US2312312A - Evaporator - Google Patents

Description

March 2, 1943.

W. E. BELINE EVAPORATOR I5 Sheets-Sheet 1 Filed Oct. 17, 1941 IIIIIIII III III III III III III IIIIIIIIIIIIIII iiiiiiii IIIIIII You/9km 6.35am

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' III." I," II III II I" III [II III III lll III-ll (Ittornegs March 2, 1943. w. E. BELiNE' EVAPORATQR Filed Oct. 17, 1941 3 Sheets-Sheet 2 3 3 I gm attorneys March 2, 1943. w. E. BELINE EVAPQRATOR Filed mix. 17, 1941 3 Sheets-Sheet 3 Zmventor Gttornegs Patented Mar. 2, 1943 sveronaron corporation of Delaware Application October 17, 1941, Serial No. 415,476

13 Claims.

' This invention relates to evaporators and while some features of the invention are of general utility in the evaporator field, the invention is particularly directed to refrigerative evaporators for use with refrigerants which evolve large volumes of vapor per ton of refrigeration and with which the pressure range of the refrigeration cycle is comparatively small. Refrlgerants of this type are particularly useful in systems using centrifugal compressors. The refrigerantknown as Freon 11 or F-ll (which are trade names) is an example of a refrigerant,

of the type mentioned. It develops suitable re-v frlgerating temperatures when evaporated at sub-atmospheric pressures. It is condensed at relatively lczv head pressures at the condensingtemperatures ordinarily available.

The volume of vapor evolved is conspicuously large. Where this is the fact, the ofitake from the evaporator must be large so that the pressure drop from the evaporator to the compressor will be small. A pressure drop between evaporator and compressor which would be tolerable with many refrigerants, is objectionable with F-ll and other refrigerants in which the cycle is carried out in a small pressure range. Though small in the absolute sense, the pressure drop is large in proportion to the total pressure range, and occasions a serious loss of efficiency.

Furthermore, where vapor is disengaged from the surface of the liquid bath in considerable volume, it is more than usually important that the pressure over the entire disengaging surface be uniform. If there is a localized low pressure area on the surface of the bath, there will be serious surges and spouting of liquid at such area. This is an important consideration in evaporators generally because surging and spouting result in objectionable priming.

The purpose of the present invention is to secure a large heat transfer surface in an evaporator used as a cooler for fluids, and particularly for liquids such as water and brine, and at the same time to secure a large vapor disengaging surface for the refrigerants with an offtake for refrigerant vapor, so large and so favorably arranged that the pressure over' the disengaging surface will be substantially uniform. The re-. sult is attained by using a cylindrical shell within which is mounted an open top trough so dimensioned as to retain a bath of the liquid refrigerant over the heat exchange tubes, which preferably are of the finned type, and which extend in a bundle or bundles from end to end of the evaporator. The tubes communicate at their ends with chambers or water boxes to supply and receive the liquid flowing to and from the heat exchange tubes. The trough is spaced from the side walls of the cylindrical shell to provide two large area oiftakes which are co-extensive with the length of the shell and which are readily so contrived as to maintain uniformity of pressure over the entire surface of the liquid in the trough.

The liquid refrigerant is fed to the trough through a diffusion plate near the bottom of the trough, so as to distribute the relatively Warm. entering liquid refrigerant uniformly throughout the length of the trough. The feed may be controlled in any of the conventional ways, common controls being a high side float or a low side float or a thermostatic expansion valve. The high side float is a very satisfactory arrangement because it operates to keep substantiallythe entire charge of refrigerant in the evaporator, this for the reason that all of the liquid condensed in the condenser except a small float-actuating pool is delivered to the evaporator as fast as condensed. Y

Where centrifugal compressors are used there is no oil problem, but in any case where oil tends to become mixed with the refrigerant, it is possible to make use of known means for withdrawing some refrigerant mixed with. oil from the evaporator and continuously purifying it by a distilling operation. Where foaming and slopovers are permitted to occur, it is possible to make use of an external superheater which will cause the oil to flow in a foam or mist through the suction line to the compressor intake, or to a separator interposed in the suction line. The invention is not concerned with these features, but, on thecontrary, is directed to the evaporator and its offtake. However, it is important to make clear that the use of the invention does not preclude the use of accessories of the'types above mentioned.

