Gas-air mixing device for a heating device and heating device

Abstract

A gas-air mixing device (15) for a heating appliance (1) is proposed. Viewed in a flow direction (16) through the gas-air mixing device (15), this device has a convergence zone (18), a throttling zone (19) with a flow diameter (22) of at least 11.0 mm, and a divergence zone (20) adjoining the throttling zone (19) with a length (25) of at least 85.0 mm, wherein, viewed in the flow direction (16), three or four gas outlets (27) are arranged concentrically with respect to a central axis (21) of the gas-air mixing device (15) and are designed as a recessed channel in the inner wall of the mixing device (15) oriented in the flow direction (16).

Description

[0001] The invention relates to a gas-air mixing device for a heater and a heating device.

[0002] Heating devices for burning a fuel gas, such as natural gas or hydrogen, generally create a combustion mixture of fuel gas and combustion air with a predetermined combustion air ratio (also known as lambda or air ratio) and feed this mixture to a burner for combustion. Such heating devices are also known as premix burners. Various processes are known for forming the combustion air ratio. Heating devices with a pneumatic gas-air connection record a control pressure in the area of ​​a throttle point (Venturi nozzle) in the combustion air supply, which allows a conclusion to be drawn about the supplied mass flow of combustion air. Using the reference pressure, the gas valve adds a mass flow of fuel gas corresponding to a predetermined combustion air ratio. The fuel gas is often mixed with the mass flow of combustion air in the area of ​​the throttle point, which can be designed as a gas-air mixing device for this purpose.The advantage of pneumatic mixture formation is that it does not require complex sensors and is therefore very robust in application and simple in construction.

[0003] In such heaters, the heating output is controlled, or a modulation point is reached, by means of the fan speed, which adjusts the mass flow of combustion air to be supplied, to which the gas valve, based on the control pressure, adds a flow rate of fuel gas corresponding to a predetermined combustion air ratio. For this purpose, the requirements for heaters with regard to their modulation range—for example, the heaters must be able to operate at an output of 10% of the rated output—pose a challenge for the design of the mixing device. Thus, the mixing device (the throttle point) must generate sufficient intake pressure for mixture formation at low outputs, but at high outputs, the pressure drop at the throttle point must not be too high.A large pressure drop at high power levels is accompanied by a number of disadvantages, such as the need for a large fan, high noise emissions and a risk of flushing the heater's siphon due to the high pressure.

[0004] To utilize the intake pressure of the throttle point, gas is usually added in the area of ​​the smallest flow cross-section of the throttle point. For example, EP 3 488 148 B1 shows a gas-air mixing device with at least six gas pockets for adding fuel gas, arranged in the area of ​​the narrowest flow cross-section of the throttle point. However, this mixing device can also only be used for a limited modulation range.

[0005] Other similar gas-air mixing devices with the same disadvantage are also disclosed in DE 10 2029 202 950 A1, EP 0 846 916 A2 and DE 10 2011 014 117 A1.

[0006] Based on this, the object of the invention is to propose a gas-air mixing device for a heater and a heating device that at least partially overcomes the described problems of the prior art. In particular, the mixing device should enable safe operation of the heater within a wide modulation range, for example, a modulation range with a lower limit of 10% of the heater's rated power.

[0007] In addition, the invention should at least not significantly increase the complexity of the mixing device and the mixing device should be easy to manufacture.

[0008] These objects are achieved by the features of the independent patent claims. Further advantageous embodiments of the solution proposed here are specified in the independent patent claims. It is pointed out that the features listed in the dependent patent claims can be combined with one another in any technologically expedient manner and define further embodiments of the invention. Furthermore, the features specified in the patent claims are further specified and explained in the description, with further preferred embodiments of the invention being presented.

[0009] A gas-air mixing device for a heater contributes to this, which, with respect to the flow direction of the gas-air mixing device, has at least the following areas: 1.) a convergence area, 2.) a (downstream) throttle area with a flow diameter of at least 11.0 mm [millimeters], and 3.) a divergence area adjoining the throttle area with a length of at least 85 mm [millimeters]. Further along the flow direction, three or four gas outlets are arranged concentrically with respect to a central axis of the gas-air mixing device or (distributed) over a circumference of the gas-air mixing device and are designed as a recessed channel in the inner wall of the mixing device, aligned in the flow direction.

