JPH0228799B2 - - Google Patents

Description

[Detailed description of the invention]

Large capacity thermal or cold storage devices at a certain temperature level range from 85〓 (29.4℃) to 120〓 (48.9℃)
solar heating for building, 200
〓(93.3℃)～250〓(121.1℃) solar Rankine engine or absorption refrigeration device, 30〓(−1.1℃)～60〓(15.6℃)
It is used to operate air conditioners during off-peak hours at -20〓 (-28℃) to 20〓 (-6.0℃), etc. Thermal storage materials used, except in the case of 32〓 (0°C) water, must be carefully mixed in proportions by special equipment and techniques, and kept away from materials that may be subject to corrosion. I have to keep it. Such heat storage materials are bulky and heavy to transport or must be used in contact with heat exchangers having large areas due to their low thermal conductivity. To minimize volume, weight and cost,
Thermal melting of materials with phase changes between solid and liquid has been proposed, tested and used experimentally. The reason is that within the above narrow temperature range 7000~
It can store 12000 BTU/ft ³ of heat, but if only a liquid phase such as water is used, its heat storage capacity is limited to 2000-3000 BUT/ft ³ . The heat of these melting materials, especially hydrated sodium and calcium salts, requires provision to prevent stratification. Most prior art techniques have used air as the heating medium. Such prior art was very bulky due to the required volume of the air duct and required encapsulating the heat in multiple containers due to the multiple air passages requiring a relatively large cross-sectional area. In some cases, the prior art has attempted to utilize liquids as heat transfer media. However, such prior art devices were primarily limited to freezing water in metal tanks, metal plates or metal tubes. However, such metal structures are subject to galvanic corrosion and corrosion which causes rapid deterioration of various components. Additionally, they were expensive, inflexible, damaged by expansion of the phase change material, and heavy and difficult to transport. Other devices required encapsulating the heat in multiple containers and were therefore very expensive. Such prior art heat encapsulation techniques typically use small containers, the walls of which are not insulated since heat transfer must occur through the walls of the containers. Small uninsulated containers were inefficient because undesired heat loss or heat inflow occurred rapidly through uninsulated walls during periods of hot or cold storage. The problem of container inefficiency has increased with the use of large numbers of small containers. This is because these containers inherently have a relatively large surface-to-volume ratio. Additionally, during the transfer of thermal energy to multiple containers, the phase change material (hereinafter also referred to as PCM) begins to melt near the uninsulated walls of each container. The inner region of the PCM is the last to melt. As a result, during most thermal storage cycles,
A relatively large portion of the energy stored is relatively close to the walls of the container. In other words,
An uneven distribution of the stored energy results, with more energy being stored on average near the uninsulated walls of the container where it is relatively easily lost to the surroundings. Thermal energy is carried away during storage by convection of the molten phase change material adjacent the uninsulated walls of the container. SUMMARY OF THE INVENTION Conventionally, there are eight main problems that prevent the use of heat in molten materials, or so-called phase change materials, for practical use in storing thermal energy. These possibilities include equipment costs, small thermal conductivity of phase change materials, corrosion, volume changes during melting, evaporation of water from salt hydrates, supercooling and stratification phenomena of said materials, and transportation costs. It is. The methods of the present invention to solve these eight problems are listed below. 1 Cost of the Equipment The first advantage of the invention is that it allows the use of plastic heat transfer tubes. The relatively low thermal conductivity of plastic heat transfer tubes can be compensated for by the method and apparatus of the present invention by greatly increasing the heat transfer surface, resulting in significant cost savings. 1
Costs can be further reduced since only one or a few tanks are used instead of multiple containers. 2. Low Thermal Conductivity Additionally, thermal conductivity limitations lie in the body of the phase change material, not in the liquid conduit material. Therefore, the large plastic heat transfer area is matched with the properties of the PCM by a large number of small plastic liquid transfer tubes evenly distributed throughout the entire mass of the PCM. The heat flow path is thus kept very short at all points. 3 Corrosion Corrosion is of particular importance if the two metals are present in the salt in any form, since the hydrate of the inorganic salt becomes the necessary medium for the battery. And the metal will corrode rapidly. It is preferred that the tubes, headers and fittings be made of plastic, or any points within the salt, of a corrosion resistant metal such as stainless steel. 4 Volume Change The problem of volume change during melting is greatly alleviated by having the outer container for the PCM and all heat transfer surfaces across the PCM be of flexible plastic material. These are large scale
Furthermore, by connecting with a specific tube, any thermal expansion force can be locally absorbed. However, the basics of the present invention are:
PCM so that the average temperature between the liquid at any point in any tube across the PCM and the liquid in an adjacent tube is approximately equal.
