CN116753519A

CN116753519A - Premixing device and gas equipment

Info

Publication number: CN116753519A
Application number: CN202310725130.0A
Authority: CN
Inventors: 赵紫峰; 丁泺火; 黄伟锋
Original assignee: Gree Electric Appliances Inc of Zhuhai
Current assignee: Gree Electric Appliances Inc of Zhuhai
Priority date: 2023-06-19
Filing date: 2023-06-19
Publication date: 2023-09-15

Abstract

The application relates to a premixing device and a gas device, which comprises a device body, a swirl component and a second gas conduit. The device body is internally provided with a gas flow passage, and the gas flow passage is provided with a first gas inlet and a premixed gas outlet. The cyclone assembly is arranged in the gas flow channel, the cyclone assembly is axially arranged along the gas flow channel, the first gas inlet is located at the upstream of the cyclone assembly, the premixed gas outlet is located at the downstream of the cyclone assembly, the cyclone assembly comprises a plurality of guide vanes distributed around the periphery of the cyclone assembly in the axial direction, the airflow flowing through the guide vanes has a radial velocity component and a tangential velocity component, and then a negative pressure area is formed in the middle of the end face of the cyclone assembly, which is close to the premixed gas outlet. The second gas conduit penetrates through the cyclone assembly, and an outlet of the second gas conduit is positioned on the end face, close to the premixed gas outlet, of the cyclone assembly. The second gas in the second gas conduit is sucked into the gas flow passage under the action of negative pressure, so that the condition that the gas flows back into the second gas conduit is avoided.

Description

Premixing device and gas equipment

Technical Field

The application relates to the technical field of gas water heaters, in particular to a premixing device and gas equipment.

Background

The gas equipment such as the gas water heater needs to utilize the gas combustion to provide heat, in order to reach high-efficient and low-emission purpose, can be before the ignition with gas and air pre-mix for the ignition combustion is the gas and obtains fully burning, has advantages such as pollutant emission is few, flame temperature is high and flame length is short. When introducing air and gas, the air flow direction can hinder the gas and get into the premixing space, and gas back-flowing risk exists in gas air feed pressure deficiency.

Disclosure of Invention

Based on this, it is necessary to provide a premixing device and a gas apparatus aiming at the problem of gas backflow, wherein the swirl component makes the first gas flowing through the premixing device have a radial velocity component and a tangential velocity component, and further a negative pressure area is formed on the end face of the swirl component, which is close to the premixed gas outlet, so as to suck the second gas in the second gas conduit, and avoid the occurrence of the situation that the gas flows back into the second gas conduit.

A premixing device comprising:

the device comprises a device body, a gas flow channel and a gas flow channel, wherein the device body is internally provided with a gas flow channel which is provided with a first gas inlet and a premixed gas outlet;

the swirl assembly is arranged in the gas flow passage, the swirl assembly is axially arranged along the gas flow passage, the first gas inlet is positioned at the upstream of the swirl assembly, the premixed gas outlet is positioned at the downstream of the swirl assembly, the swirl assembly comprises a plurality of guide vanes distributed around the periphery of the swirl assembly in the axial direction, and the gas flow passing through the guide vanes has a radial velocity component and a tangential velocity component;

and the second gas conduit penetrates through the cyclone assembly, and an outlet of the second gas conduit is positioned on the end face of the cyclone assembly, which is close to the premixed gas outlet.

In one embodiment, the device body includes a venturi, the passage in the venturi is the gas flow passage, and the swirl assembly is coaxially disposed within the inlet section of the venturi.

In one embodiment, the interface between the inlet section of the venturi tube and the converging section of the venturi tube is a first interface, and the distance between the end surface of the swirl assembly, which is close to the premixed gas outlet, and the first interface is not more than 2.5mm.

In one embodiment, an end surface of the swirl assembly proximate the premix gas outlet is coplanar with the first interface.