[0010] The heater can be a gas heater with a pneumatic gas-air connection. This can have a conveying device, in particular a fan, which can convey a mass flow (or volume flow) of combustion air. The combustion air can be supplied via a combustion air supply, with a control pressure (reference pressure) for the gas valve often being transmitted to the gas valve via a control line in an area between the fan and the throttle point. The gas valve can add a mass flow of fuel gas corresponding to the control pressure and a predetermined combustion air ratio. The heater can, in particular, be a wall-mounted heater and use condensing technology. Such a pneumatic gas-air connection advantageously enables robust adjustment of a predetermined combustion air ratio, particularly since the mass flow of fuel gas depends on the effective flow of combustion air.

[0011] Such a heater can adapt its heating output to a heat requirement, also known as modulation. This can be done within a modulation range specified for the heater. To avoid frequent, wear-inducing switching of the burner on and off, modern heaters can be operated in a wide modulation range, for example from 2.4 kW [kilowatts] to 24 kW (corresponding to 10% to 100% of the nominal output). A wide modulation range places high demands on the gas-air mixing device, which must generate sufficient suction pressure for the escaping mass flow of fuel gas at low power levels, but must have the lowest possible flow resistance (pressure loss) at high power levels and thus a high mass flow of combustion air.

[0012] The heater comprises a gas-air mixing device with a throttle section (Venturi) in which a control pressure is generated for the escaping gas flow. Depending on the control pressure, the mass flow of fuel gas provided by the gas valve is added to the mass flow of combustion air. This advantageously reduces the required installation space.

[0013] The gas-air mixing device can thus be designed as a Venturi nozzle with gas outlets. The mass flow (or volume flow) of combustion air conveyed by the conveying device flows through the gas-air mixing device and reaches an increased dynamic pressure in the area of ​​its minimum diameter, which is used to draw in the mass flow of fuel gas.

[0014] For this purpose, the gas-air mixing device (first) has a convergence region in which the flow cross-section decreases (from a first flow diameter to a first minimum flow diameter) and the flow velocity of the combustion air mass flow entering the gas-air mixing device increases accordingly. In a throttle region, the minimum flow cross-section (minimum diameter) is reached and thus also the maximum flow velocity of the combustion air mass flow. It is intended that this minimum flow diameter is not selected to be smaller than 11.0 mm and that the heater can be operated robustly with this flow diameter and a minimum power of the modulation range. The throttle region is followed by a divergence region in which the flow cross-section increases again (from a second small or minimum flow diameter to a second larger ormaximum flow diameter) and the flow velocity decreases. The divergence region is designed to have a length of at least 85.0 mm, because above this limit, a defined and robust pressure loss of the gas-air mixing device can be detected.

[0015] In other words, the gas-air mixing device, viewed in a flow direction of the heater, can comprise a convergence region characterized by a decreasing flow cross-section, a throttle region with the smallest flow cross-section and a divergence region with an increasing flow cross-section.

[0016] According to one embodiment, the convergence region can have a conical or trumpet shape. A conical shape is characterized by a straight line of the convergence region in a longitudinal section of the gas-air mixing device, which encloses an angle with respect to a central axis (in the direction of flow). It has been shown that an angle in a range of 30° to 70° is advantageous. A trumpet shape is characterized by a non-straight profile of the convergence region in a longitudinal section. For example, the profile can describe a segment of a circle, an exponential function, or other functions.

[0017] According to one embodiment, the convergence region may have a length of at least 10 mm [millimeters] mm.

[0018] The throttle area of ​​the gas-air mixing device can have a flow diameter (of the circular flow cross-section) of at least 11.0 mm. The flow diameter of 11.0 mm can be used for a heater with a modulation range of 1.7 kW to 17 kW. For heaters with higher power outputs, a correspondingly larger (minimum) flow diameter of the throttle area can be selected. The minimum flow diameter is largely determined by the minimum power output of a heater. For example, the minimum flow diameter can be determined by the relationship between the minimum flow diameter and the minimum power output (in kW) + 7.23.

