Abstract:
A refrigerant mixture. The mixture of propane and butane may be advantageously used as a substitute for R-12, thus eliminating the use of ozone depleting R-12 refrigerant. Ideally, the mixture is comprised of approximately 50% propane and 50% butane by liquid volume. Alternately, the mixture may contain up to about 75% of either propane or butane. A refrigeration process utilizing the mixture is also disclosed.

Description:
This is a continuation of application Ser. No. 07/937,303 filed on Aug. 31, 1992. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates to a novel refrigerant mixture for use in refrigeration systems. The refrigerant is not harmful to the ozone layer, and is particularly applicable in systems such as automobile air-conditioning and home refrigeration. 
     BACKGROUND OF THE INVENTION 
     A continuing demand exists for a simple, inexpensive refrigerant which can be used to reduce the level of ozone damaging compounds which can escape and harm the earth&#39;s atmosphere. In particular, there exists a need for a simple, low cost refrigerant which can be used as a substitute for refrigerant R-12, also commonly known as dichlorodifluoromethane. At normal atmospheric pressure, R-12 boils a −21.7° F., thus, any substitute must have properties sufficiently comparable that equipment can be used without costly modification. 
     In addition to the undesirable ozone depletion consequences which have been widely reported, those familiar with refrigeration systems will also recognize that R-12 and other fluorchlorocarbon refrigerants can contribute to the formation of acids under as a result of decomposition in a refrigerant system. Formation of such acids is not uncommon, and when it occurs, severe damage to metal surfaces in a refrigerant system can result. Moisture in an R-12 based refrigeration system can contribute to such acid formation, as can use of contaminated lubricating oils. 
     For the most part, the R-12 substitutes which have been proposed have been various substituted hydrocarbons, utilizing addition of bromine or other atoms, primarily in an attempt to produce a non-flammable refrigerant. Such substitutes have their own problems, such as undesirable toxicological effects on exposed individuals. 
     SUMMARY OF THE INVENTION 
     I have now invented, and disclose herein, a novel, refrigerant mixture which does not have the above-discussed drawbacks common to the fluorchlorocarbon refrigerants heretofore used of which I am aware. Unlike the refrigerants heretofore available, my product is simple, relatively inexpensive, easy to manufacture, and otherwise superior to those heretofore used or proposed. In addition, it provides a significant, demonstrated improvement with regard to protection against release of ozone depleting compounds. 
     Another important feature is the fact that my novel refrigerant is not conducive to formation of undesirable acid compounds while in use in a refrigeration system. This provides a unique safety feature when compared to many previously known refrigerants. 
     My novel refrigerant mixture is essentially a 50-50 mixture of propane and butane. However, up to as much as 75% of propane, or alternately, butane, may be utilized. 
     My novel refrigerant differs from those prior art products mentioned above in one respect in that no substitution of hydrogen molecules by halogen or other species is required. In its simplest form, my invention is the discovery that a mixture of propane and butane will provide suitable properties for direct substitution in R-12 systems. 
     Thus, the dual advantages of protection of the ozone layer, and low cost of the commonly available gases propane and butane gases, become important and self-evident in direct refrigerant substitution applications. 
     OBJECTS, ADVANTAGES, AND FEATURES OF THE INVENTION 
     From the foregoing, it will be apparent to the reader that one important and primary object of the present invention resides in the provision of a novel, improved refrigerant which does not contribute to the destruction of the ozone layer. 
     Other important but more specific objects of the invention reside in the provision of a refrigerant which may be directly substituted in R-12 based refrigeration systems, and which: 
     can be manufactured in a simple, straightforward manner; 
     results in comparatively low cost refrigerant mixtures; 
     in conjunction with the preceding object, have the advantage that they can be widely used without cost penalty in selected refrigeration systems; and, 
     which provides a refrigerant gas mixture which is easy to use, install and remove. 
     Other important objects, features, and additional advantages of my invention will become apparent to the reader from the foregoing and the appended claims and as the ensuing detailed description and discussion proceeds in conjunction with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawing: 
     FIG. 1 is a process flow diagram for an automobile refrigeration system, in which the present invention may be employed. 
     FIG. 2 is a process flow diagram for a refrigerator refrigerant circuit, showing the components of a typical residential refrigerator system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Widely utilized refrigerant systems which utilize R-12 include automotive and home refrigeration systems. Although the refrigerant mixture disclosed herein may be used with other types of refrigerant circuits, the invention will be disclosed with reference to several of the most commonly used types. 
