Flat solar water heaters are composed of heat absorbing plates, cover plates, insulation layers, shells and other parts. (1) Function
Also called heat-absorbing core panel, it is a component that absorbs energy from solar radiation and transfers heat to water.
(2) Technical requirements
① The technical requirements are a certain carrying capacity, good water compatibility, excellent thermal performance, simple processing technology and a reasonable cost. Commonly used materials include copper, aluminum alloys, stainless steel, galvanized sheets, and materials such as plastic or fiberglass in coastal areas with poor water quality.
② Selective coating: In order to increase the thermal performance of the heat absorbing plate, a coating is often sprayed on the metal surface. There are two typeses of coatings: selective coating and non-selective coating.
③Flat collectors are divided into two categories according to the type of coating, commonly known as black film and blue film (black chrome, anodized)
(3) Heat absorber
p>Also known as heat absorber, heat absorber is the core component of flat panel solar water heater. It must first complete the conversion of light and heat, and then transfer the thermal energy to water. to heat.
The heat absorber is mainly made of metal materials. It was initially a connecting structure made of steel tube plates. Later, welded type, aluminum wing type and copper-aluminum composite type appeared, each with its own advantages. Some have poor thermal conductivity, some have too high power consumption, some have too many consumables, and some havecomplicated processes. But the common point is that the heat transfer is tens to hundreds of times higher than that of glass. For example, the thermal conductivity of copper is around 320, that of aluminum is around 160, that of copper is around 40, while that of glass is only 0.64. The pressure resistance can reach 10KG/CM2, and the glass cannot even withstand 0.5KG/CM2 pressure.
Thus, the metal heat absorber can operate in natural circulation, forced circulation and direct current. Since the flow rate is proportional to the heat transfer coefficient, the heat transfer efficiency of the metal heat absorber is also much higher.
The heat absorber tube plate is combined with new technology. It requires only one punch and two sets of molds for mass production. We can say that there are fewerequipment and less investment; punching, wearing and pressing can be completed, it can be said to be simple and easy to implement; there is no need for welding or other auxiliary materials, it can be said to save labor and energy by using thin-walled copper tubes as pipes; and thin aluminum plates as fins, it can be said to be scientific in compatibility, corrosion resistance, good heat transfer and material saving.
When this structure participated in the national flat panel solar water heater competition, the average daily efficiency was 0.563 and the heat loss coefficient was 1.75, the same thermal performance than the product that won first prize. at this moment.
(4) Classification
According to the structure of the heat absorbing plate, it can be divided into tube plate type, typwing tube type, snake tube type, flat box type, round tube type and heat pipe type.
1. Tube plate heat absorption plate
The tube plate heat absorption plate of the flat plate solar collector is a heat absorption strip formed by connecting the row pipe and the plate flat in a certain combination (such as that shown in the right image), it is then welded with the upper and lower collectors to form a flat panel solar collector heat absorption plate. This is the most commonly used type of heat-absorbing plate structure at home and abroad.
2. Wing Tube Heat Absorbing Panels
Wing Tube Heat Absorbing Panels are heat absorbing strips with fins connected to both sides of a metal tube manufactured using 'a mold extrusion. and drawing process. Belt (as shown on the rightite).), then welded to the upper and lower headers to form a heat absorbing plate. The heat absorbing plate material of flat panel solar collectors is generally aluminum alloy.
The advantages of flat solar collector wing tube heat absorption plate: high thermal efficiency, tube and flat plate are integrated, no combined thermal resistance, strong resistance to pressure, aluminum alloy tube can withstand high pressure.
Disadvantages of the finned tube heat absorbing plate of the flat solar collector: the water quality is not easy to guarantee, and the aluminum alloy will be corroded; the amount of material is large and the process requires a large thickness of the tube wall and fins; the dynamic characteristics are poor, and the heat absorbing plate has a large thermal capacity.
