关键词: 地热能, 单裂隙, 二氧化碳, 传热, 模型

Abstract:

In enhanced geothermal systems, fluids flow through rough rock fractures to obtain heat. A practical rock sample from Qiabuqia area in Gonghe Basin, Qinghai, China was used to obtain the real three-dimensional morphology in single fracture using high-precise scanning. This single fracture was used to propose a three-dimensional simulation model to numerically calculate convective heat transfer of water and CO₂. The effects of inlet fluid temperature, fluid flow rate, rock initial temperature, fracture openness and injection-production pressure difference on the heat extraction performance were analyzed. Increasing temperature difference between the fluid and the rock increased the heat transfer coefficient, and decreased the fluid outlet temperature. With increasing fluid injection flow, fracture openness and injection-production pressure difference, the heat transfer coefficient increases and the fluid outlet temperature decreased. The effective strength on heat transfer of fluid flow rate was the highest, followed by injection-production pressure difference and fluid inlet temperature. The fluid flow rate was increased from 10mL/min to 80mL/min, and the heat transfer quantity with water was increased from 109W to 351.2W, and the heat transfer coefficient was increased by 140.61W/(m²·K) for each increase of 1mL/min fluid flow rate.The heat transfer quantity with carbon dioxide was increased from 36.9W to 126.6W, and the heat transfer coefficient was increased by 19.84W/(m²·K) for each increase of 1mL/min fluid flow rate. H₂O with higher specific heat capacity and thermal conductivity carried out more heat than CO₂.

Key words: geothermal energy, single fracture, carbon dioxide, heat transfer, model