US 3119004 A
Description (OCR text may contain errors)
F. R. HOOP FLASH CHAMBER Jan. 21, 1964 2 Sheets-Sheet 1 Filed Dec. 12, 1960 INVENTOR. mepm/c /2 Am QM MM Jan. 21, 1964 Hoop 3,119,004
FLASH CHAMBER Filed Dec. 12, 1960 2 Sheets-Sheet 2 United States Patent 0 3,119,004 FLASH CHAMBER Frederic R. Hoop, 509 S. Division, Grand Rapids, Miclr, assignor of onehaif to M. loukios, Grand Rapids, Mich.
Filed Dec. 12, 196i], Ser. No. 75,220 2 Claims. (Cl. 2ll938) This invention relates to apparatus for the continuous vaporization of a moving stream of liquid, and more particularly to devices known as flash chambers.
This application is a continuation-in-part of my copending application Serial No. 743,124 filed lune 19, 1958, and entitled Refrigeration System, now Patent No. 2,986,907.
The conventional way of evaporating a liquid is to place the liquid in a container which is subjected to a temperature far in excess of the temperature of the liquid. The temperature to which the container is subjected has to be high because the heat transfer from the outside of the container to the liquid adjacent the wall of the container is counteracted by the convection heat loss to the cooler portions of the liquid most remote from the container Walls. It will be readily realized that the continuous evaporation of a flowing stream of liquid by conventional methods is possible only by providing a long heated flow path for the liquid and by applying intense heat thereto.
In my aforesaid co-pendin'g application Serial No. 743,124 I have described a refrigeration system which requires the instantaneous evaporation of intermittent bursts of liquid under low pressure, in a heat exchanger powered by a thermal source whose temperature may be only slightly higher than the vaporization point of the refrigerant. In the present application I have disclosed a steam gun in which a stream of water is continuously converted into steam at a uniform pressure by a thermal source of a temperature which may be substantially the required exit temperature of the steam produced.
In both of the above fields of use, as well as in many analogous ones, the basic problem solved by my invention is the complete vaporization of a flowing liquid by an apparatus requiring a minimum of space and capable of operating with a thermal source only slightly warmer than the desired outlet temperature of the gas produced. In order to avoid the prior-art requirement of long heated passages with the resulting bulkiness, expensive manufacturing practices, and serious maintenance problems, it is necessary to transfer heat very effectively from the thermal source to all parts of the liquid in a comparatively shaft flow distance.
The present invention solves the above problems by providing an extremely low v0lume-t0surface ratio within the liquid conduits of the heat exchanger. Specifically, I have discovered that optimum performance can be achieved with a volume-to-surface ratio of between 1 and 20 mils. In order to achieve this low volume-tosurface ratio while still maintaining an appreciable fluid flow, I have provided a plurality of small liquid passages connected in parallel, through which the liquid can travel at a comparatively high velocity. The upper limit of the volume-to-surface ratio is dictated by the physical dimensions of the heat exchanger necessary to provide an adequate passage length. The lower limit of the ratio is dictated by the excessive delicacy of the apparatus, the danger of clogging very small passages by mineral deposits or impurities, and the low pressure resistance of precision apparatus.
Two of the embodiments herein are particularly adapted to operation with a low-temperature thermal source by providing concentric layers of passages surrounding the thermal source, by means of which a temperature gradient is created from the inner layer to the outer layer which causes the liquid to be gradually pre-heated before it is vaporized.
In one of the embodiments shown, the passages are further so arranged that individual passage-forming elements can be easily removed from the heat exchanger and cleaned of any mineral deposits that may have accumulated therein. Finally, one embodiment of this invention disclosed herein solves the problem of maintaining a constant high-pressure feed of liquid into the flash chamber even though only a low-pressure liquid supply is available. This arrangement is necessary in order to prevent the generated gases from backflashing into the liquid supply line in those embodiments where the vaporization process is continuous rather than intermittent.
