Tracking strategy calculation method for heat pipe type composite parabolic trough type heat collection system

Abstract

The invention discloses a method for calculating a tracking strategy of a heat pipe type composite parabolic trough heat collection system. The method comprises the following steps: step (1), determining the structure and optical parameters of the heat pipe type composite parabolic trough heat collection system; (2) defining an incident angle and a light position of an initial light; (3) judging whether the light enters an opening plane of the condenser or not and falls on a receiver or not; (4) calculating the intersection point of the light and the receiver according to the judgment result of the step (3), and counting the drop point distribution of the absorbed light on the receiver; and (5) the energy flux density distribution of the receiver and the optical efficiency of the heat collector in different tracking modes are calculated and compared, and the tracking strategy of the heat pipe type composite parabolic trough type heat collection system is determined. The technical problem that an existing calculation method of the tracking strategy of the heat collection system is not suitable for the inclined heat pipe type composite parabolic trough type heat collection system can be solved.

Description

Technical Field

[0001] The present invention relates to the field of heat collection system tracking technology, and more specifically to a heat pipe composite parabolic trough heat collection system tracking strategy calculation method. Background Art

[0002] As a renewable energy source, solar energy has the advantages of being pollution-free, having large reserves and long usable time. Its development and utilization is of great significance to saving conventional energy, protecting the natural environment and mitigating climate change. Concentrated solar thermal utilization technology has been widely used in living space heating, agricultural drying, energy collection and other fields. Among them, CPC (compound parabolic collector) has the advantages of simple structure, convenient operation, strong focusing ability, and the ability to receive direct radiation and scattered radiation at the same time. It has broad application prospects in the medium and low temperature fields.

[0003] The tracking forms of compound parabolic trough collectors mainly include fixed, single-axis tracking and dual-axis tracking. For concentrated solar thermal utilization equipment, selecting a reasonable tracking strategy is one of the effective ways to reduce the solar incident angle and improve the utilization rate of solar energy. However, there is currently no calculation method for the tracking strategy of an inclined heat pipe compound parabolic trough collector system. Summary of the invention

[0004] To this end, the technical problem to be solved by the present invention is to provide a method for calculating the tracking strategy of a heat pipe composite parabolic trough type solar collector system, so as to solve the technical problem that the calculation method of the existing solar collector system tracking strategy is not suitable for an inclined heat pipe composite parabolic trough type solar collector system.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A tracking strategy calculation method for a heat pipe composite parabolic trough solar collector system comprises the following steps:

[0007] Step (1), determining the structure and optical parameters of the heat pipe composite parabolic trough solar collector system;

[0008] Step (2), defining the incident angle and light position of the initial light;

[0009] Step (3), determining whether the light enters the opening plane of the concentrator and whether it falls on the receiver;

[0010] Step (4), calculating the intersection point between the light and the receiver according to the judgment result of step (3), and counting the distribution of the points where the absorbed light falls on the receiver;

[0011] Step (5), calculate and compare the receiver energy flux density distribution and collector optical efficiency under different tracking modes, and determine the tracking strategy of the heat pipe composite parabolic trough collector system.

[0012] In the above-mentioned heat pipe composite parabolic trough collector system tracking strategy calculation method, in step (1), the heat pipe composite parabolic trough collector system is composed of two or more collector units, each collector unit is composed of a composite parabolic trough concentrator, a heat pipe receiver, a glass cover and a connecting pipe, and the receiver is a two-phase closed thermosyphon; the optical parameters include the receiver radius r, the gap spacing g between the bottom of the receiver and the concentrator tip, the concentrator width W, the concentrator length L, the receiver circle involute expansion angle θ, the receiver circle circumferential angle ψ, the maximum receiving half angle θ C and concentration ratio C; CPC mirror profile is smoothly connected by parabola and receiver circle involute;

[0013] In the Cartesian coordinate system, the structural equation of the receiver circle involute is:

[0014]

[0015]

[0016] The structural equation of the parabola is:

[0017]

[0018] The structural equation of the receiver is:

