Patent Publication Number: US-2021161247-A1

Title: Process for thermoregulating a flexible cellular material by compression and expansion of the gas trapped in its cells and associated device

Description:
The present invention relates to a process of thermoregulating a flexible cellular material through the compression and expansion of the gas trapped in its cells and its associated device. 
     The preferred application is for the soles of shoes, allowing the foot to maintain a cool temperature even while walking on a hot road. 
     Prior art: There are few devices for refreshing shoe soles. There are many gel-filled sole devices that are placed in a freezer to store coldness, but this type of device is impractical because the cold temperature is too intense at the beginning which risks the creation of burns, and then the device quickly becomes less effective. Secondly, the duration of the cooling effect is very short (a few minutes to tens of minutes) and, for example, is not suitable for long jogging sessions. 
     There are many devices that claim the use of Peltier effect components as in KR20160066190, US2012018418 or WO2005087031. However, these devices require a significant power supply because the yields of Peltier effect components are not very good. Thus, the generation of enough refrigeration will not be possible for periods of one hour or more. In addition, these Peltier effect components are generally made of ceramic and are therefore very fragile. Finally, between the weight of components and that of the batteries, it quickly becomes too heavy in sports shoes that generally must be light. 
     There are also devices that use breathable materials to evacuate water as described in US2018220739 or porous materials for better ventilation as in CN107788617, but none of these systems allows for true thermal regulation or for a significant drop or rise in temperature. 
     Description of the invention: The novel process concerns the thermoregulation of a flexible cellular material by compression and then expansion of the gas trapped in its sealed cells when cyclic pressure is exerted on the flexible material, for example, when a person or an animal walks (the foot resting on the ground then lifting off of the ground, etc.). 
     The flexible material is preferably made of silicone or other elastomer and consists of two layers of different shore hardness (H) and thermal conductivity (λ) and are equipped with a multitude of specific cells filled with air or with gas. Each cell has two interconnected zones: zone C to store the air or gas during compression and which is positioned in the layer with higher hardness and thermal conductivity (layer C) and zone D to expand the same air or gas during decompression in the layer with lower hardness and thermal conductivity (layer D). 
     Thus, the flexible material can be used as a sole in shoes to maintain a cool temperature when the person runs, for example, on a hot surface. With each step, the foot will compress the flexible material and the cells in the layer C will act as adiabatic chambers whose gas will heat up via compression. Since layer C has a greater thermal conductivity than the layer D, there will be a better heat exchange with the outside (in this case the bottom of the shoe). 
     When the foot leaves the ground and thus there is no more compression, the flexible material will regain its volume through the play of the elasticity of the material, and the cells located in the layer (D) will act like a reactor nozzle that will expand the air and therefore cool it. Since layer D has a lower thermal conductivity, the exchanges will be weaker, and the cold will be better preserved. 
     According to another preferred arrangement, the material is adapted to the morphology of domestic animals such as cats and dogs which often burn their paw pads when traveling on a road in direct sunlight. This is particulary the case for rescue dogs. 
     According to another provision, the flexible cellular material can be used as a carpet in public buildings or businesses with a lot of foot traffic so that the numerous foot pressures provide thermoregulation. 
    
    
     
         FIGS. 1 to 3  show the device intended in sections, for example, to be placed as a sole in shoes with the layer D in contact with the foot. 
     
    
    
     in  FIG. 1 , the cellular flexible material is at rest and the gas is uniformly distributed in the cells at the temperature T a  and pressure P a . A distinction is made between the two layers C and D and the respective zones C and D of the cells. 
     in  FIG. 2 , pressure is applied to the flexible material and since layer D has a lower hardness than layer C, layer C will be less compressed. However, gas located in the D zones of the cells will be pushed into the C zones of the cells. Then, the gas will be compressed at the pressure P i  (depending on the pressure exerted, i.e., about 2 bars for a person weighing 70 kg) and will therefore heat up to the temperature T i  according to the laws of thermodynamics. 
     The temperature T i  of the gas will thus be equal to: 
       T a ×(P i /P a ) (γ−1)/γ 
 
     where γ is the adiabatic constant of the gas (approximately 1.4 for air at 293° K.) and about 376° K. if T a  is 293° K. Since layer C has a greater thermal conductivity, the heat of the gas will then dissipate more easily through this layer to reach the temperature T f  of about 365° K. for a thermal conductivity λ of the layer C de 1 W/m/° K. 
       FIG. 3  shows the material once the pressure is released (when the foot leaves the ground). The gas, pressurized, at the temperature T f , will leave the zones C to expand in the zones D and thus cool down to the temperature: 
         T=T   f ×( P   a   /P   i ) (γ−1)/γ 
 
     or about 285° K., a temperature 8° K. lower than the initial temperature T a . Thanks to the low heat exchange operated by the D layer, this temperature difference will be maintained thanks to the repeated steps cycles and despite the losses inherent to the materials and to the absorption of the runner&#39;s foot. 
     In another arrangement, the flexible material may be used as a heating method. It suffices for this to invert the sole and therefore it is the layer C which is in contact with the foot. Thus, the heat generated during the compression will be in contact with the foot while the cold zone will be in contact with the bottom of the shoe. 
     The gas contained in the cells may simply be air, but it is advantageous to use gases with a higher adiabatic constant γ such as a monoatomic gas (Ar for example) in order to obtain a higher yield.