It is therefore the object of this invention to provide means for the vaporization of a flow stream of liquid by a low-temperature thermal source.
It is a further object of this invention to provide a heat exchanger having an extremely low volume-to-surface ratio.
It is another object of this invention to provide means for feeding liquid to a flash chamber continuously at high pressure regardless of the pressure of the liquid supply.
These and other advantages of present invention will become apparent by a perusal of the following specification, taken in connection with the accompanying drawings in which:
FIG. 1 is a schematic representation of a continuous vaporization system in accordance with my invention;
FIG. 2 is a vertical section of the flash chamber unit used in the system of FIG. 1, taken along the line 11-11 of FIG. 1;
FIG. 3 is a vertical section of the flash chamber taken along line IIIIII of FIG. 2;
FIG. 4 is a vertical longitudinal section of an alternative embodiment of flash chamber according to my invention; l l f FIG. 5 is an end elevation of the flash chamber FIG. 4; and
FIGS. 6, 7, and 8 are perspective views of flash chambers particularly suited for intermittent operation, FIGS. 6 and '7 being partly cut away.
Basically, the present invention teaches the evaporation of a flowing liquid by dividing the flow paths into a plurality of small passages connected in parallel so that all portions of the liquid stream are in as intimate a con-tact as possible with the walls of the flow passages. The relationship between the volume of the flow passages and the active heat exchange surface required by this teaching is expressed by the volume-to-surface ratio. Since the volume is expressed in the cube of a length unit and the surface is expressed in the square of the same length unit, the volume-to-surface ratio is expressed in that length unit. In order to obtain convenient figures for this ratio, the mil is the most convenient length unit to work with. I have found that if the flash chamber is so constructed that the ratio of the total volume of the flow passages to the total surface of the flow passages is on the order of 1 to 20 mils, optimum performance of the flash chamber Will result.
Two basic types of flash chambers are contemplated by the present invention. Both types require a low volume to-surface ratio. One type, however, is specifically adapted to vaporize intermittent bursts of liquid flow, and is thus particularly suitable for certain refrigeration uses such as described in my copending application Serial No. 743,124, whereas the other is especially adapted to vaporize a substantially continuous flow of liquid and is therefore best adapted for use in devices such as steam guns. Both of them will be discussed separately herein.
The intermittent-flow flash chamber of FIGS. 6 through 8 has a distinct advantage over the conventional boiler type of liquid to gas phase conversion unit. A conventional boiler is constantly maintained at a pressure level equal to that required to operate the energy converter. This necessitates an injector system for the boiler capable of forcing liquid into the boiler against this back pressure. In the flash chamber, the pressure rises to the requirements of the energy converter only momentarily and the liquid can be injected substantially instantaneously (i.e. before it can vaporize) at a substantially lower pressure.
Another advantage of the flash chamber is its short starting time. A boiler must be heated to operating temperature together with its contents. In the flash chamber, while the chamber is empty, only the heat exchanger needs to be heated to operating temperature. This requires substantially less energy and consequently the starting time is but a fraction of that required for conventional boilers. The necessity for floats or other liquid level controls is also eliminated.
The continuous-flow type of flash chamber must be equipped with a high-pressure liquid input or feed to prevent flashback of the vapor generated within the flash chamber into the inlet line. My invention solves this problem by providing a solenoid-operated pump which provides a practically continuous high-pressure liquid feed to the flash chamber regardless of the pressure of the liquid supply.
In the continuous-flow type of flash chamber, I may further provide concentric layers of flow paths surrounding the thermal source. In that type of construction, preheating of the liquid is effectively accomplished as it travels through the outer layers of passages, so that its vaporization can be accomplished with a relatively small amount of thermal energy as it travels through the inner layers of passages.