[0019]

[0020] The tracking strategy calculation method of the heat pipe composite parabolic trough solar collector system, in step (2): the solar incident angle θ i The calculation formula is:

[0021] θ i =cos -1 (sinα s sinα+cosα s cosαcos(γ-γ s )) (5);

[0022] α s =sin -1 (sinλsinδ+cosλcosδcosω) (6);

[0023]

[0024] In equations (5) to (7), α is the concentrator elevation angle, α sis the solar altitude angle, γ is the concentrator azimuth angle, γ s is the solar azimuth, β is the concentrator tilt angle, λ is the latitude angle, δ is the latitude angle, and ω is the hour angle;

[0025] The projections of the incident light along the longitudinal plane and the transverse plane of the concentrator are respectively expressed by the longitudinal incident angle θ i α and the lateral incidence angle θ i γ ; Longitudinal incident angle θ i α The calculation formula is:

[0026]

[0027] Longitudinal incident angle θ i α The calculation formula is:

[0028]

[0029] In the above-mentioned heat pipe composite parabolic trough collector system tracking strategy calculation method, in step (4), when the incident light enters the concentrator opening plane and falls on the receiver: calculate the intersection of the light and the receiver, if the intersection coordinates (x, y, z) satisfy -L / 2<Z<L / 2, then mark the incident light as absorbed light, otherwise mark it as unabsorbed light;

[0030] When the incident light enters the opening plane of the condenser but does not fall on the receiver: further determine whether the reflected light after the incident light is reflected has an intersection with the receiver;

[0031] (a) If the reflected light and the receiver have an intersection point, further determine whether the coordinates of the intersection point (x, y, z) satisfy the condition -L / 2<Z<L / 2. If so, mark the incident light as absorbed light; otherwise, mark the incident light as unabsorbed light.

[0032] (b) If the reflected light has no intersection with the receiver: further determine whether the reflected light has an intersection with the concentrator. If there is an intersection, further calculate whether the secondary reflected light after the reflected light has an intersection with the receiver, and further determine whether the incident light is absorbed light or unabsorbed light according to the methods of "(a)" and "(b)". If there is no intersection, directly mark the incident light as unabsorbed light.

[0033] In the above-mentioned heat pipe composite parabolic trough solar collector system tracking strategy calculation method, in step (4), determining whether the reflected light after the incident light is reflected has an intersection with the receiver includes the following steps:

[0034] Step (4-1), calculating the intersection point of the incident light and the concentrator;

[0035] Step (4-2), calculating the incident vector and normal vector of the incident light;

[0036] Step (4-3), calculating the light reflection vector and the reflected light equation;

[0037] Step (4-4), regard the reflected light as the incident light in the next reflection process and calculate the intersection of the reflected light and the receiver.

[0038] In the above heat pipe composite parabolic trough collector system tracking strategy calculation method, in step (4), it is assumed that the incident light passes through point P0 (x0, y0, z0);

[0039] A. When the incident light falls on the receiver, the incident light I a,1 The point of intersection with the receiver's circular surface is denoted as P a,1 (x a,1 ,y a,1 , z a,1 ), then P0 and P a,1 Satisfies the following relationship:

[0040]

[0041] B. When the incident light falls on the involute segment, the incident light I i,1 The point of intersection with the involute is denoted as P i,1 (x i,1 ,y i,1 , z i,1 ), the corresponding receiver circle involute expansion angle is θ i,1 ; Then P0 and P i,1 Satisfies the following relationship:

[0042]

[0043] At the intersection point P i,1 The incident light I i,1 Vector and normal vector n i,1 The vector expression is:

[0044]

[0045] Reflected light F i,1 Vector (k i,1 , l i,1 ) in vector form:

[0046] F = I-2(n·I)·n (13);

[0047] but:

[0048] After one reflection, the reflected light F i,1 is intercepted by the receiver, the intersection point is P i,a (x i,a ,y i,a ,z i,a ), then point P i,a With P i,1 Satisfies the following relationship:

[0049]