This means that the plastic tube inside is located. This is accomplished by multiple parallel circuits with a U-bend at the end of each circuit, all alternating tubes connected to the supply header, and adjacent tubes connected to the return header. US Patent No. 3751935
Reference is made to the patent specification, which discloses a method of making a uniform temperature ice slab for an ice skating rink. This method has become the primary method of making ice rinks in the United States, and is already sold as ice mat rinks. When water, one of the many PCMs utilized in this invention, freezes into ice, the heat transfer liquid typically enters the supply header and small tube at about 24°C (about -4.4°C); Then about 32〓
(0°C) through a small tube and return header. 24〓 small plastic tube
Adjacent to a 32° plastic tube, the average temperature is 28° (approximately -2.2°C) and ice forms at a rate caused by that average temperature. On the way to the U-bend in each parallel circuit, the temperature in the supply tube is 26〓 (approximately -3.3°C), and the temperature in the adjacent return tube is 30〓 (approximately -1.1°C). ,28〓
have the same average temperature. In the U-bend where the supply and return tubes are connected, the temperature for both is 28〓. Ice is therefore advantageously produced uniformly for all tubes throughout the water tank. The water level rises in the tank because the specific volume of ice produced increases, but the excess water escapes upwards, creating a linkage of ice from one spiral layer to the other. As a result, the lateral expansion force disappears. The rise in water level provides a measure of the extent of the melting process. The excess top water is finally frozen. Similarly, in other PCMs, volume changes are controlled without thermal forces. Generally has a melting point of 32〓 (0℃) or higher
PCM contracts as it solidifies and expands at temperatures below 32°. For PCMs that contract during solidification, the tank must maintain the liquid phase above the tube level by a predetermined amount of volume change contraction.
Filled with PCM. When shrinkage occurs during thawing, the salt has a greater weight than it would have if it were in a sealed tray or tube.
Conveniently it remains in contact with the heat transfer surface. If the salt is in a sealed tray or tube, the shrinkage causes loss of contact between the salt and the upper heat transfer wall, thereby reducing thermal conductivity. 5 Evaporation The evaporation of water from the salt hydrate, which would change the composition and thermal performance, takes place evenly through the sealed plastic wall due to the property of the plastic called "moisture permeability". This means that a salt hydrate sealed in a large number of small plastic containers will eventually change its performance, and this change in performance cannot be recovered except by replacement. In the present invention, one or several relatively large containers are used to hold the salt hydrate with a removable cover;
Water can be poured into the container and any water lost through evaporation can be refilled to the appropriate level mark. 6 Supercooling The main problem with salt hydrates is supercooling, ie, falling below the freezing point without crystallization or freezing. This occurs because when a salt hydrate is heated above its melting point (freezing point), all the crystals are melted and these crystals do not mature or become nuclei when cooled again. Additives have been discovered for many salt hydrates to promote nucleation (U.S. Pat.
2677664 and 2936741). Another very simple method is practical in the case of the present invention, in which the salt hydrate with a melting point above room temperature is kept in several insulated tanks. By providing a very small protrusion from the tank on the outside of the insulation, the salt hydrate in this protrusion or finger is prevented from melting when heat is applied. In this way, frozen crystals are always present and nucleate crystals when the salt hydrate is cooled below its freezing point. For example, the crystallization rate of sodium thiosulfate pentahydrate is about 1 inch/min, so
The foot tank is entirely nucleated in an hour or less when cooling is effected by a heat transfer liquid. 7 Stratification Phenomenon Another problem of salt hydrates that is solved by the present invention is the phenomenon of stratification of solid crystals, which in the case of most salt hydrates are relatively heavy and therefore sink to the bottom. As these salt hydrates fall into relatively warm regions, they often nucleate different hydrate molecular bonds. Because the phase changes in these different hydrate molecules are not congruent, the overall composition changes, resulting in a change in performance. Furthermore,
A permanent deposit forms at the bottom. One solution to this has been to limit the vertical dimension of the precipitate to about 1 inch. In the present invention, straw mats of rubberized hair are used as spacers between the tubes and other inert low density mats. This effectively fills all the space in the tank with a small opening in the form of a filter where there is no room for the crystals to fall. Furthermore, because the double tube uniformly averages the temperature, crystal growth occurs in a uniform manner, eliminating temperature differences that would otherwise occur in one area with large crystals covering another area. In a preferred embodiment of the invention, a small, inexpensive, low output circulation pump and conduit system provides
The molten phase change material can be circulated within a relatively large thermal storage tank. In this way no stratification occurs. 8 Transportation costs On average, a solar-heated house
Required to store 1000000 BTU of heat,
Five tons of PCM at 100 BTU/lb are required and must be transported. In the present invention, the PCM
can be transported in heated tank cars and hosed in liquid form into lightweight tanks and pre-positioned and inspected heat exchange tube equipment. It is well known that the use of tank cars is a much more economical method of transporting and discharging large quantities of liquid to multiple dispensing points than by sealed containers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the invention will now be described in detail with reference to the drawings. Referring to the drawings, FIG. 1 shows a phase change heat storage device 2 that stores and releases large amounts of hot and cold heat per unit volume through the heat capacity of phase change materials. There are many phase change materials and additives that release large amounts of heat during freezing and absorb large amounts of heat during melting when a phase change occurs. Examples of such phase change materials or PCMs are further provided below. The heat storage device 2 consists of an open-topped tank or vessel 4 with semi-flexible walls, preferably of a plastic material capable of providing flexibility and, an important factor, resistance to corrosion. Most PCMs corrode metals. Prior to filling the tank with PCM 24, a preformed roll of flexible tube mat 8 and rubberized bristles 22 is placed into the tank. The mat 8 and the spacer device, e.g. a roll of rubberized hair mat 22, fill the space of the tank and thus within the entire tank.