Although it will be understood that high-temperature thermal sources such as a flame may be used with my flash chamber, the present invention is designed to be able to use a low level of thermal energy such as would be available in hot water or in hot exhaust gases even though they had cooled substantially, or from a low energy electrical source not requiring special heavy duty generating equipment. This invention is particularly adapted to operate refrigeration apparatus using the hot Water of the cooling system of an internal combustion engine as a power source. Such hot water is available in aircraft, trucks, passenger cars and small boats. It is also available in most rolling stock for railways in the form of steam, although steam has an energy level far in excess of that required to power this system. A refrigeration system powered in this manner derives all or substantially all of its energy from waste heat sources and thus does not divert energy from the main power plant. It will be realized that in order to accomplish this, the heat exchange must be rapid and must involve simultaneous heat exchange contact between the heated vanes or elements and the body of the liquid throughout substantially the entire mass of liquid injected into the flash chamber.
FIG. 1 of the drawing shows a system according to my invention for vaporization of a continuous liquid stream, such as might be used in a steam gun. The system It consists basically of a liquid supply line 12, a solenoid pump 14, a flash chamber 16, and a vapor out let 18. A suitable liquid such as water is supplied to the solenoid pump 14 from the liquid supply line 12. A check valve Ztl permits passage of the liquid into the cylinder 22 of the pump 14 but prevents the pressurized liquid in cylinder 22 from being returned to the supply line 12. A second check valve 24 is provided on the outlet side of the cylinder 22 and permits flow of liquid only in the direction from the cylinder 22 to the flash chamber 16. Liquid traveling through check valve 24 next passes through the control valve 26 by which the water input to the flash chamber 16 can be regulated. A safety valve 23 may be provided in the liquid line between valve 26 and the flash chamber 16 in order to relieve any excessive pressure which may develop in the flash chamber if the liquid passaegs in the chamber become clogged.
The solenoid pump 14 consists of a solenoid 30 connected to an appropriate power supply (not shown) through wires 32, 34 through the intermediary of a switch 36. The switch 36 is closed by a flange 38 of the piston 45% when the upper end of piston 40 has traveled almost to the upper end of cylinder 22. Well-known means may be provided in the circuit to prevent the interruption of the electrical current to the solenoid 30 until the top of plunger 46 has traveled all the way down to its lowest position adjacent the lower end of cylinder 22. When the piston 4b reaches its lowermost position, the switch 36 opens, and piston 4b is returned to its uppermost position by spring 42. By proper dimensioning of the elements described above, the downward movement of the piston 4t may be made almost instantaneous, whereas the upward movement of the piston 40 can be made comparatively slow even though it exerts considerable pressure on the liquid during such upward movement. For this reason, the liquid feed to the flash chamber can be considered continuous for all practical purposes, although it is technically pulsating.
The flash chamber 16 can be heated by any suitable heat source which provides a temperature at least as high as the desired output temperature of the steam. In the example shown, this thermal source has been depicted as an electric heating element 44- which extends axially throughout the flash chamber 16. The temperature of the heating element 44 is maintained constant by a thermostat 4s (FIG. 3) which is connected in series with the heating element 44 across the power supply (not shown) by wires 32 and 34.
The heating element 44- is surrounded by a heat exchanger 48 manufactured preferably from a metal having a very high thermal conductivity. As willbe best seen from FIG. 2, the heat exchanger 48 is longitudinally traversed by a large number of tapered bores 50 into each of which is inserted a star-shaped tapered pin 52. The pins 52 are slightly shorter than the bores 50, and they are so dimensioned that when inserted as far as they will go, they will seat themselves in the center of the longitudinal dimension of the bore into which they are fitted. The bores 5i) are closed at each end by end plates 54, 56, so that a small plenum is formed in each bore adjacent each end of the pin inserted therein. These plenums 58 are connected together in pairs at alternate ends of the flash chamber 16 by transverse conduits 6t). It will be seen from an inspection of FIG. 2 that this method of interconnection provides a continuous zig-zag path starting at bore 62 and proceeding counterclockwise three times around the heat exchanger 48 to bore 64. Since successive ones of the transverse conduits 60 are located at opposite ends of the flash chamber 16, it will be seen that the liquid stream travels along each one of the pins 52. It will also be readily seen, again from an inspection of FIG. 3, that each pin 52 divides the liquid flow path into eight narrow generally parallel passages 66. It is in these passages 66 that the bulk of the heat exchange takes place. The last (in the direction of flow) plenum of bore 64 discharges into the vapor outlet line 13.
