FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Phase change heat exchanger
APPLICANTS :
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR (S):
Singh Aditya, of Crompton Greaves Ltd, Transformer (T3) Division, Plot No 29, 31 and 32, New Industrial Area No 1 AKVN, Manideep, 462046, Madhya Pradesh, India; an Indian National.
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 the Invention:
This invention relates to the field of transformers, and cooling mechanisms thereof.
Particularly, this invention relates to a heat exchanger.
Still particularly, this invention relates to a phase change heat exchanger.
Background of the Invention:
A transformer is an electric device which transfers current from one circuit to another with or without affecting its magnitude. It includes electro-mechanical assemblies such as copper windings immersed in oil.
Power transformers rated up to a few KVA can be adequately cooled by natural convective air-cooling, sometimes assisted by fans. Some power transformers are immersed in specialized transformer oil that acts both as a cooling medium, thereby extending the lifetime of the insulation transformer. The transformers get heated due to iron and copper losses occurring in them. It is necessary to dissipate this heat so that the temperature of the winding is kept below the value at which the insulation begins to deteriorate.
Another type of cooling provided for transformers is by means of external associated auxiliary equipment such as heat exchangers, radiators, or the like.
In the case of a radiator, pipes connect the transformer to an adjacently located radiator. These pipes conduct oil from the transformer to the radiator, where they are cooled, and back again to the transformer.

The radiator may include pipe windings and heat exchange principles to regulate the temperature of oil from its relatively heated state to its relatively optimum working temperature.
Further, Heat Exchangers are deployed for efficient heat transfer from one medium to another. Many types of Heat Exchangers are designed; the types include Shell and tube heat exchanger, Plate heat exchanger, Adiabatic wheel heat exchanger, Plate fin heat exchanger, Pillow plate heat exchanger, Fluid heat exchangers, Waste heat recovery units and the like.
Prior Art:
GB163090 discloses improvements in and relating to cooling devices for electrical apparatus. It discloses means for cooling electrical apparatus, in which the container is closed and is provided with a liquid inlet and an outlet for the vapour through which the pressure on the 'liquid within the container is reduced below 25 atmospheric pressure.
It does not disclose a cost-efficient system for cooling using latent heat of vaporization of water for cooling electrical apparatus as transformer.
Objects of the Invention:
An object of the invention is to provide an efficient heat exchanger.
Another object of the invention is to provide a cost-efficient system for cooling using latent heat of vaporization.

Summary of the Invention:
According to this invention, there is provided a A phase change heat exchanger assembly comprises:
- pressurised vessel containing a first fluid adapted to readily change phase upon heating, said pressurised vessel adapted to allow a defined number of pipe windings carrying relatively hotter second fluid through its resident first fluid medium so that as the phase of the first fluid changes, the second fluid loses its heat and cools down and cooled oil again guided back to the transformer through pipes; and
- condenser adapted to be communicably coupled with said pressured vessel by means of a first pipe for receiving said gaseous state of said first fluid in order for it to condense and a second pipe adapted to transfer said condensed first fluid from said condenser to said pressurised vessel.
Typically, said pipe windings includes a defined number of windings defined in accordance with the surface area required per unit time for the fluid flowing through the windings to transfer its heat from through the pipe thickness to said resident first fluid medium, thereby causing phase change of said first fluid, under pressure, from its natural liquid state to its gaseous state.
Typically, said assembly includes a pump adapted to transfer said first fluid from said condenser to said pressurised vessel.
Typically, said first fluid is water.

Preferably, said pressure is about 0.4 bar in the pressurised vessel.
Alternatively, said first fluid is fluorobenzene,
Typically, said second fluid is oil.
Typically, said heat exchanger is coupled to a transformer which has oil which heats up, said oil being said second fluid.
Typically, said heat exchanger is coupled to a transformer which has oil which heats up, said oil being said second fluid, and said hot oil is pumped through said heat exchanger assembly by means of a pump.
Brief Description of the Accompanying Drawings:
The invention will now be described in relation to the accompanying drawing, in which:
Figure 1 illustrates a schematic of the phase change heat exchanger.
Detailed Description of the Accompanying Drawings:
According to this invention, there is provided a phase change heat exchanger
Figure 1 illustrates a schematic of the phase change heat exchanger (100).