Both areas are only a short distance from the mat tube that carries the heat transfer liquid 26 for heating (melting) and/or cooling (freezing) the PCM. The heat transfer liquid 26 is water, 32〓(0℃)
If used below, an antifreeze solution such as a mixture of water and ethylene glycol must be used. The flexible tube mat 8 has a small diameter,
For example, they are prefabricated in the factory using injection molded parallel tubes that have an inner diameter of about 1/4 inch and are usually made of synthetic plastic material, such as ethylene-vinyl acetate (EVA), and these tubes are fitted with spacers. - maintained in close and parallel spaced relation to each other by the strip assembly; The spacer strip assembly consists of a rigid plastic strip 12 and a flexible plastic strip 14 which are attached to each other to form a tight pocket for the double tube 10. There is. A more common method of preforming the grid of matte 8 before rolling it is by heat
This is accomplished by a seal. EPDM (ethylene-propylene-diene terpolymer) can be used if the temperature is too high for common plastics, synthetic rubbers or elastomeric compounds. A number of double tubes 10 are arranged parallel to each other at regular intervals (the number of tubes follows the width of the pine grid, a typical width of 4 feet; the number is 32 double tubes). , the double tubes are spaced approximately 1.5 inches from the centerline of one pair of tubes to the centerline of the next pair). A rigid vinyl strip 12 is placed below the double tube 10 and a flexible vinyl strip 14 is placed over the double tube 10 such that the flexible vinyl strip covers the rigid vinyl strip 12. The strip 12 is rigidly attached and aligned with the strip 12. These two strips 12 and 14 are then heat sealed to each other between the double tubes, so that they form a support loop or pocket 15 around each double tube.
As shown in FIG. 2, the support strips 12 and 14 are located at generally equally spaced locations along the length of the grid-like flexible tube mat 8, and are enlarged in FIG. As shown, the mats are heat sealed together as described above before being rolled to provide support for the dual tube 10. These heats 8 are manufactured to desired lengths. Two headers are arranged at one end of the mat 8. The headers are a supply header 16 on one side and a return header 18 on the other side. U at the other end of mat 8
A mold bend 20 is provided to connect the tube ends. Referring to FIG. 2, a flexible tube mat 8 and a spacer device 22, shown as a hair mat, are rubberized onto the top of the flat flexible tube grid 8 on a long table. By arranging the horsehair mats 22 in a relatively long manner, they are rolled up together. The roll is then formed from the U-shaped bent end of the pine, with the first circle being as small as possible (e.g.
Approximately 2″ to 4″ diameter). At the end of the rolling process, the roll is formed with alternating layers of flexible grids 8 of tubes. Also spacer media in the form of low density materials of flexible fibers with relatively large spaces between the fibers, e.g. rubberized bristles 2.
2 are used as well as in pole vault and high jump landing locations. This spacer device 22 serves to space the successive convolutions of the rolled grid-like flexible tube mat 8. The supply header 16 and return header 18 are on the outside of the roll, but as can be seen in FIG. 3, an extension of the spacer mat layer serves to separate the tube from the tank wall. This roll is then placed in the tank 4. Two ports are provided in the tank wall for an inlet connection assembly 27 and an outlet connection assembly 28,
8 is connected to supply header 16 and return header 18 by conventional plumbing methods. For larger tanks, two or more tube mats 8 can be placed end to end and rolled into one large roll as shown in FIG. Rather than using a single relatively long mat, a large number of tube mats 8 can be used in one large roll to limit the pressure drop of the heat exchange liquid 26 circulating within the tubes. The device 2 is equipped with a suitable temperature according to the temperature requirements of the application.
Filled with PCM24. The tank 4 is covered using a plywood or plastic cover 6 and a gasket 9 to prevent dust accumulation on the PCM 24, evaporation and contamination of the PCM, and yet provide a lightweight buoyant heat exchanger. The vessel is prevented from levitating off the relatively heavy PCM when the PCM is in a liquid state. Cover clamp is number 37
, and a removable plug 25 is shown on the cover. A heat insulator 32 is provided around the tank 4. Furthermore, the tank 4 has a nucleating element for the formation of a conduit that projects outside the insulation 32 and is exposed to ambient temperature. The purpose of the nucleation device 30 is to remove the PCM 24 inside the tank 4.
This is to maintain the frozen state of the PCM 24 when the PCM 24 is in a thawed state. These retained crystals in the nucleator 30 are of great help in starting the PCM crystals to avoid overcooling. When there are no crystals within the material, liquefied PCM tends to become supercooled, a condition that is undesirable because it delays the PCM from changing phase and reduces its effectiveness. FIG. 3 is a plan sectional view of FIG. 1, showing how the spacer mats are arranged with respect to the tube grid 8. FIG.
