WO2022002064A1

WO2022002064A1 - Heat balance mixer and sofc system comprising the same

Info

Publication number: WO2022002064A1
Application number: PCT/CN2021/103161
Authority: WO
Inventors: Fumei QIAN; Xuesong SHEN; Hongmin CAO
Original assignee: Ceres Intellectual Property Company Limited; Weichai Power Co., Ltd.
Priority date: 2020-06-30
Filing date: 2021-06-29
Publication date: 2022-01-06

Abstract

The invention discloses a heat balance mixer, comprising a mixing chamber (1). The mixing chamber is provided with at least two mixer inlets (2) and one mixer outlet (4), each of the mixer inlets is connected to an inlet pipe, the mixer outlet is connected to an outlet pipe (41), one of the inlet pipes extends from the top of the mixing chamber into the interior of the mixing chamber, the inlet pipe located inside the mixing chamber is a main mixing pipe (23), a perforated structure is provided on the outer periphery of the main mixing pipe opposite to at least one of the remaining mixer inlets, and the perforated structure comprises at least one elongated opening (24). When the heat balance mixer is working, the perforated structure on the periphery of the main mixing pipe can be used to form a cross counter-flow impact of the gases in the mixing chamber, thereby improving the mixing uniformity of the gases with large physical-property differences; and in addition, by designing the elongated opening structure, the pressure drop of mixing can be further reduced.

Description

[Title established by the ISA under Rule 37.2] HEAT BALANCE MIXER AND SOFC SYSTEM COMPRISING THE SAME

TECHNICAL FIELD

The present invention relates to the technical field of heat balance mixers and their use in SOFC systems.

BACKGROUND ART

The intake temperature and uniformity of fuel cells, such as solid oxide fuels cells (SOFC) are important factors that influence the generated power of the stack and avoid thermal shock damage in the stack. Considering the utilization of the heat of the stack exhaust gas, it is an important indicator for the design of a heat balance mixer to ensure the effective mixing of gases under different energy and density gradients. Here, heat balance means that heat transfer between two or more systems with different temperature values occurs until the systems are at the same temperature. This heat exchange process complies with the law of conservation of energy. Density/energy gradient refers to the derivative value of a continuous derivable scalar such as density and energy enthalpy in different directions in the Cartesian coordinate system, which is a first-order vector. Thermal shock damage means that when heat exchange occurs between two or more fluids with large temperature differences in a relatively short period of time, a thermal shock stress is generated due to rapid temperature change and uneven distribution, and components of a system will be damaged when the thermal stress exceeds the yield limit of the material.

Due to defects in structural design, the heat balance mixer in the prior art often cannot ensure the mixing uniformity of various gases with large physical-property differences and has a large pressure drop of mixing.

SUMMARY OF THE INVENTION

The present invention provides a heat balance mixer to improve the mixing uniformity of gases with large physical-property differences and reduce the pressure drop of mixing.

This invention provides a heat balance mixer, which comprises a mixing chamber. The mixing chamber is provided with at least two mixer inlets and one mixer outlet. Each of the mixer inlets is connected to an inlet pipe. The mixer outlet is connected to an outlet pipe. One of the inlet pipes extends from the top of the mixing chamber into the interior of the mixing chamber. The inlet pipe located inside the mixing chamber is a main mixing pipe. A perforated structure is provided on the outer periphery of the main mixing pipe opposite to at least one of the remaining mixer inlets, and the perforated structure comprises at least one elongated opening.

The perforated structure can further comprise a plurality of through holes located on the periphery of the elongated opening, and the length and width of the elongated opening are both greater than the equivalent diameter of the through holes.

The length of the elongated opening can be more than 12 times the equivalent diameter of the through holes, and the width of the elongated opening can be more than three times the equivalent diameter of the through holes.

The elongated opening can be a rectangular opening, and the through holes are round through holes.

The length of the elongated opening can be greater than the equivalent diameter of the mixer inlets disposed opposite thereto.

The lengthwise direction of the elongated opening is parallel to the axial direction of the main mixing pipe.

An end opening of the main mixing pipe can abut against the bottom of the mixing chamber, and there can be a preset distance between the perforated structure and the end opening of the main mixing pipe.

The mixing chamber can be a cylindrical chamber, and the circumferential inner wall surface of the cylindrical chamber can be an arc surface.

The cross section of the cylindrical chamber can be elliptical.

The outside of at least one of the inlet pipes can be communicated with a branch mixing pipe.

The mixer outlet can be in fluid communication with an SOFC stack inlet.

The invention also provides an SOFC system comprising the heat balance mixer.