3. Heat absorbing plate in yoube serpent
The snake tube heat absorbing plate is a metal tube bent into a serpentine shape (as shown on the right) and then welded. to a flat plate to form a heat absorbing plate. This type of structure is commonly used abroad. The material of the heat absorbing plate is generally copper, and the welding process can be high frequency welding or ultrasonic welding.
Advantages of the snake-type heat-absorbing plate of the flat panel solar collector: no additional soldering of the collector is required, reducing the risk of leakage; high thermal efficiency, no combined thermal resistance, and the copper tube will not be corroded; To ensure quality, the entire production process is mechanized; with strong pressure resistance, the copper pipe can withstand high pressure.
Disadvantages of the snake type heat absorbing plate of theflat solar collector: high flow resistance, fluid channels are not connected in parallel but in series; welding is difficult and the weld is not a straight line; but a curve.
4. Flat box type heat absorbing plate
The flat box type heat absorbing plate of the flat panel solar collector is molded separately by two metal plates and then welded. together to form an absorbent plate. The materials of heating plate and heat absorbing plate can be stainless steel, aluminum alloy, galvanized steel, etc.
Usually, the spot welding process is used between the fluid channels, and the seam welding process is used around the flat box type heat absorption plate of the flat solar collector.
Advantages of flat box type heat absorbing plate of flat plate solar collector: thermal efficiencyhigh, the tube and the flat plate are integrated and there is no combined thermal resistance; the collector needs to be welded, and the fluid channel and the collector are formed by one-time casting.
Disadvantages of flat box type heat absorbing plate of flat panel solar collector: the welding process is difficult and prone to problems of welding penetration or weak welding, pressure resistance is bad and the solder joints cannot withstand high pressure. ; The dynamic characteristics are poor, the cross section of the fluid channel is large, and the heat absorption plate has large heat capacity, sometimes the water quality is not easy to guarantee, and the alloy of aluminum and; galvanized steel will be corroded. (1) Function
The upper surface of the heat absorbing plate should be covered with a cover plate, which is necessary to transmit lightvisible but not far infrared rays. This makes the energy coming in is greater than that of far infrared rays. lost energy, thereby improving the efficiency of the heat absorbing plate. The increase in lid temperature is generally called the greenhouse effect.
(2) Technical requirements
High total light transmittance, high impact resistance, good weather resistance, good thermal insulation performance and good processing performance. (1) Function
The function of the insulating layer is to reduce the heat dissipation of the collector to the environment to improve the thermal efficiency of the collector.
(2) Technical requirements
The requirement for the insulating layer is good thermal insulation performance, that is, the thermal conductivity of the material is low and the requirement is not more than 0.055W/(m*℃), not easy to deform or volatilizer, does not produce toxic gases and does not absorb.
(3) Materials
The materials of the insulation layer include rock wool, mineral wool, polystyrene, polyurethane foam, etc. (1) Function
The function of the insulating layer shell is to integrate the heat absorption plate, cover plate and insulating material into a whole, so it must have a certain rigidity and strength and be easy to install. The materials are usually steel sheets, aluminum profiles, fiberglass or plastic.
(2) Technical requirements
In order to ensure the life of the hull, certain surfaces of the hull must be sprayed. Generally, the coating should be thin and uniform, have strong adhesion and anti-aging properties, be resistant to moisture and heat, and not rust. In addition, the surface must be beautiful and free from deformations, dirt andgrooves.
It is two-layered.
1. The volume of the thermal insulation barrel is designed according to the amount of solar heat collected by the collector tube (plate) if two thermal insulation barrels share a set of thermal energy collectors (collector tubes). or panels) In relative terms, a bowl of hot water plus a bowl of cold water basically cannot achieve the desired effect.
2. The connection between the first insulated barrel and the second insulated barrel is very simple, you just need to connect the hot water pipe from the first insulated barrel to the cold water inlet pipe from the second insulated barrel.