دانلود رایگان مقاله انگلیسی بررسی انتقال حرارت هدایت گرما در سیستم زمین گرمایی - الزویر 2018

ABSTRACT

Geothermal energy is one of the well-known types of renewable energies that can be considered as a promising alternative to fossil fuels in order to mitigate the CO2 emission in atmosphere. Geothermal energy has recently been used for heating and cooling systems in many countries of the world. Therefore, studying such kind of energy seems important and necessary. This paper studies the heat transfer processes in a borehole heat exchanger (BHE). The flow of fluid in a BHE has been considered with different geometries and heat transfer processes are modeled numerically and in a finite volume method through convection and conductivity. First, a single U-shaped BHE was modeled and its thermal properties were investigated and then other geometries were studied to obtain the best geometry and heat transfer efficiency. In order to increase the heat transfer in the inner part of the pipes, the fin with the given specifications was used and the modeling was carried out and the thermal parameters were compared for three BHE’s with different geometries. In the final part, optimization results are presented, and the interaction of parameters on the Nusselt number and friction coefficient have been investigated. Also, the desirability of optimization and reliability is given to the results presented in percentage terms. Comparing the results of this article with the results of previous research shows a very good agreement and therefore the applied method is reliable and accurate.

Conclusion

In previous parts, temperatures distributions of single U-pipe, double U-pipe and centered inlet heat exchangers have been investigated. According to the contours and figures of three BHEs, it can be seen that a coaxial borehole heat exchanger with centered inlet has more performance compared to others. Also in optimization part, considering the design parameters and their result on the Nusselt number and friction coefficient, it was observed that the Reynolds number has the most effect among the parameters. As the Reynolds number increases, in addition to increasing heat transfer, the pressure drop will also decrease. The other two parameters have roughly the same value. By increasing the diameter rate and stepping distance, the efficiency and design desirability will increase. According to these simulations two relations are presented to better understanding of parameters effect. Therefore, the paper presents best geometry for the highest heat transfer rate, and geometry with fin is also proposed to increase the heat transfer in borehole heat exchanger, which can be applied to engineering applications.