CN104990286A - Composite paraboloid solar collector - Google Patents

Abstract

The invention relates to a compound parabolic heat collector, comprising a Fresnel reflective condenser array and a heat collector, the Fresnel reflective condenser array is placed under the heat collector, and the heat collecting part of the heat collector is a heat collecting tube , the outer wall of the heat collecting tube is coated with an absorbing coating, the upper wall of the heat collecting tube is composed of a compound paraboloid composed of a heat insulating protective layer and a secondary reflection mirror, the lower wall of the heat collector is composed of a double-layer glass surface, and the heat collecting The upper and lower walls of the device are enclosed into a closed cavity, forming a layer of air wall. The present invention adopts the design of double-layer glass, which combines the advantages of the compound parabolic heat collector without heat insulation measures and the compound parabolic heat collector of the vacuum glass tube, and effectively reduces the complexity of system integration without reducing heat loss. The structure is simple, the production and operation cost is low, and the safety and stability of the heat collector are also improved.

Description

Compound Parabolic Collector

technical field

The invention relates to a reflective heat collector device, especially a reflective heat collector device based on linear Fresnel, which is used to improve the efficiency of the heat collector and realize solar energy by reducing heat dissipation between the heat collector and the external environment. Efficient use, improve energy utilization efficiency.

Background technique

The global environmental degradation and energy crisis have attracted more and more attention from all mankind. At present, as far as the whole country is concerned, there is an urgent need to develop low-cost, easy-to-use renewable energy utilization technologies. Solar energy will not pollute the environment. It is one of the cleanest energy sources. This is extremely valuable in today's increasingly serious environmental pollution .

China has a vast territory and abundant solar energy resources, so we should vigorously promote the use of solar energy in our daily life. Since solar energy is relatively scattered, the key technology in the thermal utilization of solar energy is to concentrate the sun's radiant energy and convert it into thermal energy. The solar collector is a special heat exchanger that converts the dispersed solar radiation energy into heat energy and transfers the heat energy to the working medium. The solar collector is a key component in the solar thermal utilization system. The collector absorbs the incident solar radiation and converts it into heat energy, so the ability of the collector to absorb solar radiation directly determines the efficiency of solar energy utilization.

Solar collectors are divided into non-concentrating collectors and concentrating collectors according to their concentrating capabilities. Due to the low energy density of receiving solar radiation per unit area, it is difficult for non-concentrating collectors to reach higher temperatures, and parabolic concentrators require complex tracking systems and are expensive. Compound Parabolic Collector (CPC) is a non-imaging concentrator designed according to the principle of edge optics. As long as the incident angle of light is smaller than its design value, it can be completely reflected on the heat collecting tube. It can be used as a Fresnel reflection system receiver to absorb energy. Therefore, the compound parabolic collector (CPC) has a wide application prospect. Most of the receiving devices used in the current linear concentrating solar energy devices are straight-through vacuum tube type CPC reflective concentrating receiving devices. Since the outer layer of the metal receiving tube is wrapped with a layer or double-layer vacuum glass sleeve, it has small heat loss and collects light. The advantage of high thermal efficiency, but its initial cost is high, the failure rate of the vacuum tube is high, and it is easy to cause vacuum leakage.

Therefore, it is very meaningful to need a novel composite parabolic heat collector device with simple structure, low production and operation cost, and easy large-scale commercial production and application without losing the heat collecting capacity of the heat collector. On the basis of the traditional vacuum tube parabolic heat collector, the vacuum heat collecting tube is removed, which avoids the disadvantages of high cost, high failure rate and easy leakage caused by this type of heat collecting tube. A double-layer glass partition is added to the lower part of the collector to minimize the heat conduction and convection with the external environment. While having the same effect as the vacuum tube collector, it greatly reduces the initial cost and failure rate, and realizes composite Possibility of large-scale use of parabolic collectors.

Contents of the invention

The invention aims at the problems existing in the prior art, and provides a compound parabolic heat collector which can effectively reduce operating costs and is easy for large-scale commercial application.

In order to achieve the above object, the technical solution of the present invention is: a compound parabolic heat collector, comprising a Fresnel reflective condenser array and a heat collector, the Fresnel reflective condenser array is placed under the heat collector, and the collector The heat collecting part of the heat collector is a heat collecting tube, and the outer wall of the heat collecting tube is coated with an absorbing coating. Composed of double-layer glass surfaces, the upper and lower walls of the collector form a closed cavity, forming a layer of air wall.

The double-layer glass surface is composed of inner glass and outer glass, the thickness of the outer glass is 5mm-6mm, the thickness of the inner glass is 3mm, and the gap between the inner glass and the outer glass is 9mm-12mm.

The pipe diameter of the heat collecting pipe is 70-200mm.

