FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules, 2005

COMPLETE SPECIFICATION
(SEE SECTION 10 AND RULE 13)

TITLE OF THE INVENTION

“Low Temperature Vapor Absorption Machine”

APPLICANTS:

Name Nationality Address
Voltas Ltd Indian Voltas Ltd , 2nd Pokhran Road , Thane(W) 400601

The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed:-

FIELD OF INVENTION
[001] The embodiments herein relate to a vapor absorption machines, and more particularly but not exclusively to a vapor absorption machine that can be operated at subzero temperature and a method to produce low temperature working fluid in a vapor absorption machine.

BACKGROUND OF INVENTION
[002] A Vapor Absorption Machine (VAM) is a refrigeration system that primarily works on heat source unlike conventional refrigeration system that operates on electricity. The VAM accomplishes removal of heat from the medium to be cooled through the evaporation of a refrigerant which is water at a low pressure and the rejection of heat through the condensation of the refrigerant at a higher pressure. Further, VAM employs energy in the form of heat which makes the system economic, since less expensive sources of heat are available such as hot water produced from solar heat, low & medium pressure steam, waste heat of exhaust gases of Diesel Generator set and so on.
[003] Conventional vapor absorption machine includes mainly an evaporator, an absorber, a generator and a condenser. Further, in the conventional VAM water is used as a refrigerant and lithium bromide (LiBr) as an absorbent. The diluted LiBr solution is delivered to the generator where the solution is heated with the help of available heat source. The heating of the solution causes the refrigerant (water) to vaporize and separate thereby leaving behind the concentrated lithium bromide solution. The concentrated LiBr solution obtained in the generator is sent back to the absorber. Further, the vaporized refrigerant (water) is passed to the condenser section where the water vapors get condensed. The condensed water flows down to the evaporator section and forms the refrigerant, wherein it is sprayed onto the tubes containing the fluid to be cooled. Spraying of condensed water on the tube in vacuum enables absorption of heat from the fluid flowing through the tube thereby lowering a temperature of the fluid. Evaporated water vapors are then passed into the absorber section where it is absorbed in the LiBr solution.
[004] Further, in order to achieve lower refrigerant temperature (below 0?C) in vapor absorption machines, the concentration of LiBr solution required in the absorber should be relatively very high. However, always there is limit to increase the concentration of LiBr Solution as it crystallizes at high concentration. The crystallization causes clogging of the flow of LiBr solution and thus halts the cycle. Prevention of crystallization is a big challenge and requires very complex control system.
[005] In another aspect, when the conventional VAM is operated at a low temperature, anomalous expansion of water (refrigerant) starts at a temperature of 3.5?C. Further, the refrigerant (water) freezes at a temperature of 0?C which in turn ceases the operation of the machine. Further, in yet another aspect, vacuum required in the evaporator should be very high (deep) in order to achieve lower temperature in vapor absorption machines. However, in conventional vapor absorption machine, the minimum pressure in the evaporator is about 6mm Hg (absolute), due to resistance to the refrigerant vapor (having high specific volume) to flow from evaporator to absorber, thereby unable to provide the required vacuum for subzero temperature operation.
[006] Therefore, there is a need for a vapor absorption system that is capable of achieving lower temperature (subzero temperature) working fluid.

OBJECT OF INVENTION
[007] The principal object of this invention is to provide a vapor absorption machine for lower temperature (below 0?C) operations.
[008] Another object of the invention is to overcome the crystallization of Lithium Bromide solution when the vapor absorption machine is operated under lower (sub zero) temperature.
[009] A further object of the invention is to provide a high vacuum that is required in the evaporator of vapor absorption machines for lower temperature operations.
BRIEF DESCRIPTION OF FIGURES
[0010] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:;
[0011] FIG. 1 shows a line diagram that depicts a section of vapor absorption machine according to an embodiment of the present invention;
[0012] FIG. 2 depicts a perspective view of a tube sheet pattern according to an embodiment of the present invention;
[0013] FIG. 3 is a flow chart depicting the flow of working fluid in vapor absorption machine according to an embodiment of the present invention; and
[0014] FIG. 4 is a flow chart depicting the flow of absorbent in vapor absorption machine according to an embodiment of the present invention.

