极地深层热水钻回水软管及注热软管热流特性研究

Research on thermal and flow characteristics of return-water hose and heat-injection hose of deep hot-water drill in polar regions

深层热水钻是开展极地冰下湖洁净钻探取样的重要工具。井下回水系统是深层热水钻的关键组成部分,主要包括回水软管、注热软管、潜水泵和回水腔等。回水软管用于抽取回水腔中的融水至地表以实现循环利用,而注热软管则用于将地表热水注入回水腔以防止其冻结。回水软管和注热软管的热流特性对井下回水系统设计十分重要,但目前还未开展系统研究,其压力损失和温度损失的变化规律尚不清楚。本文首先基于达西-魏斯巴赫公式和苏霍夫温降公式提出了回水软管和注热软管热流特性的理论计算方法;然后,在COMSOL Multiphysics 5.6软件建立了两种软管热流特性的数值模拟方法,并与理论计算结果进行了对比;最后,系统分析了流量、内径、长度、进口水温、导热系数、内壁粗糙度、冰层温度、壁厚等因素对回水软管与注热软管压力损失和温度损失的影响规律。研究结果指出了影响回水软管与注热软管热流特性的主导因素,得到压力损失和温度损失的大小,从而为设计安全高效的井下回水系统提供了理论支撑。

Deep hot-water drill is an important tool for clean drilling and sampling of subglacial lakes in polar regions.The underground return-water system is the key component of the deep hot-water drill,which mainly contains the return-water hose,heat-injection hose,submersible pump and water cavity.The return-water hose is used to extract molten water from the water cavity to the surface for recycling,while the heat-injection hose is used to inject surface hot water into the water cavity to prevent it from freezing.The thermal and flow characteristics of return-water hose and heat-injection hose are very important for the design of the downhole return-water system,however,it is not be the systematically researched and the variation of pressure loss and temperature loss is still not clear at present.In the paper,the theoretical calculation method of thermal and flow characteristics of return-water hose and heat-injection hose was firstly proposed based on Darcy-Weisbach formula and Sukhov's temperature-drop formula.Then,the numerical simulation method of thermal and flow characteristics of the two hoses was established in COMSOL Multiphysics 5.6 software,and the numerical results matched well with the theoretical calculation results.Finally,this paper systematically analyzed the influence of the factors,such as flow rate,inner diameter,length,water temperature at inlet,thermal conductivity,roughness of inner wall,ice temperature and wall thickness on the pressure and temperature loss of return-water hose and heat-injection hose.The results shows that the pressure and temperature in the return-water hose and heat-injection hose decreases linearly.In common,flow rate,inner diameter and length are the main factors affecting the pressure loss of return-water hose and heat-injection hose,while air temperature,flow rate,inner diameter and length are the main factors affecting the temperature loss.In addition,roughness of inner wall has little influence on the thermal and flow characteristics of the two hoses.When designing the downhole return-water system,the inner diameter of the return-water hose and the heat-injection hose should be increased as much as possible,and the construction depth of the return-water chamber should be reduced.The water temperature at inlet has bigger influence on the thermal and flow characteristics of the heat-injection hose compared with the return-water hose.Generally,the thermal conductivity of 0.4 W·(m·K)^(-1) can ensure the return-water hose and the heat-injection hose have good thermal insulation performance and it is no longer necessary to increase the wall thickness to enhance its thermal insulation performance.The temperature loss of the return-water hose is generally not more than 2℃,while the temperature loss of the heat-injection hose is about 10~20℃.The conclusions above provided an important basis for designing a safe and efficient downhole return-water system.