[0050] C. When the incident light falls on the parabola segment, the incident light I p,1 The first point of intersection with the parabola is denoted by P p,1 (x p,1 ,y p,1 , z p,1 ), the corresponding receiver circle involute expansion angle is θ p,1 ; Then P0 and P p,1 Satisfies the following relationship:

[0051]

[0052] At the intersection point P p,1 At, the incident light vector I p,1 and the normal vector n p,1 The vector expression of is:

[0053]

[0054] Reflected light F p,1 Vector (k p,1 , l p,1 ) is expressed as:

[0055]

[0056] After the incident light falls on the parabola, the reflected light must fall on the involute after at least n-1 reflections, where n is greater than or equal to 2; after n-2 reflections, the reflected light falls on the parabola, and the intersection point P with the parabola is p,n-1 (x p,n-1 ,y p,n-1 , z p,n-1 ), the corresponding receiver circle involute expansion angle is θ p,n-1 ; then P p,n-1 With P p,n-2 (x p,n-2 ,y p,n-2 , z p,n-2 ) satisfies the following relationship:

[0057]

[0058] At the intersection point Pp,n-1 At, the incident light vector I p,n-1 and the reflected light vector F p,n-2 (k p,n-2 ,l p,n-2 ) are the same, then the incident light I p,n-1 The normal vector n p,n-1 The vector expression is:

[0059]

[0060] Reflected light F p,n-1 (k p,n-1 ,l p,n-1 )The vector expression of the vector is:

[0061]

[0062] After the incident light is reflected n-1 times, the reflected light F p,n-1 It falls on the involute, and the intersection point is P i,n (x i,n ,y i,n ,z i,n ,), the corresponding receiver circle involute expansion angle is θ i,n , then point P i,n and P i,n-1 Satisfies the following relationship:

[0063]

[0064] At the intersection point P i,n At, the incident light vector I i,n and the reflected light vector F p,n-1 (k p,n-1 ,l p,n-1 ) are the same, then the incident light vector I i,n The normal vector n ,n The vector expression is:

[0065]

[0066] Reflected light F i,n (k i,n ,l i,n )The vector expression is:

[0067]

[0068] Reflected light F i,n is intercepted by the receiver, the intersection point is P p,a (x p,a ,y p,a , z p,a ), click P p,a With Pi,n Satisfies the following relationship:

[0069]

[0070] In the above heat pipe composite parabolic trough collector tracking strategy calculation method, in step (5), the energy flux density is calculated by: gridding the receiver surface, dividing the unit length receiver into N equal parts along the circumference. d cells, the area of ​​each grid is A i ; Count and calculate the energy Q carried by all the light rays falling into the i-th cell on the receiver i , then the average energy flux density on the i-th cell is I i The specific calculation formula is:

[0071]

[0072]

[0073] Where m is the number of rays falling into the i-th cell; q e is the energy of each ray; I DNI is the direct solar radiation intensity projected onto the concentrator lighting surface; n r The total number of rays in the simulation.

[0074] The calculation method of the tracking strategy of the heat pipe composite parabolic trough collector system mentioned above, the calculation formula of the collector optical efficiency is:

[0075]

[0076] The technical solution of the present invention achieves the following beneficial technical effects:

[0077] The present invention establishes a three-dimensional CPC optical model based on the ray tracing principle, and uses the model to trace the light of the tilted heat pipe type composite parabolic trough type solar collector system under different tracking strategies, so as to obtain a more accurate light absorption situation, and then the energy flux density distribution and optical efficiency with small error and high accuracy can be calculated, so that the determination of the tracking strategy of the tilted heat pipe type composite parabolic trough type solar collector system is more in line with its practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 A schematic structural diagram of a heat pipe solar concentrating heat collection system according to an embodiment of the present invention;

[0079] Figure 2 Schematic diagram of the geometric structure of the compound parabolic concentrator in an embodiment of the present invention;

[0080] Figure 3Schematic diagram of CPC tracking error in an embodiment of the present invention;

