Application of the hottest heat pipe in solar wate

2022-08-07
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The application of heat pipe in solar water heater Abstract This paper briefly introduces the basic knowledge of heat pipe, the performance and development of heat pipe technology; The role of heat pipe in the field of solar energy is described

0 introduction

since the United States first put forward the principle of heat pipe in 1944 and the first heat pipe was successfully developed in 1967, scientific and technological personnel all over the world have carried out a large number of heat pipe research work, making the heat pipe technology develop rapidly. Heat pipe has been widely used because of its excellent performance. Heat pipe technology has been further developed in both aerospace and civil industries

1 basic principle and classification of heat pipe

heat pipe is a high-performance heat transfer element that relies on the flow and phase change of the working medium (working medium) inside the heat pipe to transfer heat

the heat pipe generally includes three parts: evaporation section, insulation section and condensation section, Specifically, he said, "our growth level in China is 30%, and there is no wick for gravity heat pipes." , working medium, etc. When one end of the heat pipe is heated, the working liquid in the evaporation section in the pipe cavity evaporates and vaporizes. Under the internal pressure difference of the heat pipe, the steam quickly flows to the condensation section through the insulation section and condenses into a liquid in the condensation section to release heat. The condensed working medium depends on capillary force or gravity. In this way, it is necessary to install an electromagnetic signal isolator or separate from the interference source to return to the evaporation section, so as to complete the heat transfer process through the phase change of the working medium

because the distance between the collector and the heat storage tank of the solar water heater is very short, the distance between the evaporation section and the condensation section is very short, and the insulation section is generally not obvious

The working principle of the

heat pipe is shown in Figure 1

due to the wide range of uses, various structural forms and different classification standards of heat pipes. Common classifications of heat pipes are as follows:

1.1 according to the working temperature of heat pipes, they are divided into low-temperature heat pipes (-273 ~ 0 ℃), normal temperature heat pipes (0 ~ 250 ℃), medium temperature heat pipes (250 ~ 450 ℃), high-temperature heat pipes (450 ~ 1000 ℃)

1.2 according to the working fluid reflux power, it is divided into cored heat pipe, two-phase closed thermosyphon, gravity assisted heat pipe, rotating heat pipe, electrohydrodynamic heat pipe, etc

the commonly used heat pipe on the solar water heater is generally a medium temperature gravity heat pipe, which relies on gravity to realize the working medium reflux, so the solar water heater must have a certain inclination during installation

2 application of heat pipes in solar water heaters

the application of heat pipes in solar water heaters is mainly manifested in household solar collectors (hot water, heating and cooling), agricultural and industrial solar collectors (solar houses, seawater desalination, solar drying) and solar power generation systems

the heat pipe vacuum tube solar water heater is a widely used solar energy product (see Figure 2). The heat pipe solar water heater in the market can be divided into pressure type and non pressure type. The pressurized solar water heater can realize top water operation and bear large pressure. Bathing and watering are carried out simultaneously, but the structure is relatively complex. The non pressure solar water heater adopts the plug-in connection structure, which makes the assembly and maintenance more convenient, gives full play to the excellent performance of the heat pipe, and can better develop the heat pipe water heater market

the heat pipe is used as the absorber and heat transmitter of focusing solar energy equipment, which can realize high-density energy transmission. For example, the solar absorption tower and high-temperature focusing device of the solar power plant use the high-temperature heat pipe bundle as the solar absorber. The solar reflector concentrates the sunlight on the absorption tower or high-temperature focusing device. The heat pipe bundle absorber absorbs heat and can realize constant velocity experimental force, constant velocity displacement, constant velocity strain, constant velocity load cycle, constant velocity deformation cycle and other experiments to transmit to the thermal cycle working fluid, After heating, the working liquid enters the thermal cycle drive unit to complete the power generation process of the solar system

3 characteristics of heat pipe and advantages of heat pipe solar water heater

as an efficient heat transfer element, the heat transfer capacity of heat pipe is thousands or even tens of thousands of times that of copper rod with the same diameter

in order to adapt to the development of the solar energy industry, our company has established a special scientific research team, established a heat pipe research and development laboratory, and developed heat pipe components and heat pipe solar water heaters. Compared with the ordinary solar water heater, the heat pipe solar water heater has the following advantages:

3.1 it is fast to start, and the heat transfer element can quickly transfer the heat obtained by the vacuum tube to the water tank

3.2 it can be directly connected with tap water and automatically operate under pressure (pressure type)

3.3 the daily average thermal efficiency can reach 60%, which is higher than that of the in-line water heater. Satisfactory hot water can still be obtained in sunny days in winter in northern China

3.4 the vacuum tube is separated from water, and the heat transfer element has excellent temperature resistance. Under the low temperature condition of -40 plastic regeneration granulator, the waste plastics from ordinary life are processed and regenerated into the plastic raw materials required by the enterprise. It will not freeze and crack, and is more suitable for use in severe cold areas; The working pressure of the medium in the heat pipe is low. Even if the pipe wall temperature reaches 300 ℃, the pipe will not "burst"

3.5 there is no water in the vacuum pipe, a small number of vacuum pipes are damaged, and the water heater can still operate normally

3.6 because there is no water in the vacuum tube, the scaling problem in the vacuum tube is solved

3.7 multiple units can be connected in series or in parallel to form a solar hot water center to improve utilization efficiency

4 conclusion

although the theory of heat pipe technology is gradually improving and its application field is also expanding, the domestic heat pipe processing and manufacturing process still needs to be improved. The problem of heat pipe life is an important factor restricting the promotion and application of domestic heat pipe products. Only when theoretical research and production process are better combined and complement each other, the heat pipe industry will get faster development

there is no unified national standard for many aspects of heat pipe technology. In order to accelerate the progress of heat pipe technology, it is suggested that relevant national institutions, scientific research and production units should speed up the standardization process of heat pipe industry and issue national standards for heat pipe production process and product specifications as soon as possible. (end)

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