Compositions – Vaporization – or expansion – refrigeration or heat or energy... – With low-volatile solvent or absorbent
Reexamination Certificate
1999-03-26
2001-02-13
Ogden, Necholus (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
With low-volatile solvent or absorbent
C252S067000, C062S112000, C062S476000
Reexamination Certificate
active
06187220
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an aqueous absorption fluid composition, process and apparatus providing improved water vapor absorption and thermal transfer. Addition of small quantities of certain ethers to an aqueous absorption fluid composition provides improved heat and mass transfer resulting in improved water vapor absorption and enhanced thermal and chemical stability. The compositions of this invention are particularly suited for use in high temperature stages of thermal transfer loops used in absorption refrigeration, chilling, heat pump, energy storage and other thermal transferring applications.
2. Description of Related Art
Aqueous metal halide solutions are well known as refrigerant/absorbent solutions for absorption refrigeration systems as taught by U.S. Pat. No. 3,478,530.
Alcohols have been widely used as additives in small amounts to aqueous refrigerant absorbent solutions for improved heat transfer. Octyl alcohol in LiBr solutions is taught by U.S. Pat. No. 3,276,217 and 4,857,222; certain secondary alcohols in LiBr solutions are taught by U.S. Pat. Nos. 3,609,087 and 4,315,411; certain tertiary alcohols are taught by U.S. Pat. No. 3,580,759; and fluoroalcohols are taught by U.S. Pat. No. 3,783,631.
Amines have been used as additives in small amounts to aqueous absorption systems for increased rate of water vapor sorption of working fluid as taught by U.S. Pat. Nos. 5,419,145; 5,577,388 and 5,829,259, for example.
Certain ethers are known as solvents for refrigerant methyl chloride used in absorption refrigeration as taught by U.S. Pat. No. 2,040,905.
Ethylene glycol monobutyl ether and diethylene glycol monobutyl ether additives, in amounts of 0.001 to 1.0 percent by weight, in concentrated lithium halide aqueous solutions are known as vapor pressure depressants for use in absorption refrigeration systems, as taught by U.S. Pat. No. 3,553,136.
The use of ether, specifically tetraethylene glycol dimethylether, as an absorbent in conjunction with an azeotropic mixture of trifluoroethanol and water as a cooling medium is taught by Japanese Patent Number 61-14282 to afford a wider temperature range of a cycle than a water/LiBr system in absorption refrigeration.
An absorption fluid of aqueous solutions of metal salts of alkali metal hydroxides, nitrites, and alkaline earth and transition metal hydroxides, halides and thiocyanates and about 10 to about 30 weight percent, based on the metal salt, of an organic compound including ethers, particularly alkaline glycol ethers is taught by U.S. Pat. No. 5,529,709 to provide increased absorbent solubility and vapor pressure reduction.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved aqueous absorption fluid composition and process for thermal transfer having increased rates of water vapor absorption to result in improved thermal transfer.
It is another object of this invention to provide an improved aqueous absorption fluid composition and process for thermal transfer which allows use of reduced absorber size to obtain a specified thermal transfer.
Yet another object of this invention is to provide an aqueous absorption fluid composition which exhibits high stability to thermal decomposition and chemical reactivity to other components of the composition.
The above objects and other advantages of this invention which will become apparent upon reading this disclosure are achieved by addition of parts per million amounts of certain ethers to aqueous absorption fluids.
Components in the working fluid of an absorption thermal transfer cycle include chemicals which classified according to their use are defined in the art as follows:
“Refrigerant” is the chemical which vaporizes and condenses, or is absorbed, in large volume and the energy associated with this phase change being the essence of the system thermodynamics. In this invention water is the principal refrigerant.
“Absorbent” is the chemical(s) which have relatively low volatilities compared to the refrigerant, and high affinities for the refrigerant. Many suitable absorbents known to the art are suitable for use in this invention, such as those disclosed in U.S. Pat. No. 3,478,530, which is incorporated herein by reference. Lithium, zinc and calcium bromides and chlorides are among suitable absorbents. Lithium bromide compositions are most frequently used in large commercial refrigeration equipment. The properties of the refrigerant and absorbent(s) together in a refrigerant/absorbent(s) composition define the theoretical limits of the equilibrium thermodynamics of the absorption system. In this invention suitable absorbent(s) are at least one metal salt which is present in an amount sufficient to provide a composition functional as a refrigerant/absorbent(s) composition. Any of the above mentioned salts or combinations of salts, and also salts in combination with other non-interfering absorbents such as glycols or amines are suitable for use in this invention.
“Heat and mass transfer additive,” an absorption promoter, serving to accelerate the rate of dissolving or absorption of the refrigerant by the absorbent. Added in small quantities, the heat and mass transfer additive does not directly change the system thermodynamics. Suitable heat and mass transfer additives according to this invention include certain ethers. This invention uses certain ethers as heat and mass transfer additives and not as absorbents. The prior art has used ethers, such as glycol ethers, in significantly large concentrations as absorbents. However, glycol ethers in small quantities, as illustrated by Comparative Example XIV, do not serve as heat and mass transfer additives as intended by the present invention. None of the prior art known to the inventor teaches suitable ethers as heat and mass transfer additives. Other additives, as pointed out in the Description of Related Art section above, particularly, the addition of certain amines as described in U.S. Pat. No. 5,419,145, which is incorporated herein in its entirety by reference, known for increasing the rate of absorption of the refrigerant into the absorbent to form the refrigerant/absorbent composition may be used in conjunction with the ether heat and mass transfer additives of this invention, as long as they are non-interfering.
“Corrosion inhibitors” for addition to the working fluid compositions are known to the art, such as, for example, salts of molybdate, nitrate, chromate, etc.; bases such as lithium hydroxide used to raise pH; and organic inhibitors, such as, benzotriazole and related compounds. Corrosion inhibitors sometimes interfere with other additives and one of the advantages of the ether heat and mass transfer additives of this invention is that they are significantly less susceptible to interfering reactions with corrosion inhibitors, and in general are more stable in an absorption chiller environment than other additives known to the prior art.
Other additives, such as, for example, crystallization inhibitors and other absorption promoters may be used as long as they do not interfere with the action of the heat and mass transfer additives of this invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
This invention provides an improved absorption or absorption refrigeration fluid of the type comprising water as the refrigerant and at least one absorbent comprising a metal salt present in an amount sufficient to provide a functional refrigerant/absorbent(s) composition having an amount of ether(s) sufficient to provide higher heat and mass transfer resulting in increased rate of thermal transfer of the absorption thermal transfer system.
The metal salt absorbent reduces the vapor pressure of the aqueous refrigerant/absorbent composition sufficiently to provide a composition useful as a refrigerant/absorbent composition. Some suitable salts include at least one cation selected from the group consisting of ammonium, alkali metals, alkaline earth metals, transition metals and mixtures thereof, and at least one anion selected from the group cons
Gas Research Institute
Ogden Necholus
Pauley Petersen Kinne & Fejer
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