The heat balance mixer provided by embodiments of the present invention comprises a mixing chamber. The mixing chamber is provided with at least two mixer inlets and one mixer outlet, each of the mixer inlets is connected to an inlet pipe, the mixer outlet is connected to an outlet pipe, one of the inlet pipes extends from the top of the mixing chamber into the interior of the mixing chamber, the inlet pipe located inside the mixing chamber is a main mixing pipe, a perforated structure is provided on the outer periphery of the main mixing pipe opposite to at least one of the remaining mixer inlets, and the perforated structure comprises at least one elongated opening. When the heat balance mixer is working, gases with different physical properties flow into the mixing chamber via different inlet pipes. The gas flowing out from the perforated structure on the periphery of the main mixing pipe and the gases flowing into from opposite mixer inlets form a cross counter-flow impact in the mixing chamber, thereby increasing turbulent disturbance, enhancing the fluid mixing effect, and subsequently improving the mixing uniformity of the gases with large physical-property differences. In addition, because the perforated structure comprises an elongated opening, the pressure drop of mixing can be further reduced when the gas flows out of the main mixing pipe, and at the same time, the gas and the gases from the opposite mixer inlets can achieve an effect of premixing of a large amount of fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings used in the description are described below. These are just some embodiments of the present invention.

Fig. 1 is an overall structural schematic view of a heat balance mixer.

Fig. 2 is an external structural schematic view of a mixing chamber.

Fig. 3 is a structural schematic view of the layout of a main mixing pipe inside a mixing chamber.

Fig. 4 is a schematic view of a counter-flow impact flow field inside a mixing chamber.

Fig. 5 is a front view of a main mixing pipe.

Fig. 6 is a rear view of a main mixing pipe.

In Fig. 1 to Fig. 6, the following reference numerals are used: 1-mixing chamber, 2-mixer inlet, 3-branch mixing pipe, 4-mixer outlet, 41-outlet pipe, 21-first inlet pipe, 22-second inlet pipe, 23-main mixing pipe, 24-elongated opening, 25-through hole.

DETAILED DESCRIPTION

Embodiments of the present invention will be described below in conjunction with the drawings. The described embodiments are only some of the embodiments of the present invention.

The embodiment of present invention shown in Fig. 1 provides a heat balance mixer, comprising a mixing chamber 1. The mixing chamber 1 is provided with at least two mixer inlets 2 and a mixer outlet 4. Each of the mixer inlets 2 is connected to an inlet pipe. The mixer outlet 4 is connected to an outlet pipe 41. One of the inlet pipes extends from the top of the mixing chamber 1 into the interior of the mixing chamber 1. The inlet pipe located inside the mixing chamber 1 is a main mixing pipe 23. A perforated structure is provided on the outer periphery of the main mixing pipe 23 opposite to at least one of the remaining mixer inlets 2, and the perforated structure comprises at least one elongated opening 24.

When the heat balance mixer is working, gases with different physical properties flow into the mixing chamber via different inlet pipes. The gas flowing out from the perforated structure on the periphery of the main mixing pipe 23 and the gases flowing in from opposite mixer inlets 2 form a cross counter-flow impact in the mixing chamber 1, thereby increasing turbulent disturbance, enhancing the fluid mixing effect, and subsequently improving the mixing uniformity of the gases with large physical-property differences. In addition, because the perforated structure comprises an elongated opening 24, the pressure drop of mixing can be further reduced when the gas flows out of the main mixing pipe 23. At the same time, the gas and the gases from the opposite mixer inlets 2 can achieve an effect of premixing of a large amount of fluids.

The inlet pipe connected to the mixer inlets 2 may be a separate pipe or may also have branch pipes. The outside of at least one of the inlet pipes can be communicated with a branch mixing pipe 3. As shown in Fig. 1, the mixing chamber 1 comprises two mixer inlets 2. One of the mixer inlets 2 is connected to a first inlet pipe 21, the other mixer inlet 2 is connected to a second inlet pipe 22. The portion of the first inlet pipe 21 stretching into the mixing chamber 1 is the main mixing pipe 23. The portion of the first inlet pipe 21 located outside the mixing chamber 1 is communicated with a branch mixing pipe 3. Fluids with different physical properties are input to the first inlet pipe 21 and the branch mixing pipe 3 respectively. These two fluids with different physical properties are intersected and mixed in advance at the junction of the first inlet pipe 21 and the branch mixing pipe 3, and then enter the main mixing pipe 23 through the lower half section of the first inlet pipe 21, and then flow into the mixing chamber 1 from the perforated structure of the internal main mixing pipe 23. The third fluid is directly input into the mixing chamber 1 from the second inlet pipe 22 and is mixed with the fluids input from the main mixing pipe 23 in the mixing chamber 1. The mixed fluid flows out from a mixer outlet 4 via the outlet pipe 41.

