Tubing with hydrophobic surface
A method of forming a heat exchanger tube, particularly suited for condensing applications, contemplates cold-rolling a metallic strip to emboss a hydrophobic surface texture, to thereby form an embossed surface on the metallic strip. The method includes roll forming the metallic strip to a tubular shape, with the embossed surface on the exterior of the tubular shape, and welding the edges of the roll-formed strip to form a heat exchanger tube. Cold-rolling to emboss a hydrophobic surface texture exhibiting a contact angle of at least about 75° is contemplated, with processing including heat-treatment to minimize degradation of the hydrophobic surface texture, and roll-forming to avoid deformation of the hydrophobic surface texture,
1. A method of making a heat-exchanger tube, comprising the steps of:
providing a metallic strip;
cold-rolling the metallic strip to emboss a hydrophobic surface texture to form an embossed surface of the metallic strip;
roll-forming said metallic strip to a tubular shape, with said embossed surface of said metallic strip positioned on the exterior of the tubular shape; and
welding the edges of the roll-formed strip to form a heat-exchanger tube.
2. The method of making a heat-exchanger tube in accordance with claim 1 , wherein said cold-rolling step embosses said hydrophobic surface texture to exhibit a contact angle of at least about 75 degrees.
3. The method of making a heat-exchanger tube in accordance with claim 1 , wherein said cold-rolling step embosses said hydrophobic surface texture to exhibit a contact angle of at least about 90 degrees.
4. The method of making a heat-exchanger tube in accordance with claim 1 , including heat-treating said heat-exchanger tube to minimize degradation of said hydrophobic surface texture.
5. The method of making a heat-exchanger tube in accordance with claim 4 , wherein said heat-treating step includes a specialized heat-treatment, including a method to minimize deformation of said hydrophobic surface texture.
6. The method of making a heat-exchanger tube in accordance with claim 4 , wherein said heat-treating step comprises hydrogen annealing.
7. The method of making a heat-exchanger tube in accordance with claim 4 , wherein said heat-treating step includes providing a gas blend that includes hydrogen.
8. The method of making a heat-exchanger tube in accordance with claim 4 , wherein said heat-treating step includes providing an inert gas that minimizes oxidation of said hydrophobic surface texture.
9. The method of making a heat-exchanger tube in accordance with claim 4 , wherein said heat-treating step includes employing a specialized quick quench system.
10. The method of making a heat-exchanger tube in accordance with claim 9 , wherein said quick quench system employs forced gas flow.
11. The method of making a heat-exchanger tube in accordance with claim 9 , wherein said quick quench system comprises a relatively soft, conductive shoe for removal of heat.
12. The method of making a heat-exchanger tube in accordance with claim 1 , wherein said metallic strip comprises stainless steel.
13. The method of making a heat-exchanger tube in accordance with claim 1 , wherein said metallic strip comprises one of titanium and titanium alloy.
14. The method of making a heat-exchanger tube in accordance with claim 1 , wherein said roll-forming step includes providing forming rolls having sufficiently soft surfaces to form said tubular shape without significant deformation of said hydrophobic surface texture.
15. The method of making a heat-exchanger tube in accordance with claim 14 , wherein said forming rolls entirely comprise soft material, or have a sufficiently soft surface layer.
16. The method of making a heat-exchanger tube in accordance with claim 1 , wherein said roll-forming step includes applying lubricant to forming rollers to reduce friction and marring of the embossed surface of the heat-exchanger tube.
17. The method of making a heat-exchanger tube in accordance with claim 16 , wherein said step of applying lubricant includes applying atomized lubricant to said forming rollers.
18. The method of making a heat-exchanger tube in accordance with claim 17 , including applying said lubricant to said forming rollers at a distance of about 6 inches from forming surfaces of said forming rollers.