Method for installing groove type solar vacuum collector tube based on critical bias amount

Abstract

The application discloses a method for installing a slot type solar vacuum heat collecting tube in a biasing mode based on a critical biasing amount, which comprises the following steps: when the slot type solar vacuum heat collecting tube is biased, the geometric axis of the heat absorbing tube in the heat collecting tube deviates from the focal line downward, the biasing amount corresponding to the tangent point between the edge of the reflected light beam of the edge point of the parabolic reflector below the slot type solar vacuum heat collecting tube and the heat absorbing tube is taken as the heat absorbing tube biasing amount; the difference between the heat absorbing tube biasing amount and the maximum deflection of the heat absorbing tube under the action of gravity is taken as the critical biasing amount, and the slot type solar vacuum heat collecting tube is installed in a biasing mode according to the critical biasing amount. The slot type solar heat collecting system is installed in a biasing mode with the critical biasing amount downward, so that the solar flow density distribution of the surface of the heat absorbing tube in the heat collecting tube is more uniform under the premise of ensuring the optical efficiency of the system, the temperature gradient, stress and deformation of the heat absorbing tube are reduced, the safety performance is improved, and the method is suitable for slot type solar heat collecting systems with different geometric parameters.

Description

TECHNICAL FIELD

[0001] The present application belongs to the application field of trough type solar vacuum heat collecting tube, and more particularly relates to a method for offset installation of trough type solar vacuum heat collecting tube based on critical offset amount. BACKGROUND

[0002] Trough type solar thermal power station is the most commercialized solar thermal power station, and the existing commercial trough type solar concentrating heat collecting system mainly comprises a parabolic reflector and a vacuum heat collecting tube, wherein the vacuum heat collecting tube is located at the focal line of the parabolic reflector.

[0003] In engineering, due to installation errors and the deformation of the heat collecting tube itself, the geometric axis of the heat collecting tube will deviate from the designed focal line. When the geometric axis of the heat collecting tube deviates from the focal line to a certain extent, the solar flow density distribution on the surface of the heat collecting tube tends to be uniform.

[0004] However, the prior art has the technical problem that it is difficult to improve the uniformity of the solar flow distribution on the surface of the heat collecting tube under the premise of ensuring optical efficiency. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application provides a method for offset installation of trough type solar vacuum heat collecting tube based on critical offset amount, thereby solving the technical problem that the prior art is difficult to improve the uniformity of the solar flow distribution on the surface of the heat collecting tube under the premise of ensuring optical efficiency.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, a method for offset installation of trough type solar vacuum heat collecting tube based on critical offset amount is provided, comprising:

[0007] When the trough type solar vacuum heat collecting tube is offset, the geometric axis of the heat absorbing tube in the heat collecting tube deviates downward from the focal line, and the offset amount corresponding to the tangency of the edge of the light beam reflected by the edge point of the parabolic reflector below the trough type solar vacuum heat collecting tube and the heat absorbing tube is taken as the offset amount of the heat absorbing tube;

[0008] The difference between the offset amount of the heat absorbing tube and the maximum deflection of the heat absorbing tube under the action of gravity is taken as the critical offset amount, and the trough type solar vacuum heat collecting tube is offset installed according to the critical offset amount.

[0009] Further, the maximum deflection of the heat absorbing tube under the action of gravity is calculated by the following way:

[0010] A plurality of equidistantly distributed supports are arranged in the solar mirror field to which the trough type solar vacuum heat collecting tube belongs, and the adjacent two supports and the heat collecting tube therebetween are taken as a simply supported beam with uniform load;

[0011] The maximum deflection of the heat absorbing tube under the gravity is calculated by multiplying the uniform load by the length of the heat collecting tube between the two adjacent supports.

[0012] Further, the maximum deflection of the heat absorbing tube under the gravity is:

[0013]

[0014] wherein z max is the maximum deflection of the heat absorbing tube under the gravity, L is the length of the heat collecting tube between the two adjacent supports, G is the gravity of the heat absorbing tube in the heat collecting tube between the two adjacent supports, E ab is the elastic modulus of the heat absorbing tube, I ab，o is the sectional moment of inertia of the heat absorbing tube.

