BACKGROUND OF THE INVENTION

1. Field of the Invention.

[0001] The present invention relates to devices used to cool an interior volume such as, but not limited to, a refrigerated truck. More particularly, the present invention relates to improvements on the configuration of existing cold beams and plates used as eutectic heat exchangers. Still more particularly, the present invention relates to eutectic heat exchangers configured to improve heat transfer between the eutectic material and the exterior of the eutectic surface of the eutectic material container.

2. Description of the Prior Art.

[0002] Containers primarily in the form of beams and plates are a means of refrigerating interior volumes such as, for example, truck bodies. The container is made of a thermally conductive material. A eutectic material in the form of phase change material (PCM) is contained within these containers. The PCM is of the type known to those skilled in the art and may include, but not be limited to, water containing salt, which has a lower freezing temperature than water. The PCM is conditioned to a temperature that enables the absorption of heat that exists within the interior volume, such as heat from the interior of a truck body. The latent heat of the PCM provides the container with a high heat absorption capacity. Mechanical

refrigeration is generally used to chill the PCM to a temperature that is below the transition point, generally from a liquid to a solid but it may also be from a gas to a liquid. For this purpose, internal refrigerant tubing is placed within the PCM inside the container. The refrigerant tubing is used to transfer heating and cooling energy to and from the PCM.

[0003] Refrigerant is initially run through the tubing to cool the PCM to a very cold liquid or even a solid. As the container containing PCM absorbs heat from its surroundings, its phase changes from liquid or solid, and water vapor in the atmosphere around the container may condense and freeze on the container’s exterior surface. The accumulated frost must be removed periodically. Most often this is done by running hot refrigerant gas through the refrigerant tubing within the PCM, which heats the PCM until the exterior surface temperature of the container is above the freezing point of the condensed and frozen water vapor, causing the ice to melt and drain away.

[0004] Because the PCM must be heated to temperatures well above the freezing point of water, this method is thermally inefficient, for the added heat must then be removed, increasing the amount of refrigeration that is needed to return the PCM to its desired cooling temperature. This heating and re-cooling of the PCM is not only inefficient, it is time consuming and a costly aspect of the eutectic cooling function.

[0005] Weight is also a problem with the current beam and plate designs of the PCM containers. This is especially true for the plate form of the container, which is fabricated from heavy gauge carbon steel sheets. Any added weight is detrimental to the economic operation of a refrigerated truck, for it increases fuel cost and reduces payload.

[0006] Therefore, what is needed is an improved eutectic heat exchange apparatus that enables better cooling and vapor removal functionality than currently exists. What is also needed is such a better eutectic heat exchange apparatus that does not add unnecessary weight to a vehicle or other structure that requires interior volume cooling.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide an improved eutectic heat exchange apparatus that enables better cooling and vapor removal functionality than currently exists. It is also an object of the present invention to provide such a better eutectic heat exchange apparatus that does not add unnecessary weight to a vehicle or other structure that requires interior volume cooling.

[0008] These and other objects are achieved with the present invention, which is a eutectic heat exchange apparatus including a eutectic material container and a refrigerant conduit external to the container and the PCM. The apparatus may also include one or more optional internal heat transfer elements and one or more optional external heat exchange elements.

[0009] The apparatus includes a container body having an interior and an exterior. The PCM is retained in the interior of the container body and a refrigerant conduit is positioned adjacent to the exterior of the container body. This is in contrast to the existing eutectic devices that locate any refrigerant conduit inside the eutectic material container body. In an embodiment of the invention, the container body is double walled with an internal wall and an external wall, wherein the internal wall has an interior surface and an exterior surface, and the external wall has an interior surface and an exterior surface. The container body is used to contain the PCM within the internal wall. A plurality of refrigerant conduits are located between the exterior surface of the internal wall and the interior surface of the external wall, wherein the plurality of conduits are arranged to transport the refrigerant therethough, which refrigerant is used to cool the PCM and heat the external wall of the container body. The apparatus also has one or more optional internal heat transfer elements coupled to the interior surface of the internal wall of the container body and arranged to extend into the PCM in the container body to enhance heat exchange with the PCM. The optional internal heat transfer elements may be employed dependent upon the size of the container body. They may not be necessary for a relatively small container body.