In one embodiment, the contraction angle a1 of the contraction section of the venturi tube is 45-69 degrees, the diffusion angle a2 of the diffusion section of the venturi tube is 15-27 degrees, the throat length of the venturi tube is 30-45 mm, the diffusion section length of the venturi tube is 10-17 mm, and the inlet section length of the venturi tube is 13-20 mm.

In one embodiment, the inner diameter of a pipe section penetrating through the cyclone assembly on the second gas conduit is 5 mm-7.8 mm, the second gas conduit is arranged in the middle of the cyclone assembly, the diameter of the middle of the cyclone assembly is 10 mm-20 mm, the inner diameter of an inlet section of the venturi tube is 38 mm-44 mm, the inner diameter of a throat tube of the venturi tube is 32 mm-38 mm, and the maximum inner diameter of a diffusion section of the venturi tube is 40 mm-48 mm;

alternatively, the second gas conduit is in interference fit with the middle of the cyclone assembly.

In one embodiment, the middle part of the cyclone assembly comprises a middle shaft sleeve, the middle shaft sleeve and the gas flow channel are coaxially arranged, the second gas conduit axially penetrates through the middle shaft sleeve along the middle shaft sleeve, and an outlet of the second gas conduit is positioned on the end face, close to the premixed gas outlet, of the middle shaft sleeve.

In one embodiment, a seal is provided between the second gas conduit and the middle sleeve.

In one embodiment, the premixing device further comprises a fan access housing, the fan access housing has an outlet and a mounting port, the mounting port is used for mounting the fan and is communicated with an air outlet of the fan, the outlet of the fan access housing is in alignment communication with the first gas inlet of the device body, the second gas conduit penetrates the fan access housing to extend outwards, and a sealing element is arranged between the second gas conduit and the fan access housing.

In one embodiment, the guide vane of the cyclone assembly is a hinge vane, the axial length of the hinge vane is 16-20 mm, the installation angle r of the hinge vane and the inlet angle r of the hinge vane _in And the outlet angle r of the hinge blade _out All are 40-80 degrees.

The gas equipment comprises a combustion part and the premixing device, wherein the combustion part is arranged at the premixing gas outlet.

According to the scheme, the premixing device and the gas equipment are provided, the swirl component arranged in the gas flow channel can provide a guiding effect for the first gas flowing in from the first gas inlet, so that the first gas has a radial velocity component and a tangential velocity component after passing through the swirl component, a negative pressure area is formed on the swirl component near the end face of the premixing gas outlet, the negative pressure provides suction for the second gas in the second gas duct, the second gas is easier to enter the gas flow channel from the second gas duct, and the condition that the second gas flows backwards into the second gas duct is avoided. The second gas introduced by the second gas conduit and the first gas passing through the cyclone assembly can be discharged from the premixed gas outlet after being mixed downstream of the cyclone assembly.

Drawings

Fig. 1 is a front view of a gas apparatus according to the present embodiment.

Fig. 2 is a sectional view of the gas apparatus A-A shown in fig. 1.

Fig. 3 is a schematic structural diagram of the premixing device according to this embodiment.

FIG. 4 is a cross-sectional view of a venturi in the premixing device illustrated in FIG. 3.

FIG. 5 is a schematic view of a swirl assembly of the premixing device of FIG. 3.

FIG. 6 is a front view of a guide vane within the cyclone assembly of FIG. 5.

FIG. 7 is a top view of a guide vane of the cyclone assembly of FIG. 5.

Reference numerals illustrate:

10. a premixing device; 11. a device body; 111. a gas flow passage; 1111. a first gas inlet; 1112. a premix gas outlet; 112. a venturi tube; 1121. an inlet section; 1122. a constriction section; 1123. a throat; 1124. a diffusion section; 113. the fan is connected with the shell; 1131. a mounting port; 12. a swirl assembly; 121. a middle shaft sleeve; 122. a guide vane; 13. a second gas conduit; 20. a gas-fired appliance; 21. and a combustion section.

Detailed Description

In order that the above objects, features and advantages of the application will be readily understood, a more particular description of the application will be rendered by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. The present application may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit of the application, whereby the application is not limited to the specific embodiments disclosed below.