In accordance with an embodiment of this invention, there is provided a pressurised vessel (10) containing a first fluid (12) adapted to readily change phase upon heating, said pressurised vessel adapted to allow a defined number of pipe windings (14) carrying relatively hotter second fluid (16) through its resident first fluid medium. The number of windings is defined in accordance with the surface area required per unit time for the fluid flowing through the windings to transfer its heat from through the pipe thickness to said resident first fluid medium, thereby causing phase change of said first fluid, under pressure, from its natural liquid state to its gaseous state. As the phase of the first fluid changes, the second fluid loses its heat and cools down and cooled oil (20) again guided back to the transformer through pipes (18).
In accordance with another embodiment of this invention, there is provided a condenser (22) adapted to be communicably coupled with said pressured vessel by means of a first pipe (24) for receiving said gaseous state of said first fluid in order for it to liquefy. A second pipe (26) is adapted to transfer said condensed first fluid from said condenser to said pressurised vessel. This transfer may occur by means of a pump (28).
It is known that Boiling Temperature of a liquid is defined as the temperature at which the Vapor Pressure equals the atmospheric pressure. The Boiling Temperature of Water is 100 deg C at 1 atmospheric pressure and of fluorobenzene is 85.1 deg C. The boiling point depends on the pressure and the boiling points of water at pressures ranging 0.03 bar - 1 bar are indicated in the diagram and table 1 of the accompanying drawing.

Table 1 illustrates the boiling point temperature of water at various pressures; and

Pressure Boilin g Point
Psi Bar °F °C
0.5 0.03 79.6 26.4
1 0.07 102 38.7
2 0.14 126 2.2
3 . 0.21 141 60.8
4 0.28 153 67.2
5 0.34 162 72.3
6 0.41 170 76.7
7 0.48 177 80.4
8 0.55 183 83.8
9 0.62 188 86.8
10 0.69 193 89.6
11 0.76 198 92.1
12 0.83 202 94.4
13 0.90 206 96.6
14 0.97 210 98.7
14.69 1.0 212 100
Table 2 illustrates the various properties of water at various temperatures and various pressures.

Absolu te
pressur e Boilin
g point Specific
volume
(Steam) Density (Steam) Specific enthalpy of liquid water (sensible heat) Specific enthalpy of Steam (total heat) Latent heat of Vaporization Specif ic heat
(Bar) (°C) (m3/Kg) (Kg/m3) (kJ/Kg) (kcal/ Kg) (kJ/Kg) (kcal/ Kg) (kJ/Kg) (kcal/ Kg) kJ/Kg
0.02 17.51 67.006 0.015 73.45 17.54 2533.6 4 605.15 2460.1 9 587.61 1.8644
0.03 24.10 45.667 0.022 101.00 24.12 2545.6 4 608.02 2444.6 5 583.89 1.8694
0.04 28.98 34.802 0.029 121.41 29.00 2554.5 1 610.13 2433.1 0 581.14 1.8736
0.05 32.90 28.194 0.035 137.77 32.91 2561.5 9 611.83 2423.8 2 578.92 1.8774
0.06 36.18 23.741 0.042 151.50 36.19 2567.5 1 613.24 2416.0 1 577.05 1.8808
0.07 39.02 20.531 0.049 163.38 39.02 2572.6
2 614.46 2409.2 4 575.44 1.8840
0.08 41.53 18.105 0.055 173.87 41.53 2577.1 1 615.53 2403.2 5 574.01 1.8871
0.09 43.79 16.204 0.062 183.28 43.78 2581.1 4 616.49 2397.8
5 572.72 1.8899
0.1 45.83 14.675 0.068 191.84 45.82 2584.7 8 617.36 2392.9 4 571.54 1.8927