[0010] The form of the apparatus with a double-walled container also includes a plurality of partitions positioned between and joined to the internal wall and the external wall of the container body, wherein the plurality of partitions may establish with the internal wall and the external wall the plurality of conduits. Optionally, the apparatus includes one or more external heat transfer elements coupled to the exterior surface of the external wall of the container body and arranged to extend into an environment surrounding the container body. The optional external heat transfer elements may be employed when only natural convection exists in the space to be cooled. One or more end caps are coupled to the container body and arranged to seal the PCM within the container body. The one or more end caps include a refrigerant inlet port and a refrigerant outlet port in fluid communication with the plurality of microchannels. The container body may be a cylindrical ring shape but not limited thereto.

[0011] The apparatus of the present invention provides a more efficient arrangement for eutectic material cooling and external surface frost removal than is possible with existing eutectic refrigeration systems. It includes a PCM container body and one or more refrigerant conduits located outside of the PCM container body and arranged to enable heating of the exterior of the container body to facilitate removal of frost located on that exterior. The invention is further defined by the following detailed description, accompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIG. 1 is a side view with partial cutaway of the eutectic heat exchange apparatus of the present invention.

[0013] FIG. 2 is a cross sectional end view of the eutectic heat exchange apparatus.

[0014] FIG. 3 is a cross sectional side view of the heat exchange apparatus.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0015] A eutectic heat exchange apparatus 10 of the present invention is shown in FIGS. 1-3.

The apparatus 10 includes a container body 12, one or more optional internal heat transfer elements 14, one or more optional external heat transfer elements 16, a plurality of partitions 18, and enclosures 20 and 22. The container body 12 is shown in the form of a cylinder; however, it is to be understood that the container body 12 may be of a different shape, such as a polygon form, for example. The container body 12 is double-walled, with an internal wall 24 joined to an external wall 26 by the partitions 18. The number of partitions 18 is selectable and their placement is also selectable.

[0016] The use of a double-walled container body configuration in combination with the partitions 18 provides satisfactory structural integrity for the apparatus 10 while minimizing the weight of the apparatus 10. That is, they form a honeycomb-like construction that is both rigid and light weight. The components of the apparatus 10 are made of one or more materials suitable for carrying out the function of a eutectic cooling device. They are capable of conducting heat within the container body 12 and external to the container body 12. For example, the components may be made of a steel alloy but not limited thereto.

[0017] The end caps 20 and 22 are joined to first end 28 and second end 30 of the container body 12 in a manner that is sufficient to maintain a liquid-tight seal of the container body 12 throughout all operations of the apparatus 10 when used to cool an interior volume over a commercially reasonable life expectancy. For example, the enclosures 20 and 22 are

permanently or removable joined to ends 28 and 30 of the container body 12. Interior 32 of the container body 12 with the retainers 20 and 22 joined thereto is arranged to contain therein a PCM 34. The PCM 34 may be any sort of eutectic material suitable for the specific cooling functionality desired.

[0018] The one or more optional internal heat transfer elements 14 are joined to, and extend from, interior surface 36 of the internal wall 24 of the container body 12 into the PCM 34. The number of internal heat transfer elements 14, the extent to which they extend into the PCM 34, and their placement in the PCM 34 is selectable as a function of the desired rate at which the PCM 34 is to be cooled or heated. The optional internal heat transfer elements 14 may not be necessary if the size of the container body 12 is relatively small and heat transfer to and from the PCM 34 would not be significantly enhanced by their presence.

[0019] The one or more optional external heat transfer elements 16 are joined to, and extend from, exterior surface 38 of the external wall 26 of the container body 12 to the environment surrounding the container body 12. The number of external heat transfer elements 16, the extent to which they extend outward to the surrounding environment, and their positioning on the exterior surface 38 of the external wall 26 is selectable as a function of the desired rate at which cooling occurs. The external heat transfer elements 16 are optional in that the apparatus 10 can be used to cool an interior volume without them. They may be useful when only natural convection exists within the interior space to be cooled. They may be less necessary or unnecessary when forced convection is employed. The internal heat transfer elements 14 and the external heat transfer elements 16, which are shown in the figures as fins but which may be of other shapes and configurations, extend the heat transfer surfaces associated with PCM cooling and heating. This added surface area improves the rate of heat is absorbed from the surrounding environment by the PCM 34.

