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How to design u pipe solar collector

Views:2     Author:Site Editor     Publish Time: 2019-10-15      Origin:Site

In the past 20 years, the shortage of resources has become increasingly serious, and the development of new energy sources is also urgent. Of course, solar energy is a renewable energy source and can be inexhaustible. People will also pay great attention to its development and utilization. U pipe solar collectors are composed of copper tubes, heat absorbers, glass tubes and metal end caps. After passing through the circulating pipe and holding the water tank, the solar radiation can be used to heat up the water. The design and development of U-tube solar collectors is of course a top priority. It can solve problems such as bathing in many homes, while not consuming non-renewable energy and polluting the environment.

 

This is the content table of the article:

1. Measuring data

2. Simulating the optical and thermal performance of U-tube solar collectors, thermal behavior and output of the system.

3. Using algorithms

4. Conclusion

 

How to measuring data? 

It is necessary to calculate the efficiency of the U-tube solar collector, and also to calculate the irradiance of the sun, and of course the influence of the ambient temperature. At a certain value, the efficiency of the u pipe solar collector and the ambient temperature tend to increase and then decrease. At the same time, the efficiency of the collector will increase with the increase of solar irradiance. When the solar irradiance is lower than a certain value, the efficiency of the collector increases rapidly, and then as the radiation increases. The growth rate gradually changed, and finally stabilized. This phenomenon is due to the fact that at low solar irradiance, very low heat flow results in a relatively low heat transfer rate between the U-tube and the working fluid.

 

How to simulate the optical and thermal performance of U-tube solar collectors, thermal behavior and output of the system? 

① Establish solar radiation model: Solar radiation is an important parameter in solar energy systems. The total radiation measured on the horizontal plane is measured using a solar radiometer.

②Using the traditional steady-state mathematical model, it is generally considered that the temperature inside the vacuum tube is uniform and uniform, and the analysis method of lumped parameters is adopted.

③ The effects of vacuum tube length, inlet flow rate, inner diameter of U-tube, solar radiation, inlet temperature of fluid and shape of aluminium wing on the thermal performance of U-pipe solar collector are analyzed, and a reasonable optimization scheme is put forward.

④ Verification by simulation, the temperature change of the fluid in the U-shaped copper tube along the length direction and the radial direction of the tube is obtained. Under the same conditions of other parameters, simulate the different inlet flow velocity, U-tube inner diameter and solar radiation temperature change and flow field change, and compare with the numerical calculation results to verify the reliability and correctness of the mathematical model.

 

Which algorithm is used?? 

In order to facilitate the simulation calculation and not affect the result, some assumptions are made: the air convection and conduction heat loss inside the vacuum tube of the U-pipe solar collector are neglected, and the system is always in thermal equilibrium; the heat transfer coefficient of the vacuum tube glass and the surrounding environment Constant value: The thermal energy distribution on the copper ring surrounding the U-tube is uniform: each heat transfer process is considered to be stable.

According to the law of conservation of energy, it can be inferred that the useful energy of the solar collector should be equal to the set.

The solar radiation absorbed by the heat sink subtracts the energy lost by heat transfer from the surrounding environment.

      Qu=G-QL

Where G is the solar radiation absorbed by the collector selective coating, Qu is the energy that can be utilized, and QL is the heat exchange loss with the outside. The total heat loss coefficient of the collector is the sum of the heat loss coefficient of the vacuum tube and the heat loss coefficient of the collector tube.

UL=Ua+Ue

The vacuum tube heat loss Ua is the heat loss from the collector tube to the surrounding environment.

Ua=11Hga+1hpg

Hga is the heat conduction coefficient between the glass tube and the surrounding environment. HPS is composed of the heat conduction coefficient hpee between the heat absorbing tube and the glass tube of the cover tube and the heat auxiliary emission coefficient hoar between the heat absorbing tube and the glass tube of the cover tube.

Hpgc=σ ε pl+ε pdε gdg(1-εp) (T2b+T2g) (Tb+Tg)

Where σ is the Boltzmann constant, εp is the emission ratio of the absorption surface of the absorber tube, εg is the emission ratio of the inner surface of the outer glass tube, and dg is the diameter of the glass tube.

 

Summary

Solar energy is a non-polluting green renewable energy source, which reduces environmental pollution caused by conventional boilers and power generation, and is conducive to environmental protection. U-tube solar collectors combine the various functions of building roof landscaping, energy saving and solar energy conversion without occupying land resources. The u-pipe solar collector has high internal heat efficiency, high pressure, and low heat loss.


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