DE102021101398A1 - Device and method for disinfecting an infectious aerosol, in particular for deactivating pathogens in aerosol droplets - Google Patents

Abstract

An energy-efficient, low-maintenance, safe and reliable device (100) and a method for disinfecting an infectious aerosol, in particular for deactivating pathogens in aerosol droplets, is proposed. Disinfection by means of electromagnetic radiation has hitherto been very energy-intensive. The disinfection by the device according to the invention is realized by absorption of infrared radiation. For this purpose, the infectious aerosol is guided through the resonator (110) of an infrared laser outside of the laser medium (130) with the aid of a suction device (140). The laser medium (130) is excited by a pump (light) source (135). The power of the infrared light in the resonator is significantly higher than that of infrared radiation that is coupled out. The water in the aerosol drops absorbs the infrared radiation very efficiently. This heats up the aerosol droplets. The pathogens contained therein denature due to temperature. In this way, efficient disinfection is achieved.

Description

field of invention

The invention relates to a device and a method for disinfecting infectious aerosols, in particular for deactivating pathogens in aerosol droplets in order to reduce their spread.

The air in a room in which people are present can be contaminated by pathogens and the concentration of pathogens in the room air can be increased by the air exhaled by people, which can also contain pathogens. The pathogens are often found in aerosol droplets and are inhaled by humans, with part of the inhaled aerosol droplets separating in the respiratory tract, which can have adverse health consequences.

Effective, reliable and continuous disinfection of the room air reduces the risk of infection with pathogens, especially those that are in aerosol droplets and can therefore remain in the air for a longer period of time, such as corona viruses.

In many places of daily life, indoor air is shared by everyone present. Since the risk of infection depends on the amount of active pathogens inhaled and thus on the concentration of active pathogens in the air, reducing this concentration reduces the risk of infection.

State of the art

According to the prior art, infectious aerosols can be cleaned, for example, by atomizing or nebulizing a disinfectant and then circulating it. Filtering of the infectious aerosols, for example by means of HEPA filters, is also used as an independent or supplementary method for cleaning infectious aerosols.

The prior art also includes the disinfection of infectious aerosols with the aid of a plasma or ion field.

In most cases, the disinfection of air in closed rooms is realized in the prior art with the help of UV radiation. Compared to the use of disinfectants or pure filter systems, the use of UV radiation has the advantage of not producing any waste product during use and of making additional maintenance steps for cleaning unnecessary.

With a few exceptions, lamps or fluorescent tubes that emit light in the UV range are used as the source of UV radiation. In addition to high energy consumption, these also pose a health risk for humans. The radiation intensities of the UV light required for disinfection cause photochemical changes in human tissue. Human tissue should therefore be exposed to as little UV radiation as possible.

The use of UV radiation aims at the direct destruction of the viral RNA by provoking the breaking of covalent bonds within the molecules through the absorption of the UV radiation by the RNA.

In the pamphlet CN 111603599A the use of a UV laser is proposed for the disinfection of infectious aerosols, the beam of which is expanded by the use of mirrors and lenses to form a kind of "laser curtain" through which the infectious aerosols are guided. This type of focusing and the directivity of the laser beam reduce the risk to humans compared to UV fluorescent tubes or lamps. For reliable disinfection, the document states an output power of the laser of 200 W, which corresponds to an input power of more than 2000 W when using, for example, widespread UV high-power fiber lasers. Even if the input power of other types of lasers in the UV range can be lower, when using a UV laser, an input power of significantly more than 200 W is required in order to achieve the laser output power required for reliable disinfection (see e.g. data sheet on UV lasers from ULM/ULR-355 series from IPG Photonics (https://www.ipgphotonics.com/en/81/FileAttachment/ULM-ULR-355-200+Datasheet.pdf, accessed 2020-12-11)).

task

The object of the invention is to specify a device and a method which enables energy-efficient, low-maintenance, safe, reliable and continuous cleaning or disinfection of infectious aerosols, in particular the deactivation of pathogens in aerosol droplets.

solution

This object is solved by the subject matter of the independent claim. Advantageous developments of the subject matter of the independent claim are characterized in the dependent claims. The wording of all claims is hereby made part of the content of this description by reference.

The use of the singular is not intended to exclude the plural, which also applies vice versa, unless otherwise disclosed.

A device is proposed to solve the problem. The proposed device enables disinfection of infectious aerosols, in particular the deactivation of pathogens in aerosol droplets. To do this, it uses the infrared light of an infrared laser. The infrared laser has a pump source for exciting a laser medium. The laser medium is typically located in a resonator, typically between two end mirrors. In the case of a high-quality resonator with end mirrors, these are maximally reflective for infrared radiation. However, an external high-quality resonator that is coupled to the infrared laser is also possible. In both cases, the resonator collects the light from the infrared laser, causing the light intensity in the resonator to increase.

The infectious aerosol is guided through the resonator of the infrared laser or the external resonator with the aid of a circulation device or suction device.

The aerosol droplets absorb the infrared radiation inside the resonator and heat up as a result. The heat deactivates the pathogens by denaturing biomolecules, which are contained, for example, in the form of proteins in the envelope of viruses. A possible additional mechanism of action could be the direct destruction of the viral or bacterial structures by means of laser-induced water evaporation.

