Mixing device and method for controlling the temperature of a fluid flow

Abstract

A mixing device includes a first inlet (84) and a second inlet (86) inlet and an outlet (80). The first inlet (84) is connected to the outlet (80) via a first flow connection and the second inlet (86) is connected to the outlet (80) via a second flow connection. A circulation pump assembly (24; 46) includes an electric drive motor (30), a control device (34), for controlling the speed of the drive motor (30), and at least one impeller (68; 100) driven by the drive motor. The at least one impeller (68; 100) is positioned in the first flow connection. The flow connections are configured such that at least one hydraulic pressure generated by the impeller (68; 100) in the first flow connection acts as hydraulic resistance in the second flow connection.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a United States National Phase Application of International Application PCT / EP2018 / 070969, filed Aug. 2, 2018, and claims the benefit of priority under 35 U.S.C. § 119 of European Application 17 184 777.5, filed Aug. 3, 2017, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD[0002]The subject-matters of the invention are a mixing device, a heating system with such a mixing device as well as a method for the temperature adjustment of a fluid flow.TECHNICAL BACKGROUND[0003]Mixers or mixing devices are often used in heating facilities, in order to adjust the temperature of a heating medium or heat transfer medium. Thus for example in floor heating facilities it is common to reduce the feed temperature of the heating medium by way of admixing heating medium from the return. Adjustable mixing valves which are electromotorically driven and change the mixing ratio between hot heating medium and ...

AI Technical Summary

Benefits of technology

[0005]With regard to this problem, it is the object of the invention to provide a less expensive mixing device which has higher energy efficiency.

[0009]According to the invention, the electrical drive motor comprises a control device for the speed control of the drive motor. I.e. the control device can change the speed of the drive motor and in particular regulate it (control it with a closed loop). For this, the control device can be equipped with a frequency converter. The drive motor drives at least one impeller in the mixing device. This at least one impeller is situated in the first flow connection through the mixing device and thus, when the drive motor rotates, delivers fluid from the first inlet to the outlet of the mixing device. According to the invention, the arrangement of the flow connections in the inside of the mixing device and their design are such that at least one hydraulic pressure which is produced in the first flow connection by the impeller acts as a hydraulic resistance in the second flow connection. The hydraulic pressure in the first flow connection can therefore influence the flow in the second flow connection via the produced hydraulic resistance. In this manner, an influencing of the mixing ratio is possible solely by way of hydraulic means in the mixing device. This has the advantage that one can make do without actuating drives for a special mixing valve, so that as a whole a simpler construction of the mixing device according to the invention is achieved. Moreover, if one can make do without one or more valves for adjusting the mixing ratio, then furthermore the hydraulic resistance of the complete mixing device can be reduced, by which means energy losses in the mixing device can be reduced and minimized.

[0016]The first and the second flow path in the at least one impeller or in the two impellers which are connected to one another in a rotationally fixed manner are further preferably designed such that on rotation of the at least one impeller or of the two impellers which are connected to one another in a rotationally fixed manner, they effect pressure developments which are different from one another and in particular different speed-dependent pressure developments. This permits the pressure ratio between the two flow paths to be changed by way of a speed change of the impeller or of the impellers, so that the mutual influencing via the produced hydraulic resistances is changed and a mixing ratio of the flows through the two flow connections can therefore be changed.

[0022]According to a further preferred embodiment of the invention, the first arrangement of impeller blades is connected to the first suction port of the impeller and the second arrangement of impeller blades is connected to a second suction port which forms a second inlet opening of the impeller. This second suction port surrounds the first suction port preferably in an annular manner. As an alternative, the second suction port could also be arranged away from the first suction port in the axial direction, so that the inflow directions into the impeller through the two suction ports are directed axially opposite one another. This arrangement would have the advantage that the occurring axial forces at least partly cancel one another out. The annular or concentric arrangement of the first and of the second suction port has the advantage that such a design can be integrated relatively simply into a known pump casing.

[0026]Particularly preferably, a second circulation pump assembly can be arranged in the feed in a manner such that it provides a fluid, in particular a fluid heat transfer medium or a fluid heating medium at a preliminary pressure at the second inlet of the mixing device. Such a second circulation pump assembly can be for example a circulation pump assembly which is integrated into the heat source, in particular into the heating boiler. This second circulation pump assembly can moreover simultaneously serve for feeding the fluid or the heat transfer medium to a further heating circuit. It is possible to utilize the preliminary pressure, at which the fluid is provided at the second inlet due to the fact that the mixing device, as described above, is designed such that different pressure increases are reached for the two flow paths through the impeller. I.e., the pressure does not have to be relieved in a valve arranged upstream, so that energy losses can be minimized. The preliminary pressure can moreover contribute to the speed-dependent pressure courses through the two described flow paths of the impeller being different to the extent that the hydraulic resistance in at least one of the flow connections and in particular of the second flow connection can be varied by way of speed variation, in order to change the mixing ratio.

[0029]Further preferably, the hydraulic resistance is varied by way of changing the fluid pressure of the first and / or the second fluid flow. I.e., at least one of the fluids flows itself forms a hydraulic resistance for the other fluid flow. Particularly preferably, the both fluid flows form reciprocal hydraulic resistances. Hence by way of a pressure change in one of the fluid flows, the hydraulic resistance in the other fluid flow is changed, so that the flow rate of this other flow can be varied, so that different mixing ratios result. A changeable pressure increase in at least one of the two fluid flows is preferably effected by way of pressure increasing / boosting means, wherein the pressure increase is preferably effected by an impeller of a centrifugal pump assembly. This can be effected as was described above by way of the mixing device. The pressure in at least one flow path through the impeller changes by way of speed change of the impeller of the centrifugal pump assembly, so that the pressure in a fluid flow through this flow path can be changed.

Problems solved by technology

The disadvantages of these arrangements are the costs for the individual components and the energy losses which occur in a mixing valve.

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