DETAILED DESCRIPTION OF INVENTION
[0015] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0016] The embodiments herein achieve a lower temperature working fluid in vapor absorption machine thereby developing a vapor absorption machine that can be operated at low temperature. Referring now to the drawings, and more particularly to FIGS. 1 through 4, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.
[0017] Throughout the specification, the word dilute solution and weak solution have been used interchangeably. The dilute solution and weak solution refers to a mixture that has a relatively high refrigerant content and low absorbent content. Further, throughout the specification, the word concentrated solution and strong solution have been used interchangeably. The concentrated solution or strong solution refers to a mixture that has a relatively high absorbent content and low refrigerant content. Further, throughout the specification, the word brine solution and refrigerant have been used interchangeably. The brine solution or the refrigerant refers to the solution that is used to absorb heat from the working fluid. Furthermore, throughout the specification, the word Lithium Bromide solution and absorbent have been used interchangeably. The Lithium bromide solution and absorbent refers to the medium that is used to absorb refrigerant vapors.
[0018] Fig. 1 shows a line diagram that depicts a section of vapor absorption machine according to an embodiment of the present invention. The vapor absorption machine 100 includes a first chiller module 102, a second chiller module 104, a condenser 110, refrigerant pumps 114 and 116, solution pumps 118 and 119, a solution circulation pump 124, a heat transfer pipe 126, a high temperature generator (not shown), a low temperature generator 112 and a plurality of heat exchangers (not shown). The vapor absorption machine 100 includes brine solution as a refrigerant and lithium bromide solution as an absorbent. In one embodiment, the brine solution used is ethylene glycol. However, it is also within the scope of the invention that the brine solution may include other forms of antifreeze element added to water making the mixture stay at liquid state at temperatures below its normal freezing point.
[0019] The first chiller module 102 includes a first evaporator 130, a first absorber 132, mist eliminator 134 and spray trees 136 and 137. Further, the first evaporator 130 includes a first evaporator sump 131 and the first absorber 132 includes a first absorber sump 133. The mist eliminator 134 is provided in fluid communication between the first evaporator 130 and the first absorber 132. In one embodiment, the tube sheet pattern 147 is configured to provide flow of refrigerant vapors from the first evaporator 130 to the first absorber 132. Further, spray trees 136 and 137 are provided in both first evaporator 130 and first absorber 132 respectively such that the spray trees are configured to spray down a refrigerant in first evaporator 130 and an absorbent in first absorber 132. In one embodiment, the spray tree 136 and 137 are provided at top of the first evaporator 130 and first absorber 132. However, it is also within the scope of the invention that the spray trees 136 and 137 may be provided at different position inside the first evaporator 130 and the first absorber 132 without otherwise deterring the intended function of the spray trees 136 and 137 as can be deduced from this description.
[0020] Further, the second chiller module 104 includes a second evaporator 138, a second absorber 140, a mist eliminator 142, and spray trees 144 and 145. Further, the second evaporator 138 includes a second evaporator sump 139 and the second absorber 140 includes a second absorber sump 141. The mist eliminator 142 may be provided in fluid communication between the second evaporator 138 and the second absorber 140. In one embodiment, the mist eliminator 142 is provided with tube sheet pattern 148 that may be configured to provide the flow of vapors from the second evaporator 138 to the second absorber 140. Further, spray trees 144 and 145 are provided in second evaporator 138 and second absorber 140 respectively such that the spray trees 144 and 145 are configured to spray down a refrigerant in second evaporator 138 and an absorbent in second absorber 140. In one embodiment, the spray trees 144 and 145 are provided at top of the second evaporator 138 and second absorber 140 respectively. However, it is also within the scope of the invention that the spray trees 144 and 145 may be provided at different position inside the second evaporator 138 and the second absorber 140 without otherwise deterring the intended function of the spray trees 144 and 145 as can be deduced from this description.
[0021] The heat transfer pipe 126 is configured to extend communication between the first evaporator 130 and the second evaporator 138. Further, a bundle of tubes 146 may be provided in communication with the first absorber 132 and second absorber 140. Further, the first chiller module 102 and the second chiller module 104 are connected to each other such that the working fluid in heat transfer pipe 126 flows through the first evaporator 130 and the second evaporator 138 in series. Further, the coolant provided in bundle of tubes 146 flows through the first absorber 132 and the second absorber 140 in parallel.
[0022] Further, the first evaporator sump 131 may be connected to the spray tree 136 through the refrigerant pump 114. However, it is also with in the scope of the invention that the connection between the first evaporator sump 131 and spray tree 136 may be established by means of other actuating means without otherwise deterring the intended function of the connection as can be deduced from this description. Similarly, the second evaporator sump 139 may be provided in communication with the spray tree 144 through the refrigerant pump 116. However, it is also with in the scope of the invention that the connection between the second evaporator sump 139 and spray tree 144 may be established by means of other actuating means without otherwise deterring the intended function of the connection as can be deduced from this description.