[0081] Figure 4 A ray tracing diagram of a three-dimensional CPC collector in an embodiment of the present invention;

[0082] Figure 5 Flow chart of ray tracing of three-dimensional CPC collector in the embodiment of the present invention;

[0083] Figure 6a A graph showing changes in the solar azimuth, pitch angle, and solar radiation intensity over time in an embodiment of the present invention (summer solstice 2023);

[0084] Figure 6b A graph showing changes in the solar azimuth, pitch angle, and solar radiation intensity over time in an embodiment of the present invention (winter solstice 2023);

[0085] Figure 7a A graph showing the optical efficiency of CPC over time in an embodiment of the present invention (summer solstice 2023);

[0086] Figure 7b A graph showing the optical efficiency of CPC over time in an embodiment of the present invention (winter solstice 2023);

[0087] Figure 8a A graph showing the variation of the received radiation amount of CPC over time in an embodiment of the present invention (summer solstice 2023);

[0088] Figure 8b A graph showing how the amount of radiation received by CPC changes over time in an embodiment of the present invention (winter solstice 2023). DETAILED DESCRIPTION

[0089] This embodiment takes the heat pipe CPC collector system placed at an angle from north to south as the research object, establishes a three-dimensional CPC optical model based on the ray tracing principle, describes in detail the calculation method of the tracking strategy of the heat pipe composite parabolic trough collector system of the present invention, and obtains the optimal tracking method and reasonable step tracking time interval.

[0090] 1. Heat pipe composite parabolic concentrating collector

[0091] The heat pipe composite parabolic trough heat collection system of this embodiment is composed of a plurality of identical heat collection units connected together, each heat collection unit is composed of a composite parabolic trough concentrator, a heat pipe receiver, a glass cover plate and a connecting pipe, wherein the receiver is a two-phase closed thermosyphon. Figure 1 The structural dimensions and optical performance of the concentrator and receiver are shown in Table 1. In order to ensure the circulation of the working fluid inside the two-phase closed thermosyphon, the collector needs to be placed at a certain angle to the ground and tilted from north to south.

[0092] Table 1 CPC collector structural parameters

[0093]

[0094]

[0095] 2. CPC structure model

[0096] The CPC mirror profile is smoothly connected by the parabola and the involute of the receiver circle, such as Figure 2 As shown. Among them, the P1-P2 segment is the involute part of the receiver circle, and the P2-P3 segment is the parabola part. The optical axis P2-P3' intersects the receiver circle tangently at point F. In order to ensure that the parabola and the involute are smoothly connected at point P2, point F is defined as the focus of the parabola segment P2-P3, and point P2 is the vertex. The angle θ between the Y axis and the optical axis P2-P3' C is the receiving half angle of the concentrator. The cross section of the receiver is a circle with a radius of r, and ψ is the circumferential angle of the receiver. When the solar collector system is in operation, in order to avoid the mutual influence of thermal expansion and deformation of the solar collector elements, the gap distance between the bottom point N of the receiver and the sharp point P1 of the concentrator is selected as g.

[0097] In the Cartesian coordinate system, the CPC curve expression can be derived from the analytical geometry relationship. Among them, the structural equation of the circular involute is:

[0098]

[0099]

[0100] Where, is the involute expansion angle of the receiver circle, and L is the concentrator length.

[0101] The structural equation of the parabola is:

[0102]

[0103] The structural equation of the receiver is:

[0104]

[0105] In this embodiment, the optical efficiency of CPC is measured in three modes: fixed, east-west horizontal tracking, and north-south tilt axis and east-west horizontal axis tracking. In the fixed mode, the azimuth angle of the concentrator is 0, and the north-south tilt angle is the same as the local latitude value (41°). In the east-west horizontal tracking, the north-south tilt angle is fixed at 41°, and the initial azimuth angle of the concentrator is -2θ. C To ensure that the tracking error of the east-west horizontal axis is not higher than θ C , adjust the azimuth angle of the concentrator at 10:00 and 14:00 every day, and each adjustment angle is 2θ C When tracking the north-south tilt axis and the east-west horizontal axis, the tracking error of the east-west horizontal axis is no higher than θ C , the tracking error of the north-south tilt axis is no higher than 4°.