[0015] Further, the heat absorbing tube in the heat collecting tube is a hollow circular tube, and the sectional moment of inertia I ab，o of the heat absorbing tube can be obtained by the following formula:

[0016]

[0017] wherein D ab，o and D ab，i are the inner and outer diameters of the heat absorbing tube.

[0018] Further, the solar mirror field in which the trough type solar vacuum heat collecting tube belongs to is provided with n equidistantly distributed supports, and the heat collecting tube is supported at the focal line of the parabolic reflector, so that the solar mirror field includes n-1 trough type solar vacuum heat collecting tubes with a length of L, and the length of the heat collecting tube between the two adjacent supports is:

[0019]

[0020] wherein L tot is the total length of the solar mirror field, and n≥2.

[0021] Further, the biasing amount of the heat absorbing tube is obtained by the following method:

[0022] The focal line direction of the trough type solar vacuum heat collecting tube is taken as the y axis, and a Cartesian coordinate system is established with the sunlight reflection focal point as the origin O;

[0023] When the heat collecting tube is biased, the geometric axis of the heat absorbing tube deviates downward from the focal line, and the new geometric axis of the heat absorbing tube is O';

[0024] The tangent point of the edge of the reflected light beam of the edge point P of the parabolic reflector below the trough type solar vacuum heat collecting tube and the heat absorbing tube forms a right triangle with the point P and the point O', the included angle of the point P in the right triangle is solved, and then the distance between the point O and the point O' is calculated to obtain the biasing amount of the heat absorbing tube.

[0025] Further, the heat absorption tube biasing amount is:

[0026]

[0027] Wherein, δz* is the heat absorption tube biasing amount, β is the half solar angle, D ab，o is the outer diameter of the heat absorption tube, |PO'| is the distance from point P to point O', Ψ rim is the edge angle of the parabolic reflector.

[0028] Further, the distance from point P to point O' is:

[0029]

[0030] Wherein, W is the opening width of the trough solar vacuum heat collector.

[0031] Further, the edge angle of the parabolic reflector is:

[0032]

[0033] Wherein, f is the focal length of the parabolic reflector.

[0034] According to another aspect of the present application, a system for biasing installation of a trough solar vacuum heat collector based on a critical biasing amount is provided, comprising:

[0035] A first module for, when the trough solar vacuum heat collector is biased, the geometric axis of the heat absorption tube in the heat collector deviates downward from the focal line, and the corresponding biasing amount when the edge of the reflected light beam of the edge point of the parabolic reflector below the trough solar vacuum heat collector is tangent to the heat absorption tube is taken as the heat absorption tube biasing amount.

[0036] A second module for taking the difference between the heat absorption tube biasing amount and the maximum deflection of the heat absorption tube under the action of gravity as the critical biasing amount, and biasing installation of the trough solar vacuum heat collector according to the critical biasing amount.

[0037] Overall, the above technical solutions conceived by the present application can achieve the following beneficial effects compared with the prior art:

[0038] (1) The edge of the reflected light beam of the edge point of the parabolic reflector below the evacuated tubular collector of the trough type solar energy system is tangent to the heat absorbing tube, at this time the corresponding offset is the turning point of the optical efficiency of the trough type solar energy system. However, the heat absorbing tube will inevitably deform due to its own tube weight and the gravity of the fluid in the tube, which is called deflection in engineering. If only the offset δz* is taken as the critical offset ΔZ of the heat absorbing tube, due to the deflection of the heat absorbing tube caused by gravity, the edge of the reflected light beam of the edge point of the parabolic reflector below the evacuated tubular collector of the trough type solar energy system is no longer tangent to the heat absorbing tube, the above reflected light beam cannot completely reach the surface of the heat absorbing tube, and part of the light beam will escape into the environment, causing the optical efficiency of the system to decrease. The difference between the offset of the heat absorbing tube and the maximum deflection of the heat absorbing tube under the action of gravity is taken as the critical offset, not only considering the offset of the heat absorbing tube when the heat absorbing tube is offset, but also considering the deformation of the heat absorbing tube under the action of the gravity of the heat absorbing tube and the fluid in the tube. Based on this, the evacuated tubular collector of the trough type solar energy collection system is installed downward with the critical offset, so that the sunlight reflected by the edge point of the parabolic reflector below the evacuated tubular collector of the trough type solar energy system is completely focused on the surface of the heat absorbing tube. The solar energy flow density distribution on the surface of the heat absorbing tube in the heat absorbing tube is more uniform, the temperature gradient, stress and deformation of the heat absorbing tube are reduced, the operating safety performance of the heat absorbing tube is improved, and the method is suitable for trough type solar energy collection systems with different geometric parameters.

[0039] (2) The heat absorbing tube is composed of a glass tube and a heat absorbing tube. Since the deformation of the glass tube is small, the deformation of the heat absorbing tube is large, the deformation of the glass tube is ignored, and only the deformation of the heat absorbing tube under the action of gravity is considered. The adjacent two supports and the heat absorbing tube therebetween are regarded as a simply supported beam with uniform load, the maximum deflection of the heat absorbing tube under the action of gravity is calculated, and the calculation process is simplified under the condition of ensuring the calculation accuracy.

[0040] (3) The ideal design does not consider the deformation of the heat absorbing tube and the installation error, the geometric axis point of the heat absorbing tube coincides with the focus point of the reflected sunlight, and the parabolic reflector focuses the received sunlight to the lower surface of the heat absorbing tube located at the focal line. However, in actual application, the heat absorbing tube is offset, the geometric axis of the heat absorbing tube deviates downward from the focal line, if the offset is too large, part of the reflected light beam will escape into the environment, and cannot be collected on the surface of the heat absorbing tube, resulting in the decrease of the optical efficiency of the trough type solar energy collection system. Therefore, in order to reduce the loss of the optical efficiency of the trough type system, the offset corresponding to the tangent of the edge of the reflected light beam of the edge point of the parabolic reflector below the evacuated tubular collector of the trough type solar energy system is taken as the offset of the heat absorbing tube. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 It is a method flow chart of the evacuated tubular collector offset installation of the trough type solar energy system based on the critical offset provided by the embodiment of the present application.

[0042] Figure 2 is a structural diagram of a trough type solar light condensing collector provided by an embodiment of the present application;

[0043] Figure 3 is a light path diagram of a trough type collector when a heat collecting tube is not biased;

[0044] Figure 4 is a light path diagram of a trough type light condensing collector when a heat collecting tube is biased;

[0045] Figure 5 is a structural diagram of a trough type solar power station mirror field provided by an embodiment of the present application;

[0046] Figure 6 is a schematic diagram of a simple beam provided by an embodiment of the present application. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0048] As shown in Figure 1 , a method for biasing installation of a trough type solar vacuum heat collecting tube based on a critical biasing amount, comprising:

[0049] When the trough type solar vacuum heat collecting tube is biased, the geometric axis of the heat absorbing tube in the heat collecting tube deviates downward from the focal line, and the corresponding biasing amount when the edge of the reflected light beam of the edge point of the parabolic reflector below the trough type solar vacuum heat collecting tube is tangent to the heat absorbing tube is taken as the heat absorbing tube biasing amount.

[0050] The difference between the heat absorbing tube biasing amount and the maximum deflection of the heat absorbing tube under the action of gravity is taken as the critical biasing amount, and the trough type solar vacuum heat collecting tube is installed in a biased manner according to the critical biasing amount.

[0051] The present application proposes to install the vacuum heat collecting tube of the trough type solar heat collecting system downwardly with a suitable distance, to make the solar flow density distribution on the surface of the heat absorbing tube more uniform, reduce the temperature gradient, stress and deformation of the heat absorbing tube, and improve the safety performance under the premise of ensuring the optical efficiency of the system.

