cutting spiral and drilling tie-down holes (Copyrighted).

In the example pictured below, the sheet metal is stainless steel. While stainless steel offers corrosion resistance, reflectivity is only ~ 65%. Aluminum offers significantly better reflectivity, but is structurally weaker.

Suntwist Sheet Metal

Spiral cut from sheet metal, anchored to X-frame of galvanized steel pipe with wire.

Suntwist Smokin Hot

Aimed at the sun, residual oil on a pipe placed along the focal length burns off.

Suntwist Temp

An oven thermometer (small thermal mass) is maxed out. (Fahrenheit scale.)

Also on Fandom

Random Wiki