As an example of oil recovery by distillation, reference is made to the patent to Beline, No. 2,223,882, December 3, 1940.

As an example of the use of the superheater coil in the oiftake, either to permit the use of the thermal expansion valve or to provide for oil return through the suction line, or for both purposes, reference is made to the patent to Pownall No. 2,223,900, December 3, 1940.

It willbe understood that the evaporator hereinafter discussed 'may be used for a. variety of purposes and is not strictly limited to the refrigeration field. However, the particular evapoare welded into grooves or rebates.

rators here described were designed for use in a refrigerating system of the compressor, condenser, evaporator circuit type and specifically for use in a system in which the refrigerant is F-ll or some refrigerant having similar thermodynamic properties and in which the compressor is of the centrifugal type. This statement is made to explain certain structural details which appear in thedrawings but without implying strict limitation of the invention, or of its use,

.to a particular refrigerant or refrigerant circuit or even to refrigeration. However the invention develops its full advantages in the refrigeration held and will be discussed hereinafter on that basis.

Practical embodiments of the invention will now be described by reference to the accompanying drawings, in which:

Fig. 1 is a side view of the complete evaporator looking at the side from which the suction connection leads,

Fig. 2 is an elevation of the right end of the evaporator as viewed in Fig. 1.

Fig. 3 is a vertical transverse section through the evaporator, drawn on a scale larger than 1 Figs. 1 and 2, the plane of section being through the axis of the suction connection.

Fig. 4 is a fragmentary vertical axial section 1 showing one end of the evaporator shell with the tube sheet, water box and portions of the tubes. Fig 5 is a view partly in side elevation and partly in longitudinal section showing the trough and stiffening rings together with certain tube supports and diffuser plates. I

Fig. 6 is a section on the line 66 of Fig. 5

showing the crow foot stays used with the tube sheet and indicating how that part of the tube sheet which is above the tubes is supported.

Fig. 7 is a section on the line 1-! of Fig. 5

showing how the tubes and the trough are susof the partitions in the left invention.

I In an evaporator designed to operate at subatmcspheric pressure, the problem of staying is complicated by the fact that the pressure differential is inward when the evaporator is in operationbut is subject to possible reversal when the refrigerative circuit is shut down. It is desired to have the vapor space in the evaporator clear, so it is undesirable to use stays or stay tubes above the liquid level. The very nature of .the operation carried on in the evaporator requires that the heat transfer surface, i. e., the

' tubes, be submerged in liquid refrigerant. That fact and the need for a large area vapor offtake coextensive with the length of the evaporator drum underlie the use of the liquid retaining trough spaced from. the shell. This is a characteristic feature of the invention.

The evaporator comprises an elongated cylindrical shell II constructed of sheet steel with welded joints. Fig. 1 shows about the normal relation of length to diameter but this is subject to variations. At each end of the shell there is welded a stiffener ring I2. The ends of the shell Seated in a countersunk seatin' the outer face of each ring is a corresponding tube sheet I3. This is welded or brazed at its periphery to the stiffening ring II. It is sustained against motion inward toward the interior of the shell partly by the staying action of the tubes I4 and partly by an internal sustaining structure carried by the stiifening ring.

Extending between the two stiffening rings I2 is the so-called trough I5. The ends of this trough engage seats formed to receive it at the inner-periphery of each of the stiffening rings, and the trough is welded to these rings (see Figs. 4, 5 and 6) The trough is cylindrical in form and uniformly spaced from the shell I I. It subtends an angle slightly less than 270". At any rate, the margins of the trough are above the uppermost range of tubes I4, so as to be capable of retaining a bath of refrigerant liquid deep enough to submerge all of the tubes.

Returning now to the head staying means, a segment I6 of heavy plate is positioned against the inner face of the tube sheet I3 and is welded at its upper periphery to the corresponding stiffening ring I 2. Its lower straight edge is horizontal, and immediately above the top row of tubes I4. Across the lower edge the plate It is stiffened by a flange H which might be integral but more conveniently is formed as a separate piece welded in place.

