Patent Application
20180266746
The present invention relates to a heat insulating container that maintains the temperature of a specific object requiring temperature control, and to a method for producing the same.
A thermal storage medium melts when having its temperature arriving at a melting point due to a phase change from the solid phase to the liquid phase while absorbing heat. A thermal storage medium solidifies, on the other hand, when having its temperature arriving at a freezing point due to a phase change from the liquid phase to the solid phase while radiating heat. A thermal storage medium with such functions is effectively used as a heat insulator that maintains a certain temperature. A heat insulating container including such a thermal storage medium as a component has been developed (see, for example, PTLs 1 to 3).
PTL 1 discloses a container that maintains a certain temperature using two types of thermal storage media. This container maintains the temperature of an object using a phase change of only one of the thermal storage media at an intended temperature.
Specifically, the thermal storage media are laminated one on the other in the form of two layers to surround a thermally-insulated object. At an intended temperature, the inner thermal storage medium is in the solidified state and the outer thermal storage medium is in the melt state. When the outside temperature falls below an intended target temperature, and the temperature fall allows the temperature of the outer thermal storage medium to arrive at the freezing point, this container blocks flow in of the cold by the solidification of the outer thermal storage medium to maintain the temperature of the thermally-insulated object. This structure thus uses the phase change of only one thermal storage medium for maintaining the temperature of the object.
PTL 1: Japanese Patent No. 5402416
PTL 2: Japanese Unexamined Patent Application Publication No. 9-68376
PTL 3: Japanese Unexamined Patent Application Publication No. 2007-118972
However, a heat insulating container, such as the above container, that uses only one thermal storage medium for maintaining the temperature of an object may have an insufficient temperature maintaining function. When a heat insulating container having such a structure is to maintain the temperature of a thermally-insulated object, the heat insulating container radiates heat all at once. Thus, the heat insulating container maintains the temperature of the thermally-insulated object within an allowable range only for a short period, and may fail to maintain the temperature of the thermally-insulated object within a specific range for a long period.
For example, during transportation of a vaccine under controlled temperatures, the temperature of the vaccine needs to be controlled for a predetermined period within a narrow allowable range of 2 to 8° C. If the thermally-insulated object has its temperature fall below the allowable range as the heat radiation fails to continue for a fully long time at the time of solidification of the thermal storage medium, the vaccine would impair its intrinsic function.
The present invention is made in view of the above circumstances, and aims to provide a heat insulating container that can maintain the temperature of an object for a longer time by dispersing the effect of temperature rises resulting from heat radiation, and a method for producing the same.
In order to achieve the above object, a heat insulating container according to the present invention is a heat insulating container that maintains the temperature of a specific object requiring temperature control. The heat insulating container includes a first thermal storage medium, disposed to surround a center portion of the heat insulating container in which the object is placed, and a second thermal storage medium, disposed to surround the outer side of the first thermal storage medium. The first and second thermal storage media are both liquids at an intended target temperature of the object. The first and second thermal storage media have freezing points adjacent to and higher than a lower limit of an allowable temperature range of the object including the intended target temperature.
The two thermal storage media disposed as separate layers that surround an object cause, sequentially from the outer thermal storage medium, the phase change of solidification to radiate heat. This structure can thus extend time for which the temperature of the object is maintained by dispersing the effect of temperature rises resulting from the heat radiation.
The present invention can maintain the temperature of an object for a longer time by dispersing the effect of temperature rises resulting from heat radiation.
Embodiments of the present invention are described with reference to the drawings.
The thermal storage medium 110 is disposed to surround a center portion, in which the object V1 is placed. The thermal storage medium 120 is disposed in contact with the thermal storage medium 110 and to surround the outer side of the thermal storage medium 110. Preferably, the thermal storage media 110 and 120 uniformly surround the inside from every direction.
The thermal storage media 110 and 120 may be formed of, for example, the same material, but are preferably formed of different materials. Different materials may be formed from the same raw material with different concentrations. Specifically, a material containing TBAB as a guest and water as a host can be used, and can have its solidification start temperature changed by concentration adjustment. Examples of guest materials of the thermal storage medium that can have its solidification start temperature changed with its concentration adjustment include, beside TBAB, quaternary ammonium salts such as TBAC. In addition, examples usable as a thermal storage medium include NaCl, NH4Cl, KCl, KHCO3, THF, cyclohexane, n-pentyl ammonium bromide, and TBAF.