[0052] As shown in Figure 2 , the existing commercial trough type solar light condensing collector system mainly consists of a parabolic reflector and a vacuum heat collecting tube, wherein the vacuum heat collecting tube is located at the focal line of the parabolic reflector. The vacuum heat collecting tube includes, from the center outward, a heat transfer fluid, a heat absorbing tube, a vacuum gap and a glass tube.

[0053] This invention defines the appropriate distance required for the offset installation of vacuum collector tubes as the critical offset amount and determines the calculation method for the critical offset amount. It is applicable to trough solar collector systems with different geometric parameters and can provide theoretical guidance for the offset installation of collector tubes in trough solar collector systems. The detailed derivation process is as follows:

[0054] Along the focal line direction of the trough solar collector system ( Figure 2 Taking any vertical section as the analysis object (y-axis), and establishing a Cartesian coordinate system (x-z) with the focal point of sunlight reflection as the origin O, as follows: Figure 3 As shown. In an ideal design, the deformation and installation error of the absorber tube are not considered. The geometric axis of the absorber tube coincides with the focal point of the reflected sunlight, and the parabolic mirror focuses the received sunlight onto the lower surface of the absorber tube located at the focal line.

[0055] like Figure 3 As shown, when the collector tube is not biased, i.e., δz = 0, the solar beam is incident perpendicularly on any point P(x) on the reflector. i , z i The reflected light beam reaches the lower surface of the heat absorber tube. Let the angle between the reflected ray P-b' (coinciding with line PO) and the z-axis be the position angle Ψ of point P on the mirror. Then:

[0056]

[0057] In the formula: Ψ is the position angle of point P on the mirror, x i Let x be the x-coordinate of point P; f be the focal length of the mirror. Specifically, when point P is located at the edge of the mirror, i.e., x... i When W = ±W / 2:

[0058]

[0059] In the formula: Ψ rim For x i The tracking angle at ±W / 2 is also called the edge angle of the reflector.

[0060] like Figure 4 As shown, when the collector tube is biased, the geometric axis of the absorber tube deviates downwards from the focal line. The bias amount corresponding to the edge P-c' of the reflected beam at the edge of the mirror being tangent to the absorber tube is denoted as δz*. At this point, if the bias amount continues to increase, i.e., |δz| > |δz*, * |(δz<0,δz * When the angle is less than 0, some of the reflected light will escape into the environment and cannot be focused on the surface of the absorber tube, resulting in a decrease in the optical efficiency of the trough solar collector system. Therefore, to ensure that the optical efficiency of the trough system is not lost, the offset of the absorber tube should not be greater than |δz|. * |(δz* <0). δz* and the outer diameter D of the heat absorber tube ab，o The following relationship exists:

[0061]

[0062] In the formula: δz* is the absorber tube offset; β is the half-solar angle; D ab，o Ψ is the outer diameter of the heat absorber tube; |PO′| is the distance from point P to point O'; rim θ is the edge angle of the reflector; W is the opening width of the trough solar collector.

[0063] Considering the weight of the collector tube and the gravity of the fluid inside, the absorber tube will inevitably deform. For example... Figure 5 As shown, the total design length of the sunroof field for a commercial parabolic trough solar thermal power plant is L. tot According to the design principles of existing trough-type systems, if the sunglass field is equipped with n equally spaced supports, supporting the heat collection tubes at the focal line of the trough-type reflector (parabolic in shape, hence also called a trough-type reflector), then the sunglass field consists of n-1... Figure 2 The diagram shows a parabolic trough solar collector assembly of length L. The length L of a single parabolic trough solar collector is proportional to the total length L of the solar array. tot The following relationship exists:

[0064]

[0065] It is readily apparent that the length of the heat-collecting tube between two adjacent supports is also L. The heat-collecting tube consists of a glass tube and a heat-absorbing tube. This invention ignores the deformation of the glass tube and only considers the deformation of the heat-absorbing tube under gravity. In actual engineering, the gravity G acting on the heat-absorbing tube between two adjacent supports includes the weight of the heat-absorbing tube itself G1 and the weight of the heat transfer fluid inside the tube G2, then:

[0066]

[0067] In the formula: D ab，o and D ab，i ρ is the inner and outer diameter of the heat absorber tube; ρ1 is the density of the heat absorber tube; ρ2 is the density of the heat transfer fluid inside the tube; g is the acceleration due to gravity; L is the length of the heat collection tube between two adjacent supports.