The absorption of the infrared radiation within the resonator is in contrast to conventional methods in which the laser light is coupled out of the resonator. In the case of irradiation with laser light within a laser resonator, one also speaks of a cavity-enhanced method.

The pump source first excites atoms or molecules in the laser medium. As a result, energetically higher states are occupied. If an excited atom is brought to stimulated emission by a photon with the desired energy to be emitted, the excited atom returns to its ground state. It emits a photon of the same wavelength as the stimulating photon. Both photons move in the same direction with the same phase, i.e. coherently. By duplicating the stimulating photon, the laser medium acts like a light intensifier.

With conventional lasers, which decouple part of the light from the resonator, the intensity of the laser light inside the resonator is significantly higher than the intensity of the decoupled laser radiation. If both end mirrors reflect maximally, the intensity of the laser radiation in the resonator is even higher. By increasing the radiation intensity in the laser resonator, the proposed device requires significantly less electrical power to achieve the light intensity required for disinfection. Irradiating the aerosol droplets inside the resonator therefore increases the energy efficiency in contrast to irradiating outside the resonator.

The device proposed here keeps the photons in the resonator. Apart from other resonator losses, practically all photons generated are absorbed by aerosols.

In this case, the resonator can be realized by the laser resonator itself or by a correspondingly coupled external resonator. The use of infrared radiation also enables infectious aerosols to be disinfected without producing waste.

The proposed device is particularly suitable for disinfecting room air.

Since aerosol droplets consist mainly of water, the wavelength of the infrared laser should be selected in such a way that it meets a high level of absorption of the water. In a variant of the invention, an infrared laser can therefore be used with a wavelength in the range from 0.7 μm to 50 μm, preferably in a range from 1 μm to 30 μm, more preferably in a range from 2 μm to 7 μm and particularly preferably in a range from 2.5 µm to 4 µm.

A CO ₂ laser, which is a widely used and inexpensive type of laser, is well suited for the invention with its wavelength of 10.6 μm.

In another development of the invention, a solid-state laser that uses a doped YAG crystal can be used. Depending on the doping, the wavelength of the laser light is in the particularly preferred wavelength range of 2 μm to 7 μm. A YAG laser is typically doped with lanthanides.

An erbium-doped YAG laser (Er:YAG) with a wavelength of 2.9 µm is particularly suitable for the proposed disinfection. Water has an absorption maximum in this wavelength range.

Depending on the performance of the suction device, the air can be guided through the resonator longitudinally or transversely to the direction of propagation of the infrared radiation. A longitudinal air flow can be advantageous in particular when the irradiation time is to be extended without having to increase the flow rate.

A further simplification is the use of a closed air duct made of a material that is maximally permeable to infrared radiation and is located inside the resonator. In this way, contamination of the inner surfaces of the resonator can be counteracted, since inside the resonator only the interior of the closed air duct comes into contact with the room air.

It is of particular advantage to have an anti-reflective coating on the closed air duct for infrared light in order to minimize the reflection of infrared radiation and further increase efficiency.

In addition, the object is achieved by a method for disinfecting room air, in particular for deactivating pathogens in aerosol droplets, in which the proposed device is made available. With the help of the device, room air is guided through the resonator of the infrared laser by means of a suction device. The aerosol droplets are heated to at least 50 °C by absorbing infrared radiation. This makes sense, since denaturation of biomolecules can be expected at temperatures above 50 °C. These biomolecules can, for example, be structural proteins of viruses and bacteria that sit on the surface of viruses. The viruses and bacteria are thus deactivated by denaturing the proteins.

A further improvement is achieved if the aerosol droplets are heated to a temperature of at least 60 °C within the resonator. Reliable protein denaturation is achieved if the aerosol droplets are heated to at least 70 °C. Heating to at least 80 °C or even 90 °C further increases denaturation and thus disinfection. Maximum disinfection and thus safety is provided by heating the aerosol droplets inside the resonator to a temperature of at least 100 °C. This leads to the evaporation of the aerosol droplets, which, in combination with heat denaturation, further increases the reliability of disinfection.

Further details and features result from the following description of preferred exemplary embodiments in conjunction with the figures. The respective features can be implemented individually or in combination with one another. The options for solving the task are not limited to the exemplary embodiments. For example, range information always includes all - not mentioned - intermediate values and all conceivable sub-intervals.

• 1 einen Aufbau einer Desinfektionsvorrichtung mit einer zur Ausbreitungsrichtung der Infrarotstrahlung transversalen Luftführung;
• 2 einen Aufbau einer Desinfektionsvorrichtung mit einer zur Ausbreitungsrichtung der Infrarotstrahlung longitudinalen Luftführung;
• 3 einen Aufbau einer Desinfektionsvorrichtung mit einem geschlossenen Kanal für die Luftführung transversal zur Ausbreitungsrichtung der Infrarotstrahlung;
• 4 einen Aufbau einer Desinfektionsvorrichtung mit einem geschlossenen Kanal für die Luftführung longitudinal zur Ausbreitungsrichtung der Infrarotstrahlung;
• 5 ein Absorptionsspektrum von Wasser über einen großen Wellenlängenbereich elektromagnetischer Strahlung;
• 6 die berechnete einzustrahlende Intensität in Abhängigkeit des Durchmessers der Aerosoltropfen.