In some embodiments, the present application provides a premixing device 10 for premixing two gases together, the premixing device 10 having a premix gas outlet 1112 for outflow of the premix gas. As shown in fig. 1 and 2, the premixing device 10 may be applied to a gas apparatus 20, wherein the gas apparatus 20 includes a combustion portion 21, the combustion portion 21 is disposed at a premixed gas outlet 1112, and the gas and air may be mixed in the premixing device 10. Enters the combustion section 21 from the premix gas outlet 1112 and is combusted.

Alternatively, the premixing device 10 may be used in other gas mixing applications.

As shown in FIGS. 1 and 2, in some embodiments, the premixing device 10 includes a device body 11, a swirl assembly 12, and a second gas conduit 13. The device body 11 has a gas flow passage 111 therein, and the gas flow passage 111 has a first gas inlet 1111 and a premix gas outlet 1112. The swirl assembly 12 is disposed within the gas flow passage 111, the swirl assembly 12 is disposed axially along the gas flow passage 111, the first gas inlet 1111 is located upstream of the swirl assembly 12, and the premix gas outlet 1112 is located downstream of the swirl assembly 12. The space on the gas flow channel 111 downstream of the cyclone assembly 12 is a mixing channel for mixing two gases, and the outlet of the mixing channel is the premixed gas outlet 1112.

The swirl assembly 12 includes a plurality of guide vanes 122 distributed about its own axis, the airflow passing over the guide vanes 122 having a radial velocity component and a tangential velocity component.

A second gas conduit 13 extends through the swirl assembly 12, the outlet of the second gas conduit 13 being located on the end face of the swirl assembly 12 adjacent the premix gas outlet 1112.

The first gas flows through the cyclone assembly 12 after entering the gas flow channel 111 from the first gas inlet 1111, and has a radial velocity component and a tangential velocity component under the guiding action of the guide vanes 122 after flowing through the cyclone assembly 12, so that the first gas forms a negative pressure area in the middle of the cyclone assembly 12, and the outlet of the second gas conduit 13 is formed in the negative pressure area, so that the second gas in the second gas conduit 13 is subjected to a suction force generated by negative pressure, and the second gas is easier to enter the gas flow channel 111, thereby effectively avoiding the second gas from flowing backward into the second gas conduit 13.

All the guide vanes 122 of the cyclone assembly 12 have a guiding effect, and the guiding direction of each guide vane 122 can be divided into a radial direction component and a tangential direction component, so that the first gas flowing through the cyclone assembly 12 has a radial velocity component and a tangential velocity component. The radial direction refers to the radial direction of the cyclone assembly 12, and the tangential direction is a direction perpendicular to the radial direction. The radial direction component and the radial velocity component are both vectors that are directed radially outward of the cyclone assembly 12. The tangential direction component and tangential velocity component are both vectors that are oriented radially perpendicular to the cyclone assembly 12.

In some embodiments, as shown in fig. 5-7, the middle portion of the cyclone assembly 12 includes a middle shaft sleeve 121, where the middle shaft sleeve 121 is disposed coaxially with the gas flow channel 111. As shown in fig. 2, the second gas conduit 13 axially penetrates the intermediate shaft sleeve 121 along the intermediate shaft sleeve 121, and the outlet of the second gas conduit 13 is located on the end surface of the intermediate shaft sleeve 121 near the premix gas outlet 1112.

Further, in order to enhance the sealability between the second gas duct 13 and the middle sleeve 121, a seal may be provided between the second gas duct 13 and the middle sleeve 121.

The cyclone assembly 12 may be a plastic part, and the middle shaft sleeve 121 and the guide vane 122 are both made of plastic materials. The swirl assembly may be injection molded.

Alternatively, the middle part of the swirl unit 12 may be a cylindrical member through which the second gas duct 13 penetrates in the axial direction of the cylindrical member. A seal may also be provided between the cylindrical member and the second gas conduit 13.