[0068] The two adjacent supports and the heat absorption tubes between them can be regarded as simply supported beams with uniformly distributed loads, such as Figure 6 As shown, according to structural mechanics theory, the maximum deflection z of the heat absorber tube under gravity is easily obtained. max for:

[0069]

[0070] Wherein: G is the gravity of the heat absorbing pipe between two adjacent supports, q is the uniform load, qL=G; E ab E is the elastic modulus of the heat absorbing pipe, I ab，o is the cross-sectional moment of inertia of the heat absorbing pipe. Since the heat absorbing pipe is a hollow circular tube, its cross-sectional moment of inertia I ab，o can be obtained by the following formula:

[0071]

[0072] According to the above derivation, the present application defines the difference between the heat absorbing pipe offset amount δz* and the maximum deflection z max of the heat absorbing pipe as the critical offset amount ΔZ of the offset installation of the evacuated tubular collector, which can be obtained by the following formula:

[0073] ΔZ=δz*-z max

[0074] The present application proposes to offset install the evacuated tubular collector with the critical offset amount ΔZ, which can improve the uniformity of the solar energy flow distribution on the surface of the heat absorbing pipe, reduce the temperature gradient, stress and deformation of the heat absorbing pipe, and improve the safety of the heat absorbing pipe to a certain extent under the premise of ensuring the optical efficiency of the evacuated tubular collector.

[0075] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for installing a groove type solar vacuum collector tube based on a critical amount of bias, characterized in that, The application relates to a method for installing a trough type solar vacuum heat collecting tube. When the trough type solar vacuum heat collecting tube is offset, the geometric axis of the heat absorbing tube in the heat collecting tube deviates downward from the focal line, the corresponding offset amount when the edge of the light beam reflected by the edge point of the parabolic reflector below the trough type solar vacuum heat collecting tube is tangent to the heat absorbing tube is taken as the heat absorbing tube offset amount; The difference between the heat absorbing tube offset amount and the maximum deflection of the heat absorbing tube under the action of gravity is taken as the critical offset amount, the trough type solar vacuum heat collecting tube is installed in an offset mode according to the critical offset amount, and the sunlight beam reflected by the edge point of the parabolic reflector below the trough type solar vacuum heat collecting tube is completely converged on the surface of the heat absorbing tube. The maximum deflection of the heat absorbing tube under the action of gravity is obtained by the following method: A plurality of equidistantly distributed supports are arranged in a solar mirror field to which the trough type solar vacuum heat collecting tube belongs, and the adjacent two supports and the heat collecting tube therebetween are taken as a simply supported beam under uniform load; The gravity borne by the heat absorbing tube in the heat collecting tube between the adjacent two supports is obtained by multiplying the length of the heat collecting tube between the adjacent two supports by the uniform load, and the maximum deflection of the heat absorbing tube under the action of gravity is calculated.

2. A method for installing a slot type solar vacuum collector tube based on a critical amount of bias, as claimed in claim 1, characterized in that, The maximum deflection of the heat absorbing tube under the action of gravity is: wherein, z max is the maximum deflection of the heat absorbing pipe under the action of gravity, L is the length of the heat absorbing pipe between two adjacent supports, G is the gravity of the heat absorbing pipe in the heat absorbing pipe between two adjacent supports, E ab is the elastic modulus of the heat absorbing pipe, I ab,o is the cross-sectional moment of inertia of the heat absorbing pipe.

