US2244475A - Evaporator plate for refrigerated cabinets - Google Patents

Description

Patented June 3, 1941 2,244,475 EVAPORATOR PLATE FOR REFRIGERATED l ABINETS walter aaskin, New York, N. r.

Application March 29, 1938, Serial N0. 198,715

d Claims.

'I'hls invention relates to heat exchangers and the like and, more particularly, to an improved evaporator plate of the so-called dry-type for refrigerated storage cabinets such a`s are commonly used in soda fountains and cabinets for the storage and dispensation of ice-cream and frosted foods, etc.

One of the principal objects of the invention is to provide a heat exchanger, or an evaporator plate of the character indicated, having increased refrigerating efficiency by reason of an increased heat absorption and reduced pressure drop between the inlet and outlet.

Another object is to provide an evaporator plate ln-which the heat absorption is substantially uniform throughout the plate and in which thorough flooding is insured at al1 times.

Still a further object is to provide an evaporator plate of the character indicated in which the time required for the pull-down to the desired temperature is reduced and which will result in a considerable saving of current.

As is disclosed in my co-pending application, Serial No. 105,869, filed October 16, 1936, I have found that by forcing the refrigerant liquid through the plate in a guided directional flow, most of the disadvantages connected with the old-type plate have been eliminated. The present invention now contemplates an improvement over` the construction disclosed in said application and of which the present one is a continuation in part.

For the purpose of making the invention more comprehensible, the following preliminary introduction is deemed desirable. The efficiency of the plate depends largely on the degree of flooding. If portions of the plate become starved during the feeding operation, naturally the available surface will be reduced. Thus the time required for the pull-down to the desired temperature will be increased with a resultant waste of current. It will also be understood that a liquid will take the course of least resistance and thus, unless the current is forced through the plate in a guided directional flow, it will approach a straight line.

Furthermore, when the liquid is forced through the ducts, it will become subjected to considerable friction, the force of which stands in direct relationship to the mass, the cross-section of the ducts and the distance to be travelled. Thus, even if the evaporator or the evaporator ducts are completely flooded, the friction will still cause a pressure drop between the inlet and the outlet. The pressure drop, in return, results in decreased heat absorption and, since the pressure drop between the inlet and the outlet of each plate is multiplied by the number of plates used in the system, the drop between the terminals thereof will become considerable.

As previously indicated, this pressure drop, in turn, causes a drop in temperature and thus,

while the desired temperature may be attained at the inlet or in the first plate, it will drop gradually towards the end of the flow. It has been found that in a 12- hole system storing 60 gallons of ice cream, the pressure drop is between 5" to 6" when a temperature of 10 F. is desired. This pressure drop can easily be translated into a temperature drop by standard tables and, according to these tables, a pressure drop of 5" vacuum, when sulphur-dioxide is used as the refrigerant, will result in a temperature drop of 10 F. Thus, if a temperature of approximately 10 F. is attained adjacent the inlet, the temperature at the outlet of the systemwill become approximately 20 F. The temperature drop is, of course, dependent greatly upon the type of refrigerant used and, also, upon the pressure at which it is originally introduced into the system. The above figures apply to sulphurdioxide introduced into the system at a pressure of 13.9 vacuum, corresponding to a temperature of 10 r'.

With these phenomena in mind, the present invention has been designed with a view to reducing the pressure drop between the inlet and the outlet of the evaporator plate and between the terminals of the system Without impairing the emciency of the plate. Thus I have found that by using the instant invention, under conditions identical with the ones described, the pressure drop is only 1.5" vacuum and which would correspond to a temperature drop of only 3.

'I'his purpose of the invention may be accomplished by breaking up the current and successively restricting it and expanding it. In this manner, not only complete flooding of the evaporator ducts will be insured but also the evaporator surface will be increased to a maximum and the friction reduced to a minimum.

Attempts have been made to accomplish this result by other means; so, for instance, plates have been made in which the refrigerant current is directed in a sinuous iiow across the plate. To counteract the ever-increasing force of the friction during the course of the flow, however, the end portions of the system have to be intentionally starved in order that the temperature may lbe balanced. In this manner, it will be understood that the efficiency of the plate is impaired resulting in a waste of current.

In other constructions, attempts have been made to reduce the friction by conducting the refrigerant through a plurality of parallel ducts. It will be understood, however, that unless the various ducts are completely flooded the eiliciency of the plate will be impaired. As stated, the tendency is for the liquid to take the course of least resistance and, thus, only those ducts adjacent the intake and the outlet will be flooded. To counteract this tendency, attempts have been made to provide a header of relatively large cross-section in comparison with the cross-section of the ducts and which interconnects the several ducts at their respective ends. According to this principle, the header is supposed to become flooded rst since its resistance is less than that of the narrow ducts, and the latter will then be fed from the header. Experience has shown, however, that such construction does not, by any means, insure complete flooding of the plate.

The present invention has been constructed along the foregoing principles; namely, to reduce the friction and to insure complete flooding, but eliminates the objections connected therewith and it will be more readily understood when taken in conjunction with the accompanying drawing in which:

Figure 1 is a front elevation of an evaporator plate according to the invention;

Figure 2 is a section along the line 2-2 of Figure 1;

Figure 3 is a partial section along the line 3-3 of Figure 1;

Figure 4 is a front elevation of a modification; and.