[0020] An aspect of inclusion of a double-walled configuration of the container body 12 with the partitions 18 is that the space between partitions establishes a plurality of conduits 40 between adjacent partitions 18. The configuration of each conduit 40 is defined by the partitions 18, exterior surface 42 of the internal wall 24 of the container body 12 and interior surface 44 of the external wall 26 of the container body 12. The conduits 40 are narrow passages that may be used to transport refrigerant such as a refrigerant vapor indirectly to and from the PCM 34. The substantial heat exchange surface area provided by the internal heat transfer elements 14 from the microchannels 40 through the internal wall 24 to the PCM 34 results in a highly efficient heat transfer mechanism for cooling with the refrigerant in the conduits 40 the PCM 34 within the container body 12. In addition, the position of the conduits 40 adjacent to the external wall 26 results in a highly efficient heat transfer mechanism for warming with the refrigerant in the conduits 40 the external wall 26 of the container body 12 so that any accumulated frost on the exterior surface 38 can be quickly melted without the need to also warm the PCM 34. [0021] To chill the PCM 34, the refrigerant is evaporated at low temperature and pressure.

Locating the refrigerant conduits 40 outside of the PCM 34, rather than internally within the PCM 34 as exists with present eutectic systems, serves a number of purposes. First, heat transfer area is increased, and the rate at which heat can be added or removed from the PCM 34 is greatly enhanced. Compared to the surface area of a thin tube embedded in the PCM 34, this design offers the entire internal surface area of the enclosing container body 12, an increase of greater than 100% more efficient than existing systems. Heat transfer is further enhanced as needed by inclusion of the optional internal heat transfer elements 14 when the volume of the interior space of the container body 12 dictates such inclusion. It should be appreciated that the thermal conductivity of eutectics is quite low, especially in the frozen state. Low conductivity inhibits the rate of heat transfer to and from the PCM 34 within the container body 12. The internal heat transfer elements 14 are highly conductive and penetrate deep into the PCM 34, greatly increasing the rate at which heat can be transferred to and from the PCM 34, particularly when the interior dimensions of the container body 10 are substantial.

[0022] The air-side heat transfer or film coefficient is also quite low in conventional eutectic systems. In fact, it is the greatest barrier to the transfer of heat from the surrounding environment to the PCM 34. To overcome this resistance particularly when only natural convection exists in the volume to be cooled by the apparatus 10, the external surface area of the container body 12 is extended by inclusion of the optional external heat transfer elements 16, which project into the surrounding environment.

[0023] As noted, the partitions 18 add considerable strength to the container body 12 to make that a rigid structure. The partitions 18 also conduct heat between the internal wall 24 and the external wall 26 and render the temperature gradient across the shell that is the container body 12 negligible. Also as noted, the conduits 40 play an important role in the removal frost. Rather than evaporating refrigerant, superheated refrigerant gas may be injected into the conduits 40, directly heating the surface on which frost has accumulated. This promotes a very rapid and efficient defrost with minimal heating of the PCM 34 needed. Defrost time is reduced as is the required thermal energy.

[0024] The retainers 20 and 22 include refrigerant transfer rings 50 and 52 and PCM retention caps 60 and 62. The rings 50 and 52 are configured to contain the refrigerant charge and provide the means by which liquid or hot refrigerant gas enter and exit the conduits 40. As shown in FIGS. 1 and 3, ring 50 includes a refrigerant inlet port 42 and the ring 52 includes a refrigerant outlet port 44. Refrigerant 46 from a source that is coupled to the inlet port 42 is delivered from an open source or in a closed system through the inlet port to the conduits 40, passing between the internal wall 24 and the external wall 26 of the container body 12. The refrigerant 46 exits from the conduits 40 via the outlet port 44. The PCM retention caps 60 and 62 are arranged to retain the PCM 34 within the interior of the container body 12. That is, they cover the entire ends 28 and 30 of the container body 12. The refrigerant retention ring 50 and the PCM retention cap 60 may be permanently or removably joined together such as by press fit, bonding or brazing. The refrigerant retention ring 52 and the PCM retention cap 62 also may be permanently or removably joined together such as by press fit, bonding or brazing.

[0025] Making the components of the apparatus 12 of extruded aluminum makes the apparatus 10 a relatively lightweight design. In particular, using the ratio:

(total thermal energy absorbed) / (total weight)

as a measure, a weight reduction of 40% or more can be realized with the double-walled container body 12 configuration, decreasing significantly vehicle fuel cost and increasing significantly payload capacity.

[0026] While the present invention has been described with reference to a specific example of the configuration of the container body 12 and its related components, it is to be understood that the invention is a broader concept defined by the following claims and reasonable equivalents.