The two thermal storage media 110 and 120 disposed as separate layers that surround the object V1 cause, sequentially from the outer thermal storage medium 120, the phase change of solidification to radiate heat. The heat insulating container can maintain the temperature of an object for a longer time by dispersing the effect of temperature rises resulting from heat radiation. The structure including two or more layers of thermal storage media is also effective in further restricting the temperature rises of the object V1 resulting from heat radiation than in the structure including a single layer of a thermal storage medium.
Preferably, the thermal storage media 110 and 120 are in a layer form and disposed parallel to an isothermal surface at a time when heat flows in from the outside. Specifically, in a rectangular parallelepiped container, the layers are disposed to have their surfaces parallel to the wall surfaces. Such disposition allows the respective thermal storage media to start solidifying at different times to maintain the temperature of the object V1 for a longer time and restrict the level of the temperature rises resulting from heat radiation.
This structure facilitates solidification from the outer thermal storage medium 120. Specifically, the thermal storage medium 120 starts solidifying first, and the heat radiation resulting from the solidification prevents solidification of the thermal storage medium 110. Specifically, the thermal storage medium 110 has its temperature raised and does not start solidifying until the thermal storage medium 120 finishes radiating heat. After the thermal storage medium 120 finishes solidifying and radiating heat, the temperature of the thermal storage medium 110 falls and arrives at the solidification start temperature. Then, the thermal storage medium 110 starts solidifying. This structure allows the respective thermal storage media to start solidifying at different times to maintain the temperature of the object V1 for a longer time and restrict the temperature rises resulting from heat radiation.
Preferably, the freezing point of the thermal storage medium 120 is higher than the freezing point of the thermal storage medium 110. Specifically, freezing points Ta and Tb of the respective thermal storage media 110 and 120 are preferably determined to satisfy Ta<Tb. When the outside temperature is lower than the intended target temperature, such a structure is more likely to allow the cold to flow in to start solidification from the outer thermal storage medium 120. The same change occurs also in the structure where the solidification start temperatures are determined to be Ta=Tb, since the outer thermal storage medium 120, from which the cold flows in, starts solidifying first, and heat radiation resulting from the solidification prevents the thermal storage medium 110 from solidifying. To secure design allowance, however, the solidification start temperatures preferably satisfy Ta<Tb.
The heat insulating container 100 has its allowable temperature range determined in accordance of its purpose of use. Preferably, the heat insulating container 100 has, particularly, the lower limit of the allowable temperature range determined within the range of 1 to 3° C. This structure enables transportation of an object V1 having its lower limit temperature around 2° C., such as some vaccines or other medical supplies, under constant temperatures without the need of power for a predetermined period.
Preferably, the heat insulating container 100 includes an exterior wall 180 formed of a heat insulating member to be used for transportation for cold areas. During transportation of an object V1 for, particularly, cold areas, the thermal storage media 110 and 120 solidify around the lower limit of the allowable temperature range and radiate heat, to prevent the object V1 from being cooled further below the lower limit of the allowable temperature range. For example, some vaccines are prevented from losing their functions due to solidification.
Examples of an inactivated vaccine of the above some vaccines include a recombinant precipitated divalent human papilloma virus-like particle vaccine, a recombinant precipitated quadrivalent human papilloma virus-like particle vaccine, an inactivated polio vaccine (Salk vaccine), a dried haemophilus type-b vaccine, a precipitated 13-valent pneumococcal conjugate vaccine, and a quadrivalent meningococcal vaccine (diphtheria toxoid conjugate). Examples of a live vaccine of the above some vaccines include an oral live attenuated human rotavirus vaccine, and a pentavalent oral live attenuated rotavirus vaccine.