[0023] Further, the first absorber sump 133 may be connected to the spray tree 145 through the solution pump 118. However, it is also with in the scope of the invention that the connection between the first absorber sump 133 and spray tree 145 may be established by means of other actuating means without otherwise deterring the intended function of the connection as can be deduced from this description. Further, the second absorber sump 141 may be connected to the plurality of heat exchangers (not shown) and a drain cooler (not shown) through the circulation pump 124 and the solution pump 119. The circulation pump 124 divides the flow of weak solution coming out of the second absorber 140 into two and provides them separately into the plurality of heat exchangers. The heat exchangers are in turn connected to the high temperature generator and low temperature generator. Further, the high temperature generator may be driven by the heat source. In one embodiment, the heat source may be steam. The high temperature generator may be connected to the low temperature generator such that the hot refrigerant vapors that are produced in the high temperature generator may be used to drive the low temperature generator. Further, the condenser (not shown) may be connected to the first evaporator 130 and the second evaporator 138. Furthermore, the condenser 110 and the low temperature generator may be provided in communication with each other.
[0024] FIG. 2 depicts a perspective view of a tube sheet pattern 147 and 148 according to an embodiment of the present invention. In one embodiment, the tube sheet patterns 147 and 148 are made up of steel. However, it is also with in the scope of invention that the tube sheet patterns 147 and 148 may be made of some other materials without otherwise deterring the intended function of the tube sheet patterns 147 and 148 as can be deduced from this description. The tube sheet pattern 147 includes an absorber flow module 202 and an evaporator flow module 204. The absorber flow module 202 may be provided in the first absorber 132 of the first chiller module 102 and the evaporator flow module 204 may be provided in the first evaporator 130. A plurality of holes 206 may be reamed in the absorber flow module 202 of the tube sheet pattern 147 such that the pitch distance between the adjacent holes is in the increasing order. As referred in the fig. 2, the pitch distance d2 between the adjacent holes h2 and h3 is greater than the pitch distance d1 between the adjacent holes h2 and h1. Further, the evaporator flow module 204 is provided with a plurality of holes 208 such that the pitch distance between the adjacent holes is in the decreasing order. As referred in the fig. 2, the pitch distance d3 between the adjacent holes h4 and h5 is lesser than the pitch distance d4 between the adjacent holes h5 and h6. In one embodiment, the number of holes 206 that are reamed in the absorber flow module 202 is greater than the number of holes 208 that are reamed in the evaporator flow module 204 thereby providing least resistance to the flow of refrigerant vapor from the first evaporator 132 to the first absorber 130. Further, the absorber flow module 202 and the evaporator flow module 204 are connected to each other such that the holes 206 and 208 in absorber flow module 202 and the evaporator flow module 204 provides an aerodynamic flow pattern. Further, in one embodiment the position of holes in the absorber flow module 202 and the evaporator flow module 204 enables the refrigerant vapor from the first evaporator 130 to take a curved path into the first absorber 132.
[0025] Similarly, the tube sheet pattern 148 includes an absorber flow module 210 and an evaporator flow module 212. The absorber flow module 210 may be provided in the second absorber 140 of the second chiller module 104 and the evaporator flow module 212 may be provided in the second evaporator 138. A plurality of holes 214 may be reamed in the absorber flow module 210 of the tube sheet pattern 148 such that the pitch distance between the adjacent holes is in the increasing order. As referred in the fig. 3, the pitch distance d5 between the adjacent holes h8 and h9 is greater than the pitch distance d6 between the adjacent holes h8 and h7. Further, the evaporator flow module 204 is provided with a plurality of holes 216 such that the pitch distance between the adjacent holes is in the decreasing order. As referred in the fig. 3, the pitch distance d7 between the adjacent holes h10 and h11 is lesser than the pitch distance d8 between the adjacent holes h11 and h12. In one embodiment, the number of holes 214 that are reamed in the absorber flow module 210 is greater than the number of holes 216 that are reamed in the evaporator flow module 212 thereby providing least resistance to the flow of refrigerant vapor from the second evaporator 138 to the second absorber 140. Further, the absorber flow module 210 and the evaporator flow module 212 are connected to each other such that the holes 214 and 216 in absorber flow module 210 and the evaporator flow module 212 provides an aerodynamic flow pattern. Further, in one embodiment the position of holes in the absorber flow module 210 and the evaporator flow module 212 enables the refrigerant vapor from the second evaporator 138 to take a curved path into the second absorber 140.
[0026] Fig. 3 shows a flow chart that depicts the flow 300 of working fluid in vapor absorption machine 100 according to an embodiment of the present invention. The working fluid with first temperature that needs to be cooled or chilled is circulated in to the second evaporator 138 (step 302). In one embodiment, the first temperature of the working fluid is 0?C. Further, the working fluid may be the brine solution. In an embodiment, the brine solution used is ethylene glycol. However, it is also within the scope of the invention that the brine solution may include other forms of antifreeze element added to water making the mixture stay at liquid state at temperatures below its normal freezing point. Further, the refrigerant is sprayed down on to the heat transfer pipe (tube bundle) 126. The vacuum that is provided inside the second evaporator 138 enables the refrigerant to absorb heat from the circulating working fluid and evaporate (step 304). The absorption of heat from the circulating working fluid by the refrigerant produces the first stage of cooling the circulating working fluid thereby enabling the circulating working fluid to attain the second temperature which is relatively lower than the first temperature. In one embodiment the second temperature of the working fluid is minus 2.8?C to minus 3.0?C (step 306).