It will be noticed that the area of the tube sheet I3 which contacts the plate I6 is devoid of any staying other than the plate I6. That portion of the tube sheet I3 below the plate It is stayed by the tubes Id and requires only moderate additional staying. This takes the form of webs or bars I8 arranged in what may be called a crowfoot pattern, see particularly Fig, 6. These webs I8 extend along blank areas on the tube sheet pattern, designed to receive them. The webs I8 are welded together near the axis of the drum and at their extremities are welded to the trough member l5 or to the stiffening plate It as the case may be. They are well sustained because the welds at the ends of the webs are in the zone in which the trough is welded to the stiffener rings. It follows that each tube sheet is adequately sustained throughout its entire area.

Bolted to the rings I2 by means of bolts I9, and sealed by gaskets 2|, are the concavo-convex heads 22 which form water boxes. The head at the left in Fig. l is equipped with two water connections 23 and 24 which serve as supply and discharge connections for the water to be cooled -by the evaporator.

This water passes through the tubes. sidering the device as a water cooling evaporator, it is the fluid cooled in the device but at the same time it is a heat convector and serves as the source of heat necessary to cause vaporization of the refrigerant.

While the arrangement of water passes is not a feature of the present invention, a four-pass layout is shown. The dividing partitions 25 for the left hand head of Fig. l-are diagrammed in Fig. 8. The dividing partitions 26 for the other head are diagrammed in Fig. 9. These partitions follow blank areas on the tube sheets, as do the crow foot stays. Each gasket 2| has portions which underlie such webs, as indicated in Fig. 4.

Any other practicable pass arrangement may be used.

Refrigerant is supplied to the trough through a connection 21 (see Figs. 1, 2 and 5). This Con- 1 proved satisfactory in use.

connection is indicated as located near one end of the evaporator but it might be located near the middle or at any preferred point. The important thing is that it leads through the shell across the offtake and into the bottom of the trough where it discharges beneath a horizontal perforated baffle-plate or diffuser 28. This plate underlies the lowermost range of tubes and serves the purpose of distributing the incoming warm liquid refrigerant so that it enters the trough at the bottom and approximately uniformly throughout the entire length of the trough. Only one refrigerant supply is shown. Any preferred number may be used and they may be variously located to meet particular requirements as to distribution.

A second and much smaller connection is indicated at 2'9 and may be used as a' drain, or as a supply, or for any purpose to which it is adapted. The present invention is not limited to or very directly concerned with the details of liquid flow to and from the trough.

The trough is sustained at points intermediate the ends of the shell by an appropriate number of radial webs or struts 3!. As shown in Fig. 3, for example, there is one strut near each 'upper margin of thetrough and three uniformly spaced at intervals between these two. These struts extend only short distances in the direction of the axis of the shell ii and their spacing along the length of the shell is a matter of design. Their purpose is to space the trough from the shelland tie the two together without materially obstructing circumferential flow from the upper space within the shell downward through the annular spaces between the shell and the trough. These flows unite at the offtake 32. The oiftake is provided with a connecting flange 33 and a flexible section or expansion 'joint 34 whose forms are clearly shown in Fig. 3.

The suction connection 32 leads-from the boxlike enlargement 35 which overlies a coextensive series of openings in the shell H. These open ings are separated by narrow webs or bands .36, so that the efi'ect of one large continuous opening is closely approximated (see Figs. 1 and 3). The bands 36 offer points of attachment for the stays 3'l-whose form is best shown in Fig. 3. The length of the box-like enlargement 35 in the example illustrated is approximately half the length of the shell ii.

Its length is determined by the practical consideration of ensuring substantially uniform flow rates of vapor downward between the shell H and the trough l throughoutthe entire length of the shell.

The proportions indicated in the drawings have They are subject to variation.

The tubes Hi which extend between the tube sheets, and which communicate attheir ends with the water boxes, are preferably of the type having low integral fins. These are produced by a rolling operation and materially increase the heat transfer surface without weakening the "tubes and without occupying much space. ends of the tubes are belied out or expanded so vthat their outside diameter slightly exceeds the .outside diameters of the fins.

The

Thus, the tubes may be inserted through the opening in the tube "sheet without difficulty. The tubes. are brazed to the tube sheet.