[0106] 3. Solar incidence angle

[0107] Figure 3 The relationship between CPC and incident light at any time is shown in the figure. According to the position of the collector, the solar incident angle θ i The calculation formula is:

[0108] θ i =cos -1 (sinα s sinα+cosα s cosαcos(γ-γ s )) (5)

[0109] α s =sin -1 (sinλsinδ+cosλcosδcosω) (6)

[0110]

[0111] In equations (5) to (7), α is the concentrator elevation angle, α s is the solar altitude angle, γ is the concentrator azimuth angle, γ s is the solar azimuth, β is the concentrator tilt angle, λ is the latitude angle, δ is the latitude angle, and ω is the hour angle.

[0112] The incident solar light is projected along the longitudinal plane and transverse plane of the concentrator, and the two angles obtained are respectively called the longitudinal incident deflection angle θ i α With the lateral incidence angle θ i γAccording to the geometric relationship of light, the calculation formula of the transverse incident angle is:

[0113]

[0114] The calculation formula for the longitudinal incident angle is:

[0115]

[0116] 4. Optical model

[0117] The ray tracing diagram of light in CPC collector is as follows Figure 4 As shown. For any incident light ray I0, its transverse incident angle is θ i γ , the longitudinal incident angle is θ i α The incident light ray passes through point P0, whose coordinates are (x0, y0, z0).

[0118] (1) The incident light falls on the receiver

[0119] The incident light I a,1 The point of intersection with the receiver's circular surface is denoted as P a,1 (x a,1 ,y a,1 , z a,1 ), then P0 and P a,1 Satisfies the following relationship:

[0120]

[0121] (2) The incident light falls on the involute segment

[0122] The incident light I i,1 The point of intersection with the involute is denoted as P i,1 (x i,1 ,y i,1 , z i,1 ), the corresponding receiver circle involute expansion angle is θ i,1 ; Then P0 and P i,1 Satisfies the following relationship:

[0123]

[0124] At the intersection point P i,1 The incident light I i,1 Vector and normal vector n i,1 The vector expression is:

[0125]

[0126] Reflected light F i,1 Vector (k i,1 , li,1 ) in vector form:

[0127] F = I-2(n·)I (13);

[0128] but:

[0129] After one reflection, the reflected light F i,1 is intercepted by the receiver, the intersection point is P i,a (x i,a ,y i,a ,z i,a ), then point P i,a With P i,1 Satisfies the following relationship:

[0130]

[0131] (3) The incident light falls on the parabola segment

[0132] Incident light I p,1 The first intersection point with the parabola is P p,1 (x p,1 ,y p,1 , z p,1 ), the corresponding circular receiver expansion angle is θ p,1 , point P0 and P p,1 The relationship between them is:

[0133]

[0134] At the intersection point P p,1 At, the incident light vector I p,1 and the normal vector n p,1 The vector expression is:

[0135]

[0136] Reflected light F p,1 Vector (k p,1 , l p,1 )The vector expression is:

[0137]

[0138] After the incident light falls on the parabola, the reflected light must be reflected at least n-1 times (n≥2) before it can fall on the involute. After n-2 reflections, the reflected light falls on the parabola, and the intersection with the parabola is P p,n-1 (x p,n-1 ,y p,n-1 , z p,n-1 ), the corresponding circular receiver expansion angle is θ p,n-1 , P p,n-1 With Pp,n-2 (x p,n-2 ,y p,n-2 , z p,n-2 ) is:

[0139]

[0140] At the intersection point P p,n-1 At, the incident light vector I p,n-1 and the reflected light vector F p,n-2 (k p,n-2 ,l p,n-2 ) are the same, then the incident light I p,n-1 The normal vector n p,n-1 The vector expression is:

[0141]

[0142] Reflected light F p,n-1 Vector (k p,n-1 ,l p,n-1 ) is expressed as:

