Abstract
This study focuses on the application of ground-source heat pump systems in subway stations, specifically addressing the thermo-mechanical coupling response and heat transfer mechanism of energy slabs. Currently, the thermal performance and structural safety of such structures under real operating conditions have not been adequately investigated. Based on the Dalian Metro Line 4 project, two sets of in-situ field tests were conducted: one employing a constant inlet temperature mode to analyze the effects of inlet temperature, flow rate, groundwater conditions, and operation mode on heat transfer performance; the other using a constant heating power mode to investigate the influence of heating power and flow rate variations on heat transfer characteristics. Test results demonstrate that increasing both inlet temperature and flow rate enhances heat exchange efficiency. Under intermittent operation conditions, the average heat flux per unit area reaches 57 W/m², representing a 14.7% improvement over continuous operation. The thermo-mechanical response is significantly influenced by inlet temperature, flow rate, and stratum permeability. During the pump-off stage of intermittent operation, a reverse temperature gradient and the resulting increase in thermally induced compressive stress can be observed. In heterogeneous soil layers, uneven flow distribution tends to cause local heat transfer enhancement while reducing overall efficiency. During long-term operation, the structural response remains within the elastic range, with a maximum thermal stress of 4.15 MPa and a maximum vertical displacement of 2.84 mm, both far below the limits specified in current codes and standards. This study systematically reveals the working mechanism of energy slabs under multi-field coupling effects, providing theoretical basis and experimental support for their design and application in thermally activated underground structures.
Full Text
Preamble
In-situ Experimental Study on the Thermal Performance and Thermomechanical Response of Energy Slabs in a Subway Station
Cheng Wang¹, Hao Wang¹, Zhongtao Wang¹
¹State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024
Abstract
This study investigates the thermomechanical coupling response and heat transfer mechanisms of energy slabs applied to ground-source heat pump systems in subway stations. Currently, the thermal performance and structural safety of such structures under actual operating conditions remain insufficiently understood. Based on the Dalian Metro Line 4 project, two sets of field in-situ tests were conducted: one employing a constant inlet temperature mode to analyze the effects of inlet temperature, flow rate, groundwater conditions, and operation mode on heat transfer performance; the other utilizing a constant heating power mode to investigate the influence of heating power and flow rate variations on heat transfer characteristics.
The experimental results demonstrate that increasing both inlet temperature and flow rate enhances heat transfer efficiency. Under intermittent operation conditions, the average heat flux per unit area reaches 57 W/m², representing a 14.7% improvement over continuous operation. The thermomechanical response is significantly influenced by inlet temperature, flow rate, and stratum permeability. During the pump-off phase of intermittent operation, a reverse temperature gradient can be observed, leading to increased thermally-induced compressive stress. In heterogeneous soil layers, uneven flow distribution tends to cause localized heat transfer enhancement while reducing overall system effectiveness. During long-term operation, the structural response remains within the elastic range, with a maximum thermal stress of 4.15 MPa and a maximum vertical displacement of 2.84 mm, both well below the limits specified in current design codes.
This study systematically reveals the working mechanism of energy slabs under multi-field coupling effects, providing theoretical foundations and experimental support for the design and application of thermally-activated underground structures.
Keywords: Energy slabs; shallow geothermal energy; heat transfer power; thermomechanical coupling; subway station; in-situ test