Thinner or thicker mats may be chosen depending on the heat transfer cycle time for heat charging and release of the PCM storage material, thereby varying the length of the tube grid and mat. The details will be explained later. From FIG. 1 the details of the elements can be seen. FIG. 4 shows another heat storage device 2. FIG. The device has a rectangular tank 5, which is preferably made of a thermoplastic material, thereby having properties that are semi-flexible and corrosion resistant to the various compounds used as PCM. can be provided. However, especially if the PCM is water, the tank may be made of metal and a plastic liner or coating layer applied to the metal is used. The rectangular shape of tank 5 is
To facilitate the use of a flexible tube mat 8 without using a spacer material in the longitudinal direction of the tube mat 8. The pine 8 is arranged in different ways by arranging the pine around the spacer rod 40. Rods 40 are arranged in two rows,
One is located near the top of the tank 5, and the other is located near the bottom. In each row, the spacers and support rods 40 are evenly spaced, e.g., about 1.5 inches to 6 inches center to center, and are arranged parallel to each other. The supply header 16 and the return header 18 are arranged on the upper flange of the tank 5, where they are secured in place by header retaining clips 38 attached to the flange wall of the tank 5. . The other end of the mat 8, which has a U-shaped bend 20, is attached to the upper flange of the tank opposite from the header. The U-shaped bend 20 is
It is secured in place on the flange by using anchor strips 36 with the same number of hooked fingers as mold bends.
After assembly, tank 5 is filled with PCM 24.
Although tank 5 has a cover 7 to prevent contamination by evaporation and falling foreign matter, the clamp cover of FIG. 1 is not necessary since the tube assembly is secured by spacer rod 40.
The tank is attached to the insulating surface 34 and the insulating material 3
2, everything around it is insulated. The nucleating device 30 penetrates the insulation 32 to the outside of the tank. As shown in FIG.
0 maintains a certain crystal, and all others,
The PCM 24 is in a molten state inside the tank 5. These captured crystals within the nucleator 30 help initiate the refrigeration cycle without undergoing supercooling. FIG. 5 is a schematic diagram of a heat storage system, which includes a tank 50 containing a PCM that stores thermal energy by latent heat of fusion;
As shown in FIG. 1, there is a pump 52 for pumping heat transfer liquid 26 through a number of small tubes 8 and 10, and various heat input devices on the left and connected to pipes 53 and valves 55. It has a heat output device. Although some valves have been omitted, it will be readily apparent to those skilled in the art how to select the various piping circuits for each heat input and output device. FIG. 5 describes only an exemplary system, in which:
A number of different heat input and output devices are shown for purposes of illustration. As can be seen, any given piece of equipment includes only certain desired input and output devices. Valves 55 are shown as being thermally actuated, and the respective temperatures at which they operate, ie, open and close, are determined by the operating temperatures of the respective heat input and heat output devices utilized in the facility. Selected according to range. Additionally, as will be discussed in more detail below, the PCM used in thermal storage tank 50 is selected to have a melting temperature appropriate for the particular heat output and input devices utilized. For example, the radiant floor heater 80 has a relatively large effective area and therefore operates effectively when the circulated liquid 26 is heated to the appropriate temperature by the PCM within the tank 50. On the other hand, the base board heater 78 has a very small effective area and therefore has a somewhat higher temperature by using a PCM in a tank where the liquid 26 being circulated melts at a corresponding relatively high temperature. It operates effectively when heated to . Has a melting temperature suitable for specific equipment with specific heat input and output equipment
The selection of PCM is explained according to a specific example. For example, from the top left side down, the exemplary heat input devices are: solar collector 54, air coil 56, heat pump 58, electrical resistance liquid heater 60, fossil fuel boiler 62, ice skating ring grid 64, and It has a refrigerator or freezer compartment 66. From the top right side down, the exemplary heat output devices are:
agricultural or industrial processing heater 70, water heater 72,
It includes a heating heater 74 in an air duct, a heat pump 76, a radiating baseboard heater 78, a radiating floor heater 80, a Rankine engine 82, an absorption air conditioner 84, and an air coil or cooling tower 86. Various heat input devices, designated 54-66, are all used to melt the PCM in tank 50 selected to the appropriate temperature level of the heat input device. For example, solar heat collector 5
4, as the fluid 26 is sent from the heat collector 54 to the tank 50, the fluid 26 is heated to 130°C (55.6°C).
Heat until. Pump insulator 57 prevents substantial temperature changes in liquid 26. It should be understood that such pump insulator 57 should be distributed throughout the device, but has been omitted to simplify the drawing. In tank 50, 118
Solid PCM, sodium thiosulfate pentahydrate, which melts at (47.8℃) takes heat from the fluid 26,
The temperature leaves the fluid tank 50 and the collector 54
As the temperature increases, melting is started by lowering the temperature from 130〓 (55.6°C) to a slightly lower temperature, for example, 125〓 (57.1°C). After a few hours, the length of time depends on the total area and spacing of small tubes 8 and 10, the PCM will be removed from tube 3 of the nucleator.