In certain embodiments, the second gas conduit 13 extends through a middle portion of the cyclone assembly 12, and the second gas conduit 13 is in an interference fit with the middle portion of the cyclone assembly 12. For example, the second gas conduit 13 is an interference fit with the intermediate shaft sleeve 121.

The blade shape of the guide vanes 122 of the cyclone assembly 12 includes, but is not limited to, hinges, ping Zhishe, fan blades, pusher blades, and the like.

In one embodiment, as shown in FIGS. 5-7, the turning vanes 122 of the cyclone assembly 12 are hinge vanes having an axial length L4 of 16 mm-20 mm, a mounting angle r of the hinge vanes, an inlet angle r of the hinge vanes _in And the outlet angle r of the hinge blade _out All are 40-80 degrees.

The flow rate of the first gas entering the gas flow channel 111 is mainly along the axial direction of the gas flow channel 111 before passing through the cyclone assembly 12, and after being guided by each guide vane 122, the flow direction is changed, so that a negative pressure area is formed, and additional suction force is provided for the second gas.

Further, as shown in fig. 1 to 3, the premixing device 10 further includes a fan access housing 113, the fan access housing 113 has an outlet and a mounting port 1131, the mounting port 1131 is used for mounting a fan and is communicated with an air outlet of the fan, and the outlet of the fan access housing 113 is in para-position communication with the first gas inlet 1111 of the device body 11. After the fan is started, air can be blown into the air flow channel 111 from the first air inlet 1111, and the first air flows through the cyclone assembly 12 and is mixed with the second air downstream of the cyclone assembly 12.

The second gas conduit 13 extends outwardly through the blower inlet housing 113, and a seal is provided between the second gas conduit 13 and the blower inlet housing 113 to ensure a seal between the blower inlet housing 113 and the second gas conduit 13. One end of the second gas conduit 13 is inserted into the cyclone assembly 12, and the other end of the second gas conduit 13 is located outside the device body 11 for communication with a second gas supply device. The second gas may be a gas.

The second gas supply means may provide a certain forward power to the second gas, but this power does not necessarily suffice for high power combustion applications, but the negative pressure region in the middle of the swirl assembly 12 in the present application adds a power to the second gas, resulting in a higher flow rate of the second gas.

The fan mounted by the mounting port 1131 of the fan access housing 113 may be a model 51F fan, so that the first gas flow rate in the gas flow channel 111 meets the combustion requirement.

Still further, as shown in fig. 3 and 4, in some embodiments, the device body 11 includes a venturi 112 with the passage within the venturi 112 being a gas flow passage 111, and the swirl assembly 12 is coaxially disposed within an inlet section 1121 of the venturi 112.

The venturi 112 can accelerate the flow rate of the mixed gas so that the gas can more quickly flow out of the premix gas outlet 1112, increasing the combustion efficiency of the premix gas. Moreover, the first gas flowing through the swirl assembly 12 has a radial velocity component and a tangential velocity component, and the first gas is further modified in flow rate in the venturi 112 such that the first gas and the second gas are more evenly mixed, thereby improving combustion efficiency.

In some embodiments, the interface of the inlet section 1121 of the venturi 112 and the converging section 1122 of the venturi 112 is a first interface, and the separation between the end surface of the swirl assembly 12 proximate the premix gas outlet 1112 and the first interface is no more than 2.5mm. Limiting the spacing between the swirl assembly 12 and the initial interface (i.e., the first interface) of the convergent section 1122, the space occupation of the swirl assembly 12 to the convergent section 1122 is controlled as much as possible, ensuring airflow velocity within the throat 1123.

In one embodiment, the swirl assembly 12 is centered on the middle sleeve 121, the end surface of the middle sleeve 121 near the premix gas outlet 1112 is located in the inlet section 1121, and the distance between the end surface of the middle sleeve 121 and the converging section 1122 of the venturi 112 is no greater than 2.5mm.

