METHOD FOR TREATING AN OUTER SURFACE OF A HEAT TRANSFER FLUID TUBE

Abstract

A method for treating an outer surface of a heat transfer fluid tube especially for a receiver of a solar thermal power plant, having the steps of providing the heat transfer fluid tube and treating the outer surface with a hydrogen plasma jet so that a porosity in the range of a nano-scale is created in a thin layer of that outer surface.

Claims

1. A method for treating an outer surface of a heat transfer fluid tube, the method comprising: providing the heat transfer fluid tube, treating the outer surface with a hydrogen plasma jet so that a porosity in the range of a nano-scale is created in a thin layer of that outer surface.

2. The method according to claim 1, wherein the material of the heat transfer fluid tube is nickel alloy.

3. The method according to claim 1, further comprising: before treating the outer surface with a hydrogen plasma jet, applying a high absorbing material, other than the material of the heat transfer fluid tube, as an extra layer on the surface of the heat transfer fluid tube.

4. The method according to claim 3, wherein the material of the heat transfer fluid tube is stainless steel or nickel alloy and the material of the extra layer is tungsten with a thickness of about one micrometer.

5. The method according to claim 1, wherein the hydrogen plasma jet has an energy level with an Ion flux above 10e.sup.24 m.sup.2s.sup.1.

6. The method according to claim 1, wherein the heat transfer fluid tubes are in a receiver in a solar thermal power plant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention now will be explained in more detail with reference to the appended drawing. The drawings show only an example of a practical embodiment of the invention, without limiting the scope of the invention, in which:

[0016] FIG. 1 shows a cross-section through a heat transfer fluid tube where the inventive method is applied,

[0017] FIG. 2 shows an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF INVENTION

[0018] FIG. 1 shows a cross-section of a heat transfer fluid tube 1. According to the present invention the outer surface 2 of this heat transfer fluid tube is treated with a hydrogen plasma jet 3. The schematic shown hydrogen plasma jet 3 comes from a hydrogen plasma source, which is not shown in greater detail. Also not shown are additional equipment for moving the tube and the hydrogen plasma jet relative to each other, which are needed for applying the hydrogen plasma to all three dimensions of the heat transfer fluid tubes surface. Applying a hydrogen plasma jet 3, having an energy level with an Ion flux above 10e.sup.24 m.sup.2s.sup.1, transforms a thin layer of the outer surface 2 to a porous crust with nano-scale porosity.

[0019] FIG. 2 shows a cross-section of an embodiment of the present invention. Here a high absorbing material, other than the material of the heat transfer fluid tube, is applied as an extra layer 4 on the surface of the heat transfer fluid tube 1. Subsequently the surface of this extra layer 4, which now forms the outer surface 2 of the heat transfer fluid tube 1, is treated with the hydrogen plasma jet 3. Therewith, high temperature resistant tube material like nickel alloy can be combined with high absorption material tungsten as an additional surface layer on the outer surface of the tube. Advantageously, this additional tungsten layer of about one micrometer thickness is treated with the hydrogen plasma as long as the complete tungsten layer has a porosity of less than 50 nm.

[0020] Advantageously the aforesaid describes method is used for heat transfer fluid tubes of a receiver in a solar thermal power plant. But the method is also applicable to heat transfer fluid tubes in e.g. a furnace or other installations, where a very high-efficient absorption of incident radiation is needed.