0 is completely melted (Fig. 1). The amount of heat stored in the above example in the tank 50 by the PCM melting at 118〓 (47.8°C) can be transferred to the right heat output device when desired by appropriate valve actuation. Sent by 26. For example, a heating coil within the air duct 74 is selected and then heat is applied to the structure (not shown) by heating air that is circulated through the air duct to the building to be heated. Alternatively, water heater 72 is heated by liquid 26. Similarly, an agricultural or processing heater 70 may be heated, for example, by circulating a heat transfer liquid 26 to accomplish an agricultural use, such as grain drying, or a floor radiant heater 80 may be heated by circulating a heat transfer liquid 26 to accomplish an agricultural use, such as grain drying. It is heated by circulation. If the relatively high temperature PCM, for example 150〓
If trisodium phosphate dodecahydrate, which melts at (65.6°C), or magnesium chloride, hexahydrate, which melts at 243°C (117.2°C) is selected, the solar collector 54 will be effectively utilized and the base - Heat can be supplied to heat extraction devices such as board heaters 78, Rankine engines 82 and absorption air conditioners. For example, the heat pump 76 uses water such as 32〓
Utilizing PCMs that melt at 55°C (12.8°C), such as sodium sulfate decahydrate mixed with chloride as disclosed in U.S. Pat. No. 3,986,969. is most preferred. In other words, approximately 32〓(0℃)~55〓(12.8
It has a relatively low melting temperature in the range of
The PCM is advantageously used to heat the liquid 26 that is used to deliver heat to the evaporator of the heat pump 76. In a similar manner, other heat input devices are preferably connected to a number of heat output devices through the heat storage tank 50. Each example will be explained one by one. Air coil 56 is used to melt ice in tank 50 caused by operation of heat pump 76. The heat pump 58 pumps the PCM inside the tank 50.
Used during off-peak hours at night to melt at 118°C (47.8°C), the PCM then provides heat during the day to the air coil in duct 74 or to the radiant floor heater 80. Electric heater 60 can provide heat to base board radiator 78 to melt the PCM in tank 50 at 150° C. during off-peak hours for use during the day. The fossil fuel boiler 62 has been miniaturized so that it can be used as a direct heating device in churches;
Heat can be stored in the tank 50 in advance and radiated into the church on Sunday morning by means of the radiant heater 80. Ice Rink 64 is kept frozen during peak daylight hours by cold air stored in PCM such as 22% ethylene glycol and water, which melts at -11°C. These PCMs were frozen the night before by the operation of the heat pump 76. Cold storage compartment 66 is similarly cooled by storing cold air from heat pump 76 during off-peak hours. Cooling Tower 86 has PCM of 55〓(12.8
℃) during the night so that it can be supplied to the air conditioner through the air coil 56 during the day. There are many other combinations in which heat storage devices are used. It should be understood that there are multiple heat inlets and outlets connected in various alternating combinations. FIG. 5 only shows by way of example some of the possible heat input and heat output devices that are conveniently used. FIG. 6 is an enlarged sectional view of a part of the heat storage device 2. FIG. The cross-section shows two layers of pine 8 with open wired rubberized bristles 22 spaced approximately 1" apart. The rubberized bristles have very large voids within the pine tissue. The flexible tube mat 8 uses a small diameter double tube 10 to maintain most of the space for the PCM 24 while keeping the layers of the mat 8 properly spaced apart. Manufactured in a factory, the tubes 10 are injection molded of a thermoplastic material suitable for a wide temperature range and are corrosion resistant. Regions 24A of the PCM contain the frozen PCM around the tube during the release cycle to transfer heat. The regions 24B between the tubes show the molten state. During the filling cycle, this is reversed. The heating zone dividing lines 42 are placed at equal distances between the tubes and the heat flow is directed to each In addition, for each pair of tubes 10 connected to the inlet header 27, the tube is cooler during the discharge cycle so that the PCM surrounding the tube is further cooled and filled. PCM surrounding tube during heating cycle
is further melted. Figure 6 shows the vicinity of the midpoint (near the U-shaped bend), so there is almost no temperature difference, and the PCM2 is cooled.
4A is quite balanced. Solid PCM is placed around the tube during the freezing period.
It should be understood that there is and the molten PCM is halfway between the tubes, and during the melting period the molten PCM is around the tubes and the solid PCM is at the midpoint. Since liquids can transfer heat by conduction and convection, ie, within the melting space of the tube, and solid PCM can only transfer heat by conduction, the freezing period takes longer than the thawing period. However, it is not the case that the solid salt has a conductivity that is greater than the combined effect of conduction and convection of the liquid. In the prior art, it is clear that stratification is greatly reduced by stirring, as explained in the problem section above (see US Pat. No. 2,677,664). This agitation is not available when the salt is confined in multiple containers or tanks. In a heat storage system 2 delivering liquid salt in a cylindrical tank and having a depth of about 4 to 5 feet and a diameter of about 2 to 6 feet, when the liquid salt is above its melting temperature, the heat exchanger spiral Through a central vertical conduit tube located in the center of the shaped rolls, there is intensive recirculation that maintains a homogeneous molten state of the mixture to prevent stratification. FIG. 7 shows a vertical axial column pump 88 having a motor mounted at its center in cover 6, which pumps liquid salt 24B vertically downward through conduit tube 92. A central conduit 9 having an impeller 90 capable of
2 is used as a roll core, around which a roll of tube mat 8 is wound together with spacers into a roll. The lower end of conduit 92 is spaced from the bottom of tank 4 at a suitable spacing distance, for example, in the range of about 1/2 to 1 1/4 of the inside diameter of conduit 92. The upper end of the conduit tube 92 is spaced apart from the liquid thermal salt 24B by an appropriate distance compared to the spacing of the lower end above the bottom of the tank.
