Abstract:
A heat transfer device, including an evaporator, a condenser, a compressor fluidly coupled to the evaporator and the condenser. A refrigerant/oil mixture is routed to the compressor, the evaporator, and the condenser. An apparatus for moisture detection in the refrigerant/oil mixture includes the apparatus being in fluid communication with the mixture. The apparatus includes a refractive index determining device, a dielectric constant determining device, and a controller. The refractive index determining device produces a first signal representative of a refractive index of the mixture. The dielectric constant determining device produces a second signal representative of a dielectric constant of the mixture. The controller receives the first signal and the second signal. The controller determines a moisture content of the mixture dependent upon the first signal and the second signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a heat transfer device and, more particularly to the detection of moisture in the refrigerant/oil mixture used in a heat transfer device. 
         [0003]    2. Description of the Related Art 
         [0004]    In a conventional heat transfer device, as shown in  FIG. 1 , device  10  includes a condenser  12 , an evaporator  14 , fluid lines  16 ,  18 , and  20 , a compressor  22 , a filter receiver/dryer  24 , an expansion valve  26 , pressure switches  28  and  30 , and service ports  32  and  34 . Warm airflow  36  passes through evaporator  14 , giving up heat to evaporator  14  and the refrigerant passing therethrough. This cools the air and results in cool airflow  38  being directed to a room or passenger compartment of a vehicle. The heat is then transferred to condenser  12  by action of compressor  22  where the heat then is transferred to the environment by passing an airflow  40  through condenser  12  to thereby result in heated air flow  42  passing through condenser  12  and transferring heat from refrigerant passing through condenser  12  to the ambient environment. One of the problems with a heat transfer device is the destructive effects of moisture that may be contained in the refrigerant/oil mix. 
         [0005]    A problem related to the operation of heat transfer devices, refrigeration systems, air conditioning systems and other systems using a refrigerant/oil mixture is damage to such equipment caused by moisture or water in the refrigerant. Moisture in the system can cause acid formation which is destructive to the internal parts of the system. For example, a motor having windings exposed to the refrigerant are vulnerable to the presence of water and moisture related contaminants. Water enters the refrigerant through leaking gaskets, pipes, tubes, joints, malfunctions of charging systems. Even only a few drops of water in the refrigerant can lead to the formation of a sufficient level of acid to cause failure of the system due to continued operation with the acid or contaminants that may result from the action of the acid in the refrigerant. Another problem is that the moisture causes the reduction of lubrication properties of the oil as it absorbs some moisture causing premature wear of parts in the compressor. A significant percentage of failures of heat transfer equipment is caused by the presence of water and water related contaminants in the refrigerant. 
         [0006]    What is needed in the art is an easy, cost-effective apparatus and method of detecting moisture in the refrigerant/oil mixture. 
       SUMMARY OF THE INVENTION 
       [0007]    In one aspect, the invention consists of a heat transfer device, including an evaporator, a condenser, a compressor fluidly coupled to the evaporator and the condenser. A refrigerant/oil mixture is routed to the compressor, the evaporator, and the condenser. An apparatus for moisture detection in the refrigerant/oil mixture includes the apparatus being in fluid communication with the mixture. The apparatus includes a refractive index determining device, a dielectric constant determining device, and a controller. The refractive index determining device produces a first signal representative of a refractive index of the mixture. The dielectric constant determining device produces a second signal representative of a dielectric constant of the mixture. The controller receives the first signal and the second signal. The controller determines a moisture content of the mixture dependent upon the first signal and the second signal. 
         [0008]    Another aspect of the present invention consists of a method of determining a moisture content of a refrigerant/oil mixture of a heat transfer device. The method includes the steps of testing the mixture to determine a refractive index of the mixture, testing the mixture to determine a measured dielectric constant of the mixture, estimating a dielectric constant of the mixture dependent upon the refractive index, determining the moisture content of the mixture dependent upon the measured dielectric constant and the estimated dielectric constant. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0010]      FIG. 1  illustrates a typical heat transfer device in the form of an air conditioner that is utilized with an embodiment of the present invention; 
           [0011]      FIG. 2  is a schematical cross section view of an embodiment of a moisture detection device of the present invention that can be connected to the heat transfer device of  FIG. 1 ; and 
           [0012]      FIG. 3  is a schematical flow chart illustrating the steps of the moisture detection apparatus of  FIG. 2  in evaluating the moisture content of the refrigerant/oil mixture of the heat transfer device of  FIG. 1 . 
