Description

Air purification, contaminated with dangerous biological components or toxic substances, by treatment at high temperatures, is known in the literature [1, 2, ... 8 ].

All these devices consist mainly of an air heating module at a temperature between 200-300 degrees Celsius and a countercurrent heat exchanger used for cooling the treated air and recovering the heat. The recovered heat is used to preheat the air to be treated. This type of breathing apparatus is superior to devices that filter pathogens and toxic substances using the passage of air through filter materials. During operation, however, the pores of the filter materials become clogged with pathogens and filtered toxic substances, which leads, in a relatively short time, to the loss of purifying capacities and the need to replace them. Following their use, infected consumables are generated that require controlled destruction.

Appliances based on thermal air purification have longer service times which are determined only by the capacity of the electricity sources. They do not generate infected consumables.

Despite the obvious advantages, this type of device still retains some drawbacks. These are related to the mass and the excessive volume of the heater and heat exchanger and the high consumption of electricity. To these inconveniences are added the complicated workmanship of making the apparatus and the high consumption of platinum or palladium used in making the thermooxidation catalyst.

The device we propose comes with new solutions for the construction of the thermal-heating reactor (1) and replaces the countercurrent heat exchanger with two regenerative heat recuperators (2) that solve the problems listed above.

In the variants presented in the literature, the heater was built of several sheets of sheet spaced apart and superimposed in a package. The package was pierced by metal tubes in which electrical resistors were mounted. Heat was transferred by direct conduction from the electrical heater to the sheet metal sheets and then to the air. The realization was difficult and involved a large volume and mass of the heater .

The construction of the proposed air purification apparatus is shown in fig. 1 and FIG. 2. Figure 1 represents a cross section of the apparatus, in the area of the thermal reactor. Figure 2 is a longitudinal section of the apparatus.

The solution proposed for the construction of the thermal reactor (1), shown in fig. 1, uses a nonwoven blanket of stainless steel wire (3) (steel wool) with a wire diameter between 25-100μm. The wires are heated by an electrical resistor (4) wound on a ceramic plate (5) placed between the layers of wires. Due to the fineness of the wires, the heat exchange surface between the wires and the air is very large, the heating of the air being done instantly and evenly. This reduces the time required for the air to stay in the thermal reactor (1) resulting in a reduction in the volume and mass of the reactor (1). The reactor channel (6) is dug into a block of ceramic fibers (7). The walls of the channel (6) are lined with aluminum foil (8). Aluminum is the material that has maximum infrared reflectivity. The blanket of stainless steel wires (3) (steel wool) is heated by the electrical resistance (4) by radiation in the infrared spectrum. The phenomenon of radiation transfer is intensified by the reflection of radiation on the aluminum surfaces (8) that line the walls of the channel (6) of the thermal reactor (1). The thermal transfer between the electrical resistance (4) and the stainless steel wires (3) is reduced in weight due to the small contact surface between the resistance and the wires due to the small diameter of the wires. This proposed technical solution is the only one that can ensure a uniform heating of the steel wire blanket (3) .

Heating by the Joule effect would form overheated points at the contact of the stainless steel wire - supply electrode which could lead to the ignition of the stainless steel wire blanket (3). Due to the fineness of the wires, the steel wire blanket (3) would ignite in the air at over 550 degrees Celsius. Due to this, Joule heating cannot be used in the construction of the thermal reactor (1) .

Another heating solution, that of electromagnetic induction currents, cannot be used due to the small diameter of the wires. The development of Eddy currents requires significant thicknesses of the material to form.

The solution found and proposed is the only one that allows the use of stainless steel wires (3) (steel wool) in the construction of the thermal reactor (1) .

Another advantage brought by the use of steel wool (3) is the possibility of using it as a support for the thermooxidation catalyst. In order to be used as a support for the thermooxidation catalyst, the stainless steel wires are subjected to an anodizing process [9] [10] with the aim of producing a surface roughness, with the formation of nanopores of 50-150 nm. The TiO ₂ catalystdoped with various metal oxides is deposited in these pores .

In figure no. 1 shows a cross section through the thermal reactor (1). The channel (6) dug into the ceramic fiber body (7) is filled with a blanket of stainless steel wires (3) placed on either side of the electrical resistance (4) wound on the ceramic plate (5) . The walls of the channel (6) are plated with aluminum foil (8) which ensures the reflection of IR radiation back on the stainless steel wires (3). Constructed in this way, the thermal reactor (1) ensures both air heating and catalytic thermal oxidation .