spaced below the level of The motor for pump 88 is shown as a small motor with a shaft connected directly to propulsion impeller 90. Above the impeller a bearing support 91 is arranged, which spider-like support 91 is attached to the upper end of the conduit 92 and has a number of passages for the liquid to descend downwardly through the bearing support 91. There is. Liquid (molten) salt 24B flows downwardly through conduit 92 pumped by the action of impeller 90, at the bottom of tube 92 the flow spreads outward to the bottom of tank 4 and at the top of conduit tube 92. The flow is raised uniformly by recirculation up to a point where the flow enters the top of the conduit and is again pumped downwardly by the impeller 90. The recirculation flow can ensure that the mixing ratio of water and salt is uniform in the tank when the PCM is in the liquid (molten) state, and therefore also in the subsequent crystallization. As an example of the stratification problem that can be avoided, sodium thiosulfate pentahydrate (melts at 118〓 when pure,
When a suitable commercially available product containing impurities melts at 115°C, excess water tends to rise to the top of the container when it melts. The resulting lack of water at the bottom tends to form water-poor crystals, ie, the crystals are in the hydrate form with a higher melting point than the desired pentahydrate crystals. Furthermore, the tendency to stratify with excess water rising to the top of the container is a progressive phenomenon. Thus, with each successive thawing and refreezing cycle, an increasingly unfavorable 2
Water salt crystals tend to collect at the bottom of the container, and more water tends to collect at the top, until the dihydrate crystal precipitate occupies about 1/3 of the total volume of the material. Similar layering problems occur with PCM and other compositions as discussed above. Such stratification does not occur when liquid (molten) PCM is circulated in the tank 4 by pumping the PCM in the manner shown. A switch is used to automatically operate the pump 88 motor at the appropriate time. In view of the fact that it is preferable for the circulation pump 88 to operate extremely reliably over long periods of time, there are preferred pumping devices that are used to obtain a very high degree of reliability. The motor is a relatively low power single phase AC motor of the variable polarity induction type. Such a variable polarity motor has a relatively small starting torque and a significantly increased operating torque when it is operated at normal operating speeds. As a result, there is no need to use an on/off switch. The variable polarity motor is operated continuously with alternating current, thereby avoiding the problem of switching the motor on and off.
As the PCM solidifies around the impeller 90,
The motor is stopped and the PCM is then melted around the impeller. Due to the low starting torque of the variable polarity motor, the motor does not deform relative to the solid impeller and does not overheat. Almost no electricity is wasted. Immediately surround the impeller
As soon as a local portion of the PCM is melted, the impeller is driven by a continuously operating motor, no matter how long it is constrained by the solid (frozen) state of the PCM. so that it will automatically start rotating again. FIG. 8 shows a flexible tube mat 8 in the form of a grid, the mat 8 being rolled up on a roll with less expensive spacing parts than the mat 22 shown in FIG. A plastic spacing member 94 or plastic pipe, shown as a relatively large diameter tube, is secured to the double tube 10 of the flexible mat 8 by adhesive or heat sealing or mechanical bonding. Space member 94
extend transversely to the length of tube mat 8 and are spaced apart at intervals of about 1 to 3 feet. These components consist of single spaced components that are easily manufactured and assembled. Figure 9 shows tube spacer 94 (Figure 8)
shows the tube grid rolled up into a roll as it is placed in tank 4. Insulator 3
2.Headers 16 and 18, tube nipple 1
7 and the U-shaped bend 2 are identical to those shown in FIG. Spacer tube 94 serves to interchange support strips 12 and 14 as shown in FIGS. 2 and 3. As a result, tube mat 8 consists of double tubes 10 supported by spacer members 94. Dual tube 10 has an inner diameter (ID) ranging from approximately 1/8 inch to 3/8 inch. It is to be understood that the passageway of the tube may be oval shaped if desired. In the embodiment described above, the inside diameter of each pair of tubes 10 is approximately 1/4 inch. Example I The electricity usage company charges $0.060/KWH during non-peak hours from 10 am to 10 pm, and $0.015/KWH from 10 pm to 10 am. A small office building uses 20 tons of cooling water to maintain air conditioning during the summer season from 9 a.m. to 6 p.m. The following shows how operating costs are saved for the storage device according to the invention. The amount of ice required to turn 32〓 of ice into 44〓 of water with a temperature difference of 12〓 is calculated as follows. (a) 12 hours x 20 tons x 12000 BTU ÷ hours/tons ÷
144 BTU/pound of ice ÷ 56 pounds of ice/cubic foot requires 357 cubic feet of ice in a PCM tank 50 or 50A. Diameter 6
The 5-foot tall plastic tank is the largest practical size, holding 120 cubic feet up to a height of 4 1/4 feet. Therefore, three 6-foot diameter tanks are required. The plastic tube space within the ice is formed such that all of the ice melts in 9 hours and all of the water refreezes in 12 hours. This is because when the speed is low, there is the above period. The space determines the total heat transfer area of the helical tube mat installed in the tank and therefore its length. 14 BTU/hr ft ² /〓 was found to be transferred from ice slabs on both sides of the pine up to 1 inch thick. Assuming that there is an average temperature difference of 4 〓 when the ice freezes, the chilled anti-freeze solution will be approximately 24
This means that if you enter with 〓 and exit with 30〓, the average will be 28〓. A cooling suction temperature of about 18° produces the desired temperature pattern. The calculation is as follows. (b) 20 tons x 12000BTU/hour/ton/14BTU/hour/ft ²
/〓/4〓=4.286 ft ² And the pine is 4 feet wide, so a pine placed in three 6-foot diameter tanks has an average of 4286/4 = 1072 running feet. Such a tank has a cross-sectional area of 85ft ² . The spirally wound pine occupies virtually the entire space within the cylindrical tank. Thus, each coil passage has a width of 85/1.072 = 0.079 feet or 0.95 inches. Therefore, in the three tanks 1072 traveling feet is 357 feet per tank.