[0027] Further, the arrangement of the first chiller module 102 and the second chiller module 104 enables the circulating working fluid to flow through the heat transfer pipe (Tube Bundle) 126 provided in the first evaporator 136. The vacuum that is provided inside the first evaporator 136 enables the refrigerant to absorb heat from the circulating working fluid and evaporate (step 308). The absorption of heat from the circulating working fluid by the refrigerant produces the second stage of cooling the circulating working fluid thereby enabling the circulating working fluid to attain the third temperature which is relatively lower than the second temperature. In one embodiment the third temperature of the working fluid is minus 5?C. Further, the working fluid under third temperature is obtained from the outlet of the heat transfer pipe (tube bundle) 126 (step 310).
[0028] The absorption of heat from the working fluid by the refrigerant results in the evaporation of the refrigerant. The refrigerant vapors thus formed tend to increase the pressure in the evaporator section. The increased pressure in turn increases the boiling temperature and the desired cooling effect may not be obtained. Therefore, it is necessary to remove the refrigerant vapors from the vessel into the lower pressure absorber. The tube sheet pattern 147 and 148 which offers least resistance to the vapor flow enables the complete flow of refrigerant vapors from the first evaporator 130 and the second evaporator 138 to the first absorber 132 and the second absorber 140 respectively.
[0029] Fig. 4 shows a flow chart depicting the flow of absorbent in vapor absorption machine according to an embodiment of the present invention. The strong absorbent solution with first concentration flows from the high temperature generator 106 to the spray tree 137 provided in the first absorber 132 (step 402). In one embodiment, the first concentration of the absorbent is 64.5% ± 0.3%. The spray tree 137 sprays down the absorbent into the first absorber 132. The absorbent absorbs the refrigerant vapor that flows into the first absorber 132 from the first evaporator 130 (step 404). Further, the flow of refrigerant vapor from the first evaporator 130 to the first absorber 132 may be by means of the tube sheet pattern 147. The absorption of refrigerant vapor by the absorbent reduces the concentration of absorbent to the second concentration level (step 406), wherein the second concentration may be relatively lesser than the first concentration. Further, the absorbent of second concentration may get accumulated in the first absorber sump 133. In one embodiment, the second concentration of the absorbent is 62.5% ± 0.3%. Further more, the solution pump 118 pumps the absorbent of second concentration to the spray tree 145 provided in the second absorber 140. The spray tree 145 sprays down the absorbent in to the second absorber 140. The absorbent sprayed in to the second absorber 140 absorbs the refrigerant vapor from the second evaporator 138 (step 408). Further, the flow of refrigerant vapor flows from the second evaporator 138 to the second absorber 140 may be by means of the tube sheet pattern 148. The absorption of refrigerant vapor from the second evaporator 138 by the absorbent sprayed down into the second absorber 140 reduces the concentration of absorbent to the third concentration level, wherein the third concentration may be relatively lower than the second concentration (step 410). In one embodiment, the third concentration of the absorbent is 59.5% ± 60%. The absorption of the refrigerant vapor by the absorbent condenses the refrigerant vapors and releases heat. The heat released from the condensation of refrigerant vapors and their absorption by the absorbent may be removed to the cooling water that is circulated through the bundle of tubes 146 provided within the first absorber section 132 and the second absorber section 140. Further, the weaker solution of the absorbent with third concentration may be passed onto the high temperature generator and the low temperature generator through the solution circulation pump 124, solution pump 119, plurality of heat exchangers and a drain cooler, thereby the concentration of the weaker solution may be increased in the generator section. Further, the strong solution from the high temperature generator may be passed on to the first absorber and the cycle may be continued.
[0030] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
CLAIMS
We Claim:
1. A vapor absorption machine for achieving working fluid at sub zero temperature, said machine comprising:
a first chiller module having a first evaporator with a first evaporator spray tree, a first absorber with a first absorber spray tree, a first tube sheet pattern and a first absorbent sump;
a second chiller module having a second evaporator with a second evaporator spray tree, a second absorber with a second absorber spray tree and a second tube sheet pattern;
a heat transfer pipe configured to allow the working fluid to flow into the second evaporator and subsequently into the first evaporator; and
a bundle of tubes configured to allow a flow of cooling water into the second absorber and the first absorber,
wherein
said second absorber spray tree is in fluid communication with the first absorbent sump;
the working fluid is a brine solution.
2. The machine as claimed in claim 1, wherein
said first tube sheet pattern includes a first portion configured to be provided in the first absorber section and a second portion configured to be provided in the first evaporator section, wherein
said first portion defines a plurality of holes having a pitch in decreasing order and said second portion defines a plurality of holes having a pitch in increasing order thereby attenuating resistance to a flow of vapors from said first evaporator to said first absorber.
3. The machine as claimed in claim 2, wherein
said second tube sheet pattern includes a first portion configured to be provided in the second absorber section and a second portion configured to be provided in the second evaporator section, wherein
said first portion of said second tube sheet pattern defines a plurality of holes having a pitch in decreasing order and said second portion of said second tube sheet pattern defines a plurality of holes having a pitch in increasing order thereby attenuating resistance to a flow of vapors from said second evaporator to said second absorber.
4. The machine as claimed in claim 1, wherein each of said first and second chiller modules includes a mist eliminator.
5. The machine as claimed in claim 2, wherein a number of holes provided in said first portion of said first tube sheet pattern is more than a number of holes provided in said second portion of said first tube sheet pattern.

