Influence of different porous media and groundwater-source heat pump operation modes on thermal breakthrough in energy extraction area

In order to study the influence of different porous media on the temperature field in the energy extraction area of the groundwater-source heat pump, establishes an aquifer water-thermal coupling model to simulate and analyse the changes of the groundwater temperature field when the groundwater-source heat pump operates under five kinds of porous media conditions.Proposes the reasonable well spacing and the optimal operation mode based on the time of thermal breakthrough and the temperature diffusion degree of recharging water. The results indicate that under the condition of natural cross flow of groundwater flowing from the pumping well to the recharge well, fine sand is the most prone to thermal breakthrough, followed by medium sand and medium coarse sand, and coarse sand and gravel are the least likely to prone thermal breakthrough. The obvious extent that the heat influence radius of recharging water decreases with the increase of permeability coefficient is ranked as coarse sand, medium coarse sand, gravel, medium sand and fine sand, but the heat influence radius of gravel is significantly smaller than that of other porous media. The reasonable well spacing of different porous media with different permeability coefficients can be obtained from the fitting curve. The operation mode of large temperature difference and small flow rate contributes to alleviate or avoid thermal breakthrough, and the optimization effect is more obvious when the porous media is fine sand.