An alternative form of flash chamber is the flash chamber 67 shown in FIGS. 4 and 5. In this embodiment, liquid is introduced into the flash chamber through the liquid inlet 1'7, and steam is discharged from it through the vapor outlet 13. The heat exchanger consists of numerous turns of a flat hollow strip 68 wound around the heating element 44 preferably in a plurality of layers. The strip 63 is provided with internal vanes 69 which form the narrow parallel passages 66 analagous to those shown in FIG. 2.
FIGS. 6, 7, and 8 show several types of flash chambers particularly adapted for intermittent operation, such as in refrigeration systems. In FIG. 6, the numeral 70 indicates a housing in which is mounted a plurality of vanes 71. The vanes 71 are positioned in side-by-side parallel relationship with their ends secured to opposite walls of the housing 70. The vanes are spaced apart to form refrigerant passages 72 between them. The conduit 17 forms the refrigerant inlet for the flash chamber and the conduit 18 the outlet. The vanes 71 are preferably of a material having good heat conductivity characteristics such as copper. The vanes 71 are relatively thin and are closely spaced with the passages 72 having an average width of 0.005 of an inch. The clearance between the housing 70 and the top and bottom ends of the vanes 71 is also kept at a minimum, being only that which is sufficient to permit the refrigerant to reach all of the several passages 72.
This flash chamber is designed to provide a rapid heat exchange between the vanes 71 and the refrigerant discharged into it so that the refrigerant is converted from its liquid to its gaseous phase substantially instantaneously. Its volume is also kept at a minimum to insure the discharge of the resulting gaseous refrigerant into the outlet 18 rather than its storage within the flash chamber. To this end it has been found that a flash chamber having a heat exchange surface of approximately 70 square inches (70 l0 square mils) and a refrigerant holding volume of approximately 0.15 cubic inch (150 10 cubic mils) Works satisfactorily. Thus the capacity of the flash chamber for refrigerant is only approximately 0.2% of its heat exchange area (in inches), which corresponds to a voume-to-surface ratio of 2.14 mils. These figures are recited to illustrate proportion and are not to be considered as a limitation upon the actual dimensions of the flash chamber. The functional importance of this will be brought out subsequently.
The heat exchanger may be heated by any suitable means, but because of the nature of the refrigerant and the rapid heat exchange inherent in the structure, a low energy level heat source is all that is required. As illustrated in FIG. 7, the heat source may be a small electrical resistance element '74 mounted at one end of the housing 70. This element is enclosed in a shield 75 and energized through the electrical wiring 76.
FIG. 8 illustrates the flash chamber energized by different means. In this arrangement the housing '70 is surrounded by a jacket 77 spaced from the housing 70 to form a compartment 78 encompassing the housing 70. As illustrated, the jacket is designed to be filled with hot water supplied through the conduit 79 and discharged through the conduit 80. It will be recognized that by enlarging the conduits 79 and 80 to accommodate a gaseous medium, exhaust gases may be passed through the compartment 78 for the purpose of heating the flash chamber 86.