3. A method for installing a slot type solar vacuum collector tube based on a critical amount of bias, as claimed in claim 1, characterized in that, The heat-absorbing pipe in the heat collecting pipe is a hollow circular pipe, and the cross-sectional moment of inertia of the heat-absorbing pipe I ab,o This can be obtained from the following formula: wherein D ab,o and D ab,i D and d are the inner and outer diameters of the heat absorbing tube.

4. A method for critical-bias-based installation of a slot-type solar vacuum collector tube, as claimed in claim 1, wherein, The trough type solar vacuum heat collecting tube belongs to a solar field which is provided with n equidistantly distributed supports to support the heat collecting tube at the focal line of the parabolic reflector, and the solar field comprises n- 1 trough type solar vacuum heat collecting tube with a length of L The length of the heat collecting tube between two adjacent supports is: wherein L tot Ltot is the total length of the field of sunglasses, n≥2.

5. A method for installing a slot-type solar vacuum collector tube with critical biasing amount based on biasing, according to any one of claims 1-4, characterized in that, The heat absorbing tube offset amount is obtained by the following method: The focal line direction of the trough type solar vacuum heat collecting tube is taken as the y-axis, and a Cartesian coordinate system is established with the sunlight reflection focal point as the origin O; When the heat collecting tube is offset, the geometric axis of the heat absorbing tube deviates downward from the focal line, and the new geometric axis of the heat absorbing tube is O'; The tangent point of the edge of the light beam reflected by the edge point P of the parabolic reflector below the trough type solar vacuum heat collecting tube is tangent to the heat absorbing tube, the tangent point, the point P and the point O' form a right triangle, the included angle of the point P is solved, and then the distance between the point O and the point O' is calculated to obtain the heat absorbing tube offset amount.

6. A method for critical-bias amount based installation of a slot type solar vacuum collector tube bias, as claimed in claim 5, wherein, The heat absorbing tube offset amount is: wherein, delta z is the offset of the heat pipe, β is the half solar angle, D ab,o is the outer diameter of the heat pipe, is the distance from point P to point O’, Psi rim is the edge angle of the parabolic mirror.

7. A method for critical-bias based installation of a slot-type solar vacuum collector tube, as claimed in claim 6, wherein, The distance from the point P to the point O' is: wherein W is the opening width of the slot-type solar vacuum collector.

8. A method for critical-bias based installation of a slot-type solar vacuum collector tube, as claimed in claim 7, wherein, The edge angle of the parabolic reflector is: wherein f is the focal length of the parabolic mirror.

9. A system for the critical-bias-based offset installation of a slot-type solar vacuum collector tube, characterized by The application further relates to a device for installing a trough type solar vacuum heat collecting tube. The first module is used for obtaining the heat absorbing tube offset amount when the trough type solar vacuum heat collecting tube is offset, the geometric axis of the heat absorbing tube in the heat collecting tube deviates downward from the focal line, and the corresponding offset amount when the edge of the light beam reflected by the edge point of the parabolic reflector below the trough type solar vacuum heat collecting tube is tangent to the heat absorbing tube; The second module is used for arranging a plurality of equidistantly distributed supports in a solar mirror field to which the trough type solar vacuum heat collecting tube belongs, and taking the adjacent two supports and the heat collecting tube therebetween as a simply supported beam under uniform load; The gravity borne by the heat absorbing tube in the heat collecting tube between the adjacent two supports is obtained by multiplying the length of the heat collecting tube between the adjacent two supports by the uniform load, the maximum deflection of the heat absorbing tube under the action of gravity is calculated, the difference between the heat absorbing tube offset amount and the maximum deflection of the heat absorbing tube under the action of gravity is taken as the critical offset amount, the trough type solar vacuum heat collecting tube is installed in an offset mode according to the critical offset amount, and the sunlight beam reflected by the edge point of the parabolic reflector below the trough type solar vacuum heat collecting tube is completely converged on the surface of the heat absorbing tube.

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