FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&

THE PATENTS RULES, 2003
PROVISIONAL
Specification
(See section 10 and rule 13)
LiBr VAPOUR ABSORPTION HEAT PUMP
THERMAX LIMITED
an Indian Company
Chinchwad, Pune 411 019, Maharashtra, India
THE FOLLOWING SPECIFICATION DESCRIBES THE INVENTION.

FIELD OF INVENTION:
This invention relates to a LiBr Vapour Absorption Heat Pump (VAHP).
PRIOR ART:
It is already known in the prior art that the LiBr Vapour Absorption Heat Pumps are used for producing cooling effect by utilizing heat as energy source. The performance of LiBr VAHP is dependent on number of
factors such as heat source temperature, design of absorption system,
LiBr solution circulation rate etc. It is also known that by decreasing LiBr solution circulation rate, performance of overall system can be substantially improved. For decreasing the solution circulation rate, one has to either operate at lower concentration level of LiBr in water in the absorber or at higher concentration level of LiBr in water in the
generator. Though technologies for operating at lower concentration
levels by improving absorber heat transfer are well developed, there has been no major breakthrough in the technology for operating at higher concentration level of LiBr in solution. One of the major limitations is operating at higher concentration level leads to blockage of pipelines and heat transfer surfaces due to crystallization of LiBr when cooled down to near ambient temperatures before entry to absorber.
DRAWBACKS
The main drawback of the conventional LiBr Vapour Absorption Heat
Pump is that the high concentration of LiBr solution is susceptible to
crystallization of LiBr salt at temperature close to normal ambient
temperature.
OBJECTS OF THE INVENTION:

An object of this invention is to propose a new method to substantially depress the temperature at which LiBr salt in water begins to crystallize.
Another object of this invention is to propose addition of crystallization inhibiting additive to LiBr solution to avoid blockage of pipelines / heat exchanger due to crystallization of LiBr at higher concentration levels than that normally used in absorption cycles.
Another object of this invention is to propose composition of crystallization inhibiting additive for LiBr solution to be used in LiBr VAHP for improving its cycle performance.
SUMMARY OF INVENTION:
In particular this invention relates to a method of improving the performance of LiBr VAHP by utilizing crystallization inhibiting additive in LiBr solution whereby there is substantial decrease in the temperature at which LiBr salt in water begins to crystallize and form large size crystals.
Further, this invention relates to the development of a crystallization inhibiting additive composition for LiBr solution.
BRIEF DESCRIPTION OF THE DRAWING:
The invention will be described in detail with reference to a preferred
embodiment. Reference to this embodiment does not limit the scope of
the invention.
In the accompanying drawing:
Figure 1 illustrates the overall system incorporating LiBr solution with
crystallization inhibiting additive in LiBr VAHP wherein (1) is high

temperature generator, (2) is high temperature heat exchanger, (3) is low temperature heat exchanger, (4) is weak solution pump, (5) is evaporator, (6) is absorber, (7) is low temperature generator and (8) is condenser.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWING:
CYCLE DESCRIPTION
The operation of conventional LiBr VAHP described in relation to the accompanying drawing is as follows:
In this system water is used as refrigerant and LiBr solution as absorbent. The refrigerant water is circulated and sprayed over the evaporator tubes in the evaporator (5) where it turns into water vapour. It absorbs heat
from the chilled water, which passes through the evaporator tubes and hence cools the same. Refrigerant water vapour enters absorber (6) and is absorbed by LiBr solution sprayed over the absorber tubes. The heat of absorption is taken away by cooling water flowing through the absorber tubes. The weak solution of LiBr formed thereby in the absorber is pumped to high temperature generator (1) by weak solution pump (4) through low temperature heat exchanger (3) and high temperature heat exchanger (2). In the high temperature generator LiBr solution is heated and gets concentrated. The refrigerant vapour thus formed is sent to tube side of low temperature generator where it condenses. The concentrated solution from high temperature generator is sent to the shell side of low temperature generator (7) where it is further concentrated to form strong solution. The water vapor generated is then condensed in condenser (8) by cooling water flowing through the condenser tubes. The refrigerant water condensed in the condenser and tube side of low temperature

generator is throttled and returned to the evaporator. The strong solution generated in low temperature generator is cooled down in the low temperature heat exchanger and spread over the absorber tubes to complete the cycle.
In VAHP cycle, since the strong solution is cooled down to temperature which is fairly close to its crystallization temperature, there is always possibility of crystallization occurring in the low temperature heat exchanger or in the pipeline connecting low temperature heat exchanger to absorber where strong solution temperature is at it's lowest. Strong solution is sprayed on absorber tubes, which are at temperatures very close to crystallization temperatures of strong solution.
In the method in accordance with this invention, crystallization inhibiting additive is added in the LiBr solution. Due to action of additive, very small LiBr salt particles present in LiBr solution tend to remain in colloidal form rather than coagulating and forming large size crystals. The action of additive depresses crystallization tendency and subsequent formation of large size crystals at normal temperatures of crystallization. Such large size crystals are normally responsible for blockage of pipeline or deposition of crystals on heat exchanger surface.
Suitable additives are those, which form complexes with lithium and / or bromine ions in aqueous solutions. The additives and complexes formed may decrease the crystallization driving force causing super saturation, increase the critical super saturation needed for effective nucleation and / or decrease the crystal growth. Useful additives include compounds, which form complexes with the lithium and bromine ions in solution, and

which alter the surface energy of crystal embryos formed in solution just prior to nucleation.
The present invention is directed primarily towards increasing the strong solution concentration to levels above the conventional strong solution concentrations. The other objective is toward lowering the minimum operating temperature of LiBr solutions to levels below the conventional minimum temperatures. To this end crystallization inhibiting compound of selected types and amounts are added to aqueous solution of LiBr and water. The additives are present in low concentrations typically up to about 10,000-15000 ppm.
In this invention there is provided a method of improving LiBr VAHP performance by adding suitable additive to the LiBr solution.
According to another aspect of this invention there is provided a method of improving LiBr VAHP performance by increasing Coefficient of Performance (COP) of the system by addition of suitable crystallization inhibiting additive in LiBr solution.
According to yet another aspect of this invention there is provided a method of improving LiBr VAHP performance by increasing the capacity of LiBr VAHP by addition of suitable crystallization inhibiting additive in the LiBr solution.
This invention envisaged a system comprising of set of heat exchangers such as generators, absorber, condenser, evaporator, solution heat exchangers, pumps suitably connected and incorporating LiBr solution

containing crystallization inhibiting additive so as to improve the performance of LiBr VAHP.
ADVANTAGES
1. Substantial decrease in temperature at which crystallization of LiBr solutions takes place
2. Improvement in performance i.e. higher COP
3. Improved recoverability
While considerable emphasis has been placed herein on the specific structure of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby 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.
Dated this 7th day of April 2006

Mohan Dewan
of R .K. Dewan & Co Applicant's Patent Attorney