The exemplary embodiments are shown schematically in the figures. The same reference numerals in the individual figures designate elements that are the same or have the same function or that correspond to one another in terms of their functions. In detail shows:

• 1 a structure of a disinfection device with an air duct transverse to the propagation direction of the infrared radiation;
• 2 a structure of a disinfection device with an air duct longitudinal to the propagation direction of the infrared radiation;
• 3 a structure of a disinfection device with a closed channel for the air flow transverse to the direction of propagation of the infrared radiation;
• 4 a structure of a disinfection device with a closed channel for the air flow longitudinal to the direction of propagation of the infrared radiation;
• 5 an absorption spectrum of water over a wide range of wavelengths of electromagnetic radiation;
• 6 the calculated intensity to be irradiated as a function of the diameter of the aerosol droplets.

1 shows a disinfection device 100 with an air duct that is transverse to the propagation direction of the infrared radiation 105 through the resonator 110. The disinfection device 100 comprises an infrared laser. This includes the resonator 110, which is defined by the two end mirrors 120. The solid, liquid or gaseous laser medium 130 is located between the two end mirrors 120 in a defined volume. This is excited by a pump (light) source 135 . The air in the room is guided through the resonator 110 transversely to the propagation direction of the infrared radiation 105 and outside the laser medium 130 with the aid of the suction device 140 . The flow path 145 of the room air is indicated with straight arrows. This can also flow through the resonator in the opposite direction. The arrows with a wavy line indicate the photons of the infrared radiation 105.

2 shows a disinfection device 200 with an air duct through the resonator 210 that is longitudinal to the propagation direction of the infrared radiation 205. Analogous to FIG 1 includes the disinfection device 200 an infrared laser. This includes the resonator 210, which is defined by the two end mirrors 220. The solid, liquid or gaseous laser medium 230 is located between the two end mirrors 220 in a defined volume. This is excited by a pump (light) source 235 . The air in the room can be guided through the resonator 210 longitudinally to the propagation direction of the infrared radiation 205 and outside of the laser medium 230 with the aid of the suction device 240 . The arrows indicate the flow path 245 of the room air. This can also flow through the resonator in the opposite direction. All other elements in 2 correspond to those in 1 .

The dwell time of the room air in the resonator 210 can be increased by the longitudinal air flow to the propagation direction of the infrared radiation 205 and thus the irradiation time of the aerosol droplets can be extended compared to a transversal air flow. In this way, the flow rate can be increased and/or the recording power of the laser can be reduced while the energy transferred to the aerosol droplets remains the same. As a result, the circulation time can be shortened and/or the energy efficiency of the device can be increased.

3 shows a disinfection device 300 with an air duct through the resonator 310 that is transverse to the propagation direction of the infrared radiation 305. Analogous to FIG 1 includes the disinfection device 300 an infrared laser. This includes the resonator 310, which is defined by the two end mirrors 320. The solid, liquid or gaseous laser medium 330 is located between the two end mirrors 320 in a defined volume. This is excited by a pump (light) source 335 . The air in the room can be guided through the resonator 310 through a closed air duct 350 outside of the laser medium 330 with the aid of the suction device 340 . The air duct 350 can consist of a material that is transparent to infrared radiation 305 , preferably a material that is maximally transparent to infrared radiation 305 , for example zinc sulfide. Reflection and absorption of infrared radiation 305 by the air duct 350 material itself is preferably minimized. This can also include anti-reflective coating of the surface. The arrows indicate the flow path 345 of the room air. This can also flow through the resonator in the opposite direction. All other elements in 3 correspond to those in 1 .

4 shows analogous to 1 a disinfection device 400 with a direction of propagation of the infrared radiation 405 longitudinal air flow through the resonator 410. Analogous to 1 includes the disinfection device 400 an infrared laser. This includes the resonator 410, which is defined by the two end mirrors 420. The solid, liquid or gaseous laser medium 430 is located in a defined volume between the two end mirrors 420. This is pumped by a pump (light) source 435 stimulated. The air in the room can be guided through the resonator 410 through a closed air duct 450 outside of the laser medium 430 with the aid of the suction device 440 . The air duct 450 should consist of a material that is transparent to infrared radiation 405 , preferably a material that is maximally transparent to infrared radiation 405 , for example zinc sulfide. Reflection and absorption of infrared radiation 405 by the air duct 450 material itself is preferably minimized. This can also include anti-reflective coating of the surface. The arrows indicate the flow path 445 of the room air. This can also flow through the resonator in the opposite direction. All other elements in 4 correspond to those in 1 .

Important parameters of an exemplary configuration of the laser used in the disinfection device are calculated on the basis of the following points.

1) Calculation of the energy E required to heat the aerosol droplets by a temperature ΔT

mit
c : spezifische Wärmekapazität von Wasser 4,2 J / (g • K)
m_R: gesamte Masse aller zu erhitzender Aerosoltropfen im zu desinfizierenden Raum.The energy E required to heat all aerosol droplets in a room by a temperature difference ΔT is $$E_{W\ddot{\text{a}}\mathrm{right}me}=c\cdot m_R\cdot \mathrm{\Delta }T$$

With
c : specific heat capacity of water 4.2 J / (g • K)
m _R : total mass of all aerosol droplets to be heated in the room to be disinfected.