       
    
    
       [0013]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring now to the drawings, and more particularly to  FIG. 2 , there is illustrated a moisture detection apparatus  50  that includes a cylinder  52 , a piston  54 , a heater/cooler  56 , with a mixture under test  58  illustrated as being within the boundaries of chamber  52  and piston  54 . Moisture detecting apparatus  50  further includes a sample inlet  60 , a sample return  62 , valves  64  and  66 , an actuator  68 , a gas identifier  70 , a temperature sensor  72 , a dielectric sensor  74 , a refractometer  76 , a controller  78 , and an output device  80 . 
         [0015]    Piston  54  is sealed to cylinder  52  and is variable in its position as illustrated by the dual-headed arrow in  FIG. 2 . Actuator  68  moves piston  54  to vary the volume of the mixture under test  58 . Actuator  68  is under the control of controller  78  and positions piston  54  as commanded by controller  78 . The moisture detection apparatus additionally utilizes sample inlet  60  and sample return  62 , which may be attached respectively to service ports  34  and  32  of heat transfer device  10  shown in  FIG. 1 . Such a connection may be permanent with moisture detection apparatus  50  being permanently assigned to heat transfer device  10 . Alternatively, moisture detection apparatus  50  may be temporarily connected to service ports  32  and  34  for the obtaining of a sample of the refrigerant/oil mixture, testing the sample and then returning the sample to heat transfer device  10 . Valves  64  and  66  serve to isolate mixture  58  that is under test from the rest of the refrigerant/oil mixture of heat transfer device  10 . This allows a controlled amount of mixture  58  to be contained in moisture detection apparatus  50 . 
         [0016]    Mixture  58  may be cooled or heated with heater/cooler  56  with the temperature of mixture  58  being detected by temperature sensor  72 . The gas and oil type may be known and that information may be input into controller  78  by conventional means. Otherwise, gas identifier  70  is utilized to detect the type of refrigerant contained in mixture  58 . Dielectric sensor  74  is in fluid communication with sample  58  so that the dielectric constant of mixture  58  may be determined. Refractometer  76  is in communication with mixture  58  for the determination of the refractive index of mixture  58 . Signals are produced by gas identifier  70 , temperature sensor  72 , dielectric sensor  74 , and refractometer  76  that are received by controller  78 . Controller  78  processes the signal received from these devices to determine the moisture content of mixture  58 . Although mixture  58  is referred to as a refrigerant/oil mixture, that terminology is not meant to exclude the presence of moisture, which is detected by moisture detection apparatus  50 . Results from the determination of the moisture detection process carried out by controller  78  is output onto output device  80  to indicate information about mixture  58 , including the moisture content thereof. Additionally, it is contemplated that output device  80  may display the type of refrigerant, the type of oil, the outputs of the signals from gas identifier  70 , temperature sensor  72 , dielectric sensor  74 , and refractometer  76 , as well as maintenance and calibration information related to the components of moisture detection apparatus  50 . Output device  80  may additionally display information regarding the status of the testing as the testing of mixture of  58  is undertaken. Output device  80  may also output printed information, provide data for downloading and be in communication with data devices of various sorts and by various communication schemes. 
         [0017]    Now, additionally referring to  FIG. 3 , there is illustrated the steps carried out by controller  78  as it interacts with the elements of moisture detection apparatus  50 . Method  100  includes several steps including a step  102  in which the refrigerant/oil mixed sample is obtained by moisture detection apparatus  50 . This may include the steps of closing valve  66 , opening valve  64 , and moving piston  54  within cylinder  52  to increase the volume therein. Once the refrigerant/oil sample is obtained within moisture detection apparatus  50  and valve  64  is closed, the mixture is condensed to a liquid at step  104 , which may be by a combination of cooling by the use of heater/cooler  56  or by compression by the movement of piston  54 . The liquid of mixture  58  is then tested utilizing refractometer  56  to determine the refractive index of the oil/refrigerant mixture  58 , at step  106 . Information from step  106  is transferred to block  126 , represented schematically herein as a circle with an X in it, identified as block  126 , which may be controller  78  using algorithms, or combination of hardware and software to carry out the moisture detection steps of method  100 . 
