دانلود رایگان مقاله انگلیسی مبدل های حرارتی چاه: بررسی فنی - الزویر 2018

abstract

The available literature on the WellBore Heat eXchangers (WBHX) has been analyzed giving prominence to three aspects. First, the heat transfer through the geothermal reservoir and between the formation and the well has been analyzed. Then, the design of the WBHX and the modelling of the heat exchange has been reviewed. Lastly, the analysis of the performance of the WBHX in the production of thermal and/or electrical energy has been focused. Regarding the modelling of the heat transfer in the reservoir and between the wellbore and the formation, the sensitivity studies in literature highlight as key parameter the residence time of the fluid into the device. At fixed flow rate the residence time of the fluid in the WBHX is function of the well diameter. From analyzed papers, it raises the need of the insulation of the upward pipe in order to avoid heat losses. The range of produced thermal power is 0.15÷2.5 MW and of electrical power is 0.25÷364 MW. The WBHX is a promising technology if and only if is applied in the more convenient geothermal assets. The continuous study of the possible designing solutions and the improvements to enhance heat transfer is fundamental to allow this technology ready to market.

Conclusions

The analysis of literature and the results obtained by the authors demonstrates the feasibility of the extraction of geothermal energy without brine production by means of the WBHX. The low efficiency in heat recovery respect to the conventional geothermal plants makes this solution not profitable for the hydrothermal systems. Anyway, considering the advantage of avoiding risks and costs related to the extraction and reinjection of the fluids, the WBHX may encourage a positive social response to geothermal plants and it could be an opportunity for the exploitation of conventional and unconventional geothermal systems. Therefore, a research to improve the performance and the applicability of the WBHX is worthwhile. In details, the aspects to be deepen are the heat carrier fluid, the pipes materials, the design and the conversion systems. Regarding the heat carrier fluid, the evaluation of using nanoparticles in the heat carrier fluid is undergoing. The basic idea is the increase of the volumetric heat capacity of the pure fluid. First results, obtained based on available correlations, suggest a 1% increase of the heat exchange adding a 3% in volume of Aluminum oxide in water. There is a lack of specific studies on materials that are made up the pipes of the WBHX. In order to improve the heat recovery of the device, the research should focus on the possibility to use for the internal pipe a material able to isolate it, reducing the heat losses during the recovery of heated fluid. Instead, the grouting material mainly affects the heat exchange with the formation. Therefore, improvements are needed more on the grouting materials than in materials constituting the external casing.