It is desirable to sustain the tubes at points 1 intermediate their length and in Fig. 5 two secondary supports are shown. .form of plates. They are perforated in a These take the pattern conforming to the tube sheet pattern so that the tubes Pass through the plates 38 and are sustained thereby- At its lower margin each.

. or retainers 39, see Figs. 3 and 5. They are confined at their upper margins by angle braces 4| which extend across the upper margins of the plates 38 and which are welded at their ends to the sides of the trough near the upper margins thereof.

Where the evaporator is used without a superheater, some type of eliminator is desirable to arrest liquid refrigerant sprayed up fromthe surface of the liquid in the troughwhile permitting ofi-fiow of vapor. Such an eliminator structure is shown in Fig. 3. It comprises panels 42 each made up of a rectangular marginal frame which sustains two spaced confining sheets of woven wire. Between these two sheets there is confined a layer of metal wool. In commercial practice, use was made of a metal wool made of copper turnings and sold under the trade name of Brillof'. Various other eliminator structures of known form can be substituted. Those described have proved satisfactory.

The panels 32 are sustained by the Z-bars 33 which are welded along the upper margins of the trough l5 and by a tubular beam 44 which extends from end to end of the shell and is welded at its ends to the respective stlfiener rings i2. The panels 52 are clamped in place by a holddownstrip 45 connected to the pipe at by the bolts 36.

The shell I i may be sustained by the supporting brackets 41 and it may carry the supporting pads 48 which, in the example illustrated, were When so used, that portion of the warm refrig-- erant feed which is used for superheating is'fed to and from the coil 53 by means of connections 54 and 55. Only a portion of the refrigerant supplied to the evaporator passes through this coil 53 and afteripassing through the coil 53 such refrigerant is delivered to the trough within the evaporator through any suitable connection, for example, connection 29 shown in Figs. 1 and 5.

It will sufiice to explain that the superheating of the off-flowing vapor by the coil 53 permits the use of a thermostatically controlled valve to regulate the main supply of refrigerant which enters through the connection 21. The evaporator is well adapted for use in the Pownall system and this system not only permits thermostatic control but also permits the return of oil from the evaporator through the suction connection.

Where the present evaporator is used with a centrifugal compressor, there is no oil problem. In such case, the Pownall superheater would serve only as a superheater. nall system can also be used to return oil through the suction connection. Where that is desired, the eliminators 42 must be removed. This is However, the Pow-- suggested in Fig. where the parts 42 to 46 are omitted. This arrangement will permit a limited amount of oily liquid refrigerant and foam to slop-over and pass through the suction connection to the superheater, all according to the Pownall invention.

As stated, the present invention is not limited to use with the Pownall system, or with any particular system, but may be used with high pressure float feed or low pressure float feed or any feed which will produce the necessary floodmally above the upper range of tubes.

However, it is desired to bring out the point that the evaporator is adapted for use with the Pownall system when desired and has the advantage that large flow passages are afforded to the superheater.

In an evaporator, constructed according to the invention and used in refrigerative systems, the

ofitake 32 leads to the suction line of a compressor and this compressor operates to maintain in the evaporator a lowered pressure corresponding to the desired temperature of evaporation. The liquid which passes through the tubes I4 is in efiect a heating medium, for it delivers, through the tubes to the volatile refrigerant outside the tubes, the heat units necessary to supply the latent heat of vaporization. Obviously evaporation cannot be carried on continuously unless this latent heat is supplied. I

In the claims the term heat conveying medium will be used to define the water or other fluid passed through the tubes, because this phrase accurately defines the thermodynamic function of that fluid.

While the invention has been described in considerable detail, no necessary liimitation to the illustrated structure is implied and changes within the scope of the following claims are possible and are contemplated.

I claim:

1. An evaporator comprising in combination a shell; tube sheets with tubes extending therebetween; connections for passing a heat conveying medium through said tubes; a trough structure within said shell serving to retain a volatile liquid in contact with said tubes, the trough being spaced from the shell to provide an ofitake which passes between said shell and trough; and a coiinection for supplying volatile liquid to said trough.

