Chemistry: analytical and immunological testing – Determination of water
Reexamination Certificate
1995-04-17
2003-02-04
Alexander, Lyle A. (Department: 1743)
Chemistry: analytical and immunological testing
Determination of water
C436S164000, C436S169000, C436S177000, C422S051000, C422S067000, C422S086000, C422S105000
Reexamination Certificate
active
06514765
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an acid test kit and, more particularly, to an acid test kit used in vapor compression refrigerators and the like in which an indicator paper is held in a transparent tube-like fixture to monitor the acid level in the system simply, quickly and inexpensively.
Vapor compression refrigerators, heat pumps, and air conditioners must always be concerned with the presence of acids in the refrigerant which can severely shorten the life of both the compressor and the refrigerant. These acids can be formed by chemical reactions with components and/or materials of construction, lubricating oils, and/or impurities. The instability of the refrigeration, and thus the formation of acids, is accelerated by elevated temperatures which result from improper operation, such as a failed condenser fan, or clogged air flow path.
Checking the refrigerant and/or oil acid is a common maintenance procedure because acidic refrigerant can be cleaned up before permanent damage to the hardware and refrigerant occur. Acidic refrigerant will also result in hermetic compressor motor burn-out because the acid will degrade the motor winding's electrical insulation. Moreover, the presence of acid indicates the existence of other decomposition products, such as non-condensable gases, which result in elevated pressures and increased compressor pressure ratios leading to reduced efficiency and overloaded compressor operation.
To avoid the above-mentioned problems, refrigeration systems are tested for acid content. Typically, the oil would be tested for acid, because the highest concentration of acid is found in the oil of a non-operating system (shut down). It is, however, much easier to test the refrigerant for acid instead of testing the oil for acid, since the refrigerant is pressurized and existing service valves provide an easy way of sampling the refrigerant. Testing of the refrigerant vapor, rather than the refrigerant liquid, of the system is much more convenient because testing the liquid refrigerant results in a much greater refrigerant loss and the exiting liquid will cause frostbite if not properly handled.
Visual sensors or indicators for use in detecting the corrosive state of a fluid in a heat exchanger system are known as seen, for example, in U.S. Pat. No. 5,127,433. A permanently installed sensor has a sight glass or window through which corrosiveness is determined by viewing a flap or ball displaying a color indicating either the need to change the fluid or to add corrosion inhibitors. Alternatively, corrosiveness can be indicated by a ruptured or broken diaphragm located between the sight glass and the fluid. This form of sensor is limited to applications such as automobile cooling systems where the sensor is provided in the overflow conduit or in the hot fluid conduit upstream of the radiator.
Humidity and corrosion indicators for packaged goods in which thin cobaltous chloride film is used as the sensing element are described in U.S. Pat. No. 3,084,658. An elastomeric grommet sealed by a transparent disk is inserted into an opening in a package wall. A disk impregnated with the cobaltous chloride is secured beneath a window and can be replaced.
With respect to closed refrigeration systems, other types of indicator systems are known for testing the presence and concentration of contaminants in a refrigerant. For example, U.S. Pat. Nos. 4,923,806 and 5,071,768 show apparatuses for testing liquid or vapor contaminants in a closed system regardless of whether the apparatus is operating or not. A disposable testing tube made of transparent material is used at the end of a compressor discharge line or elsewhere in the system. One section of the tube is provided with water removal and moisture indicating chemicals, such as cobaltous chloride and another section is provided with acid indicating chemicals such as a solution of bromophenol blue, ethanol and glycerol. This construction is relatively complicated and requires a separate, specially configured flow restrictor in addition to a tube holder, and an expensive testing tube in which the multiple contaminant testing chemicals and filter screens are permanently located.
Likewise, U.S. Pat. No. 5,377,496 shows an acid contamination indicator for closed loop vapor compression refrigeration systems in which the indicator is permanently or removably installed in the bypass line around the system compressor where the refrigerant is always in the gaseous phase. A casing has a visual indicator bed of bromophenol blue as the acid indicating medium which is contacted by the refrigerant after flowing through a filter and a flow restrictor orifice. Porous retainer disks are held against the bed by springs. Moreover, the indicator, which changes color when exposed to acids or bases, are solid, and thus they must be exposed to the test stream in some fashion. Accordingly, this solid indicator must be mixed with an inert substance to provide some porosity, contact surface area and increased volume and then packaged in a clear tube. The vapor refrigerant is then passed through the porous mixture arranged in a bypass loop between the suction and discharge ends of a compressor or in the main refrigerant flow path between the compressor discharge and a heat exchanger to observe a color change. Again, we have recognized that this is an unduly complicated construction which requires a substantial outlay for installation.
Another type of contaminant detector is marketed by Refrigeration Technologies of Fullerton, California under the trademark “CHECKMATE”. A specific volume of gas passes through a detection tube at a predetermined termination pressure. However, an expensive sealed Pyrex detection tube containing a color-changing chemical and whose ends are pierced when fully assembled can only be used once even when the test is negative, and thus this approach entails considerable expense regardless of its technical merits.
In a vapor-compression system, refrigerant flows from the condenser to the expansion valve, where it flashes into a two-phase mixture and then enters the evaporator. Superheated refrigerant vapor, with some entrained oil, leaves the evaporator and is compressed in the compressor, before being condensed in the condenser to complete the cycle. When in chemical equilibrium, the majority of the acid in the system is contained in the oil, but acid is also present in the liquid and vapor refrigerant. The presence of water in the system, which is a very real possibility, causes an even greater concentration of the acid in the liquid rather than in the vapor. To further complicate the problem, the relative liquid and vapor acid concentrations are a function of the system's liquid and vapor volume and therefore are system dependent. These factors all render the measurement of acid level in the refrigerant's equilibrium vapor phase an uncertain indication of acid level in the compressor oil.
Although the acid content in the refrigerant vapor can not be exactly correlated to the compressor oil acid content, it is, however, accurate enough to indicate the relative status of the oil in the system. It is clear that when acid is detected in the vapor, the acid level in the oil is significantly higher. Independent of the system, it can be generally stated that a refrigerant vapor acid level about 1-2 parts per million (ppm) in the refrigerant vapor clearly means the oil acid content is high, and the system should be cleaned up to reduce the acid level. Furthermore, a refrigerant vapor acid of 10 ppm, clearly indicates the compressor's oil acid level is well beyond safe operating levels and the system will fail shortly if the refrigerant and acid is not changed or cleaned.
We have discovered that a pH paper can provide a simple fast and extremely inexpensive way to test for acidity in a refrigeration system. It allows for testing with the system on or off, and in other applications as well. In addition, it does not have to be installed in a line but can be temporarily connec
Samad Nidal A.
Scaringe Robert P.
Alexander Lyle A.
Crowell & Moring LLP
Mainstream Engineering Corporation
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