Another novelty proposed in this new type of air purifier is the replacement of the countercurrent heat exchanger with two recuperators-regenerators (2).

The construction of a countercurrent plate heat exchanger, which ensures the non-mixing of the air passing through the two routes, becomes difficult when working with temperatures higher than 250-300 degrees Celsius. No adhesives or putties are known to ensure sealing and to remain elastic in the range of temperatures between 350-500 degrees Celsius.

The solution came, as shown in FIG. 2. Longitudinal section through the air purification device, by replacing the countercurrent exchanger, with two recuperators-regenerators (2). Their simpler construction eliminates the need to use adhesives. In the construction of regenerative recuperators, we started from the particularity of the air flow that had to be purified. Breathing is done in two stages: inspiration and expiration. Each lasts about 5 seconds and involves moving a volume of 0.5 liters of air. During inspiration, 0.5 liters of infected air passes through the regenerator (2) no. 1, is preheated to a temperature close to that in the channel (6) of the thermal reactor (1), enters it and heats up to 350-500 degrees Celsius. The heat is taken from the heating element (4) by means of steel wool threads (3) and aluminum reflective foil (8) . After passing through the reactor (1) and the catalytic thermooxidation of pathogens and toxic substances, the air passes through the regenerator (2) no. 2, mounted at the other end of the channel (6). The air gives off the heat of the regenerator elements (9) and when it cools it enters the respiratory system.

During the period of 5 seconds corresponding to the expiration, the 0.5 liters of air cross in the opposite direction the regenerator (2) no. 2, preheats and enters the heat reactor (1). Here it is also thermally sterilized by regenerator (2) no. 1, after the release of heat is released into the atmosphere .

This type of operation ensures the sterilization of both inhaled and exhaled air. For this reason it is especially recommended for use in the medical environment where it protects both the carrier and the patient.

The regenerator (2) is constructed of a cylinder of ceramic fibers (10) having longitudinally inside a cylindrical channel (11) in which are placed the elements of the regenerator (9) , which constitute the thermal mass.

When designing the regenerator (2) we started from the need to comply with several requirements :

- To withstand working temperature, up to 350-450 degrees Celsius;

- Have a sufficient transfer surface to ensure cooling of the air from the treatment temperature to the ambient temperature over a passage length of only 5-7cm;

- To have a high permeability when the air passes on the crossing direction; - The thermal conductivity in the direction of air passage should be low to reduce heat loss;

- The thermal conductivity in the direction perpendicular to the direction of air passage should also be low due to the reduction of heat losses ;

- The thermal capacity of the regenerator elements (9) must be greater than or equal to the sensitive heat given / received by the 0.5 liters of air, when passing through the regenerator during the 5 seconds.

In order to meet all these requirements at the same time, a solution was chosen in the construction of the regenerator, which we will present below.

The regenerator (2) consists of overlapping discs, loaded into the cylinder channel (11) . The discs are made by rolling an aluminum foil of 0.03- 0.01 mm, 5-10mm wide, transversely corrugated, with 1mm the height between the corrugated tips. A rare fiberglass fabric was included between the layers of corrugated aluminum foil, acting as a spacer. This ensures both the preservation of the opening of the channels formed by corrugation and a decrease in thermal conductivity in the direction perpendicular to the longitudinal direction of air passage.

The division of the thermal mass of the generator (2) into several superimposed discs was made to increase the resistance to heat transfer in the direction of air flow, having the effect of reducing heat loss and increasing the efficiency of the regenerator (2).

In figure no. 2 shows a longitudinal section of the air purifier. The thermal reactor (1) is flanked on one side and on the other by the two regenerators (2). Each regenerator has 5 regenerating elements inside (9). The thermal reactor (1) and the regenerators (2) are mounted in a sheet metal cylinder (12) which mechanically protects them. At the top, a sheet metal cover (13) is provided with a nozzle (14) to which the flexible hose (15) which connects to the face mask is fixed. A jack is mounted on the cover (13) which connects to the power supply. Two conductors (16) make the electrical connection between the resistor (4) and the jack.

To simplify the device, it was decided to use a battery used to recharge mobile phones as a power source. This battery uses Li-Ion batteries and is equipped by the manufacturer with a circuit that stabilizes the voltage supplied to 5V throughout the operation of the device. The capacity of this battery can be chosen between 10,000-20,000 mA / hour, ensuring an uninterrupted operation of 3-6 hours.

Bibliography

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