跨越非饱和/饱和层状土壤条件下竖直地埋管换热器传热性能与影响机制研究

The design of vertical ground heat exchanger is mainly based on heat conduction mechanisms and homogeneous soil currently. However, the effect of heat transfer performance with ground heat exchanger caused by different heat transfer mechanisms in unsaturated and saturated condition with soil stratification is ignored. This makes the theoretical design parameters of ground heat exchanger have great deviation with the actual situation, which affects the reliability of ground-coupled heat pump system and initial investment. The purpose of the project is to study the heat transfer performance with vertical ground heat exchanger in unsaturated and saturated condition with soil stratification and reveal the influence mechanisms of heat transfer performance with ground heat exchanger under the different heat transfer mechanism. The study will be performed from the following aspects: (1) Theoretical heat transfer model of vertical ground heat exchanger will be established in unsaturated and saturated condition with soil stratification, and it will be validated through experiments. And the migration characteristic of heat transfer performance with vertical ground heat exchanger will be revealed.(2) The influence mechanisms of heat transfer performance with vertical ground heat exchanger will be explored and the quantitative evaluation of multi-factors which affect the heat transfer performance of ground heat exchanger will be carried out. （3）The optimization research of the key design parameters in vertical ground heat exchanger will be completed and the correction method of design parameters selection will be presented. The research will be expected to effectively improve the reliability of ground-coupled heat pump system and reasonable control the initial investment. It can also provide a theoretical basis and reference for the application and development for ground-coupled heat pump.

目前竖直地埋管换热器设计依据主要是基于导热机制及均质土壤情况进行考虑的，忽略了非饱和/饱和土壤中不同传热机制作用及土壤分层对地埋管换热器传热性能的影响，这会使地埋管换热器理论设计参数与实际情况产生较大偏差，影响土壤源热泵系统的可靠性及初期投资。本项目旨在通过研究同时跨越非饱和/饱和层状土壤条件下竖直地埋管换热器的传热性能，揭示不同传热机制共同作用下地埋管换热器传热性能影响机制。研究内容主要包括（1）跨越非饱和/饱和土壤层状土壤条件下竖直地埋管换热器传热机理模型构建及验证，揭示地埋管换热器传热性能迁移规律；（2）探寻影响竖直地埋管换热器传热性能影响机制，量化评估多因素对地埋管换热器传热性能的影响（3）完成竖直地埋管换热器关键设计参数优化研究，提出竖直地埋管换热器设计参数修正方法。本项目预期研究成果可有效提高土壤源热泵系统的可靠性及控制系统初期投资，为土壤源热泵系统的发展和应用提供理论基础。

现阶段，对地埋管换热器的研究集中于纯导热模型，有的考虑渗流对导热的影响，有的考虑土壤分层对导热的影响。而在实际情况中，竖直地埋管换热器大多同时跨越饱和及非饱和土壤，不过由于此问题较为复杂，深入分析尚未完善。. 本项目建立了跨越非饱和/饱和土壤层地埋管换热器热湿耦合传热模型和热渗耦合传热模型。并结合实验研究和理论分析，验证所构建传热机理模型的可靠性。同时通过构建模型的数值仿真研究表明：当饱和土壤层中无渗流时，土壤传热的热量均匀的向U型管四周扩散；当饱和土壤层中有渗流时，渗流方向的土壤传热性能提高，而对于相邻无渗流层土层的径向传热性能影响较小；渗流作用加强了渗流层内的地埋管换热器换热能力，且加强强度先逐渐变小后趋于稳定，对相邻非饱和土壤层内的管段换热能力先抑制后加强。. 基于上述模型研究了仅仅考虑水平湿迁移和同时考虑竖直和水平湿迁移两种情况下，分层非饱和土的饱和度分布情况对地埋管换热器单管换热特性的影响。研究表明，考虑竖直和水平湿迁移时由各层土壤饱和度变化而引起的土壤温度场波动更显著。同时考虑竖直和水平湿迁移比仅考虑水平湿迁移的工况热性能稍好，但在实际工程中可忽略不计。当低饱和度的土壤位于分层结构的上层时，地埋管换热器传热性能更好。同时考虑饱和及非饱和土壤层互相影响下的地埋管换热器换热性能，更接近在实际土壤作用下的换热器换热性能，可为实际工程中地埋管换热器的设计和性能仿真提供理论依据和参考。