FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
The Patents Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A method for the manufacture of a heat pipe INVENTOR
Name : Shanmugam Venkatachalam Ravi
Nationality : Indian National Address : Crompton Greaves Ltd
Corporate R&D and Quality
Analytical Laboratory
Kanjur Marg(E), Mumbai - 400042,
Maharashtra, India
APPLICANTS
Name : CROMPTON GREAVES LIMITED
Nationality : Indian Company
Address : CG House, Dr Annie Besant Road, Prabhadevi, Mumbai 400025, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed :


FIELD OF INVENTION
This invention relates to a method for the manufacture of a heat pipe.
This invention also relates to a heat pipe manufactured by the method.
BACKGROUND OF INVENTION
Heat pipes are very simple, efficient and cost effective heat transfer devices with no moving parts for transferring heat from one location to another. Heat pipes have thermal conductivity many thousands of times of that of copper. Because of their extraordinary heat transfer capacity and rate, heat pipes are often referred to as superconductors. Heat pipes are often used in cooling applications where conventional cooling techniques like heat sinks are not suitable. Heat pipes have a variety of cooling applications covering almost the entire spectrum of temperatures encountered in heat transfer applications, for example, they are used in air conditioners, refrigerators, heat exchangers, transistors, capacitors, laptops, personal computers or work stations. A typical heat pipe comprises a sealed tubular container partly evacuated and containing a working fluid. The container may be made of conductor material such as copper or aluminum and the working fluid may be, for example helium, nitrogen or water depending upon the use or
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application of the heat pipe. In order to improve the heat transfer efficiency, the heat pipe may be provided internally with a wick structure such as wire mesh, powder metal or fiber which has a capillary action.
Several methods are reported for the manufacture of heat pipes. Korean Patent No 2003055743 describes a method for the manufacture of a heat pipe comprising injecting a working fluid into a container, freezing the working fluid in the container by a freezing unit, evacuating the container partly with a vacuum unit and sealing the open end of the container. Because of the use of the vacuum unit and freezing unit, the method is expensive. It is also time consuming and gives low productivity. Therefore, it is not suitable for automation and mass production. Korean Patent No 2002066785 teaches a method of manufacturing a heat pipe in which a container containing the working fluid is heated and air is removed from the container by vacuum pump. This method also suffers from most of the drawbacks discussed earlier. Japanese Patent No 10238976 teaches a method wherein non-condensable gas in the container is removed by vacuum created by vacuum pump. The container is a long pipe comprising multiple heat pipes. Cost of production of heat pipes by this method increases as vacuum pump is involved. Japanese Patent No 10238974
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relates to a method of manufacturing a heat pipe which comprises temporarily sealing a working fluid in a container provided with working fluid injection tube at one end, heating the container and removing non-condensable gas in the container into the fluid injection tube and sealing the container. This method is complicated, time consuming and expensive due to the steps involved in temporarily sealing the working fluid in the container and providing the container with the working fluid injection tube. German Patent No 19628546 relates to a method of manufacturing a heat pipe which employs a piston and cylinder arrangement. The piston is moved in the container to create vacuum and introduce working fluid into the container. This method calls for leak proof piston. Besides, it can only be used in the manufacture of a heat pipe without wick. Japanese Patent No 10111089 describes a method of manufacturing a heat pipe comprising introducing a predetermined quantity of water into a long small diametered pipe through one end thereof from an airtight container filled with water. The container and pipe are heated to the boiling point of the water. Non-condensable gas and steam escape from the other end of the container. A predetermined length of the pipe is cooled by a cooler so as to allow the steam therein to condense after both the ends of the pipe are sealed airtight. This method is very time consuming and complicated and gives low
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productivity. In this method the quantity of the working fluid formed by the condensate will depend upon parameters like cooling temperature, area of pipe cooled or time of cooling or temperature within the pipe which can not be precisely controlled. This can often lead to the working fluid content in the heat pipe being more or less thereby reducing the efficiency of the heat pipe. Besides, it requires a cooler to form the condensate and is suitable only for small diametered heat pipe.
OBJECTS OF INVENTION
An object of the invention is to provide a method for the manufacture of a heat pipe which is simple and easy to carry out and is less expensive.
Another object of the invention is to provide a method for the manufacture of a heat pipe which is less time consuming and gives increased productivity.
Another object of the invention is to provide a method for the manufacture of a heat pipe which is suitable for mass production and automation.

Another object of the invention is to provide a heat pipe manufactured by a method which is simple and easy to carry out and is less expensive.
Another object of the invention is to provide a heat pipe manufactured by a method which is less time consuming and gives increased productivity.
Another object of the invention is to provide a heat pipe manufactured by a method which is suitable for mass production and automation.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a method for the manufacture of a heat pipe comprising the steps of removing air from an open ended tubular container by passing a working fluid as vapour thereof through one open end of the container followed by sealing the other open end of the container, injecting a predetermined quantity of the working fluid as liquid thereof through the said one end of the container followed by sealing the said one end of the container and allowing the working fluid in the container to cool down and condense to create a vacuum therein.
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The tubular container may be made of any good thermal conductor material such as copper or aluminum.
The working fluid used in the container is selected depending upon parameters like the application of the heat pipe. The working fluid may be any known working fluid such as helium, nitrogen, ammonia or water. Preferably, the working fluid is water.

According to an embodiment of the invention, the tubular containr is
provided with a wick which may be any known type such as wire mesh, powder metal or fiber.
The tubular container can be held in any position for carrying out the said steps of the method.
The ends of the tubular container can be sealed using any known techniques like press sealing, crimping or plugging.
According to the invention there is also provided a heat pipe manufactured by the method described above.

According to the invention a predetermined quantity of the working fluid is injected into the tubular container as liquid. Therefore, the quantity of the working fluid in the container is accurately controlled and optimized so as to give heat pipe of optimum performance and heat transfer efficiency. The quantity of working fluid injected as liquid thereof will depend up on parameters like diameter of the heat pipe, type of heat pipe ie whether with or without wick or intended heat transfer rate. The method of the invention does not require any complicated and sophisticated equipments like vacuum unit or refrigerator unit or cooler to evacuate the heat pipe or condense the working fluid. The various steps of the method are very simple and easy and less time consuming to carry out. Therefore, the method of the invention is simple and easy to carry out besides being less time consuming. It gives increased productivity and is suitable for mass production and automation. It can also be used for making heat pipe of any diameter.
It is to be clearly understood that in the event the method of the invention is carried out in an atmosphere of the working fluid as vapour then the step of removing air from the tubular container is obviously not required and the working fluid as liquid can be straight away injected into the tubular
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container. Such a variation of the method of the invention is to be clearly understood and construed to be within the scope of the invention.

We claim :
1. A method for the manufacture of a heat pipe comprising the steps of removing air from an open ended tubular container by passing a working fluid as vapour thereof through one open end of the container followed by sealing the other open end of the container, injecting a predetermined quantity of the working fluid as liquid thereof through the said one end of the container followed by sealing the said one end of the container, and allowing the working fluid in the container to cool down and condense and create a vacuum therein.
2. A method as claimed in claim 1, wherein the working fluid is water.
3. A method as claimed in claim 1 or 2, wherein the tubular container is provided with a wick.
4. A heat pipe manufactured by the method as claimed in anyone of claims 1 to 3.