If the aerosol droplets in a room are irradiated with infrared light for a time Δt, eg 15 minutes, the time Δt is available for the heating, and the necessary power P _heat results from infrared radiation $$P_{W\ddot{\text{a}}\mathrm{right}me}=\frac{c\cdot m_R\cdot \mathrm{\Delta }T}{\mathrm{\Delta }T}$$

2) Calculation of the absorption of the aerosol-air mixture in the layer thickness Δd and the required laser power P _L .

This heat output must be applied by absorbing infrared radiation. That is, the absorbed laser power Pabs must correspond exactly to the required thermal power P _heat . So it applies $$P_{abs}=P_{W\ddot{\text{a}}\mathrm{right}me}$$

To calculate the absorbed laser power Pabs, it is useful to consider the effective cross section σ _K of an aerosol drop. For the calculation, a cube with edge length ϕ _K should be assumed instead of a sphere.

ist. Bei geringerer als vollständiger Absorption im Aerosoltropfen (bzw. Aerosolwürfel) wird der effektive Wirkungsquerschnitt ${\sigma }_K^{e1}$

gegenüber σ_K reduziert auf $${\sigma }_K^{e1}={\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\right)\right)$$

wobei
α die e^-1-Eindringtiefe der Strahlung im Bulkwasser (volumenfüllendes Wasser) ist.It can be assumed that in the case of almost complete absorption in the drop, the effective cross section σ _K is equal to the geometric cross section $${\sigma }_K={\varnothing }_{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">K</figure-callout>}}{}^2$$

is. If the absorption in the aerosol droplet (or aerosol cube) is less than complete, the effective cross section becomes ${\mathrm{<figure-callout\; id="1"\; label="\sigma \; K\; e"\; filenames="DE102021101398A1\_0038.png,DE102021101398A1\_0039.png"\; state="\{\{state\}\}">\sigma </figure-callout>}}_{Ke}^1$

compared to σ _K reduced to $${\mathrm{<figure-callout\; id="1"\; label="\sigma \; K\; e"\; filenames="DE102021101398A1\_0038.png,DE102021101398A1\_0039.png"\; state="\{\{state\}\}">\sigma </figure-callout>}}_{Ke}^1={\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\right)\right)$$

whereby
α is the e ^-1 penetration depth of the radiation in bulk water (volume-filling water).

absorbiert, wobei λ die Wellenlänge des Laserlichts ist. Durch diese verminderte Absorption verlängert sich die Eindringtiefe α zu α_R mit $${\alpha }_R=\frac{\alpha }{\left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}}$$

If the droplet size is in the range of the wavelength or smaller, the absorption is further weakened. According to Rayleigh then only one proportion $$\left(1-exp\left(-\pi \cdot \frac{{\varnothing }_K}{\lambda }\right)\right)$$

absorbed, where λ is the wavelength of the laser light. Due to this reduced absorption, the penetration depth α increases to α _R with $$a_R=\frac{a}{\left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}}$$

verringert sich damit weiter auf $${\sigma }_K^e={\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)$$

The effective cross section ${\sigma }_K^e$

thus further decreases $${\sigma }_K^e={\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)$$

aller im Laservolumen V_L befindlichen n_L Aerosoltropfen gleichen Durchmessers ist dann $${\sigma }_L^e=n_L\cdot {\sigma }_K^e=n_L\cdot {\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)$$

The total effective cross section ${\sigma }_L^e$

of all n _L aerosol droplets of the same diameter in the laser volume V _L is then $${\sigma }_L^e=n_L\cdot {\sigma }_K^e=n_L\cdot {\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)$$

der Gesamtmasse m_L der im vom Laser bestrahlten Volumen V_L befindlichen Aerosoltropfen zu der Masse m_K eines einzelnen Tropfens. Fener gilt für die Masse m_K eines einzelnen Tropfens: $$m_K=\rho \cdot V_K=\rho \cdot {\varnothing }_K{}^3=\rho \cdot {\varnothing }_K\cdot {\sigma }_K$$

mit
p = Dichte von Wasser.The number n _L of the n _L aerosol droplets in the laser volume V _L results from the ratio $$n_L=\frac{m_L}{m_K}$$

the total mass m _L of the aerosol droplets in the volume V _L irradiated by the laser to the mass m _K of a single droplet. Furthermore, the following applies to the mass m _K of a single drop: $$m_K=\rho \cdot V_K=\rho \cdot {\varnothing }_K{}^3=\rho \cdot {\varnothing }_K\cdot {\sigma }_K$$

With
p = density of water.

mit V_L dem Volumen des vom Laserstrahl beleuchteten Bereichs und V_R dem Volumen des zu sterilisierenden Raumes. Damit ergibt sich $$m_L=m_R\cdot \frac{V_L}{V_R}=m_R\cdot \frac{{\varnothing }_L{}^2\cdot \mathrm{\Delta }d\cdot \pi }{4\cdot V_R}$$

mit
Ø_L = Durchmesser des Laserstrahls und
Δd = Länge des vom Laserstrahl bestrahlten Volumens V_L.The following applies to the aerosol mass m _L in the laser beam $$\frac{V_L}{V_R}=\frac{m_L}{m_R}$$

where _VL is the volume of the area illuminated by the laser beam and _VR is the volume of the space to be sterilized. This results $$m_L=m_R\cdot \frac{V_L}{V_R}=m_R\cdot \frac{{\varnothing }_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">L</figure-callout>}}{}^2\cdot \mathrm{\Delta }\mathrm{i.e}\cdot \mathrm{<figure-callout\; id="4"\; label="\pi "\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{4\cdot V_R}$$

