Apricus issued freeze protected heat pipe patent

Apricus Solar Co., Ltd has been awarded a patent for the freeze protected heat pipe design used in Apricus ETC solar collectors.  

The freeze protected heat pipe design was the result of extensive research conducted at the Apricus owned manufacturing facility.  The patented production method uses a food grade salt additive to modulate the structure of the water as it freezes, avoiding the swelling and damage which plain water causes.

The challenge with heat pipes used in evacuated tube solar collectors is to select a working fluid that has a high phase change heat transfer capacity and that remains stable at high temperatures.   Water is a great choice, but freezes in cold regions which causes the heat pipes to swell and eventually rupture.  Additives that may seem obvious choices to provide freeze protection such as alcohol or glycol are not stable at high temperatures resulting in an air pocket developing in the heat pipe, impairing function.

In addition to thousands of cycle testing in Apricus's own lab, the heat pipes have passed the new heat pipe freeze resistant testing that is now part of the European Solarkeymark test standard for solar thermal collectors (that use heat pipes).  

Testing was completed by TUV test labs in accordance with the SKN_N0106_AnnexF_R0 testing standard.  The test involves 20 cycles of -20^oC / -4^oF freezing (>30 minutes) and +10^oC / 50^oF thawing (>30 minutes).

To learn more about how Apricus heat pipes work click here.