0.2 60.09 7.650 0.131 251.46 60.06 2609.8 6 623.35 2358.4 0 563.30 1.9156
0.3 69.13 5.229 0.191 289.31 69.10 2625.4 3 627.07 2336.1 3 557.97 1.9343
0.4 75.89 3.993 0.250 317.65 75.87 2636.8 8 629.81 2319.2 3 553.94 1.9506
0.5 81.35. 3.240 0.309 340.57 81.34 2645.9 9 631.98 2305.4
2 550.64 1.9654
0.6 85.95 2; 732 0.366 359.93 85.97 2653.5 7 633.79 2293.6 4 547.83 1.9790
0.7 89.96 2.365 0.423 376.77 89.99 2660.0
7 635.35 2283.3 0 545.36 1.9919
0.8 93.51 2.087 0.479 391.73 93.56 2665.7
7 636.71 2274.0 5 543.15 2.0040
0.9 96.71 1.869 0.535 405.21 96.78 2670.8
5 637.92 2265.6 5 541.14 2.0156
1 99.63 1.694 0.590 417.51 99.72 2675.4 3 639.02 2257.9
2 539.30 2.0267

Typically, said first fluid is water. The pressure may be 0.4 bar in the pressurised vessel.
Alternatively, said second fluid is fluorobenzene,
Typically, said second fluid is oil.
The heat exchanger is typically coupled to a transformer (30) which has oil which heats up. This hot oil needs cooling and is therefore pumped through the pipes through the pressurised vessel using said windings.
Hot Oil at a temperature of around 80-85 deg C is brought from a transformer to the Pressure Vessel maintained at 0.4 bar pressure.
Water is passed through the pressurised vessel and hence comes in contact with tubes containing hot oil. As the Boiling point of Water at the said pressure is 76 deg C, it evaporates upon contact with the hot tubes. Water uses the heat from transformer Oil, as latent heat of Vaporization and passes from the pressure vessel to the condenser where water is condensed back into its liquid state and is injected back to the pressure vessel to complete the cycle.
Hot Oil from the transformer upon loosing its heat to the water returns back to the transformer from the bottom.
Specific Heat Cp of water is approx 4.2 KJ/kgK whereas the latent heat of vaporization is 2300 KJ/kgK at 75 deg C . Hence, the heat transfer efficiency when

the phase changes is multifold as compared to the efficiency when the phase does not change.
Latent Heat of Vaporization of Fluoro Benzene is 34.625 kJ/mol
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim;
1. A phase change heat exchanger assembly comprising:
- pressurised vessel containing a first fluid adapted to readily change phase upon heating, said pressurised vessel adapted to allow a defined number of pipe windings carrying relatively hotter second fluid through its resident first fluid medium so that as the phase of the first fluid changes, the second fluid loses its heat and cools down and cooled oil again guided back to the transformer through pipes; and
- condenser adapted to be communicably coupled with said pressured vessel by means of a first pipe for receiving said gaseous state of said first fluid in order for it to condense and a second pipe adapted to transfer said condensed first fluid from said condenser to said pressurised vessel.

2. An assembly as claimed in claim 1 wherein, said pipe windings includes a defined number of windings defined in accordance with the surface area required per unit time for the fluid flowing through the windings to transfer its heat from through the pipe thickness to said resident first fluid medium, thereby causing phase change of said first fluid, under pressure, from its natural liquid state to its gaseous state.
3. An assembly as claimed in claim 1 wherein, said assembly includes a pump adapted to transfer said first fluid from said condenser to said pressurised vessel.
4. An assembly as claimed in claim 1 wherein, said first fluid is water.

5. An assembly as claimed in claim 1 wherein, said pressure is about 0.4 bar in the pressurised vessel.
6. An assembly as claimed in claim 1 wherein, said first fluid is fluorobenzene.
7. An assembly as claimed in claim 1 wherein, said second fluid is oil.
8. An assembly as claimed in claim 1 wherein, said heat exchanger is coupled to a transformer which has oil which heats up, said oil being said second fluid.
9. An assembly as claimed in claim 1 wherein, said heat exchanger is coupled to a transformer which has oil which heats up, said oil being said second fluid, and said hot oil is pumped through said heat exchanger assembly by means of a pump.