With
Ø _L = diameter of the laser beam and
Δd = length of the volume V _L irradiated by the laser beam.

erhält man $$\begin{array}{c}{\sigma }_L^e=\frac{m_L}{m_K}\cdot {\sigma }_K^e=\frac{m_L}{m_K}\cdot {\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\\ =\frac{m_R\cdot {\varnothing }_L{}^2\cdot \mathrm{\Delta }d\cdot \pi }{m_K\cdot 4\cdot V_R}\cdot {\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\\ =\frac{m_R\cdot {\varnothing }_L{}^2\cdot \mathrm{\Delta }d\cdot \pi }{\rho \cdot {\varnothing }_K\cdot {\sigma }_K\cdot 4\cdot V_R}\cdot {\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\\ =\frac{m_R\cdot {\varnothing }_L{}^2\cdot \mathrm{\Delta }d\cdot \pi }{\rho \cdot {\varnothing }_K\cdot 4\cdot V_R}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\end{array}$$

By substituting n _L in ${\sigma }_L^e$

you get $$\begin{array}{c}{\sigma }_L^e=\frac{m_L}{m_K}\cdot {\sigma }_K^e=\frac{m_L}{m_K}\cdot {\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\\ =\frac{m_R\cdot {\varnothing }_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">L</figure-callout>}}{}^2\cdot \mathrm{\Delta }\mathrm{i.e}\cdot \pi }{m_K\cdot 4\cdot V_R}\cdot {\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\\ =\frac{m_R\cdot {\varnothing }_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">L</figure-callout>}}{}^2\cdot \mathrm{\Delta }\mathrm{i.e}\cdot \pi }{\rho \cdot {\varnothing }_K\cdot {\sigma }_K\cdot 4\cdot V_R}\cdot {\sigma }_K\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\\ =\frac{m_R\cdot {\varnothing }_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">L</figure-callout>}}{}^2\cdot \mathrm{\Delta }\mathrm{i.e}\cdot \pi }{\rho \cdot {\varnothing }_K\cdot 4\cdot V_R}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\end{array}$$

wobei P_L die Leistung des noch nicht abgeschwächten Lasers ist.The absorption A is the absorbed part of the laser power P _L . It is defined by $$P_{abs}=P_L\cdot A$$

where P _L is the power of the not yet attenuated laser.

und dem Querschnitt des Laserstrahls: $$\begin{array}{c}A=\frac{{\sigma }_L^e}{{\varnothing }_L{}^2\cdot \frac{\pi }{4}}\\ =\frac{m_R\cdot {\varnothing }_L{}^2\cdot \mathrm{\Delta }d\cdot \pi }{{\varnothing }_L{}^2\cdot \frac{\pi }{4}\cdot \rho \cdot {\varnothing }_K\cdot 4\cdot V_R}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\\ =\frac{m_R\cdot \mathrm{\Delta }d}{\rho \cdot {\varnothing }_K\cdot V_R}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\end{array}$$

Under the almost always fulfilled assumption that the laser light is not completely absorbed by the aerosol droplets, the absorbed portion A results from the area ratio of the effective cross section ${\sigma }_L^e$

and the cross-section of the laser beam: $$\begin{array}{c}A=\frac{{\sigma }_L^e}{{\varnothing }_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">L</figure-callout>}}{}^2\cdot \frac{\mathrm{<figure-callout\; id="4"\; label="\pi "\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{4}}\\ =\frac{m_R\cdot {\varnothing }_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">L</figure-callout>}}{}^2\cdot \mathrm{\Delta }\mathrm{i.e}\cdot \pi }{{\varnothing }_L{}^2\cdot \frac{\mathrm{<figure-callout\; id="4"\; label="\pi "\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{4}\cdot \rho \cdot {\varnothing }_K\cdot 4\cdot V_R}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\\ =\frac{m_R\cdot \mathrm{\Delta }\mathrm{i.e}}{\rho \cdot {\varnothing }_K\cdot V_R}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)\end{array}$$

The result for the absorbed laser power is: $$P_{abs}=P_L\cdot =P_L\cdot \frac{m_R\cdot \mathrm{\Delta }\mathrm{i.e}}{\rho \cdot {\varnothing }_K\cdot V_R}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)$$

bzw. $$\frac{c\cdot m_R\cdot \mathrm{\Delta }T}{\mathrm{\Delta }T}=P_L\cdot \frac{m_R\cdot \mathrm{\Delta }d}{\rho \cdot {\varnothing }_K\cdot V_R}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)$$

oder - nach Kürzen und Auflösen - $$P_L=\frac{c\cdot \mathrm{\Delta }T\cdot \rho \cdot {\varnothing }_K\cdot V_R}{\mathrm{\Delta }t\cdot \mathrm{\Delta }d\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{\alpha }\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)}$$

als Ergebnis für die benötigte Laserleistung.The absorbed laser power Pabs must correspond exactly to the required thermal power P _heat . So it applies $$P_{W\ddot{\text{a}}\mathrm{right}me}=P_{abs}$$

or. $$\frac{c\cdot m_R\cdot \mathrm{\Delta }T}{\mathrm{\Delta }T}=P_L\cdot \frac{m_R\cdot \mathrm{\Delta }\mathrm{i.e}}{\rho \cdot {\varnothing }_K\cdot V_R}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)$$

or - after shortening and dissolving - $$P_L=\frac{c\cdot \mathrm{\Delta }T\cdot \rho \cdot {\varnothing }_K\cdot V_R}{\mathrm{\Delta }t\cdot \mathrm{\Delta }\mathrm{i.e}\cdot \left(1-exp\left(-\frac{{\varnothing }_K}{a}\cdot \left\{1-e^{-\pi \cdot {\varnothing }_K/\lambda }\right\}\right)\right)}$$

as a result for the required laser power.