[0143]

[0144] After the incident light is reflected n-1 times, the reflected light F p,n-1 It falls on the involute, and the intersection point is P i,n (x i,n ,y i,n , z i,n ), the corresponding circular receiver expansion angle is θ i,n , click P i,n With P p,n-1 The relationship between them is:

[0145]

[0146] At the intersection point P i,n At, the incident light vector I i,n and the reflected light vector F p,n-1 (k p,n-1 ,l p,n-1 ) are the same, then the incident light vector I i,n The normal vector n i,n The vector expression is:

[0147]

[0148] Reflected light F i,n Vector (k i,n ,l i,n )The vector expression is:

[0149]

[0150] Reflected light F i,n is intercepted by the receiver, the intersection point is P p,a (x p,a ,y p,a , z p,a ), click P p,a With P i,n The relationship between them is:

[0151]

[0152] The receiver surface is meshed and the unit length receiver is divided into N equal parts along the circumference. d cells, the area of ​​each grid is A i By counting and calculating the energy Q carried by all the light rays falling into the i-th cell on the receiver i , the average energy flux density I on the cell can be calculated i , the specific calculation formula is:

[0153]

[0154]

[0155] Where m is the number of rays falling into the i-th cell; q e is the energy of each ray; IDNI is the direct solar radiation intensity projected onto the light collecting surface of the concentrator; n r The total number of rays in the simulation.

[0156] The calculation formula of the collector optical efficiency is:

[0157]

[0158] The algorithm flow of the optical model of the heat pipe CPC collector system in this embodiment is as follows: Figure 5 As shown, the specific steps include:

[0159] Step (1), determining the structure and optical parameters of the heat pipe composite parabolic trough solar collector system;

[0160] Step (2), defining the incident angle and light position of the initial light;

[0161] Step (3), determining whether the light enters the opening plane of the concentrator and whether it falls on the receiver;

[0162] Step (4), calculating the intersection of the light and the receiver according to the judgment result of step (3), and counting the distribution of the points where the absorbed light falls on the receiver; judging whether the reflected light after the incident light is reflected has an intersection with the receiver includes the following steps:

[0163] Step (4-1), calculating the intersection point of the incident light and the concentrator;

[0164] Step (4-2), calculating the incident vector and normal vector of the incident light;

[0165] Step (4-3), calculating the light reflection vector and the reflected light equation;

[0166] Step (4-4), treating the reflected light as the incident light in the next reflection process and calculating the intersection point of the reflected light and the receiver;

[0167] Step (5), calculate the receiver energy flux density distribution and collector optical efficiency.

[0168] 5. Comparison of the effects of heat pipe composite parabolic trough collector systems under different tracking methods

[0169] Figure 6a and Figure 6b They are respectively the changing values ​​of the solar azimuth, altitude angle and direct solar radiation intensity over time on the summer solstice and winter solstice in 2023 in the area where this embodiment is located.

[0170] Figure 7a and Figure 7b They are respectively curves showing the change of the optical efficiency of the CPC collector over time in three tracking modes on the summer solstice and the winter solstice of this embodiment.

[0171] Figure 8a and Figure 8b Curves of the change of the radiation heat received by the CPC collector over time in three tracking modes on the summer solstice and the winter solstice are respectively given for this embodiment.

[0172] From the above analysis results, it can be seen that the heat pipe type compound parabolic concentrating collector of this embodiment can be placed in a north-south tilted manner and tracked in a single-axis east-west horizontal manner. Among them, the east-west horizontal axis is adjusted twice a day to ensure that the lateral incident angle is less than the concentrator receiving half angle. The above tracking strategy is used to conduct actual tests on the tilted heat pipe type compound parabolic trough type solar collector system of this embodiment, and it is found that this tracking strategy can obtain a relatively ideal heat collection effect compared with other tracking methods.

