FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENT RULES, 2003
PROVISIONAL SPECIFICATION [SECTION 10; RULE 13]
'IMPROVED REFRIGERATED CABINET"


VOLTAS LIMITED, A LIMITED LIABILITY COMPANY INCORPORATED UNDER THE INDIAN COMPANIES ACT, 1913, HAVING OUR REGISTERED OFFICE AT VOLTAS HOUSE 'A', DR.BABASAHEB AMBEDKAR ROAD, CHINCHPOKLI, MUMBAI 400 033
THE FOLLOWING SPECIFICATION DESCRIBES THE PMVENTION:


IMPROVED REFRIGERATED CABINET
Introduction
This invention relates to an improved refrigerated cabinet which uses phase change in eutectic solution stored in non-metallic container(s) for holding low temperatures in frozen/ cooled substances in a refrigeration system that is intermittently powered
Prior Art
A typical refrigerated cabinet requires continuous power supply to maintain a low temperature inside the refrigerated cabinet. However, a continuous power supply may not be available at all places and in such cases, in the prior art, the low temperature is maintained inside the refrigerated cabinet by providing an outer shell covering the whole or part of the refrigerated cabinet thereby creating an enclosed space around it and by filling the said space (annular space) with pre cooled materials having high specific heat so that said materials with high specific heat absorb/ extract the heat ingress into the refrigerated cabinet, thereby reducing the increase in temperature inside the refrigerated cabinet.
The examples of requirement of providing such system are: Ice cream vendor on the street, Vendor of refrigerated water, Cold drinks vendor, Vaccine storage in rural areas, etc.
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The examples of materials used in this system are: glycol solution, dry ice, ordinary ice with salt, etc.
Use of Prior Art Technology in a Typical Application
Exhibit 1 below shows a sectional view of a Freezer-on-Wheels that uses prior art for keeping ice cream frozen. Freezer-on-Wheels (FOW) is a refrigeration device that uses compression refrigeration cycle to chill ice cream to a temperature low enough to prevent it from melting for upto 10 hours. With its refrigerated cabinet (1) loaded with ice cream, the compressor (8) is run overnight at the FOW docking point where electric power is available. The evaporator coil (3) extracts heat from the refrigerated cabinet as well as from the glycol solution (6) filled in the annular space between the inner tank (4) of the cabinet and an outer tank (5). During daytime, the FOW is removed from its docking point and loaded on a tricycle that is pedaled manually by the cycle-puller-cum-ice-cream-salesman while he moves on the streets vending ice cream.
While ice cream is being vended, the lid (2) of the cabinet needs to be opened frequently for effecting sales, allowing the ambient warm air to enter each time. This would reduce the holdover time (time taken for the cabinet air temperature to rise to an undesirable level) to a large extent. Therefore, in the prior art, a glycol solution (6) is filled in the annular space between the inner tank (4) of the cabinet and an outer tank (5) (tank-in-tank), as depicted in Exhibit 1. The evaporator coil (3) is also contained in this annular space.
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Exhibit 1: Freezer-on-Wheels Based on Prior Art
1 Refrigerated cabinet

Thus, the evaporator cools the glycol solution, which, in turn, cools the inner tank and the ice cream that is stored inside it. The high specific heat of the glycol solution allows the refrigeration system to extract a large amount of heat from it. In turn, during the day, the chilled glycol solution extracts/ absorbs heat from the inner tank and the ice cream to keep it frozen. This increases the holdover time in an FOW based on prior art to about 10 hours.
Disadvantages of Prior Art
Glycol is corrosive to all known metals. In an FOW, the tanks and the evaporator coil are constructed from metals (GI for the tank, zinc-coated steel and aluminum for the evaporator coil). Therefore, corrosion limits the life of the FOW. Use of copper in lieu of zinc-coated steel in the evaporator, and stainless steel for the inner tank, bring about incremental improvements in the life, but even they get corroded in 2-3 years.
Secondly, the glycol used in prior art does not freeze (undergo change of phase). The amount of heat extraction/ absorption cannot, therefore, be more than the product of its specific heat, mass and temperature change.
The following invention is therefore proposed.
Summary of Invention
The invention will now be described with reference to Exhibit 2 below, which shows a sectional view of the same application, i.e. Freezer-on-Wheels, using the invention.

