1. A method of forming riblets in aerodynamic surfaces to reduce drag, comprising:
forming a composite material layup;
applying a layer of adhesive to the layup;
molding the riblets into a an adhesive-covered surface of the layup; and
curing the layup.
2. The method of claim 1, further comprising:
forming a plurality of parallel grooves in the surface of a tool, and
wherein the step of molding the riblets includes using the tool to mold the riblets.
3. The method of claim 1, further comprising:
the step of molding the adhesive layer to form the riblets.
4. The method of claim 2, further comprising:
before the step of molding the riblets, applying a paint to the tool surface.
5. The method of claim 1, wherein:
forming a composite material layup includes stacking plies of prepreg material and applying a layer of uncured resin to the stacked plies, and,
molding the riblets includes forcing a grooved tool face into contact with the layer of uncured resin.
6. A method of forming aerodynamic surface features on the outer skin of an aircraft, comprising:
molding a generally rigid part having the approximate shape of the skin and including an outer surface having a plurality of substantially parallel riblets over which air may flow; and,
applying the part to the skin.
7. The method of claim 6, further comprising:
forming a plurality of substantially parallel grooves in the surface of a tool, and
wherein the step of molding the part is performed using the tool.
8. The method of claim 7, further comprising:
applying a paint to the tool surface after the step of forming the grooves.
9. The method of claim 6, further comprising:
forming a layup of composite materials;
placing the part over the layup;
compacting the layup and the part in a mold; and
co-curing the part and the layup.
10. The method of claim 6, further comprising:
removing a layer of material from a section of the skin, and
wherein the step of applying the part to the skin includes placing the part over the section of the skin where the material has been removed.
11. The method of claim 10, further comprising:
applying an adhesive between the part and the skin section.
12. A method of reworking-an outer skin of an aircraft, comprising:
removing a layer of material from a section of the skin;
molding an insert having the same general shape as the layer of material that has been removed, including forming a plurality of parallel riblets in the outer surface of the insert; and,
replacing the layer of material with the insert.
13. The method of claim 12, further comprising:
forming a plurality of substantially parallel grooves in the surface of a tool, and
wherein step of molding the insert is performed using the tool.
14. The method of claim 13, further comprising:
applying a paint to the tool surface after the grooves have been formed.
15. The method of claim 12, wherein replacing the layer of material includes introducing an adhesive between the insert and the skin.
16. The method of claim 12, wherein removing the layer of material includes grinding away riblets that are present on the skin.
17. For use in aerospace vehicles, an aerodynamic structure, comprising:
an outer skin including integrally formed, substantially parallel riblets extending in the direction of airflow over the skin.
18. The aerodynamic structure of claim 17, wherein the riblets include side walls forming an acute angle.
19. The aerodynamic structure of claim 17, wherein the acute angle is between approximately 25 degrees and 35 degrees.
20. The aerodynamic structure of claim 17, wherein the riblets have a height of between approximately 0.0018 inches and 0.00135 inches.
21. The aerodynamic structure of claim 17, wherein the centerlines of the riblets are spaced apart between approximately 0.00285 inches and 0.00315 inches.
22. The aerodynamic structure of claim 17, wherein the riblets each have a base having a width less than approximately 0.001 inches.
23. The aerodynamic structure of claim 17, wherein the outer skin further includes integrally formed, substantially flat grooves between the riblets extending in the direction of airflow over the skin.
24. For use in aerospace vehicles, an aerodynamic structure, comprising:
an outer skin including integrally formed, substantially parallel, alternating riblets and substantially flat grooves extending in the direction of airflow over the skin,
the riblets having\u2014
(i) side walls forming an acute angle of between approximately 25 degrees and 35 degrees,
(ii) a height of between approximately 0.0018 inches and 0.00135 inches,
(iii) center lines spaced apart between approximately 0.00285 inches and 0.00315 inches,
(iv) a base having a width less than approximately 0.001 inches and,
a top having a width of less than approximately 0.0006 inches.
