Study On The Heat Transfer Mechanism Of The Capillary Heat Exchanger In The Shallows Near The Coast

For the heat pump system with capillary heat pump technology in the shallows,the capillary network as a heat exchanger is buried under the shoal seabed.The heat transfer between the heat exchanger and the shoal coarse sand backfill contains heat transfer between the coarse sand particles,heat transfer of water in the pores,and heat convection resulting from the flow of water in the pores.In winter heating systems,heat convection from the water stream can be taken from the shoal.The heat exchanger has the advantages of corrosion resistance,easy fixing and low cost of the heat exchanger.It is not affected by the water environment,and not easy to scale,and it can effectively ensure the normal operation of the heat pump system.This system is a novel seawater source heat pump application technology.In recent years,China has not only carried out quite a lot of research work on the practical application of buried pipes,but also many scientists try their best to make many numerical calculation analysis and experimental tests about this.But there are relatively few studies about the research on heat transfer of capillary heat exchangers and actual engineering.At the same time,most of the research on the heat transfer of buried pipes is based on a single heat conduction theory,they ignored the influence of groundwater seepage,which will inevitably deviate from the actual design of the capillary heat exchanger.Because the capillary heat exchanger is deposited in the shallows,it is affected by the rising tide and ebbing tide of seawater,and the natural seepage in sandy soil will affect its heat transfer performance.The heat transfer process between the capillary heat exchanger and the seepage environment in the shallows is also one of the most important factors which affecting performance of the heat pump system.The influence of underground seawater seepage is not clear in the existing research.In view of this,this paper studies it by combining theoretical simulation with engineering experiment.In this paper,the research method combining theory and engineering is established,and the model is built for numerical simulation.The test is carried out at the demonstration project site to verify the reliability of the heat transfer model of the shoal capillary heat exchanger under seepage conditions.And The heat transfer characteristics of the shoal capillary heat exchanger under different influencing factors(with or without seepage,different seepage directions,different seepage speeds,different buried depths,different inlet velocity of heat exchangers)were analyzed by numerical simulation.The main research results are as follows:(1)The shoal capillary heat exchanger with horizontal seepage flow has the best heat transfer performance,followed by vertical seepage.The heat transfer coefficient of the heat exchanger under the seepage condition is obviously increased compared with the heat transfer coefficient of the heat exchanger without seepage.And the seepage can effectively improve the heat transfer performance of the capillary heat exchanger in the shoal,especially in the horizontal direction.(2)The increase of percolation velocity can promote the heat transfer coefficient of the shoal capillary network.The heat exchange area of the capillary network is large.The enhancement of seepage can promote the heat transfer better when the flow velocity in the tube is large enough.(3)With the increase of the inlet velocity of the heat exchanger,the time for the medium in the tube to complete a cycle in the heat exchanger will be shortened.When the seepage condition is fixed,the temperature difference between the inlet and outlet of the capillary heat exchanger decreases with the increase of the inlet velocity of the heat exchanger.(4)The increase of buried depth can promote the heat transfer efficiency of the capillary heat exchanger,but when the seepage velocity is high enough,the effect of buried depth on the heat transfer performance of the capillary heat exchanger is not obvious,especially with the increase of groundwater seepage velocity.(5)Under the condition of seepage affecting heat exchanger in winter,the significance of each factor on heat exchanger performance is analyzed.Within a certain range of conditions,different seepage velocity,different flow velocity in tube and different depth of heat exchanger,have a significant effect from high to low on heat exchanger performance.