6. The machine as claimed in claim 3, wherein a number of holes provided in said first portion of said second tube sheet pattern is more than a number of holes provided in said second portion of said second tube sheet pattern.

7. A method for achieving a sub zero temperature working fluid in a vapor absorption machine, said method comprising:
allowing passage of the working fluid having a first temperature into a second evaporator through a heat transfer pipe to attain a second temperature;
allowing passage of the working fluid with said second temperature into a first evaporator through the heat transfer pipe to attain a third temperature;
allowing a passage of an absorbent having a first concentration into a first absorber to attain a second concentration; and
allowing a passage of the absorbent having said second concentration into a second absorber to attain third concentration.
8. The method as claimed in claim 7, wherein each said allowing passage of the working fluid having the first temperature into the second evaporator through the heat transfer pipe to attain the second temperature and said allowing passage of the working fluid with said second temperature into a first evaporator through the heat transfer pipe to attain a third temperature includes spraying a refrigerant on the heat transfer pipe.
9. The method as claimed in claim 8, wherein said allowing a passage of the absorbent having the first concentration into the first absorber to attain second concentration includes diluting the absorbent having the first concentration with refrigerant vapors from the first evaporator.

10. The method as claimed in claim 9, wherein said allowing a passage of the absorbent having said second concentration into said second absorber to attain third concentration includes diluting the absorbent having the second concentration with refrigerant vapors from the second evaporator.
11. The method as claimed in claim 7, wherein

said working fluid is brine solution;
said first temperature is 0 degree Celsius;
said second temperature is in the range of -3 to -2.8 degree Celsius; and
said third temperature is -5 degree Celsius.
12. The method as claimed in claim 7, wherein
said absorbent is lithium bromide;
said first concentration is in the range of 64.2% to 64.8%;
said second concentration is in the range of 62.2% to 62.8%; and
said third concentration is in the range of 59.5% to 60%.