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The refrigerated cabinet (8) is loaded with the substance to be cooled/ frozen (say ice cream). The refrigeration system comprising compressor (1), condenser (2), evaporator coil (4), and other parts of the system is run when power is available. The evaporator coil extracts heat from the substance to be cooled/ frozen kept in the cabinet, as well as the eutectic bottles made of non-corrodible plastic containing glycol (6), which freezes (undergoes phase change from liquid to solid) giving up a large amount of latent heat to the evaporator. Since the latent heat of this glycol is higher than its specific heat at operating temperatures, it has a larger capacity to release and extract heat while in use, compared to prior art.
When power supply is not available (say when FOW is mounted on a tricycle and used for vending ice cream on the streets), cabinet temperature tends to rise due to heat ingress from outside, especially when the lid (7) is opened to sell ice cream. The frozen glycol temperature is lower than cabinet temperature, because its temperature cannot rise unless it fully melts. Due to the glycol temperature being lower than the cabinet temperature, glycol absorbs heat from the cabinet and slows down the rise in cabinet temperature.
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Exhibit 2: Freezer-on-Wheels Based on Voltas Invention
Outer liner
Evaporator coil
Inner liner
6 Plastic bottles (stacked or horizontally partitioned) containing glycol
2 Condenser
1 Compressor

Technical Challenges Faced and Overcome
1. Reduced cooling
Plastics are poor conductors of heat. In the invention, the metallic inner and outer tank have been replaced by plastic bottles containing the glycol solution, to prevent corrosion of metallic tanks'. Therefore heat has to be transferred from the evaporator coil (4) to the plastic bottles (6) containing glycol, to the glycol solution contained therein, when power supply is not available. This was likely to cause significant loss of cooling, leading to reduction in holdover time.
This challenge was overcome by using a glycol solution that has a higher freezing point than the one used in prior art FOWs. Therefore it undergoes change of phase (freezes) at operating temperatures, thus enabling larger heat extraction from it in the form of latent heat while the compressor is run at night. This led to an increase in holdover time from 8-10 hours in prior art to 16 hours in FOWs using the invention.
2. Non-uniform cooling
In the FOW using prior art, the temperature of glycol is maintained fairly uniformly through the height of the tank due to the natural convection within glycol. Maintenance of uniform temperature vertically is also helped by the fact that the outer and inner tanks within which glycol is contained, are constructed from metals (GI and stainless steel), which are good conductors of heat. In the present invention, thermal conductivity of the metals to help maintain uniform temperatures is not
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available due to the substitution of the steel tanks by plastic bottles. Therefore temperature is less uniform than in prior art. The vertical temperature gradient that was observed, made the top of the freezer unacceptably warm, posing another technological challenge that had to be overcome.
This challenge was overcome by introducing horizontal partitions at different heights within the bottle, or by replacing full height plastic bottles with smaller bottles stacked vertically, as shown in Exhibit 3 below. The temperature gradient within each compartment/ bottle.was thus limited to an acceptable value.
Advantages of Invention vis-a-vis Prior Art
1. Longer life of the appliance due to elimination of metallic corrosion - 8-10 years against 2-3 years. This is a financial and environmental benefit.
2. Reduction in material content due to substitution of GI outer tank and stainless steel inner tank. This is a financial and environmental benefit.
3. Use of zinc coated tubing for evaporator coil instead of copper coil is feasible due to possibility of corrosion having been eliminated. This is a financial and environmental benefit.
4. Cost reduction due to material content reduction. This is a financial benefit.
5. Reduction in weight due to elimination of steel tanks. This is a social benefit due to lesser strain on cycle-puller-cum-salesman.
6. Increase in holdover time from 8-10 hours to 16 hours: financial benefit due to reduced spoilage of substances like ice cream kept in the refrigerated cabinet.
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Exhibit 3: Replacement of Full-Height Bottles with Stack of Pads

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Dated this 6th day of June, 2008


Himanshu Kane. Applicant's Agent.
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