25. A method of forming a structure for aircraft having aerodynamic surface features to reduce skin friction exerted by a turbulent boundary layer at the surface of the skin to reduce drag, comprising:
fabricating a mold tool, including forming a plurality of parallel, V-shaped grooves in a surface of the tool;
forming a multi-ply layup of uncured composite materials;
placing the layup in the mold tool;
applying a layer of moldable material over the layup;
closing the mold tool;
applying pressure to the mold tool to compact the layup and force the V-grooves into the moldable material so as to integrally form substantially parallel riblets in the outer surface of the compacted layup; and
co-curing the layup and the moldable material.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A process for regasification of LNG to form natural gas, said process comprising the steps of:
(a) circulating an intermediate fluid between a vaporizer and an ambient air heater, the intermediate fluid being warmed by exchanging heat with the ambient air as the intermediate fluid passes through the ambient air heater, the intermediate fluid being cooled by exchanging heat with LNG as the intermediate fluid passes through the vaporizer; and,
(b) subjecting the ambient air heater to a defrosting cycle by intermittently regulating the temperature of the intermediate fluid fed to the ambient air heater to a temperature greater than zero degrees Celsius using a source of supplemental heat,
wherein the ambient air heater comprises a horizontal tube bundle and a vertical tube bundle, when a temperature of the intermediate fluid is above 0\xb0 C. the intermediate fluid is directed only through the horizontal tube bundle, and when the temperature of the intermediate fluid is less than or equal to 0\xb0 C. the intermediate fluid is directed through the vertical tube bundle.
2. The process of claim 1, wherein step (b) is conducted downstream of the ambient air heater.
3. The process of claim 1, wherein the source of supplemental heat is selected from the group consisting of an exhaust gas heater, an electric water or fluid heater, a propulsion unit of a ship, a diesel engine, a gas turbine propulsion plant, and an exhaust gas stream from a power generation plant.
4. The process of claim 1, wherein regasification of the LNG is conducted onboard an LNG carrier and the source of supplementary heat is heat recovered from the engines of the LNG carrier.
5. The process of claim 1, wherein heat exchange between the ambient air and the intermediate fluid in the ambient air heater is encouraged through use of forced draft fans.
6. The process of claim 1, wherein the intermediate fluid is selected from the group consisting of a glycol, a glycol-water mixture, methanol, propanol, propane, butane, ammonia, a formate, fresh water and tempered water.
7. The process of claim 1, wherein the intermediate fluid comprises a solution containing an alkali metal formate or an alkali metal acetate.
8. The process of claim 7, wherein the alkali metal formate is potassium formate, sodium formate or an aqueous solution of ammonium formate.
9. The process of claim 7, wherein the alkali metal acetate is potassium acetate or ammonium acetate.
10. The process of claim 1, wherein the ambient air heater is one of a plurality of ambient air heaters and step (b) is performed on each of the plurality of ambient air heaters sequentially.
11. The process of claim 1, wherein heat exchange between the ambient air and the intermediate fluid in the ambient air heater is encouraged through use of forced draft fans and the horizontal tube bundle lies above the vertical tube bundle in closer proximity to forced draft fans.
12. A regasification facility for regasification of LNG to form natural gas, said apparatus comprising:
a vaporizer for regasifying LNG to natural gas;
an ambient air heater for heating an intermediate fluid using ambient air as the primary source of heat;
a circulating pump for circulating the intermediate fluid between the vaporizer and the ambient air heater, the intermediate fluid being warmed by exchanging heat with the ambient air as the intermediate fluid passes through the ambient air heater, the intermediate fluid being cooled by exchanging heat with LNG as the intermediate fluid passes through the vaporizer; and
a control device for regulating the temperature of the intermediate fluid fed to the ambient air heater to a temperature greater than zero degrees Celsius using a source of supplemental heat to subject the ambient air heater to a defrosting cycle,
wherein the ambient air heater comprises a horizontal tube bundle and a vertical tube bundle, when a temperature of the intermediate fluid is above 0\xb0 C. the control device directs the intermediate fluid only through the horizontal tube bundle, and when the temperature of the intermediate fluid is less than or equal to 0\xb0 C. the control device directs the intermediate fluid through the vertical tube bundle.
13. The apparatus of claim 12, wherein the source of supplemental heat is located downstream of the ambient air heater.
14. The apparatus of claim 12, wherein the source of supplemental heat is selected from the group consisting of an exhaust gas heater, an electric water or fluid heater, a propulsion unit of a ship, a diesel engine, a gas turbine propulsion plant, and an exhaust gas stream from a power generation plant.
15. The apparatus of claim 12, wherein the regasification facility is provided onboard an LNG carrier and the source of supplementary heat is heat recovered from the engines of the LNG carrier.
16. The apparatus of claim 12, further comprising a forced draft fan for encouraging heat exchange between the ambient air and the intermediate fluid in the ambient air heater.
17. The apparatus of claim 12, wherein the ambient air heater is one of a plurality of ambient air heaters and the control device is arranged to subject each of the plurality of ambient air heaters sequentially to a defrosting cycle.
18. The apparatus of claim 12, wherein heat exchange between the ambient air and the intermediate fluid in the ambient air heater is encouraged through use of forced draft fans and the horizontal tube bundle lies above the vertical tube bundle in closer proximity to forced draft fans.