In some embodiments, the interface of the inlet section 1121 of the venturi 112 and the converging section 1122 of the venturi 112 is a first interface with which the end face of the swirl assembly 12 proximate the premix gas outlet 1112 is coplanar. The outlet of the second gas conduit 13 is just located on the first interface, so that adverse effects of the cyclone assembly 12 on the gas flow rate in the venturi 112 are reduced as much as possible, the gas flow resistance in the venturi 1123 is reduced, and further, the gas supply pressure adjusting range corresponding to the second gas in the second gas conduit 13 is wider, and the condition that the first gas flows back into the second gas conduit 13 due to overlarge resistance is avoided.

In one embodiment, the swirl assembly 12 is centered on a center sleeve 121, and the end surface of the center sleeve 121 proximate the premix gas outlet 1112 is coplanar with the first interface.

In some embodiments, as shown in FIG. 4, the constriction angle a1 of the constriction 1122 of the venturi 112 is 45-69 and the diffusion angle a2 of the diffusion 1124 of the venturi 112 is 15-27. The venturi 112 has a throat 1123 length L1 of 30mm to 45mm, a diffuser 1124L 2 of 10mm to 17mm, and an inlet 1121 length L3 of 13mm to 20mm.

The specific parameters of the venturi 112 may be varied for different operating conditions, and may be adjusted according to the actual operating conditions, but the above parameter ranges are ultimately required to be met so that the air supply pressure and mixing performance meet the combustion requirements. If the contraction angle a1 of the contraction section 1122 of the venturi 112 is smaller than 45 °, the second gas concentration fluctuation in the mixed gas flowing out from the premixed gas outlet 1112 is large, and the second gas is gas for the combustion apparatus, and the gas concentration fluctuation is large, which finally means that the flame cannot be stably maintained.

In some embodiments, the inner diameter of the pipe section of the second gas conduit 13 penetrating the cyclone assembly 12 is 5 mm-7.8 mm, and the diameter D4 of the middle part of the cyclone assembly 12 is 10 mm-20 mm. For example, the outer diameter of the intermediate shaft sleeve 121 may be 10mm to 20mm. The inner diameter D1 of the inlet section 1121 of the venturi 112 is 38mm to 44mm, the inner diameter D2 of the throat 1123 of the venturi 112 is 32mm to 38mm, and the maximum inner diameter D3 of the diffuser section 1124 of the venturi 112 is 40mm to 48mm.

If the diameter of the middle part of the cyclone assembly 12 is larger than 20mm, the cyclone assembly 12 occupies a relatively large space in the airflow channel 111, the flow rate of the position where the cyclone assembly 12 is arranged in the airflow channel 111 is relatively small, the air resistance is relatively large, and the gas flow rate is affected. The above parameter optimization design is performed so that the various performances of the premixing device 10 and the gas equipment 20 are well balanced.

The middle part of the cyclone assembly 12 refers to a part near the axis of the cyclone assembly 12, and a plurality of guide vanes 122 are connected with the middle part of the cyclone assembly 12 and are arranged in a divergent way around.

In addition to the premixing device 10 according to any of the foregoing embodiments, the gas apparatus 20 according to some embodiments of the present application further includes a fan mounted at the mounting opening 1131 of the fan access housing 113 for blowing air into the gas flow channel 111. The first gas may be air and the second gas may be gas.

In the gas equipment 20 provided by the above-mentioned scheme, the swirl component 12 disposed in the gas flow channel 111 can provide a guiding effect for the first gas flowing in from the first gas inlet 1111, so that the first gas has a radial velocity component and a tangential velocity component after passing through the swirl component 12, and further a negative pressure area is formed in the middle of the end surface of the swirl component 12, which is close to the premixed gas outlet 1112, and the negative pressure provides suction for the second gas in the second gas conduit 13, so that the second gas is easier to enter the gas flow channel 111 from the second gas conduit 13, and the second gas is prevented from flowing backward into the second gas conduit 13. The second gas introduced through the second gas conduit 13 and the first gas passing through the swirl assembly 12 may be discharged from the premix gas outlet 1112 after being mixed downstream of the swirl assembly 12.

