Experimental And Simulation Study On Heat Transfer Performance Of Shoal Heat Pump Under The Action Of Tide Induced Seepage

The "Thirteenth Five-Year Plan for Renewable Energy Development" stated that:in the energy supply system,renewable energy has occupied a very important position.At present,many countries regard the development of the renewable energy industry as an important move to promote energy production and transformation.Research on the comprehensive utilization of marine energy and soil energy in coastal areas is rarely reported.The birth of shoal heat pumps promotes the research process in this field,improves the efficiency of low-grade energy utilization,reduces the cost of low-grade energy extraction,and realizes clean energy cooling,Heating is a renewable energy technology that is feasible and effectively reduces the burden on the environment.The laying position of the buried pipe of the shallow heat pump has natural advantages.There is strong groundwater seepage in the coastal porous media sand layer.With the periodic fluctuation of seawater,the direction and size of the seepage change continuously.The cold and heat can be taken away by sea water in time,and the energy accumulation phenomenon will be greatly weakened.The combination of seawater energy and soil energy makes the buried heat exchanger of shallow heat pump have huge energy-saving potential.In order to study the influence of the periodic seepage induced by tides on the heat transfer performance of shoal heat pump buried pipes,experiments and simulations were used to theoretically calculate and analyze the heat transfer of shoal heat pump horizontal buried pipes.The accuracy of the numerical model is verified by comparing the results of experiments and simulations by studying the heat transfer process of the buried tube heat exchanger of the shallow heat pump under the condition of no seepage;analogous to the numerical model of the shallow heat pump test bench,and constructing the actual tube length transfer of the shallow heat pump Thermal model,respectively discuss the effects of periodic seepage in the shoal and sand porosity on the heat transfer of the buried pipe heat exchanger,so as to reasonably arrange the horizontal U-shaped buried pipe group under different shoal sand conditions.The results show that:(1)Obtained from the experimental and simulation results without seepage:(1)When the inlet temperature of the circulating medium is constant,regardless of the dry or wet sand heat transfer experiment,the temperature difference between the inlet and outlet of the circulating medium decreases with time and then becomes stable.During the experiment,the rate of decrease gradually decreases;The increase of the flow rate and the increase of the temperature difference between the inlet temperature and the surrounding sand layer can reduce the time for heat transfer to stabilize.(2)Under the same working conditions,the wet sand experiment takes less time to reach the heat transfer equilibrium than the dry sand experiment;the heat transfer of the wet sand experiment is also higher than that of the dry sand experiment under the same working condition,and the summer working condition is increased by 8% to14%.The winter conditions have increased by 12% to 17%.Therefore,the heat transfer capacity of buried pipes in green sand is higher than that of buried pipes in dry sand.(2)In the actual shoal heat pump tube length numerical simulation results,the following conclusions are drawn:(1)Under the same porosity sand layer,when there is no seepage heat transfer simulation,the temperature field around the buried pipe spreads evenly around;in the case of heat transfer with seepage,the temperature field around the buried pipe migrates along the seepage direction,and The greater the seepage velocity,the larger the migration range;with the enhancement of seepage effect,the horizontal thermal action range of the buried pipe increases,and the vertical thermal action range decreases.(2)Under the same porosity sand layer,the heat transfer per linear meter of the buried pipe heat exchanger and the average heat transfer coefficient are proportional to the seepage velocity.Compared with the results of heat transfer without seepage: when the shoal sand is fine sand,the tidal seepage velocity changes within 8m/d～20m/d,the heat transfer per linear meter increases by 2.51～3.07 times,and the average heat transfer coefficient increases 2.95～3.91 times;when the shoal sand is medium-coarse sand,the tidal seepage velocity changes within 10m/d～25m/d,the heat exchange per linear meter increases by 2.77～3.35 times,and the average heat transfer coefficient increases by 3.36～4.40 When the shoal sand is coarse sand,the tidal seepage velocity changes within 20m/d～40m/d,the heat exchange per linear meter increases by3.52～3.95 times,and the average heat transfer coefficient increases by 4.53～5.42 times.(3)At the same seepage velocity,the heat transfer capacity of the buried pipe under the fine sand layer is greater than that under the medium coarse sand and coarse sand.When there is no seepage,the heat transfer per linear meter and the average heat transfer coefficient obtained by simulating fine sand with small porosity are about 6%to 20% higher than the other two sand layers;when there is seepage in the sand layer,the fine sand The average heat transfer and average heat transfer coefficient per linear meter of underground pipes in the state of the art are only about 1% to 5% higher than those of the other two sand layers.Therefore,in the presence of seepage,the influence of the porosity of the porous medium on the heat transfer of the buried pipe in the shallow shoal is negligible.(4)In the shoal,the parallel arrangement is more suitable than the staggered arrangement of pipe groups.The side-by-side arrangement with a larger horizontal spacing has an increase in heat exchange per linear meter by 5.4%～6.05%,and an average heat transfer coefficient increased by 7.4%～10.0%;compared to the side-by-meter with a small horizontal spacing,the average heat transfer coefficient has increased by 7.4%～10.0%;compared with the same horizontal spacing Compared with the staggered arrangement,the heat transfer per linear meter has increased by9.9%～11.6%,and the average heat transfer coefficient has increased by 14.0%～15.8%.Choosing a suitable pipe layout plan can effectively use the horizontal and vertical spatial positions,weaken the accumulation of cold and heat in the sand layer around the buried pipe,and improve the operating energy efficiency of the buried pipe heat exchanger of the shallow heat pump.