The mixing chamber 1 can have various structural shapes. For example, a cylindrical chamber, a rectangular chamber, or a spherical chamber. The mixing chamber 1 is a cylindrical chamber in this embodiment. As shown in Fig. 1, the circumferential inner wall surface of the cylindrical chamber is an arc surface. Such a configuration is favorable to the formation of large-scale turbulent disturbance in the mixing chamber 1 and enhances the mixing effect of fluids. The cross section of the foregoing cylindrical chamber may be a circle, an ellipse, or in other shapes. In this embodiment, the cross section of the cylindrical chamber is an ellipse.

The layout of the plurality of mixer inlets 2 and the mixer outlet 4 on the mixing chamber 1 can be adjusted according to the actual pipe assembly route and space conditions. The layout shown in Fig. 1 is one design of this solution. The cylindrical top of the mixing chamber 1 is designed to have a mixer inlet 2, and another mixer inlet 2 and a mixer outlet 4 are arranged on two circumferential sides of the mixing chamber 1. The mixer inlet 2 located at the top of the cylindrical top is adjacent to the circumferential side of the other mixer inlet 2. This design facilitates prompt and effective mixing with the fluid input from the second inlet pipe 22 after the main mixing pipe 23 stretches into the mixing chamber 1.

In this embodiment, a perforated structure is provided on the outer periphery of the main mixing pipe 23 in order to improve the mixing effect of a plurality of fluids, so that the mixed fluid flowing out of the perforated structure and the fluid input from the second inlet pipe 22 form a cross counter-flow impact here to increase turbulent disturbance and enhance the fluid mixing effect. The flow field is schematically shown in Fig. 4. The three arrows on the right of Fig. 4 represent the flow direction of a mixed fluid of the first and second fluids input from the main mixing pipe 23, and the three arrows on the left of Fig. 4 represent the flow direction of the third fluid input into the mixing chamber 1 from the second inlet pipe 22.

The perforated structure in this solution further comprises a plurality of through holes 25 located on the periphery of the elongated opening 24, and the length and width of the elongated opening 24 are both greater than the equivalent diameter of the through holes 25. The length of the elongated opening 24 is more than 12 times the equivalent diameter of the through holes 25, and the width of the elongated opening 24 is more than three times the equivalent diameter of the through holes 25, thereby ensuring that the elongated opening 24 has a large circulation area relative to the through holes 25 to further reduce the pressure drop of mixing. The elongated opening 24 can be designed to be a rectangular opening, an oblong opening, or a relatively flat oval opening, etc., and the through holes 25 can be round holes, square holes, etc. The elongated opening 24 is a rectangular opening in this embodiment, and the through holes 25 are round through holes, and as shown in Fig. 3 and Fig. 5, the length and width of the elongated opening 24 are both much greater than the diameter of the through holes 25. The purpose of providing a plurality of through holes 25 is to increase the velocity of the fluid flowing out of the main mixing pipe 23 and to increase the small-scale turbulence inside the mixing chamber 1 to enhance fluid mixing. However, if the fluid flows out only through the small openings, the pressure drop during mixing will increase. Therefore, in this solution, a wide and long elongated opening 24 is opened on a side of the main mixing pipe 23 directly facing the mixer inlets 2, so that the fluid circulation area is greatly increased, thereby reducing the pressure drop of mixing and achieving the purpose of premixing of a large amount of fluids arriving here, while the small-diameter through holes 25 are distributed on both sides or on the periphery of the elongated opening 24 to further improve the mixing effect by using the high flow rate and small-scale turbulence generated by them.

Preferably, the length of the elongated opening 24 is greater than the equivalent diameter of the mixer inlets 2 arranged opposite thereto. Such setting can further increase the circulation area of the elongated opening 24, thereby further reducing the pressure drop of mixing.

It should be noted that the elongated opening 24 can extend along the axis of the main mixing pipe 23 or can form a certain angle with the axis of the main mixing pipe 23. The lengthwise direction of the elongated opening 24 can be arranged parallel to the axial direction of the main mixing pipe 23.

An end opening of the main mixing pipe 23 abuts against the bottom of the mixing chamber 1, and there is a preset distance D between the perforated structure and the end opening of the main mixing pipe 23. As shown in Fig. 3 and Fig. 5, the lower end of the perforated structure has a preset distance D from an end of the main mixing pipe 23, and the end opening of the main mixing pipe 23 abuts against the bottom of the mixing chamber 1. Therefore, this design will cause the fluid in the main mixing pipe 23 to flow to the bottom of the mixing chamber 1 and then turn back upwards and then flow out from the elongated opening 24, which increases the counter-flow reverse impact of the internal flow field of the main mixing pipe 23, thereby further improving the counter-flow mixing effect as shown in Fig. 4 and also being favorable to the mixing of two fluids inside the main mixing pipe 23.

