Patent Publication Number: US-6212901-B1

Title: Dry ice cooler

Description:
FIELD OF THE INVENTION 
     Coolers, that is, containers that maintain a lower temperature than the surrounding atmosphere. 
     BACKGROUND OF THE INVENTION 
     The earliest cooler may have been a shaded basket. Since then dramatic improvements have been made to the design. These improvements stem from three basic technological advances: Availability of insulating materials, better manufacturing, and the ability to pump heat from liquids or gases which are then used to keep the inside of the container cool. 
     Insulating materials that are available all reduce heat transfer between their sides, and are built to suit their intended uses. These materials include walls separated by vacuum (to prevent convection) or a solid foam or simply by air. They likewise may include reflective surfaces (to reflect radiated heat). 
     Construction advances allow the insulating material to fit seamlessly to become a container. Construction also makes coolers practical in a wide variety of uses, despite the relative fragility of insulating materials, because the insulating material is housed in excellent casings. 
     Cold materials, including most commonly ice, are then put into the cooler to maintain the lower temperature. The cold material will be at a lower temperature than the atmosphere surrounding the cooler. When heat gets through the insulating material into the cooler, raising its temperature, the cold material absorbs that heat. The cooler will therefore reach a stable temperature lying between that of the outside atmosphere and that of the cold material. Where exactly the temperature lies in that range depends on several factors including contents of the cooler, efficacy of the insulating material, and surface areas. 
     The most effective cold materials are not only cold, but have had the latent heat of a state change extracted from them. For example, to become ice the latent heat of freezing is extracted from water. Thus, the best cold materials change state as they absorb heat Most often this means that they melt, but they may also liquify or even sublimate. 
     This is only one major problem with ice. It turns back to water, which floods the cooler, and makes it difficult for the remaining ice to keep the cooler cold. The second major problem with ice is that it is not cold enough. That is, because it changes state at 0° Celsius (32° Fahrenheit), this (and only rarely lower) is the temperature that it draws the cooler toward. As explained above, the cooler generally does not reach the temperature of the cold material; and thus, when cooled by ice, the cooler will not keep frozen foods frozen. 
     The problem that ice turns to water (spillage) has been inadequately solved several ways, including holding the ice within its own container, which reduces its surface area and cooling properties. The relative warmth of ice&#39;s freezing point has not been solved. 
     Colder materials, that is, materials that change state at lower temperatures, obviously will hold the cooler colder. For example, dry ice sublimates at −77.2° Celsius (−107° Fahrenheit). This takes care of any problems with messy melted dry ice spillage but produces CO 2 , which is corrosive. 
     Another problem with dry ice is too much cooling ability. It can drop temperatures below freezing, as follows from the explanation above, which might be colder than desired. A related problem is its uneven cooling; that is, as a block of dry ice, such as that produced by U.S. Pat. No. 5,528,907, which is incorporated by reference for its information on the properties of CO 2 , shrinks, its cooling ability drops. 
     What is needed is a way to control the rate of heat transfer to a block of dry ice, and to use such a block in a cooler in a commercial and practical manner, which allows the cooler to hold a temperature below or above freezing, as desired by its owner. This allows a cooler with separate chambers for frozen and not frozen foods, that is, to perform like a fridge. 
     SUMMARY OF THE INVENTION 
     A cooling assembly being a structure into which a cold material is inserted in contact with a transfer element through which heat transfers, which heat transfer is adjusted by covering the transfer element more or less. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the apparatus of this invention will be described in detail below in connection with the following drawings, in which like numbers refer to like components: 
     FIG. 1 is an orthogonal view of a cooler incorporating features of the present invention; 
     FIG. 2 is a side elevation of the cooler of FIG. 1; 
     FIG. 3 is a bottom elevation of a lid of the cooler of FIG. 2, taken along line  3 — 3  of FIG. 2, showing an example of the heat transfer control feature of the present invention; and 
     FIG. 4 is a sectional view taken along line  4 — 4  of FIG. 3, showing a cavity in the lid shown in FIG. 3, into which cooling material is inserted, including a cover and a controlled heat transfer assembly. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is preferably incorporated into a cooler, generally referred to in FIG. 1 as  10 . A typical cooler  10  which is available from a variety of sources has an outer insulating wall, generally referred to as  12 , and a chamber, generally referred to as  14 , inside these walls. This chamber  14  is preferably suitable to have water ice poured in to it, that is, its inner walls  16  are preferably waterproof. 