         [0018]    At step  108 , dielectric sensor  74  tests the dielectric constant of the oil/refrigerant mixture and sends the results to controller  78  represented again as block  126 . The refractive index of mixture  58 , along with the dielectric constant of mixture  58 , coupled with the temperature as determined in block  124  can be utilized to determine the moisture content of mixture  58 . The measured dielectric constant is compared to a calculated dielectric constant, which results from the refractive index measurement of mixture  58 . The difference between the measured dielectric constant and the computed dielectric constant represents a variance caused by moisture in mixture  58 . With this information, controller  78  can determine at step  128  whether the moisture content is in the proper range. If the answer is No, then a message is output onto output device  80  at step  130  indicating that the water content is higher than expected and a message such as “water content is suspected” may be displayed on output device  80 . If, at step  128 , the value is in a proper range, then no water content is suspected and such a message is displayed at step  132  on output device  80 . Alternatively, numeric values that are calculated representative of moisture content can be displayed on output device  80 . 
         [0019]    If, in method  100  the type of oil and/or refrigerant are not known, then method  100  proceeds to step  110  and, at step  112 , with mixture  58 , or at least a portion of it, being vaporized and gas identifier  70  is utilized to identify the refrigerant gas and the oil in steps  114 ,  116 ,  118 , and  120 . The type of oil is determined after the vaporization of the refrigerant, which leaves the oil in a liquid state. The type of oil can then be inferred by a dielectric measurement of the oil alone. For example, Polyalkylene glycol (PAG) oil has a higher dielectric constant than Polyolester (POE) oil. Method  100  illustrates that if only the refrigerant or the oil are known, then that portion of method  100  can be skipped. Otherwise, the identification of the refrigerant and type of oil are also utilized at block  126  so that controller  78  can then determine what the dielectric constant and refractive index should be for the now identified refrigerant and oil. As mentioned previously, the identification of the refrigerant and oil type can be input into controller  78  so that steps  112  through  120  may be skipped over by proceeding from step  110  to step  122 . 
         [0020]    At step  122 , mixture  58  is returned to heat transfer device  10 . The return of mixture  58  can be accomplished by ensuring that valve  64  is closed, opening valve  66 , and actuating actuator  68  to reduce the volume contained in the combination of cylinder  52  and piston  54  by reducing the displacement thereof. 
         [0021]    Gas identifier  70  may utilize a commercially available gas identifier or utilize one that is custom made for moisture detection apparatus  50 . Dielectric sensor  74  may be two spaced apart electrodes in contact with mixture  58  connected to circuitry that is sensitive to the capacitance across the electrodes. A voltage that is proportional to the dielectric constant of the fluid is generated and the measure of the dielectric constant can be computed based upon the application of a known voltage on the electrodes that are spaced a known distance apart. Refractometer  76  may utilize a lens and prism or may utilize the technique of measuring the velocity of different colors of light within mixture  58 . 
         [0022]    It is known that refractive index of a refrigerant/oil mixture varies by the refrigerant volume fraction thereof. This is one of the items that is utilized to additionally determine the water content by being able to discern the relative volumes of the refrigerant and oil in refrigerant/oil mixture  58 . The refractive index, or index of refraction, is a measure of the speed of light in that particular substance. The ratio of the speed of light in a vacuum relative to the speed of light in the tested medium is the measure of the refractive index. It is believed that the velocity at which light travels in a vacuum is a physical constant; however, light travels at a slower speed through a given material, such as mixture  58 . The refractive index is equal to the velocity of light in a vacuum divided by the velocity of the light in mixture  58 . For example, the refractive index of water is 1.33, meaning that light travels 1.33 times as fast in a vacuum than it does in water. The refractive index may vary based on the wavelength of light. It is known that there is a relationship of the dielectric constant to the refractive index, with the dielectric constant being the square of the complex numeric rendition of the refractive index. 
         [0023]    The present invention advantageously allows the quick measurement of moisture of a refrigerant/oil mixture  58  within a heat transfer device  10  to thereby determine whether the system  10  should continue to operate or other action should be taken such as steps to remove the moisture therein. Another advantage of the present invention is that it can be utilized with legacy air conditioner systems without modification of the mechanical system. Controls can be further integrated to utilize the results from the moisture testing apparatus to determine whether continued use of the heat transfer device should be contemplated or discontinued. In addition to the two pressure switches  28  and  30 , which are in place to ensure the proper amount of refrigerant/oil mixture is present, the present invention can determine whether too much moisture is present and can be wired into the system to shut heat transfer device  10  down in the event that the level of moisture is too high within refrigerant/oil mixture  58 . Yet another advantage of the present invention is that it can be easily connected, the system tested, and the moisture detection apparatus removed, similar to other pieces of test equipment that may be connected to service ports  32  and  34 . The present invention provides a simple, portable system to test for moisture content while returning the test sample to the refrigerant in the system to preclude the escape of refrigerants into the atmosphere. 
         [0024]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.