Figure 5 is a section along the line 5--5 of Figure 4.

The evaporator plate, generally indicated at IIJ, comprises two superimposed metal sheets II and I2, preferably of rectangular shape. The sheet II is embossed to form a continuous sinuous corrugation I3, while sheet I2 is flat. The two sheets are welded together by seam welding or spot welding along the fiat portions I4 between corrugation I3 and along the edges of the sheet. In the plate illustrated in the drawing, the seam welding process has been employed and the seams formed thereby are indicated by the reference numeral I5.

A continuous sinuous passage for the refrigerant will thus be formed, which will hereinafter be described in greater detail. This passage will act as an expansion chamber for the liquid or vaporized refrigerant.

The outer edges of the sheet II and the portion IG between the two terminals of the corrugation are also embossed to correspond with the flat portions between the corrugations and preferably welded to the fiat sheet I2. In this manner, leakage or escape of the refrigerant will be prevented.

As previously stated, the invention contemplates a reduction of the frictional force as well as complete ooding of a maximum area of the evaporators. The invention described in my co-pending application has partly attained this goal, but I have found that the diagonally running ducts, despite the improvement over the prior constructions, still oier considerable resistance. I have now established that by combining the sinuous passage-way or expansion chamber with the features of the straight paralllel ducts, still better results can be obtained. Thus, in terms of broad inclusion, the invention contemplates an evaporator plate having an expansion chamber comprising the combination of a continuous sinuous passage-way with parallel straight ducts which divide each convolution into a plurality of parts. Such a construction successively restricts and expands the refrigerant, the result of which will be not only reduced friction but also a complete flooding of the passageway.

Referring to Figure 1 of the drawing, the refrigerant, such as sulphur-dioxide, isobutane, or methyl chloride, ammonia, Freon, etc., is introduced into the expansion chamber through the inlet opening I'I by means of an expansion valve of conventional construction. This valve is not shown in the drawing since it does not form part of the invention. The current runs in the direction of the arrow into the inlet duct I8 of the first convolution-of the passageway. The bight I9 of the first and last convolution is divided into two parallel straight ducts 20 and 2| by the seam welding I5 along the at portions I, whereas the intermediate bights IBD have additional ducts 20h and 2Ib. Thus, as soon as the current reaches the bight of each convolution, it will be divided into two parts. This division causes successive restriction and expansion of the refrigerant and results in reduction of the resistance. It also causes the expansion chamber to become flooded more rapidly and the sinuous form of the passageway provides a maximum evaporator surface. In view thereof the time required for the desired pull-down will be greatly reduced.

The expansion chamber is preferably fed from below in order to take advantage of the centrifugal force to insure a complete flooding of the ducts.

After the current has passed the last convolution, it passes through the outletl duct 22 to the outlet opening 23. It may then be conducted to other plates of the system which are flooded in a similar manner.

It will be understood that the number of parallel ducts in each convolution or the number of convolutions may be selected according to practical demands. If the current is led horizontally across the plate as shown in Figure 1, I have found that two ducts for each convolution is most suitable. On the other hand, when the current is vertical it may be desirable in certain circumstances to divide each convolution into three parallel ducts.

The illustration in Figure 4 shows an embodiment of this latter modification. The refrigerant is introduced through the inlet opening 24 directly into the bight 25 and thus the vertical ducts 26, 21 and 28 are flooded simultaneously. The current then passes down the companion passage 29 to the bight of the next convolution which is flooded in a similar manner. The current finally passes down the outlet duct 30 to the outlet opening 3| from which it may be conducted to other plates of the system.

It will be understood that the above detailed description is merely illustrative of the inventors concept and different embodiments may be made without departing from the spirit thereof.

What isy claimed is:

l. In an evaporator plate for refrigerating systems, means for providing a sinuous, continuous passage extending over said plate forming a plurality of merging, alternately reversed U-shaped elements having conduits therein, at least one of the legs of said U-shaped elements being enlarged and the conduits therein being divided into a plurality of parallel ducts terminating in the bend of the respective U-shaped element, said bend being restricted in width with respect to said enlarged leg, whereby the flow of the refrigerant will be successively restricted and expanded to vary the turbulence of the current in said passage.

2. In an evaporator plate" for refrigerating systems, means providing a sinuous passage extending over said plate forming a plurality of merging, alternately reversed U-shaped elements having conduits therein, the legs of said U-shaped elements alternately being widened and the conduits therein being divided into a plurality of parallel ducts terminating in the bend of the respective U-shaped element, said bends having substantially the same width as said ducts, whereby the 110W of the refrigerant will be successively restricted and expanded to vary therturbulence of the current in said passage.

' 3. In an evaporator plate for refrigerating sysi in the bends, said bends having substantially the same width as said depressions, whereby the flow 0f the refrigerant will be successively restricted and expanded to vary the turbulence of the current in said passage.

4. In an evaporator plate for refrigerating systems, means for providing a sinuous, continuous passage extending over said plate forming a plurality of merging, alternately reversed U-shaped elements having conduits therein, at least one of the legs of said U-shaped elements being enlarged and the bend being restricted in width with respect to said enlarged leg, whereby the ow of the refrigerant will be successively restrict'ed and expanded to'vary the turbulence of the current in said passage.

WALTER RASKIN.

Images