Breathable thermal bag with reflective insulation

Abstract

A thermal bag for transporting food, comprising a flexible body with a base and an interior space for holding the food, characterized in that it comprises a multi-layered wall structure formed by: - An inner layer of porous material permeable to water vapor; - An intermediate layer bonded to the inner layer, formed by a corrugated material whose folds define a plurality of continuous vertical channels; - An outer layer bonded to the intermediate layer, comprising a low-emissivity thermal reflective coating arranged on its inner surface; and - At least a plurality of ventilation openings arranged in the upper area of the outer layer, said openings being in direct fluid communication with the vertical channels of the intermediate layer.

Description

Breathable thermal bag with reflective insulation TECHNICAL SECTOR The present invention falls within the technical field of the food packaging and logistics industry, specifically in the design and manufacture of flexible packaging intended for the transport and home delivery of hot food that requires simultaneous and passive control of the temperature and relative humidity inside. BACKGROUND OF THE INVENTION Currently, transporting hot food (especially crispy or fried foods) presents a thermodynamic challenge. Existing solutions force a choice between two inadequate options: 1. Sealed containers: They retain heat, but trap the water vapor emitted by the food. This vapor reaches its dew point upon contact with the cooler walls, condensing and precipitating onto the food, which ruins its texture. 2. Ventilated containers: These allow the evacuation of water vapor, but lack thermal insulation, causing a rapid loss of energy by convection and radiation to the outside. There is no known flexible packaging in the state of the art that integrates a passive thermodynamic system capable of separating mass transfer (vapor evacuation) from heat transfer (thermal insulation). EXPLANATION OF THE INVENTION To solve the aforementioned technical problems, the present invention proposes a container consisting of a multilayer structure that acts as a passive heat and mass exchanger. The invention is based on the synergy of three structural elements that alter the thermodynamic properties of the system: 1. Inner permeability layer: Composed of a porous or mesh-like material that physically separates the food from the evacuation chamber, allowing the passage of steam, but retaining the fats. 2. Intermediate convection layer: Defined by a corrugated sheet. The crests of this undulation generate a plurality of continuous vertical channels. 3. Outer insulating and reflective layer: Whose inner face comprises a low emissivity coating to reflect infrared radiation. Physical and Thermodynamic Justification: The system solves the technical problem by combining two physical principles: 1. Mass Evacuation by "Chimney Effect" (Natural Convection): The hot water vapor generated by the food passes through the inner layer and enters the corrugated channels. Due to the difference in thermal density between the hot inner gas and the cooler outer gas, a draft pressure (upward mass flow) is generated, which can be approximated by the natural draft velocity equation: [Equation 1] Natural shot velocity Where: • is the speed of the rising gas. • is the acceleration due to gravity. • is the height of the corrugated channel. • is the absolute temperature of the air inside the container. • is the absolute temperature of the outside air. This flow expels the steam through the upper openings without needing to ventilate the entire food cavity. 2. Heat Retention by Radiant Reflection: Simultaneously, heat loss by thermal radiation from the food to the outside is minimized thanks to the reflective coating of the outer layer, governed by the Stefan-Boltzmann Law: [Equation 2] Stefan-Boltzmann Law Where: • is the heat flow lost by radiation. • is the emissivity coefficient of the material (reduced thanks to the reflective layer) . • is the Stefan-Boltzmann constant. • is the area of ​​the outer surface. • 44 are the absolute indoor and outdoor temperatures, respectively. By applying a material with an extremely low emissivity coefficient () to the inner face of the outer layer, the radiant heat flux () is drastically reduced, bouncing the thermal energy back towards the food. BRIEF DESCRIPTION OF THE DRAWINGS To complement the description and aid in a better understanding of the invention, the following illustrative drawings are included: 1. Figure 1: Shows an exterior perspective view of the closed thermal bag. 2. Figure 2: Shows a perspective view with a partial cut and a side view (exploded view) of the layers that make up the wall of the bag. PREFERRED EMBODIMENT OF THE INVENTION As shown in the figures, the packaging preferably takes the form of a flexible bag with a bottom base (6). The main wall structure consists of a vapor-permeable inner layer (5), preferably a treated paper or cellulose mesh. Attached to this is an intermediate layer (4) made of a micro-corrugated material, the folds of which define a plurality of vertical channels. Finally, closing the structure is an outer layer (3) that incorporates a thermal reflective coating on its inner surface. The water vapor generated by the hot food inside passes through the inner layer (5) and enters the channels of the middle layer (4). The gas rises through these channels, driven by natural convection, until it is expelled to the outside through a series of ventilation openings (2) located under the upper seal (1) of the outer layer (3). In turn, the radiant heat emitted bounces off the reflective inner surface of the outer layer (3), returning to the food and maintaining its temperature.

Claims

1. A thermal bag for transporting food, comprising a flexible body with a base and an interior space for holding the food, characterized in that it comprises a multi-layered wall structure formed by: - ​​An inner layer of porous material permeable to water vapor; - An intermediate layer bonded to the inner layer, formed by a corrugated material whose folds define a plurality of continuous vertical channels; - An outer layer bonded to the intermediate layer, comprising a low-emissivity, thermally reflective coating arranged on its inner surface; and - At least a plurality of ventilation openings arranged in the upper area of ​​the outer layer, said openings being in direct fluid communication with the vertical channels of the intermediate layer.

2. A thermal bag, according to claim 1, characterized in that the inner layer is made of greaseproof cellulose paper or breathable mesh. 3.Thermal bag, according to any of claims 1 or 2, characterized in that the outer layer is made of Kraft paper laminated with a reflective metallized film on its inner face.