Claims

1. A tracking strategy calculation method for a heat pipe composite parabolic trough solar collector system, characterized in that: The steps include: Step (1), determining the structure and optical parameters of the heat pipe composite parabolic trough solar collector system; Step (2), defining the incident angle and light position of the initial light; Step (3), determining whether the light enters the opening plane of the concentrator and whether it falls on the receiver; Step (4), calculating the intersection point between the light and the receiver according to the judgment result of step (3), and counting the distribution of the points where the absorbed light falls on the receiver; Step (5), calculate and compare the receiver energy flux density distribution and collector optical efficiency under different tracking modes, and determine the tracking strategy of the heat pipe composite parabolic trough collector system.

2. The tracking strategy calculation method for the heat pipe composite parabolic trough solar collector system according to claim 1 is characterized in that: In step (1), the heat pipe composite parabolic trough collector system is composed of two or more collector units, each of which is composed of a composite parabolic trough concentrator, a heat pipe receiver, a glass cover and a connecting pipe, and the receiver is a two-phase closed thermosyphon; the optical parameters include the receiver radius r, the gap spacing g between the bottom of the receiver and the concentrator tip, the concentrator width W, the concentrator length L, the receiver circle involute expansion angle θ, the receiver circle circumferential angle ψ, the maximum receiving half angle θ C and concentration ratio C; CPC mirror profile is smoothly connected by parabola and receiver circle involute; In the Cartesian coordinate system, the structural equation of the receiver circle involute is: The structural equation of the parabola is: The structural equation of the receiver is:

3. The tracking strategy calculation method for the heat pipe composite parabolic trough solar collector system according to claim 2 is characterized in that: In step (2): the solar incident angle θ i The calculation formula is: i i =cos -1 (sina) s sina+cosa s cosαcos(γ-γ s )) (5); a s =sin -1 (sinλsinδ+cosλcosδcosω) (6); In equations (5) to (7), α is the concentrator elevation angle, α s is the solar altitude angle, γ is the concentrator azimuth angle, γ s is the solar azimuth, β is the concentrator tilt angle, λ is the latitude angle, δ is the latitude angle, and ω is the hour angle; The projections of the incident light along the longitudinal plane and the transverse plane of the concentrator are respectively expressed by the longitudinal incident angle θ i α and the lateral incidence angle θ i γ ; Longitudinal incident angle θ i α The calculation formula is: Longitudinal incident angle θ i α The calculation formula is:

4. The tracking strategy calculation method for the heat pipe composite parabolic trough solar collector system according to claim 3 is characterized in that: In step (4), when the incident light enters the concentrator opening plane and falls on the receiver: calculate the intersection of the light and the receiver, if the intersection coordinates (x, y, z) satisfy -L / 2<Z<L / 2, then mark the incident light as absorbed light, otherwise mark it as unabsorbed light; When the incident light enters the opening plane of the condenser but does not fall on the receiver: further determine whether the reflected light after the incident light is reflected has an intersection with the receiver; (a) If the reflected light and the receiver have an intersection point, further determine whether the coordinates of the intersection point (x, y, z) satisfy the condition -L / 2<Z<L / 2. If so, mark the incident light as absorbed light; otherwise, mark the incident light as unabsorbed light. (b) If the reflected light has no intersection with the receiver: further determine whether the reflected light has an intersection with the concentrator. If there is an intersection, further calculate whether the secondary reflected light after the reflected light has been reflected again has an intersection with the receiver, and further determine whether the incident light is absorbed light or unabsorbed light according to the methods of "(a)" and "(b)". If there is no intersection, directly mark the incident light as unabsorbed light.

5. The tracking strategy calculation method for the heat pipe composite parabolic trough solar collector system according to claim 4 is characterized in that: In step (4), determining whether the reflected light after the incident light is reflected has an intersection with the receiver includes the following steps: Step (4-1), calculating the intersection point of the incident light and the concentrator; Step (4-2), calculating the incident vector and normal vector of the incident light; Step (4-3), calculating the light reflection vector and the reflected light equation; Step (4-4), regard the reflected light as the incident light in the next reflection process and calculate the intersection of the reflected light and the receiver.