     In this preferred embodiment the cooler  10  has a second chamber, generally referred to as  18 , adapted to use at colder temperatures than chamber  14 . It is practical that the walls  20  of chamber  18  be likewise waterproof. Although a cooler  10  with two chambers, is shown in FIG. 1, the present invention is equally suited to single or more than two chambered coolers, and can likewise be used in other situations where convenient, adjustable cooling is required, including soft pouches that need cooling, hard-to-reach places in aircraft, ships, spaceships, electronics and computers, and other applications. 
     In this two-chambered preferred embodiment, a larger lid  22  is attached by hinges  24  to the walls  12  of the cooler  10 . This lid  22  closes over the opening, generally referred to as  26 , on top of the chamber  14  and insulates and seals that chamber  14  from the surrounding atmosphere. 
     The lid  22  has an opening or cavity, generally referred to as  28 , preferably through its side, although opening  28  can be through any side of any structure incorporating the cooling assembly being described. This opening  28  has a preferably insulated cover  30 , which is designed to fit snugly inside the opening  28 . 
     A cold material such as a dry ice block created following U.S. Pat. No. 5,528,907, which is incorporated by reference, is inserted through insertion opening  28  and serves to draw heat from the chamber  14  through an opening, generally referred to as  32 . In this preferred embodiment this heat transfer passes through a plate  34 . This plate  34  may be a {fraction (1/16)} inch thick plate of aluminum, or other material determined through tests and calculations to have heat transmission properties desired for the application to which a cooling assembly is being suited. Plate  34  need not be a plate, but can be any element that has heat transmission properties desired; or plate  34  might simply be omitted. 
     In this preferred embodiment using a plate  34 , the material and thickness of the plate  34  may be estimated using the formula:            Heat                 Flow     =     K          (       t   1     -     t   2       )     Thickness         ,                   
     where K is a constant for the material (for example, 237 for aluminum), t 1  is the higher temperature, t 2  is the lower temperature, and thickness is the thickness of the material through which heat is flowing. 
     Once a material for plate  34  is chosen, the actual heat flow through plate  34  from its exterior surface to its cavity surface may preferably be regulated by adjustable sliding cover  36  adjacent the exterior surface to cover, partially uncover, or completely uncover the plate  34 . Cover  36  travels between an open position substantially uncovering the exterior surface and a closed position in which the exterior surface is at least partially covered by the adjustable cover. Cover  36  is preferably made of insulating material that serves to better prevent heat transfer through it and therefore through the underlying plate  34 . 
     A two chamber cooler  10  will preferably have a second lid  38 , which again preferably matches the size of the chamber  18  that it closes. 
     FIG. 2 is a side view of the cooler  10  of FIG.  1 . Commercial coolers  10  commonly have handles  40  for the convenience of their owners. Also, if the cooler  10  is designed to also accept water ice, in combination with other cold materials such as dry ice or alone, then it is convenient to have a pour spout  42  toward the bottom of the cooler  10  for pouring out the inevitable water. 
     FIG. 3 is a bottom view of the lid  38  taken along line  3 — 3  of FIG.  2 . FIG. 4 is a sectional view of the lid  38  taken along line  4 — 4  of FIG. 3, and shows details of the construction of a preferred embodiment of a cooler assembly. In this embodiment the lid  38  is built using a shell  42  of a casing material such as hard plastic, steel, or the like. This shell  42  surrounds, contains, and protects a filling or layer of insulating material  44  such as foam, air, foamed fiberglass, steel, aluminum, or even a vacuum. 
     A cavity, generally referred to as  46 , is opened into the lid  38 , into which the cold material is inserted, followed by a cover or lid, generally referred to as  48 . Cover  48  is made of an outside shell  50  or casing  50  for which the above materials may be used surrounding an insulating layer  52  or filler  52  selected from the materials likewise listed above. This cover  48  is preferably designed to fit the opening, generally referred to as  54 , of the cavity in the lid  38  snugly to prevent heat transfer into the cold material  56  that is not mediated and regulated by the plate  34  and cover  36 , which themselves block a second opening, generally referred to as  58 , into the cavity  46 . 
     The cooling assembly is shown in the lid of a cooler. Because of uneven cooling and convection, and well as limiting contact of cooled materials with the plate  34 , thereby excessively cooling the materials in contact with the plate, this is the preferred placement. Those skilled in the art will know to implement equally suitable placements, which may require grilles to distance the cooled materials from the plate  34 , or may require ventilation shafts or even passive or active valve systems.