The secondary reflection mirror surface is in the shape of a compound parabola, and the secondary reflection mirror surface is arranged in cooperation with the linear Fresnel reflection condenser lens array (1).

The Fresnel reflective concentrating array includes several flat or curved strip-shaped optical mirrors, each of which has a width of 500-1000 mm and a length of 2000-5000 mm.

Compared with the prior art, the present invention has the following beneficial effects:

1. Effective absorption of solar energy: On the basis of the existing linear Fresnel reflective collector system, a high-transparency glass is added inside the CPC collector. Since the incident angle of the light path through the double-layer glass will not change, Adding glass has no effect on the optical path of the Fresnel reflector, and the heat absorbed by the collector is not affected.

2. Improvement of collector efficiency: Compared with the traditional CPC collector with only the bottom layer of glass plate, there is a layer of stagnant air layer in the double-layer glass plate of the collector, which greatly reduces the impact caused by external natural convection. The temperature in the heat collecting cavity is lowered. Due to the existence of the static air layer in the double-layer glass, the heat exchange between the external environment and the CPC cavity is mainly completed by heat conduction, and the thermal conductivity of the air is very low, so the heat dissipation in the cavity is significantly reduced. Less heat dissipation means more energy is absorbed, which increases the efficiency of the collector.

3. The comparison between this project and the CPC heat collector with vacuum tube: the CPC heat collector with vacuum outer tube is equivalent to creating an insulating environment outside the heat collecting tube to reduce heat dissipation, and the heat collector of the claim adds a glass plate to collect heat. The interior of the cavity is equivalent to an environment where only the lower surface has heat conduction. Since the thermal conductivity of the air is very low, it can also be regarded as the interior of the CPC cavity is in an adiabatic state. The principle is the same as that of the CPC collector with vacuum tubes. This method is adopted It will greatly reduce the difficulty of making the CPC collector. Considering from an economic point of view, although the CPC heat collector with the vacuum outer tube has a good heat preservation function, due to the high cost and high failure rate of the vacuum tube CPC heat collector, a large amount of cost is huge for putting into use. improvement, thus realizing the possibility of large-scale use.

4. The possibility of this implementation is verified by numerical simulation. The simulated model is a section of solar collector model with collector tube diameter D=180mm and tube length L=5000mm, the inlet temperature of working fluid is 300K, and the flow time is set to 100s. The simulation results are attached in Figure 2. From the simulation results, it can be seen that the air temperature in the collector cavity with double-layer glass surfaces rises significantly, which is 20°C higher than the average temperature in the collector cavity without double-layer glass surfaces, and the average temperature at the outlet The temperature increased by about 1.1°C. At the lower part of the collector close to the glass surface, the temperature of the collector without double-layer glass is about 310°C, while that of the collector with double-layer glass is about 340°C. It fully shows that the double-layer glass surface effectively hinders the convective heat transfer between the external environment and the cavity. The heat retention capacity in the collector cavity is improved. If it is used in engineering, the efficiency of the collector will be significantly improved when the pipe length is tens of meters.

Description of drawings

Fig. 1 is a schematic diagram of the structure principle of the present invention;

Fig. 2 is a diagram of simulation results of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Referring to accompanying drawing 1, compound parabolic heat collector of the present invention, comprises Fresnel reflective light-concentrating array 1, cavity 2, heat collector 3, thermal insulation protection layer 4, secondary reflection mirror surface 5, absorbing coating 6, collector Heat pipe 7, inner glass surface 8, outer glass surface 9.

The heat collector 3 cooperates with the linear Fresnel reflection concentrator array 1 to form a solar focusing reflection system, and the independently fixed heat collector 3 constitutes an energy absorption system, and the outer wall of the heat collection tube 7 absorbing device is coated with a selective absorption coating 6, The heat collector 3 is composed of an inner glass surface 8 and an outer glass surface 9. The lower wall double-layer glass surface and the upper wall surface thermal insulation protection layer 4 are enclosed to form a closed cavity 2, which can effectively reduce energy loss.

The Fresnel reflective concentrating array 1 in the solar reflective system includes several flat or slightly curved long optical mirrors, which can be flipped around their own central axis to track the sun for reflection and concentrating, and are easy to modularize. The specific size of each mirror surface can be selected according to the parameters in the prior art, with a width of 500-1000mm and a length of 2000-5000mm.