6. The tracking strategy calculation method for the heat pipe composite parabolic trough solar collector system according to claim 5 is characterized in that: In step (4), assume that the incident light passes through point P0 (x0, y0, z0); A. When the incident light falls on the receiver, the incident light I a,1 The point of intersection with the receiver's circular surface is denoted as P a,1 (x a,1 ,y a,1 , z a,1 ), then P0 and P a,1 Satisfies the following relationship: B. When the incident light falls on the involute segment, the incident light I i,1 The point of intersection with the involute is denoted as P i,1 (x i,1 ,y i,1 , z i,1 ), the corresponding receiver circle involute expansion angle is θ i,1 ; Then P0 and P i,1 Satisfies the following relationship: At the intersection point P i,1 The incident light I i,1 Vector and normal vector n i,1 The vector expression is: Reflected light F i,1 Vector (k i,1 , l i,1 ) in vector form: F = I-2(n·I)·n (13); but: After one reflection, the reflected light F i,1 is intercepted by the receiver, the intersection point is P i,a (x i,a ,y i,a ,z i,a ), then point P i,a With P i,1 Satisfies the following relationship: C. When the incident light falls on the parabola segment, the incident light I p,1 The first point of intersection with the parabola is denoted by P p,1 (x p,1 ,y p,1 , z p,1 ), the corresponding receiver circle involute expansion angle is θ p,1 ; Then P0 and P p,1 Satisfies the following relationship: At the intersection point P p,1 At, the incident light vector I p,1 and the normal vector n p,1 The vector expression of is: Reflected light F p,1 Vector (k p,1 , l p,1 ) is expressed as: After the incident light falls on the parabola, the reflected light must fall on the involute after at least n-1 reflections, where n is greater than or equal to 2; after n-2 reflections, the reflected light falls on the parabola, and the intersection point P with the parabola is p,n-1 (x p,n-1 ,y p,n-1 , z p,n-1 ), the corresponding receiver circle involute expansion angle is θ p,n-1 ; then P p,n-1 With P p,n-2 (x p,n-2 ,y p,n-2 , z p,n-2 ) satisfies the following relationship: At the intersection point P p,n-1 At, the incident light vector I p,n-1 and the reflected light vector F p,n-2 (k p,n-2 ,l p,n-2 ) are the same, then the incident light I p,n-1 The normal vector n p,n-1 The vector expression is: Reflected light F p,n-1 (k p,n-1 ,l p,n-1 )The vector expression of the vector is: After the incident light is reflected n-1 times, the reflected light F p,n-1 It falls on the involute, and the intersection point is P i,n (x i,n ,y i,n ,z i,n ,), the corresponding receiver circle involute expansion angle is θ i,n , then point P i,n and P i,n-1 Satisfies the following relationship: At the intersection point P i,n At, the incident light vector I i,n and the reflected light vector F p,n-1 (k p,n-1 ,l p,n-1 ) are the same, then the incident light vector I i,n The normal vector n ,n The vector expression is: Reflected light F i,n (k i,n ,l i,n )The vector expression is: Reflected light F i,n is intercepted by the receiver, the intersection point is P p,a (x p,a ,y p,a , z p,a ), click P p,a With P i,n Satisfies the following relationship:

7. The tracking strategy calculation method for the heat pipe composite parabolic trough solar collector system according to claim 6 is characterized in that: In step (5), the energy flux density is calculated by meshing the receiver surface and dividing the unit length receiver into N equal parts along the circumference. d cells, the area of ​​each grid is A i ; Count and calculate the energy Q carried by all the light rays falling into the i-th cell on the receiver i , then the average energy flux density on the i-th cell is I i The specific calculation formula is: Where m is the number of rays falling into the i-th cell; q e is the energy of each ray; I DNI is the direct solar radiation intensity projected onto the concentrator lighting surface; n r The total number of rays in the simulation.

8. The tracking strategy calculation method for the heat pipe composite parabolic trough solar collector system according to claim 7 is characterized in that: The calculation formula of the collector optical efficiency is:

Images