US 1968049 A
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July 31, 1934. T. MlDGLEY, JR., Al. 1,968,049
HEAT TRANSFER AND REFRIGERATION Original Filed Feb. 8, 1930 mensa s1, 1934 y 1.96am HEAT TRANSFER AND BEFBIGEEYATION Thomas Midgley, Jr., Worthington, Albert L. Henne, Columbus, and Robert B. McNary,
Dayton, Ohio, assignors, by meine assignments, to General Motors Corporation, a corporation of Delaware Original application February 8, 1930, Serial No. 426,974. Divided and this application November 19, 1931, Serial No. 576,052
This applicationrelates to' the art of transferringV heat from one point to another and specifically to the art of refrigeration, and is a division of application Serial No. 426,974, now
5 Patent No. 1,833,847, granted November 24, 1931.
Heretofore, as far as we are aware, refrigerants and heat transfer agents have been chosen chieily'for their boiling points and stability in the refrigerating or heat transfer cycle irrespective of other desirable'properties, such as noninammability and non-toxicity.
It is the object of our invention, on the other hand, to provide a process of refrigeration and, generically, a process of heat transfer in which these desirable properties, such as non-inflammability and non-toxicity, are obtained in combination with the desired boiling points.
Broadly stated, the part of our process which deals With the controlling'of the properties of the refrigerating or heat transfer agents consists in replacing hydrogen by fluorine or other halogen, or both, in aliphatic hydrocarbons in which at least one hydrogen has already been replaced by uorine.
' Broadly stated, the part of our process which relates to the transfer of heat or the production of refrigeration comprises changing the physical state of, for example, by condensing or evaporating, a halo-nuoro derivative of an aliphatic hydrocarbon, and dissipating to, or withdrawing from, anV object to Abe heated or cooled, the latent heat necessary for changing the physical state of the said derivative. By a halouoro derivative of an aliphatic hydrocarbon We mean a derivative containing more than one uorine atom withor without other halogen atoms, or one fluorine atom with onev or more other halogen atoms.
Referringnow specically to our mode of con- 4()A trolling4 the properties of the refrigerating or heat transfer agent, aliphatic monouorides form the structural nucleus on which the agents are built. Broadly speaking, if in the structural formula CHaF we increase the fluorine content (number of atoms) by the substitution of fluorine for hydrogen, stability increases, inammability decreases, and toxicity decreases. 1f we keep the uorine content constant and substitute another halogen for hydrogen in the 50,nucleus, the boiling point increases, the stability decreases, the toxicity increases, and the inflammability decreases. 'I'he degree to which these variations take place depends on what the other halogen (chlorine, bromine, or iodine) 5511s;v As the ratio of the halogen content to the hydrogen content increases the inflammability decreases.
Because there are several variables, and because of the value of relative proportions, we
'have'placed the compounds of the group just 60,
discussed on plots wherein Fig. 1 is a plot applying the rules of substitution to typical groups having one carbon atom, and
Fig. 2 is a plot applying the rules to groups 65 having -two carbon atoms.
Fig. 3 is a key to Fig. 2, showing the radicals corresponding to the numbers used in Fig. 2.
Referring to the plots generally, the dashed lines indicate iluorine substitutions and the solid lines indicate chlorine substitutions. Similar plots are obtained with bromine and iodinerin place of chlorine except that the plot is elongated in the direction of higher temperatures with bromine, While with iodine the temperatures are still more elevated. The amount of elongation is readily determined by applying the boiling points of some of these compounds.
Referring specifically to Fig. 1, this plot contains all the compounds which can be derived 30 from CHsF by chlorine and/or uorine substitutions, together with data which assist in the `formation of the plot. On the base line appear the numerals zero to four which show halogen content, and the vertical line gives the approxg5 imate boiling points in degrees centigrade. At each point of intersection is given -the chlorine and uorine content and the complete formula of the corresponding compound isfound by making this halogen substitution for hydrogen in the formula CH-r. We have drawn a horizontal dashed line at about 25 centigrade to indicate approximately the optimum vapor pressure conditions which we desire for operating an air cooled refrigerator. It is obvious that one may deviate more or less from this line to obtain optimum conditions which include some other factors, so that within the neighborhood of this line we can provide a suitable refrigerant to meet a wide variation in limitations imposed. If under other refrigerating conditions another optimum line is found desirable, the same choice may be p made in the neighborhood of that line. In fact,
the actual operation of the refrigerator and the providing of the characteristics of the refrigerant are here combined as one problem so as to obtain the most desirable process of refrigeration under a given set of conditions.