It is remarkable that the laser power P _L does not depend on the mass m _R of the aerosol droplets to be heated. This is due to the fact that with small absorption, the absorption increases to the same extent as _mR . The size of the irradiated volume V _L and the diameter Ø _L of the laser beam are also irrelevant, but the length of the irradiated volume Δd is.

wobei δt die Verweildauer der Aerosolpartikel im bestrahlten Volumen V_L bezeichnet. Es folgt $$\delta t=\frac{V_L}{V_R}\cdot \mathrm{\Delta }t$$

If the air loaded with aerosol droplets in a room with a volume V _R is to be disinfected within a time δt, the entire air must be sucked through the irradiated volume V _L within the time δt. The following then applies: $$\frac{\delta t}{\mathrm{\Delta }t}=\frac{V_L}{V_R}$$

where δt denotes the residence time of the aerosol particles in the irradiated volume V _L . It follows $$\delta t=\frac{V_L}{V_R}\cdot \mathrm{\Delta }t$$

3) Example calculation for a heating of the aerosol droplets by 80 K

5 shows - for the calculation of the penetration depth α - a spectrum of the absorption of electromagnetic radiation by water. The degree of absorption is plotted as a function of the wavelength. The penetration depth α results from the reciprocal of the plotted absorption.

In the wavelength range from 0.7 µm to 50 µm, the absorption of electromagnetic radiation by water in the infrared is particularly high, which is why this range can be used for efficient disinfection. The absorption spectrum of water shows a maximum in the infrared at a wavelength of 2.9 µm, making an Er:YAG laser particularly suitable for disinfection.

Let ΔT be 80 K. A room with a room size V _R of 100 m ³ should be disinfected in Δt = 15 minutes. The layer thickness within which disinfection takes place is Δd = 30 cm. For an Er:YAG laser with a wavelength of approx. 2.9 µm, the penetration depth is α = 0.8 µm.

The diameter of the aerosol droplets in human breath is between 0.6 µm and 100 µm (see eg de.wikipedia.org/wiki/Aerosol). Aerosol droplets that are to be effectively sterilized by a disinfection device must be able to reach it. However, aerosol droplets larger than 25 µm fall to the ground within seconds; they should therefore hardly reach the disinfection device. With a planned cleaning period of Δt = 15 minutes, only aerosol droplets that float for at least one minute can be disinfected. This applies to aerosol droplets with a diameter of up to 10 µm (see, for example, the settling speed of aerosol droplets at de.wikipedia.org/wiki/Aerosol). Unless otherwise stated, calculations are made with Ø _K = 5 µm in the following.

und für einen CO₂-Laser der Wellenlänge 10.6 µm und α = 10 µm $$P_L\approx 2kW$$

With the density of water ρ = 1 000 kg/m ³ one obtains for an Er:YAG laser $$P_L\approx 600W$$

and for a CO ₂ laser with a wavelength of 10.6 µm and α = 10 µm $$P_L\approx 2kW$$

und die Verweildauer δt eines Aerosoltropfens im bestrahlten Volumen V_L bei einem Strahldurchmesser Ø_L von 10 cm bei rundem Strahlquerschnitt beträgt: $$\delta t=\frac{V_L}{V_R}\cdot \mathrm{\Delta }t=\frac{\mathrm{\Delta }d\cdot {\left(\raisebox{1ex}{${\varnothing }_L$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\right)}^2\cdot \pi }{V_R}\cdot \mathrm{\Delta }t=\frac{\mathrm{0,3}m\cdot {\left(\frac{\mathrm{0,1}}{2}\right)}^2{m}^2\cdot \pi }{100m^3}\cdot 15\cdot 60s=21ms$$

The suction device 140 requires a circulation capacity of $$\frac{100m^3}{15min}=\frac{100\cdot 1000l}{15\cdot 60s}=111\raisebox{1ex}{$l$}\!\left/ \!\raisebox{-1ex}{$s$}\right.$$

and the dwell time δt of an aerosol droplet in the irradiated volume V _L with a jet diameter Ø _L of 10 cm and a round jet cross-section is: $$\delta t=\frac{V_L}{V_R}\cdot \mathrm{\Delta }t=\frac{\mathrm{\Delta }\mathrm{i.e}\cdot {\left(\raisebox{1ex}{${\varnothing }_L$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\right)}^2\cdot \pi }{V_R}\cdot \mathrm{\Delta }t=\frac{0.3m\cdot {\left(\frac{0.1}{2}\right)}^2{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="DE102021101398A1\_0039.png"\; state="\{\{state\}\}">m</figure-callout>}}^2\cdot \pi }{100m^3}\cdot 15\cdot 60s=21ms$$

4) Classification of the required laser output power for the intended purpose of the disinfection

Lasers with the output powers calculated in Section 3) are associated with significant acquisition costs and, in particular, high operating costs. For an output power of 100 W, a power consumption of more than 1000 W is required when using fiber lasers, which already have a high electro-optical efficiency. In addition, the lasers used in a conventional manner (the beam is coupled out of the resonator by means of a coupling-out mirror) would also require large volumes, in addition to the high costs.

