| Nowadays, the usage of solar energy has become the worldwide trend. The solar collector is the key component in the solar thermal utilization whose effective utility has been the main concern, its quality standard express the overall utilization of solar system. The U-tube solar collector provide the combined effects of a highly selective surface coating and vacuum insulation of the absorber element so that they can have high heat extraction efficiency compared with the flat plate collectors. Currently, a few theoretical study focus on the U-tube solar collector. In this essay, most of attention concentrates on the theoretical study. From the basic thermal theory and simulation point, the optimizing way for the U-tube solar collector was developed. The completed works on the essay was displayed in the following:1) Set the solar radiation model. From the experiment equipment, the solar radiation set on the horizontal plate was got, by apply the matlab programming the beam radiation and the diffuse radiation was attained and the solar radiation on the tilted plate was finally achieved, which provide reliable data for the following computation.2) Through analysis of U-tube solar collector, the unsteady state mathematical model was developed and the mean outlet temperature was got. For the small heat capacity of U-tube solar collector, this paper focuses on the heat transfer under the steady-state. Respectively from the overall analysis and simplification of the aluminum fin angle, thermal parameters: efficiency, heat loss coefficient and transferring coefficient were derived. Moreover, by computing in the Matlab program, the temperature of each part within the internal structure and thermal efficiency were finally got.3) From the theoretical analysis, consider the impact of various parameters on the mean outlet temperature of the U-tube solar collector. By changing the length of the collector, the fluid inlet velocity, the copper tube diameter, the solar radiation, the inlet temperature and the different structure of aluminum fin the internal heat transfer and efficiency of the U-tube solar collector were found. Working on the analyzing results, the optimal design scheme was proposed, which is useful for the betterment design and the matching parameters.4) Since the actual test is quite difficult to test the internal temperature distribution and flow field of the U-tube solar collector, the use of FLUENT simulation can be great assistant. Differencing the fluid inlet velocity, the U-tube diameter and the solar radiation, the temperature of the fluid along the tube length direction were finally achieved. Compared with the conclusions summarized in the above chapter, the trend agrees well, which demonstrated the reliability and validity of the model developed above.5) Simulated U-tube solar collector within the wavy aluminum fin in the FLUENT program. Compared with the traditional U-tube solar collector, the built-in wavy aluminum fin can achieved 6% higher efficiency. As a result, varying the structure of aluminum fin can effectively improve the thermal performance and have a better future.In this essay, focusing on the thermal theory, the optimization suggestions were put forward, which will provide theory support and make contributions to the continually development of solar heating system. |