[0019] According to one embodiment, the throttle region can have a length of at least 10 mm.

[0020] The divergence region can, in particular, have a conical shape and an opening angle in a range of 4° to 7°. The opening angle refers to the angle enclosed by an inner wall of the convergence region.

[0021] According to one embodiment, the gas outlets can have a depth of 0.9 mm to 1.5 mm, where the depth refers to the depth available for the gas flow. The wall thickness of the inner wall can be in a range of 0.05 to 0.15 mm and refers to the distance of the flow channel of the gas outlet from the flow cross-section of the gas-air mixing device.

[0022] According to one embodiment, the width of the gas outlets can be determined based on the depth, the wall thickness of the inner wall, and the flow diameter of the throttle area. In particular, the available flow cross-section of the fuel gas can be between 8% and 20% of the flow cross-section of the combustion air in the throttle area.

[0023] According to one embodiment, the gas outlets are arranged entirely within the throttle region. Thus, viewed in the flow direction of the gas-air mixing device, they can be arranged directly after the convergence region and / or directly before the divergence region.

[0024] According to one embodiment, the gas-air mixing device can have a connection area for connecting to a silencer. The connection area can be arranged in particular in the convergence area and, for example, comprise a device for connecting to a silencer, such as a click, clamp, or screw connection. This enables simple and quick installation.

[0025] According to one embodiment, the gas-air mixing device can be formed as a single piece and made, for example, of a plastic or a metallic material. Manufacture can be carried out, for example, using an injection molding process.

[0026] According to a further aspect, a heating device is also proposed, comprising a gas-air mixing device as proposed here. Furthermore, the heating device can comprise a fan for conveying a mass flow of combustion air, an ignition electrode, and a gas valve. The heating device can form a pneumatic gas-air system.

[0027] The details, features, and advantageous embodiments discussed in connection with the gas-air mixing device can also be found in the heater presented here, and vice versa. In this respect, reference is made in full to the explanations therein for a more detailed characterization of the features.

[0028] This therefore provides a gas-air mixing device for a heater and a heater that at least partially solve the problems described with reference to the prior art. In particular, the gas-air mixing device and the heater contribute to enabling safer operation of a heater within a wide modulation range. Tests have shown that safe operation of a heater within a modulation range from 2.4 kW to 24 kW and / or from 10% of the heater's rated power up to the rated power is possible using a gas-air mixing device as proposed here.

[0029] In addition, a gas-air mixing device proposed here can be easily used on a state-of-the-art heater and could therefore also be retrofitted to existing heaters.

[0030] The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments cited. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures, and in particular the proportions shown, are only schematic. They show: Fig. 1: a heating device proposed here, and Fig. 2: a gas-air mixing device proposed here in a sectional view, Fig. 3: a further view of a gas-air mixing device proposed here, and Fig. 4: a sectional view of a gas outlet of a gas-air mixing device proposed here.

[0031] Fig. 1 shows, by way of example and schematically, a heater 1 proposed here. This heater can have an air supply 4 for combustion air. A gas-air mixing device 15 can be arranged in the air supply 4. Viewed in a flow direction 16 of the heater 1, a conveying device 2 designed as a fan, which can convey a mass flow of combustion air, can be arranged upstream of the gas-air mixing device 15. A gas valve 5 can, by means of the gas-air mixing device 15, add a mass flow of fuel gas to the mass flow of combustion air conveyed by the conveying device 2. For this purpose, the gas valve can be connected to a gas supply 8. The mixture of fuel gas and combustion air can be fed to a burner 3 via a mixture channel 12 and burned there. A heat exchanger 13 can be arranged on the burner 3, which can transfer heat generated during combustion to a heating circuit 14 with a supply line 6 and a return line 9.

[0032] Downstream of the burner 3, an exhaust pipe 10 can supply combustion products to an exhaust system 11. A control and regulating device 7 of the heater 1 can be electrically connected at least to the gas valve 5 and the conveying device 2.

[0033] An ignition electrode 17 can be arranged on the burner 3, designed to form an ignition spark in order to ignite the combustion mixture emerging from the burner 3.