The main reason for the low efficiency is that the vast majority of the laser photons are not absorbed and thus remain unused.

5) Increase in effectiveness

The method becomes significantly more effective if all or at least a large part of the photons can be used. In this context one also speaks of photon recycling.

Probably the most effective realization of this idea is to use the increase in intensity inside an optical resonator 110, 210, 310, 410. Such a method is also referred to as a cavity-enhanced method. Other mirror or scattering methods based on geometric optics (e.g. integrating sphere) are far less efficient.

Hierbei ist
R₁ der Reflexionsgrad des im herkömmlichen Laser eingesetzten Auskoppelspiegels und
R₂ der Reflexionsgrad des hinteren Endspiegels (120; 220; 320; 420).For negligible losses inside the laser cavity 110, 210, 310, 410, the ratio V of the power P _in circulating in the cavity 110, 210, 310 to the output power P _L is given by $$V=\frac{P_{in}}{P_L}=\frac{\left(1-R_1\right)\cdot \left(1+R_2\right)}{{\left(1-\sqrt{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="DE102021101398A1\_0038.png,DE102021101398A1\_0039.png"\; state="\{\{state\}\}">R</figure-callout>}}_1\cdot R_2}\right)}^2}$$

here is
R ₁ is the degree of reflection of the output mirror used in conventional lasers and
R ₂ the reflectance of the rear end mirror (120; 220; 320; 420).

Usually z. B. for CO ₂ lasers R ₂ ≈ 0.995 and R ₁ ≈ 0.5. This results in V ≈ 10.

For a section 4) analog radiation power, Er:YAG lasers in the 10 watt class or CO ₂ lasers in the 100 watt class would be sufficient. The recording capacity can be reduced by an order of magnitude compared to conventional methods. For the present application, the output mirror would be replaced by a highly reflective end mirror (120; 220; 320; 420), with R ₁ ≈0.995, for example.

If an external resonator with two end mirrors with R ₁ = R ₂ ≈ 0.995 is coupled to a commercial laser, the result is $$V\approx 400$$

For example, if the commercial laser has a power of 10 W, an excessive power of 4,000 W can be generated in the external resonator.

6) Sample calculation for small drops

6 shows the required laser power P _L for the wavelengths λ = 10.6 µm (CO2 laser) and λ = 2.9 µm (Er:YAG laser) as a function of the diameter for spherical aerosol droplets with a diameter of less than 10 µm. The laser power P _L for a wavelength λ=2.9 μm are shown with a dashed line and those for λ=10.6 μm with a solid line. All other parameters are as in section 3).

glossary

aerosol

Heterogeneous mixture (dispersion) of solid or liquid suspended particles in a gas. In the context of this application in particular a dispersion of aqueous aerosol droplets in air.

heat denaturation

In heat or heat denaturation, a change in the molecular structure of biomolecules is brought about by increasing the temperature. In most cases, no covalent chemical bonds are broken or formed as a result of the heat effect. Instead, hydrogen bonds are broken or newly formed, which often results in a change in the tertiary structure of proteins. This usually results in a loss of biological activity. Denaturation by heat can be achieved, for example, by absorption of infrared radiation by water in which the biomolecules are located.

Cavity Enhanced Process

Methods in which the substance to be irradiated with the laser is introduced directly into the beam path of the laser inside the laser resonator (cavity) instead of using the coupled laser beam outside the resonator are referred to as cavity-enhanced methods. In this case, the strong increase in the radiation intensity within the resonator is used.

laser

Conceptually, a laser consists of three components:

laser medium

In the laser medium, photons are created as a result of the optical transition of excited atoms or molecules into a lower-energy state. The central condition for a laser medium is that a population inversion can be produced, ie the upper state of the optical transition is occupied with a higher probability than the lower one. Such a medium must have at least three energy levels and can be gaseous (e.g. CO ₂ ), liquid (e.g. dye solutions) or solid (e.g. crystal, semiconductor material).

pump source

In order to bring about a population inversion, energy must be pumped into the laser medium. So that this pumping process does not compete with the stimulated emission, it must be based on another quantum mechanical transition. Therefore, a laser medium must have at least three different states. The pumping can bring the atoms or molecules of the laser medium into excited states optically (irradiation of light) or electrically (e.g. gas discharge, electric current in laser diodes).

resonator

A resonator consists, for example, of two parallel mirrors (so-called end mirrors, which have a high degree of reflection), between which there is, for example, an active laser medium. Photons whose propagation runs perpendicular to the mirrors remain in the resonator and can repeatedly trigger (stimulate) the emission of further photons in the laser medium. One of the two mirrors can be designed to be partially transparent, so that part of the light can emerge and be put to use.

However, all of the light can also be collected in the resonator and its intensity increased. In addition, the resonator can be externally coupled to a laser, i.e. the laser medium is not in the external resonator.