The energy absorption system is composed of the compound parabolic heat collector. The heat collecting tube 7 is covered with an absorbing coating 6, and the upper wall surface is provided with a thermal insulation protection layer 4 to effectively prevent heat loss. A secondary reflection mirror 5 is provided in the thermal insulation layer. The secondary reflection mirror surface 5 is in the shape of a paraboloid. Part of the light entering the heat collector is directly absorbed by the heat collection tube 7, and the other part is reflected by the secondary reflection mirror surface 5 to the heat collection tube 7 and absorbed by the heat collection tube 7. The lower wall of the heat collector is drawn from the inner , The outer glass surface 8, 9 is composed of double-layer glass surfaces, the distance between the two layers of glass surfaces is 9mm-12mm, the double-layer glass surface forms a layer of air wall due to the small gap between the two layers of glass, and the air basically does not move. The glass surface 9 is in contact with the outside world. Because the thermal conductivity of the air is very low, the double-layer glass surface has an excellent thermal insulation effect, which greatly reduces the heat loss of the heat collector due to convection heat dissipation and increases the heat collection. And because the light path after the light passes through the double-layer glass is parallel to the original light path, the reflection of sunlight will not be affected.

The process is as follows: the sunlight is concentrated and reflected by the linear Fresnel reflective concentrator array 1 and concentrated on the heat collecting tube 7, and the light energy is converted into heat energy through the selective absorption coating 6, and the heat is conducted by the tube wall of the heat collecting tube 7 It is transferred to the inside to raise its temperature to the working temperature; the working fluid flows in the tube and takes away the heat absorbed by the tube. Due to the existence of the double-layer glass surface, the heat loss inside the heat collecting chamber is greatly reduced, so that the heat absorbed by the pipe is transferred to the working fluid inside the pipe, and the absorption rate and utilization rate of solar energy are generally improved.

Specifically, when the present invention operates, the Fresnel reflection concentrating array 1 sunlight is reflected on the outer glass surface 9 at the bottom of the heat collector, and the light passes through the double-layer glass surface composed of the outer glass surface 9 and the inner glass surface 8, The optical path remains unchanged, and the focused incident light enters the interior of the cavity 2 surrounded by the inner glass surface 8 and the compound parabolic secondary reflection mirror 5 with the heat insulating protective layer 4, or directly reaches the selective absorption coating on the heat collecting tube 7. layer 6 is absorbed by it, or is absorbed by the selective absorbing coating 6 reflected by the compound parabolic secondary reflector 5 twice or multiple times on the heat collecting tube 7, and a very small part of the light will be reflected multiple times in the cavity It is lost to the outside world through the double-layer glass surface 8. In the cavity, the absorbed solar energy is converted into heat energy, and a part of the energy that would originally be lost to the atmosphere through the complex heat conduction-convection-radiation coupling heat transfer process is due to the double-layer glass surface. With the existence of the air wall formed by the glass surface, the heat conduction and convection are greatly reduced, and most of the energy is absorbed by the heat collecting tube. The absorbed energy is transferred to the working medium flowing in the tube in the form of heat through the heat collecting tube 7, so that the solar thermal energy is continuously converted into heat.

The invention provides a heat collector device based on linear Fresnel reflection. Because of its simple structure of the solar concentrating system, compared with the traditional vacuum glass tube heat collector, the manufacturing process is simple, and the manufacturing cost is greatly reduced. Compared with traditional non-vacuum glass tube collectors, energy loss is reduced. The invention is relatively simple to transform a traditional heat collector, has low price, strong scalability, and certain economy and reliability.

Claims (5)

1. A compound parabolic heat collector, comprising a Fresnel reflective condenser array (1) and a heat collector (3), and the Fresnel reflective condenser array (1) is placed in the heat collector (3), and its characteristics In that: the heat collecting part of the heat collector (3) is a heat collecting tube (7), the outer wall of the heat collecting tube (7) is coated with an absorbing coating (6), and the upper wall of the heat collecting tube (7) is made of The thermal insulation protection layer (4) and the compound paraboloid (5) composed of the secondary reflection mirror surface are composed, the lower wall surface of the heat collector (3) is composed of double-layer glass surface, and the upper and lower wall surfaces of the heat collector (3) are enclosed to form an airtight The cavity (2) forms a layer of air wall. 2. The compound parabolic heat collector according to claim 1, characterized in that the double-layer glass surface is composed of inner glass (8) and outer glass (9), and the thickness of the outer glass (9) is 5mm-6mm , the thickness of the inner glass (8) is 3mm, and the gap between the inner glass (8) and the outer glass (9) is 9mm-12mm. 3. The compound parabolic heat collector according to claim 1, characterized in that, the diameter of the heat collecting pipe (7) is 70-200mm. 4. The compound parabolic heat collector according to claim 1, characterized in that, the said secondary reflector surface (5) is in the shape of a compound paraboloid, and the secondary reflector surface (5) and the linear Fresnel reflective condenser Array(1) fits the setup. 5. The compound parabolic heat collector according to claim 1, characterized in that, the Fresnel reflection concentrating array (1) includes several flat or curved elongated optical mirrors, and the width of each mirror is 500-1000mm, length 2000-5000mm.