Operation In the system 10 of FIGS. 1, 2, and 3, water is supplied to the solenoid pump 14 through the supply line 12. Electrical power is also supplied to wires 32, 34. If the piston 40 is in its uppermost position, the switch 36 will be closed and the solenoid 30 will be energized. The solenoid 30 then pulls piston 40 downward, and the resulting vacuum in cylinder 22 causes closing of the check valve 24 and opening of the check valve 20. Water is thereupon drawn in from supply line 12 into cylinder 22. When the piston 40 has reached its lowermost position and cylinder 22 is filled with water, the switch 36 opens and the solenoid 30 releases the piston 40. The spring 42 now pushes piston 40 upward, and the resulting pressure in cylinder 22 causes check valve 20 to close and check valve 24 to open. If the control valve 26 is now opened, the pressure exerted by spring 42 on piston 40 causes water to be forced through check valve 24 and control valve 26 into the liquid inlet line 17 of flash chamber 16. Since the heating element has also been eneruntil it vaporizes.
gized by the energizing of wires 32, 34, the heat exchanger 48 heats up. As the water circulates through the heat exchanger in the pattern previously described, the entire water stream is uniformly and gradually heated The resulting steam pressure forces the steam out through the vapor outlet 18, from whence it can be conveyed to apparatus (not shown) suitable for putting it to use.
If it is desired to clean the passages 66, it is merely necessary to remove the end plate 54, dislodge the pins 52, and pull them out. The taper of the pins 52 and of the bores 50 makes withdrawal of the pins 52 easy once they have been the least bit loosened.
In the embodiments of FIGS. 6, 7, and 8, refrigerant is introduced in short bursts into the inlet 17 through an appropriate check valve (not shown). The introduction of the liquid into the flash chamber 86 can be accomplished at a very low pressure. As soon as the burst or charge of liquid hits the vanes 71, however, the liquid is promptly vaporized and its pressure is tremendously increased. This pressure increase closes the check valve in the inlet line 17, thus preventing the admission of further liquid, and forces the vapors created out through the outlet conduit 18. When substantially all of the vapor has been forced out through the conduit 18, the pressure within the flash chamber 86 falls once again to a low level and permits the introduction of the next burst of liquid.
It will be seen that I have provided highly effective heat exchanging means for vaporizing a flowing stream of liquid. As a matter of example, a flash chamber designed to produce one cubic foot of steam per minute at 60 lbs. gauge pressure at a temperature of 307 degrees F. need be little more than 6 inches in length and 6 inches in diameter. Obviously, many modifications of the basic concept herein disclosed are possible, and I do not desire to be limited by the embodiments shown herein, but only by the scope of the following claims.
1. A flash chamber for vaporizing a flowing liquid stream comprising: a thermal source, a liquid inlet, a vapor outlet, and a heat exchanger, said heat exchanger including a liquid flow path connecting said inlet and said outlet, said flow path being divided throughout at least a substantial part of its length into a plurality of passages connected in parallel, said heat exchanger being arranged to surround said thermal source, and said flow path being arranged in a plurality of concentric layers surrounding said thermal source and in such a manner that fluid flowing along said flow path traverses said layers consecutively in a direction toward said thermal source, said flow path being defined by a plurality of bores extending through said heat exchanger substantially parallel to its axis, each extremity of said bores being in communication with an extremity of an adjacent bore, and in which said passages are defined by pins inserted in said bores, said pins having longitudinal grooves formed in their surface.
2. The device of claim 1, in which said bores and pins have a matching taper and are dimensioned so that said pins will seat centrally of said bores in the longitudinal direction when inserted therein; in which removable clo sure means are provided to close the wider end of said tapered bores to permit withdrawal of said pins for cleaning purposes; and in which conduits providing the communication between adjacent bores are also accessible for cleaning upon removal of said closure means.
References Cited in the file of this patent UNITED STATES PATENTS 620,994 Teste Mar. 14, 1899 709,926 Porto-Riche Sept. 30, 1902 1,032,532 Constantinescu July 16, 1912 (Other references on following page) UNITED STATES PATENTS 2,866,885 2,905,447 David Mar. 25, 1919 Garretson July 24, 1951 Arvins et a1. Mar. 30, 1954 5 4,066 Combest Aug. 31, 1954 142,580 Tucker Jan. 29, 1957 of 1880 8 Mcllrath Dec. 30, 1958 Huet Sept. 22, 1959 FOREIGN PATENTS Great Bfitain Apr. 5, 1881 Great Britain May 23, 1920