Other example of the object V1 include perishable foods. Perishable foods respectively have their suitable storage temperatures. With respect to vegetables, for example, the suitable storage temperature for cucumbers ranges from 10 to 12° C., that for cabbages is 0° C., and that for tomatoes (fully ripened) ranges from 8 to 10° C. With respect to fruits, the suitable storage temperature for netted melons ranges from 2 to 5° C., and that for bananas (yellow ripened) ranges from 13 to 16° C. Particularly, the optimum temperature for storing yellow ripened bananas is around 15° C. (that for green ripened bananas is around 13.5° C.). Bananas may fail to be smoothly ripened if even temporarily placed under the temperature of lower than or equal to 13° C., or may have its peel discolored due to chilling injury. Bananas thus require a strict temperature control.
A method for producing the heat insulating container 100 having the above structure is described. First, a container body having the exterior wall 180 formed of a heat insulating member is prepared. Then, at least two layers of thermal storage media (thermal storage media 110 and 120) having freezing points adjacent to and higher than the lower limit of an allowable temperature range of the object V1, including the intended target temperature, are prepared.
The prepared layers of the thermal storage media having their temperatures adjusted to the intended target temperature are disposed on the inner side of the exterior wall 180 to form the heat insulating container 100. Here, the thermal storage media 110 and 120 are liquids, and the layers are laminated by disposing thermal storage packages. The object V1 is placed on the inner side of the innermost thermal storage medium 110. This structure restricts the temperature rises of the object V1 resulting from the heat radiation, and can extend the time for maintaining the temperature by dispersing the effect of the temperature change.
The temperature changes were measured between different thermal storage medium structures to verify that the heat insulating container 100 is more efficient than an existing container.
A temperature change Td represents the temperature change resulting from cooling, from one side, a stack of a thermal storage medium (TBAB at a concentration of 40 wt % with a weight of 25 g) and a thermal storage medium (TBAB at a concentration of 30 wt % with a weight of 25 g). A temperature change Ts represents the temperature change resulting from cooling only one thermal storage medium (TBAB at a concentration of 40 wt % with a weight of 50 g). The double-layer thermal storage media have freezing points made different through concentration adjustments.
Specifically, the temperature changes Td and Ts are equivalent to the temperature changes of the object V1 in the heat insulating containers 100 containing the same amount of thermal storage media, while one of which has double-layer thermal storage media and the other has a single-layer thermal storage medium, measured when both heat insulating containers 100 are cooled from the outside under the same conditions.
The temperature change Ts of the single-layer thermal storage medium shows one large peak due to the heat radiated from a phase change. The temperature change Ts shows, following the peak, a rapid cooling of the object V1. On the other hand, the temperature change Td of the double-layer thermal storage media shows two separate peaks. The temperature change Td shows a first peak resulting from the heat radiation after solidification of the outer thermal storage medium, and then shows a second peak resulting from the heat radiation after solidification of the inner thermal storage medium. Both peaks in the temperature change Td are lower than and continue about 1.5 times longer than the peak shown in the temperature change Ts. The above results reveal that the constant temperature has been maintained for a longer period and the temperature rises due to heat radiation is restricted in the container having the two-layer structure.
Verification (2) of Effect of Double-Layer Structure
The temperature changes of the heat insulating container 100 including a double-layer thermal storage media having the same freezing point and the same weight were measured. Specifically, the temperature changes of thermal storage media resulting from cooling, from one (outer) side, a stack of an inner thermal storage medium 110 (TBAB at a concentration of 40 wt % with a weight of 25 g) and an outer thermal storage medium 120 (TBAB at a concentration of 40 wt % with a weight of 25 g) were measured.
However, after experiments similar to the above are repeated, the sequence of the solidification start times of the thermal storage media 110 and 120 may be disturbed, and the thermal storage medium 110 may start solidifying before the thermal storage medium 120 finishes solidifying. In that case, the thermal storage media 110 and 120 made of the materials having the same freezing point do not have the difference between their solidification start temperatures. On the other hand, the following method of using thermal storage media having different weights is available to fully reproduce the temperature maintenance resulting from the difference between the solidification start times and the sequential solidifications.