For the generation of laser radiation, atoms or molecules in the laser medium are excited by pumping from lower energy levels into energetically higher ones. Of these, the laser medium must relax to an intermediate state. Now a stimulation of an atom or molecule by a Pho is sufficient ton with the energy to be emitted, so that the excited atom or molecule falls back from the intermediate state to its ground state and emits a photon of identical energy (i.e. identical wavelength and frequency) and identical phase position as the stimulating photon. By duplicating the stimulating photon, the laser medium acts like a light intensifier. The second photon can then in turn stimulate other excited atoms or molecules to emit and a chain reaction occurs.

degree of reflection

The degree of reflection is the ratio between reflected and incident intensity, e.g. in the case of electromagnetic waves.

radiant energy

Radiant energy is the energy transported by electromagnetic waves. The SI unit of radiant energy is the joule.

radiation intensity

The power density related to an area during the transport of energy is referred to as radiation intensity. It is usually specified in the unit W/cm2.

radiant power

Radiant power is the differential amount of energy transported by electromagnetic waves per period of time. The SI unit of radiant power is the watt.

YAG laser

The yttrium aluminum garnet laser is a solid-state laser that uses a YAG crystal as the laser medium and mostly emits infrared radiation. Yttrium aluminum garnet is mainly used as a monocrystalline host crystal and, depending on the desired properties, above all the wavelength to be emitted, is doped with various lanthanides, including erbium (Er:YAG laser).

Reference List

100

disinfection device

105

infrared radiation

110

resonator

120

end mirror

130

laser medium

135

Pump (light) source

140

suction device

145

flow path of the room air

200

disinfection device

205

infrared radiation

210

resonator

220

end mirror

230

laser medium

235

Pump (light) source

240

suction device

245

flow path of the room air

300

disinfection device

305

infrared radiation

310

resonator

320

end mirror

330

laser medium

335

Pump (light) source

340

suction device

345

flow path of the room air

350

air duct

400

disinfection device

405

infrared radiation

410

resonator

420

end mirror

430

laser medium

435

Pump (light) source

440

suction device

445

flow path of the room air

450

air duct

cited literature

cited patent literature

CN 111603599A

cited non-patent literature

Data sheet on UV lasers of the ULM/ULR-355 series from IPG Photonics (https://www.ipgphotonics.com/en/81/FileAttachment/ULM-ULR-355-200+Datasheet.pdf, accessed on December 11, 2020)

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• CN 111603599A [0010, 0087]

Claims (10)

Device (100; 200; 300; 400) for disinfecting an infectious aerosol, in particular for deactivating pathogens in aerosol droplets, with: 1.1 an infrared laser for generating infrared light, the infrared laser having the following components: 1.1.1 a pump source; 1.1.2 a laser medium (130; 230; 330; 430) which can be excited by the pump source; 1.2 a resonator (110; 210; 310; 410) with a high quality, which increases the infrared light of the infrared laser; 1.3 a circulation device (140; 240; 340; 440) for the infectious aerosol; 1.4 wherein the infectious aerosol is passed through the resonator (110; 210; 310; 410) for disinfection with the aid of the circulation device (140; 240; 340; 440). Device (100; 200; 300; 400) according to the preceding claim, characterized in that the wavelength of the infrared laser is - in a range from 0.7 µm to 50 µm, - preferably in a range from 1 µm to 30 µm, - furthermore preferably in a range from 2 μm to 7 μm and - particularly preferably in a range from 2.5 μm to 4 μm. Device (100; 200; 300; 400) according to one of the preceding claims, characterized in that the infrared laser is a CO ₂ laser. Device (100; 200; 300; 400) according to one of Claims 1 or 2 , characterized in that the infrared laser is a doped YAG laser. Apparatus (100; 200; 300; 400) according to the immediately preceding claim, characterized in that the YAG laser is doped with erbium. Device (100; 200; 300; 400) according to one of the preceding claims, characterized in that the infectious aerosol is passed through the resonator (110; 210; 310; 410) transversely or longitudinally to the direction of propagation of the infrared radiation. Device (100; 200; 300; 400) according to one of the preceding claims, characterized in that the infectious aerosol is passed through the resonator (110; 210; 310; 410) in a closed air duct (350; 450), the material , from which the air duct (350; 450) is made, is maximally permeable to infrared radiation. Device (100; 200; 300; 400) according to the immediately preceding claim, characterized in that the air duct (350; 450) is anti-reflective for infrared light. Method for disinfecting an infectious aerosol, in particular for deactivating pathogens in aerosol droplets, with the following steps: 9.1 a device (100; 200; 300; 400) according to one of the preceding device claims is made available; 9.2 the infectious aerosol is guided through the resonator (110; 210; 310; 410) of the infrared laser with the aid of the suction device (140; 240; 340; 440); 9.3 the aerosol droplets are heated to at least 50 °C by the infrared radiation in the resonator (110; 210; 310; 410) of the infrared laser. Method according to the immediately preceding claim, characterized in that the aerosol droplets in the resonator (110; 210; 310; 410) of the infrared laser are heated by the infrared radiation to at least 60°C, preferably to at least 70°C, more preferably to at least 80° C, more preferably to at least 90 °C and more preferably to at least 100 °C.

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