Provide running feet. Considering pressure drop, pine length should actually be limited to about 90 feet in length. Therefore, more than one pine should be installed in each tank, i.e., 4 pine in the tank, each 89 feet long, or 12 pine, all 89 feet long. should be installed. The spacer material is 0.95" less by the width of the pine which is 0.31", so about 5/8". As another example, we are using 6 pieces of 60 foot long pine and it is the header and U
Although the cost increases due to the need for additional mold bends, the pressure drop can be reduced, more flow can be achieved, and a faster response can be achieved. The current operating cost of air conditioning equipment in orifice building is approximately (c) $0.06/KWH x 12000BTU/hour/ton/746BTU/KW
H×3.0COP = $0.32 ton/hour. This small office building was built for 25 weeks, 9 hours/day at 50% full load for 5 days/week.
Assuming the day works, the calculation would be: (d) 25 x 5 x 9 x 0.5 x 20 = 11,250 ton-hours, or $3,600 cost. Since the refrigerant suction temperature is lower since ice refrigeration is about 18– versus 34– with respect to cooling water, it is assumed that the COP (coefficient of operation) of the refrigeration heat pump is about 2.5 instead of 3.0. The cost is calculated as follows. (e) $0.015 x 12000/746 x 2.5 = $0.096/ton-hour and for 11250 tons-hour the cost is $
It is 1080. Compared to operating without storage in a small office building, this represents a savings of $2,520 per year, or a 70% savings. Examples use sodium thiosulfate pentahydrate. That is, this phase change material PCM-118 is
Melts at 118〓 or 115〓 in case of certain impurities, requires 5000 BTU/hour at 0〓 during an average temperature of 30〓 in the house one cloudy day and two nights Heat can be stored in between. Since the calculation base is 65〓, 35/65× in 40 hours
50000 or 26923 BTU/hour or 1076920 BTU should be stored. With a latent heat of 928 BTU/lb and a heat sensitivity of 100 and 135 of 18 BTU/lb, 1076,920 BTU divided by 110 BTU/lb indicates that 9790 lb of salt is required. Since the salt is suitably filled in one or more tanks 50 at the factory, the weight of the filled container is a factor. That is, the practical limit for transporting and moving underground a house is about 1000 pounds. PCM-118, which has a specific gravity of 1.6, can weigh approximately 1,000 pounds and store more than 100,000 BTU in a 2-foot-diameter, 4-foot-tall plastic container. Ten such tanks 50 are required in this embodiment and can provide approximately 1100000 BTU.
The heat transfer liquid from the solar collector enters the tank at about 130〓 and leaves at 116〓, averaging 123〓 and thus 8〓 higher than the melting point of 115〓. In other embodiments, the opposite is true; filling the tank 50 involves entraining molten liquid around the tube, which molten liquid facilitates heat transfer by liquid convection. It takes two daylight days to fill the tank with heat, at a rate of 900 BTU/ft ² /day from the collector.
Moreover, assuming 25,000 BTU/hour, it is necessary to heat the house for 8 hours during the day, and then 1,276,000 BTU is 1,476,000/900 × 2 of the heat collector.
= 820ft ² is required. Filling time is 16 hours (2 days with 8 hours solar) and discharge (frozen)
The time is 40 hours. PCM-115 has a thermal conductivity about 1/3 lower than ice, with a moderate overall coefficient of about 5 BTU/hr/ft ² /〓 from both sides, or an overall coefficient of 10 when the salt is solid. . The partial liquid phase is relatively high, but can also be the same. The calculation of the pine area is as follows. 1076000BTU/10BTU/hour・ft ²・°F×8〓×16 hours=84
0ft ² and is a 4 foot tall pine with 210 running feet divided into 10 tanks or 21 feet long per pine.
Since the ten tanks 50 are each 2.0 inches in diameter, their area is 3.14 ft ² and 3.14 ft ² /21 feet = 0.15 feet = 1.8 inches is the width of each coil passage in the helix. Subtracting the pine thickness of 0.3 inches, the spacer material is 1.5 inches thick. Since the salt shrinks as it freezes, there will be more molten salt than covers the tube, and the frozen salt will be within the height of the tube in tank 50. The header 16 is made of ABS (acrylonitrile).
It is made from plastic pipe made of butadiene styrene (butadiene styrene) or CPVC (chlorinated polyvinyl chloride) with ABS or CPVC nipples 17 glued to the header, and has low cost and adequate heat and corrosion resistance. The mat tube is made of media or high density polyethylene with butyl rubber to add flexibility to help create a tight sealing joint. stainless·
The steel V-bend and stainless steel tube clamp are metal only to avoid galvanic corrosion. In the above embodiment of the house, the PCM thermal storage tank can be placed underground. Such insulated tanks are mounted outside a suitable foundation house or other building such as a concrete pad. PCM Examples Listed below are various PCM materials with their respective melting points that are useful and economically inexpensive. As mentioned above, practical materials contain a minimum of impurities that slightly change the melting point;
The following list should therefore be understood from a practical point of view.