The above parameters such as the position of the main mixing pipe 23, the size and length of the elongated opening 24, the number of the through holes 25 on two sides of the elongated opening 24, the diameter of the through holes 25, and the distance D from the bottom end surface can be selected according to actual engineering conditions and with the help of CFD simulation, such as the flow rate of each fluid, the connection positions of the pipes, and the volume limit of the mixing chamber 1.

The beneficial effects of this solution are illustrated below.

1) Ensure a heat balance during mixing of gases with large physical-property differences.

For the heat balance mixer designed above, the following flow scheme is used to verify its mixing effect. For three fluids at the inlet, which have a large physical property difference gradient (density and enthalpy) , the formula for heat balance of mixing is:

m ₁ × C _P1 × T ₁ + m ₂ × C _P2 × T ₂ + m ₃ × C _P3 × T ₃ = m _mix × C _pmix × T _mix

C _p = aT ⁰ + bT ¹+ cT ² + dT ³ + eT ⁴

where C is constant pressure specific heat capacity, m is mass flow, T is temperature, numeral subscripts “1, 2, 3” correspond to three fluids, respectively, the subscript “mix” represents a mixed fluid, and a to e are constant coefficients. This solution can ensure the heat balance of mixing of gases with large physical-property differences.

2) Reduce the pressure drop of mixing.

For different designs, e.g. design 1 with no elongated opening is opened on the main mixing pipe, and design 2 with an elongated opening on the main mixing pipe, the solution provided by the invention can effectively reduce the pressure drop of mixing.

To sum up, this invention uses hydromechanics turbulence theory and thermodynamics-related theories to improve the mixing uniformity of fluids with different physical properties by means of counter-flow impact and reverse impact between fluids in the design of the mixer structure. The invention applies an elongated opening and small-diameter jet through holes to the inside of the mixer, which can improve the mixing effect while reducing the pressure drop of mixing. The present invention solves the technical difficulties of the cathode side of the solid oxide fuel cell with high requirements for intake temperature and intake uniformity and can be applied to SOFC systems.

Various modifications to these embodiments will be apparent. The general principle defined herein can be implemented in other embodiments without departing from the scope of the present invention.

Claims

A heat balance mixer, comprising:

a mixing chamber (1) having at least two mixer inlets (2) and a mixer outlet (4) ;

wherein:

each of the mixer inlets (2) is connected to an inlet pipe;

the mixer outlet (4) is connected to an outlet pipe (41) ;

one of the inlet pipes extends from the top of the mixing chamber (1) into the interior of the mixing chamber (1) ;

the inlet pipe located inside the mixing chamber (1) is a main mixing pipe (23) ;

a perforated structure is provided on the outer periphery of the main mixing pipe (23) opposite to at least one of the remaining mixer inlets (2) ; and

the perforated structure comprises at least one elongated opening (24) .
The heat balance mixer according to claim 1, wherein the perforated structure further comprises a plurality of through holes (25) located on the periphery of the elongated opening (24) ; and the length and width of the elongated opening (24) are both greater than the equivalent diameter of the through holes (25) .
The heat balance mixer according to claim 2, wherein the length of the elongated opening (24) is more than 12 times the equivalent diameter of the through holes (25) ; and the width of the elongated opening (24) is more than three times the equivalent diameter of the through holes (25) .
The heat balance mixer according to claim 2 or 3, wherein the elongated opening (24) is a rectangular opening, and the through holes (25) are round through holes.
The heat balance mixer according to any preceding claim, wherein the length of the elongated opening (24) is greater than the equivalent diameter of the mixer inlets (2) disposed opposite thereto.
The heat balance mixer according to any preceding claim, wherein the lengthwise direction of the elongated opening (24) is parallel to the axial direction of the main mixing pipe (23) .
The heat balance mixer according to any preceding claim, wherein an end opening of the main mixing pipe (23) abuts against the bottom of the mixing chamber (1) ; and there is a preset distance between the perforated structure and the end opening of the main mixing pipe (23) .
The heat balance mixer according to any preceding claim, wherein the mixing chamber (1) is a cylindrical chamber, and the circumferential inner wall surface of the cylindrical chamber is an arc surface.
The heat balance mixer according to claim 8, wherein the cross section of the cylindrical chamber is elliptical.
The heat balance mixer according to any preceding claim, wherein the outside of at least one of the inlet pipes is in communication with a branch mixing pipe (3) .
An SOFC system comprising a cell stack having a stack inlet, and a heat balance mixer according to any preceding claim, wherein the mixer outlet is in fluid communication with the stack inlet.