In the description of the present application, it should be understood that, if any, these terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., are used herein with respect to the orientation or positional relationship shown in the drawings, these terms refer to the orientation or positional relationship for convenience of description and simplicity of description only, and do not indicate or imply that the apparatus or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the application.

Furthermore, the terms "first," "second," and the like, if any, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present application, the terms "plurality" and "a plurality" if any, mean at least two, such as two, three, etc., unless specifically defined otherwise.

In the present application, unless explicitly stated and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly. For example, the two parts can be fixedly connected, detachably connected or integrated; can be mechanically or electrically connected; either directly or indirectly, through intermediaries, or both, may be in communication with each other or in interaction with each other, unless expressly defined otherwise. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.

In the present application, unless expressly stated or limited otherwise, the meaning of a first feature being "on" or "off" a second feature, and the like, is that the first and second features are either in direct contact or in indirect contact through an intervening medium. Moreover, a first feature being "above," "over" and "on" a second feature may be a first feature being directly above or obliquely above the second feature, or simply indicating that the first feature is level higher than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is less level than the second feature.

It will be understood that if an element is referred to as being "fixed" or "disposed" on another element, it can be directly on the other element or intervening elements may also be present. If an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and the like as used herein, if any, are for descriptive purposes only and do not represent a unique embodiment.

The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The foregoing examples illustrate only a few embodiments of the application, which are described in detail and are not to be construed as limiting the scope of the claims. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.

Claims

1. A premixing device, comprising:

2. The premixing device of claim 1, wherein the device body includes a venturi, the venturi interior passage is the gas flow passage, and the swirl assembly is coaxially disposed within an inlet section of the venturi.

3. The premixing device of claim 2, wherein the interface of the inlet section of the venturi and the converging section of the venturi is a first interface, and the separation between the end face of the swirl assembly proximate the premix gas outlet and the first interface is no greater than 2.5mm.

4. A premixing device according to claim 3, wherein an end face of the swirl assembly proximate the premix gas outlet is coplanar with the first interface.

5. The premixing device according to claim 2, wherein the contraction angle a1 of the contraction section of the venturi tube is 45 ° to 69 °, the diffusion angle a2 of the diffusion section of the venturi tube is 15 ° to 27 °, the throat length of the venturi tube is 30mm to 45mm, the diffusion section length of the venturi tube is 10mm to 17mm, and the inlet section length of the venturi tube is 13mm to 20mm.

6. The premixing device according to claim 2, wherein the inner diameter of a pipe section penetrating through the cyclone assembly on the second gas conduit is 5 mm-7.8 mm, the second gas conduit is arranged in the middle of the cyclone assembly, the diameter of the middle of the cyclone assembly is 10 mm-20 mm, the inner diameter of an inlet section of the venturi tube is 38 mm-44 mm, the inner diameter of a throat tube of the venturi tube is 32 mm-38 mm, and the maximum inner diameter of a diffusion section of the venturi tube is 40 mm-48 mm;

7. The premixing device of any one of claims 1 to 6, wherein a central portion of the swirl assembly includes a central sleeve coaxially disposed with the gas flow passage, the second gas conduit passing axially through the central sleeve, an outlet of the second gas conduit being located on an end face of the central sleeve proximate the premix gas outlet.

8. The premixing device of claim 7, wherein a seal is provided between the second gas conduit and the middle sleeve.

9. The premixing device of any one of claims 1 to 6, further comprising a blower access housing having an outlet and a mounting port for mounting a blower and communicating with an air outlet of the blower, the outlet of the blower access housing being in aligned communication with the first gas inlet of the device body, the second gas conduit extending outwardly through the blower access housing, a seal being provided between the second gas conduit and the blower access housing.

10. Premix apparatus according to any of claims 1-6, wherein the guide vanes of the swirl assembly are hinge vanes having an axial length of 16-20 mm, the mounting angle r of the hinge vanes, theInlet angle r of hinge blade _in And the outlet angle r of the hinge blade _out All are 40-80 degrees.

11. A gas plant comprising a combustion section and a premixing device as claimed in any one of claims 1 to 9, the combustion section being arranged at the premix gas outlet.