【table】

【table】

[Table] Examples of heat transfer liquids When used below 32〓, a mixture of water and an antifreeze agent such as ethylene glycol. When using at 32〓 to about 210〓, add water. For use above the boiling point of water, there are a number of heat transfer fluids already commercially available. Ethylene glycol is used up to approx. They are Dowtherm heat transfer liquids, sold by Dow;
Therminol heat transfer liquid sold by Monsanto
and Caloria heat transfer liquid sold by Exxon. Another Example of Refrigeration Another example of an apparatus in which off-peak refrigeration is advantageously used is for cooling freezer cases in a supermarket. The PCM effectively used in this device is sodium chloride hexahydrate, which melts at 12ⓓ. Freeze a suitable amount of this material overnight during the night when electricity costs are low. Then, when electricity rates rise during the day, various refrigerator cases are cooled using the mixture of water and ethylene glycol as a heat medium. The examples presented herein illustrate various devices made of phase change materials for thermal energy storage according to the present invention. These examples are for special uses,
It is not limited to dimensions or materials. Those skilled in the art can easily make various design changes to the technology covered by the technical scope of the claims.

[Brief explanation of drawings]

1 is a front view of a heat storage device showing in cross section a cylindrical open top tank with helical tubes and spacer mats; FIG. FIG. 3 is a cross-sectional view of a helical tube grid and spacer mat placed in an insulated cylindrical tank and rolled up; FIG. FIG. 5 is a cross-sectional view similar to FIG. 1 of a heat storage device showing a rectangular tank with tube mats stretched around spacer bars and extending vertically up and down; FIG. Schematic circuit diagram showing a heat storage device piped to a heat output device; FIG. 6 is an enlarged section showing a portion of the device of FIG. 1 showing the tubes, spacer material and partially frozen phase change material; A cross-sectional view, FIG. 7, is a front view of a heat storage device similar to that shown in FIG. 1, but with a circulation pump to prevent stratification, FIG. FIG. 9 is a front view showing a flexible tube grid rolled up using tube spacers instead of using the mats shown in the figure, and FIG. 1 is a sectional view of a helical tube grid thus constructed and placed in an insulated tank; FIG. 2... Phase change thermal/cold storage device, 4... Container (tank), 5, 50... Tank, 8... Flexible tube.
Grid, 10... double tube, 12... rigid plastic strip, 14... flexible plastic strip, 22... hair mat (spacer device), 26... heat transfer liquid, 20... U-shaped bend, 1
6... Supply header, 18... Return header, 24...
PCM (phase change material), 40...Spacer rod, 5
8,76...Heat pump.

Claims (1)

[Scope of Claims] 1. In a heat exchange system capable of transferring heat of fusion of a phase change material between a moving heat transfer liquid and a stationary liquid or solid phase change material, the above and below melting points of the phase change material in a tank an insulating tank formed of a material capable of withstanding temperatures of 4, 32; 5,
34; 50 and small diameter flexible plastic conduits 10 spaced apart within said tank to provide a number of parallel liquid circuits through which said heat transfer liquid flows. a phase change material 24 substantially filling said tank and surrounding said grid of plastic conduits, the area at the top of said tank being configured to absorb expansion and expansion of said phase change material within said tank. The phase change material is absent to accommodate shrinkage, and a liquid supply header and a liquid return are connected to the grid of plastic conduits to transport the heat transfer liquid 26 into and out of the conduits. The grid, which includes headers 16 and 18 and is formed of flexible plastic conduits, provides a generally uniform transfer of thermal energy between the heat transfer liquid in each conduit and the phase change material across the tank. The heat transfer liquid 26 is arranged to flow in opposite directions in adjacent conduits within the grid to provide a heat transfer liquid 26, and the plastic conduits are horizontally spaced generally evenly apart from each other in order to a spacer device 22, 40 or 94 provided within the tank in association with the grid to facilitate flow of the phase change material in liquid form within the tank; A device characterized by being adapted to uniformly melt or freeze. 2. The grid of small-diameter flexible synthetic resin conduits arranged at slight intervals is rolled into a spiral roll shape when viewed from above and below. equipment. 3. The spacer device comprises a flexible synthetic resin conduit and a non-corrosive, highly spaced lightweight mat rolled into the spiral roll configuration. equipment. 4. According to claim 2, the spacer device comprises a plurality of spacer members extending transversely to the conduit and substantially vertically within the tank. The device described. 5. the liquid supply and liquid return headers extend generally vertically within the tank, and each of the conduits extends in a generally horizontal plane of the helix with a machine direction turn point near the center of the helical roll;
The liquid in each conduit flows in a substantially horizontal plane from said supply header along an inner helical passageway to a flow direction turn point, and then flows in a substantially horizontal plane along an outer helical passageway to said return header. Apparatus according to claim 2. 6. Said spacer device comprises two rows of spacer rods, one row of equally spaced rods being near the top of said tank and the other row of said equally spaced rods being near the top of said tank. Claim 1, characterized in that said grid of small diameter flexible plastic conduits located near the bottom and spaced apart by small distances extends up and down over said spacer rods. The device described.