2. The combination defined in claim 1 in which and there is a vapor discharge connection ne the bottom of the shell.

3. The combination with the structure defined 4. An evaporator comprising in combination,

an elongated generally cylindrical trough open at its top; a surface heat exchanger in the trough; a connection for supplying volatile liquid to said trough; a cylindrical enveloping shell enclosing the trough and forming therewith offtakes which lead from the top of the trough down both sides'between trough and shell, said offtakes extending substantially the entire length of the trough; means associated with said shell and forming an outlet chamber of larger crosssection than either offtake and communicating with both offtakes through approximately half the length of the shell; and an outlet connection leading from said chamber.

, ing of the trough so that the liquid level is nor- 5. An evaporator comprising in combination a cylindrical shell; stiifener rings fixed in the ends of the cylindrical shell; tube sheets with tubes extending therebetween, said tube sheets being supplying volatile liquid to said trough.

6. An evaporator comprising in combination a cylindrical shell; stiffener rings fixed in the ends of the cylindrical shell; tube sheets with tubes extendingtherebetween, said tube sheets being connected with said stiffener rings; connections for passing a heat conveying medium through said tubes; a trough structure mounted within said shell with its ends entering sustained by and sealed to said stiffener rings, said trough serving to retain a volatile liquid in contact with said tubes, the trough being spaced from the shell to provide an ofitake which passes between the shell and the trough; a connection for supplying volatile liquid to said trough; and secondary sustaining means mounted at intervals between said stiffener rings and comprising members which space the trough from the shell and members within the trough which sustain the tubes at points intermediate the tube sheets and are sustained by the trough.

7. An evaporator comprising in combination a shell; tube sheets with tubes extending therebetween; connections for passing a heat conveying medium through said tubes; a trough structure within said shell serving to retain a volatile liquid in contact with said tubes, the trough being spaced from the shell to provide an offtake which passes between said shell and trough; a connection for supplying volatile liquid to said trough; and eliminator members seated on respective edges of the trough and inclined inward so that they meet along a ridge adjacent the top of the shell.

8. The combination defined in claim 7 in which the eliminator comprises panels each made up of a layer of metallic Wool and suitable confining and sustaining frames therefor.

' the shell is cylindrical and the/trough is spaced from the shell at both its sides and at its bottom, i

9. An evaporator comprising in combination a shell; tube sheets with tubes extending therebetween; connections for passing a heat conveying medium through said tubes; a trough structure within said shell extending the entire length thereof, said trough structure serving to retain a volatile liquid in contact with said tubes,

the trough being spaced from the shell to provide an ofistake which passes between the shell and the trough; an outlet connection having an enlargement arranged to communicate with said ofitake throughout approximately half the length and at the mid-portion thereof; and a connection for supplying volatile liquid to said trough.

10. An evaporator comprising in combination a shell; tube sheets with tubes extending therebetween, connections for passing a heat conveying medium through said tubes; a trough structure within said shell serving to retain a volatile liquid in contact with said tubes, the trough being spaced from the shell to provide an offtake which passes between said shell and trough: a connection for supplying volatile liquid to the bottom of said trough; and a perforated diffuser overlying said connection and extending from end to end of said trough.

11. An evaporator comprising in combination a shell; tube sheets with tubes extending therebetween, connections for passing a heat con- 'veying medium through said .tubes; a trough to the bottom of said trough; a perforated dif fuser overlying said connection and extending from end to end of said trough; and an elim- 'inator overlying said trough and serving to arrest liquid droplets entrained by ofi-flowing vapor.

12. An evaporator comprising in combination a shell; tube sheets with tubes extending therebetween, connections for passing a heat conveying medium through said tubes; a trough structure within said shell serving to retain a volatile liquid in contact with said tubes, the trough being spaced from the shell to provide an ofitake which passes between said shell and trough; a connection for supplying volatile liquid to the bottom of said trough; a perforated diffuser overlying said connection and extending from end to end of said trough: and combined babies and tube supporting means extending across said trough intermediate said tube sheets and above said diffuser, said baflles being so arranged as to permit level-equalizing flow while resisting liquid surges on said trough.

13. An evaporator comprising in combination a shell; tube sheets with tubes extending therebetween, connections forpassing a heat cohveying' medium through said tubes; a trough structure within said shell serving to retain a volatile liquid in contact with said tubes, the trough being spaced from the shell to provide an oiitake which passes between said shell and

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