     Turning now to FIG. 1, there is shown an automotive type refrigeration system  10 ; this type of system is commonly utilized to cool the passenger compartment of cars and trucks. Critical components of the refrigeration system  10  include the compressor  11  which is used to raise the pressure (and the temperature) of a circulating refrigerant  12  from the cold, low pressure suction side  14  to the high temperature, high pressure discharge side  16 . The refrigerant  12  pressure is raised so that it is capable of being condensed based at the internal temperature achievable in the condenser  18 . Actual operating temperatures and pressures will vary widely and may be reviewed in a variety of texts on refrigeration. However, for a convenient point of reference, when the outside air entering an automotive condenser is 100° F., the high pressure circuit may operate at about 220 to 270 psig, while the low pressure circuit may operate at about 20-30 psig. Thus, the low pressure circuit pressure corresponds to a temperature of the cold refrigerant of roughly 20 to 30° F. Refrigerant  12  vapors which are condensed in condenser  18  are passed through a receiver  20 , to accumulate the liquid refrigerant. The receiver may also include a desiccant (internal and not shown) for removal of water from the circulation refrigerant  12 , so as to minimize the tendency of the refrigerant to form harmful, normally acid decomposition products. 
     In order to allow the high pressure refrigerant  12  to enter the low operating pressure evaporator  22 , the refrigerant is metered through a thermal expansion valve  24 . The liquid refrigerant  12  is allowed to escape into the lower pressure evaporator  22 , and most of the refrigerant  12  will enter as a liquid to a pool  24  at the bottom of the evaporator  22 . As heat is introduced to the evaporator  22  (as via an airstream  26  passing through the air passageways  28 ), liquid refrigerant  12  boils and becomes low pressure vapor, and travels to the low pressure side suction side  14  of the compressor  11 , to repeat the process. 
     In most automotive type refrigeration systems, dichlorodifluoromethane (R-12) is used as the refrigerant. Unfortunately, this compound has been found to contribute to depletion of the upper atmospheric ozone layer. As a result, its use is being discontinued, as urged or as required by specific limitations in legislation in the United States and elsewhere. 
     I have found that a mixture comprised essentially of propane and butane can be directly substituted for R-12 in air-conditioning and refrigeration systems. Although the preferred composition is about 50% propane by liquid volume, with the remainder butane, the composition may be somewhat varied without encountering great difficulty. In fact, a mixture consisting essentially of up to about 75% propane, with the remainder butane, may be used. Preferably, as noted above, at least 50% propane may be used. In most cases, not less than 25% propane is desirable. 
     The aforementioned mixture is advantageous in that it does not contain halogen substituted molecules to cause problems such as acid formation and the resultant metal attack problems internal to the refrigeration circuit, as may be encountered with dichlorodifluoromethane. Also, both propane and butane are commonly available, at lower cost than most currently available refrigerants. Particularly in automotive applications, as set forth above, the flammable properties of propane and butane should not cause particular concern, in the quantities required for small refrigeration circuits, in view of the quantities of flammable fuel already successfully and safely transported on a regular basis. 
     My refrigerant mixture is also amenable for use in a home refrigerator system, such as is depicted in FIG. 2. A refrigerator  40  is shown having therein a compressor  42 , a condenser  44 , an expansion valve  46 , an evaporator  48 , and a low pressure vapor line  50  which returns to the compressor  42 . Operation of the system is similar to that set forth above for the automotive refrigeration system, and need not be repeated in detail as it will be quickly recognized by those skilled in the art and to whom this invention is addressed. For reference, it is common for R-12 based refrigerator systems to operate at about 120 psig on the high pressure side, and at about 0 psig on the low pressure side. As a 50-50 mixture of propane and butane will condense at about 75 psig, this mixture provides a change of state of the refrigerant within an ideal range. 
     I have now discovered that the refrigerant gas commonly used in home refrigerator systems, dichlorodifluoromethane (R-12) may be advantageously replaced by a propane-butane mixture, preferably containing about 50% butane and the rest essentially propane. Also, I have discovered that the refrigerant mixture of about 50% propane and about 50% butane is more energy efficient than utilization of an R-12 refrigerant in home refrigerators. The exact savings, however, will vary according to the mixture utilized and the size of the system, particularly the compressor. 
     Thus, it can be seen that I have developed and have set forth herein an exemplary refrigerant mixture, and a method for use of same in common refrigeration machinery. The material is of low cost, is easily prepared, and does not tend to produce harmful acid breakdown products in refrigeration systems. Further, the mixture is quite compatible with refrigeration oils, and can be safely used in refrigeration systems. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalences of the claims are therefore intended to be embraced therein.