The temperature changes of the heat insulating container 100 having a double-layer structure including the thermal storage media 110 and 120, which have different freezing points and different weights, were measured. Specifically, the temperature changes of the thermal storage media 110 and 120 resulting from cooling, from one (outer) side, a stack of the thermal storage medium 110 (TBAB at a concentration of 40 wt % with a weight of 25 g) and the thermal storage medium 120 (TBAB at a concentration of 35 wt % with a weight of 50 g) were measured. In this case, the thermal storage medium 110 has a freezing point higher than the freezing point of the thermal storage medium 120.
As illustrated in
In consideration of the above verification results, in the heat insulating container 100, the outer thermal storage medium 120 preferably has a weight larger than the weight of the inner thermal storage medium 110. This structure can securely solidify the outer thermal storage medium 120 first. Even if heat unevenly flows into the container (heat is unevenly insulated), the thermal storage media 110 and 120 having different weights are more likely to solidify in sequence than in the case where the thermal storage media 110 and 120 have the same weight.
In the above embodiment, the thermal storage medium 120 is disposed in contact with and on the outer side of the thermal storage medium 110. However, a heat conducting member 250 may be interposed between the thermal storage medium 110 and the thermal storage medium 120.
As illustrated in
The heat conducting member 250 interposed between the thermal storage media 110 and 120 facilitates heat conduction between the thermal storage media 110 and 120, and restricts the temperature rise of the object V1 and can manage the upper limit temperature of a low allowable temperature range.
The temperature changes of the object V1 in the two heat insulating containers 100 and 200 that differ in terms of whether the heat conducting member 250 is included were compared.
As illustrated in
In the above embodiment, the heat insulating container 100 does not include a heat insulating member, but may include a heat insulating member.
The temperature changes of the object V1 in the two heat insulating containers 100 and 300 that differ in terms of whether the heat insulating members 360 and 370 are included were compared.
As illustrated in
In the above embodiment, the heat insulating container 100 includes two layers of thermal storage media 110 and 120, but may include three or more layers of thermal storage media.
This structure prevents the outside temperature from directly affecting the inner thermal storage media 110 and 120 with a buffering function of the thermal storage medium 430, which is located outermost of all the multiple thermal storage media, and can maintain the constant temperature regardless of the outside temperature. This structure can highly effectively maintain the temperature of the object regardless of the outside temperature. The thermal storage medium 430 may have a freezing point the same as the freezing points of the thermal storage media 110 and 120.
When the heat insulating container 400 is used, the thermal storage media 110 and 120 having the freezing points determined around the lower limit of the intended allowable temperature range are disposed in the container at the temperature equivalent to the intended target temperature. The temperature of the thermal storage medium 430 is set lower than the freezing points of the thermal storage media 110 and 120, and the thermal storage medium 430 is set in a solid phase.
Then, the thermal storage media 120 and 110 cooled by the thermal storage medium 430 sequentially cause phase changes from the melt state to the solidified state. During the phase changes, the object is prevented from falling below the freezing point. Each temperature rise resulting from the heat radiation at the solidification is restricted by the other two layers of the thermal storage media, so that the upper limit temperature is kept low. In addition, the temperature range between the lower limit and the upper limit can be reduced, so that the temperature can be maintained more accurately.
This structure prevents the outside temperature from affecting the thermal storage media 110 and 120 with the buffering function of the outermost thermal storage medium 430, and can maintain the constant temperature regardless of the outside temperature, although the outside temperature is higher than the upper limit of the intended temperature range until the thermal storage medium 430 melts. Specifically, the thermal storage medium 430 enables maintaining the temperature of a thermally-insulated object regardless of the outside temperature.
Experiments were conducted under the same conditions by cooling, from one side, a single-layer thermal storage medium and triple-layer thermal storage media, each made of the same material and having the same amount in total. The single-layer structure maintained the temperature range of 2 to 10° C. for ten hours, whereas the triple layer structure maintained the temperature range of 2 to 9° C. for 20 hours. The experiments verified that the triple-layer thermal storage media highly effectively maintain the temperature.
This international application claims benefit of priority from Japanese Patent Application No. 2015-110613 filed on May 29, 2015. The entire contents of Japanese Patent Application No. 2015-110613 are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-110613 | May 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/065527 | 5/26/2016 | WO | 00 |