` In Fig. 2 we have shown the same mode of controlling the properties of a refrigerant carried to compounds of the same type as in Fig. 1 but having two carbon atoms. The key to the chart is given in Fig. 3. For example, compound 9.1 is CH3.CH2F, compound 2.9 is CHF2-CC12F, compound 1.4 is CHzECHClz. and compound 2.2 is CHF2.CHF2.
When we choose as our nucleus a compound having two or more carbon atoms we find that the structural formula gives a choice as to where the substitutions of the halogens shall be made. For example, the structural formula of CaHsF is CHs--CHzF which has4 a boiling point at about 32 C. If we make a iluorine substitution for hydrogen in the second radical of this structural formula so that it reads CHa-CHFz we have a refrigerating agent whose boiling point is about --26 C. If we make the fluorine substitution for hydrogen onto the other carbon atom so that the formula reads CHzF-CHzF the boiling point of thisrefrigerant is about 5 C. Thus, the rst type of substitution yields a compound boiling substantially lower than the compound obtained by the second type of substitution, and the chart shows this to be general. The substitution of chlorine, bromine or iodine for hydrogen raises the boiling point, but the substitution in a radical which does not already contain a halogen raises the boiling point more than when the substitution is made in a radical which already contains a halogen.
The plot may be expanded in like manner Vwith other aliphatic mono-iluorides. As the number of carbon atoms increases the complexity and extent of the plot will increase together with .the number of halogens present. `These halogen derivatives of aliphatic mono-fluorides may be represented by the formula CnHmFpXr in which C represents carbon and n the number of carbon atoms in the molecule which is always equal to one or more.
H represents hydrogen and m the number of atoms thereof, which may equal zero and still fulll the'requirements of our invention.
F represents uorine and p the number of atoms thereof which is always equal to one or more.
X represents chlorine, bromine or iodine or combinations thereof and r the total number of such atoms. r may be zero when p is greater than one.
Among the chemical groups that these refrigerants fall in are halogen derivatives of aliphatic mono-fluorides, halogen derivatives of alkyl mono-fiuorides, aliphatic fluoro halides, alkyl iiuoro halides, uoro derivatives of methyl fluoride, fiuoro-halo derivatives of methane and fluoro chloro derivatives of methane.
Thus by our mode of making nuorine and/or other halogen substitution in a monoiiuoride, we can meet any conditions of refrigeration and provide our refrigerant with the desired properties, such as non-toxicity and non-inflammability, along with such properties as stability and proper boiling points.
Referring more specifically to the part of our process which relates to the actual transfer of heat, We accomplish this transfer of heat by changing the physical state of, for example, condensing or evaporating our aliphatic hydrocarbon derivative which contains more thanA one luorine atom with or without other halogen atoms, or one fiuorine atom with one or more other halogen atoms, and by dissipating to or withdrawing from an object to be heated or cooled, the latent heat necessary for the change in physical state. More specifically, to produce refrigeration, we may evaporate the desired derivative in the vicinity of a body to be cooled, while if a heating effect is desired, we may condense the derivative in the vicinity of a body to be heated, it being understood, of course, that the terms evaporation and condensation include the separation of a gas from, and the absorption of a gas in, an absorbent respectively.
Our invention Will probably nd its greatest utility by adjusting both the mode of preparing the refrigerant to obtain desirable characteristics and the mode of using the refrigerant to obtain a process of refrigeration or heat transfer which meets the limitations imposed. We prefer to employ refrigerants boiling above h60" C.
Obviously our invention is not limited in its application to any specific form of apparatus for carrying out the mode of operation described and it will not be Anecessary for a complete understanding of the invention to show a specific embodiment of apparatus. Nor is the present invention limited to the examples set forth, for a particular advance of the present invention resides in the fact that a great number of new refrigerants with graduated properties is rendered available, and that one is accordingly enabled to secure the most suitable refrigerant for varied purposes.
What is claimed is as follows:
1. The method of transferring heat which comprises condensing and subsequently evaporating CHzClF.
2. The method of producing refrigerationy which comprises evaporating in the vicinity of a body to be cooled and subsequently condensing C HzClF. Y
ALBERT L. HENNE. THOMAS MIDGLEY, JR. ROBERT R. MCNARY.