[0034] Fig. 2 shows, by way of example and schematically, a longitudinal section in the direction of the central axis 21 of the gas-air mixing device 15. This comprises a trumpet-shaped convergence region 18 with a length 23. Seen in the flow direction 16, the throttle region 19 with a length 24 and with a minimum diameter 22 of the flow cross-section adjoins the convergence region 23.

[0035] A divergence area 20 can be connected to the throttle area 19. This can have a length 25 of 85 mm and an opening angle 26 of 5.5°. A connection area 28 for connecting to a silencer of the heater 1 can be provided outside in the convergence area 18 or in the throttle area 19.

[0036] The gas-air mixing device 15 may include gas outlets 27. These can add a mass flow of fuel gas provided by the gas valve 5 to the mass flow of combustion air conveyed by the conveying device 2 and flowing through the gas-air mixing device 15.

[0037] Fig. 3 shows, by way of example and schematically, a top view of the convergence region 18 of the gas-air mixing device 15. Three gas outlets 27 are clearly visible, evenly distributed around the circumference. The gas outlets 27 can enclose an angle 31, which is a measure of the width of the gas outlets 27.

[0038] Fig. 4shows, by way of example and schematically, a sectional view of a gas outlet 27. This can have a channel depth 30 and a wall thickness of the inner wall 29.

[0039] As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and therefore do not necessarily specify any interdependence and / or sequence of these objects, quantities, or processes. Should a dependence and / or sequence be required, this is explicitly stated here or will be obvious to the person skilled in the art upon studying the specifically described embodiment. To the extent that a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or part of the majority of these components, but this is not mandatory. List of reference symbols

[0040] 1 Heater 2 Conveyor system 3 Burner 4 Air supply 5 Gas valve 6 Flow 7 Control unit 8 Gas supply 9 Return 10 Exhaust pipe 11 Exhaust system 12 Mixing channel 13 Heat exchanger 14 Heating circuit 15 Gas-air mixing device 16 Flow direction 17 Ignition electrode 18 Convergence area 19 Throttle area 20 Divergence area 21 Central axis 22 Diameter 23 Length of convergence area 24 Length of throttle area 25 Length of divergence area 26 Opening angle of divergence area 27 Gas outlet 28 Connection area 29 Wall thickness of the inner wall 30 Channel depth 31 Gas outlet angle

Claims

1. Gas-air mixing device (15) for a heater (1), at least comprising, as seen in a flow direction (16) of the gas-air mixing device (15), a convergence region (18), a throttle region (19) with a flow diameter (22) of at least 11.0 mm and a divergence region (20) adjoining the throttle region (19) with a length (25) of at least 85.0 mm, wherein, as seen in the flow direction (16), three or four gas outlets (27) are arranged over a circumference of the gas-air mixing device (15) and are designed as a recessed channel in the inner wall of the mixing device (15) that is aligned in the flow direction (16).

2. Gas-air mixing device (15) according to claim 1, wherein the divergence region (20) has an opening angle (26) in a range of 4 ° [degrees] to 7 °.

3. Gas-air mixing device (15) according to one of the preceding claims, wherein the gas outlets (27) have a channel depth (30) in a range from 0.9 mm to 2.5 mm and the wall thickness (29) of the inner wall in the region of a gas outlet (27) is in a range from 0.05 mm to 0.15 mm.

4. Gas-air mixing device (15) according to one of the preceding claims, wherein the gas outlets (27) have a cumulative flow cross-section of 8% [percent] to 20% of the flow cross-section of the combustion air in the throttle region (19).

5. Gas-air mixing device (15) according to one of the preceding claims, wherein the convergence region (18) has a conical or trumpet-shaped form.

6. Gas-air mixing device (15) according to one of the preceding claims, wherein the gas outlets (27) are arranged in the throttle region (19).

7. Gas-air mixing device (15) according to one of the preceding claims, wherein the gas-air mixing device (15) comprises a connection region (28) adapted for connection to a silencer of the combustion air supply (4).

8. Gas-air mixing device (15) according to one of the preceding claims, wherein the gas-air mixing device (15) is manufactured in one piece.

9. Heating device (1) comprising a gas-air mixing device (15) according to one of the preceding claims.

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