| It is of great and far-reaching significance to promote the high-quality development of geothermal energy under the strategic goals of carbon peaking and carbon neutrality.This paper focuses on the scientific issues of the efficient heat transfer mechanism of gravity heat pipe and the effect of gravity heat pipe on lawn warming,builds gravity heat pipe lawn heating system,adopts the technical route of combining theoretical research,experimental research and numerical simulation,carries out theoretical analysis and experimental research on the characteristics of gravity heat pipe for winter lawn warming,provides theoretical basis and technical support for lawn warming,prolongs green period and innovates new ways of geothermal energy utilization.The main research results are as follows The main research results are as follows.(1)In the cold and dry climate of northern winter,a new method of using gravity heat pipe technology to extract geothermal energy for lawn warming and greening is proposed;through theoretical analysis of thermal resistance,it is calculated that when the gravity heat pipe works,the thermal resistance of heat conduction between the condensation section wall of the heat pipe and the lawn soil accounts for 92%of the thermal resistance of the whole heat transfer process,the thermal resistance of convective heat transfer between groundwater and the condensation section of the gravity heat pipe accounts for 6.8%of the thermal resistance of the whole heat transfer process The above calculation provides a theoretical basis for the analysis of the heat supply between the heat pipe and the lawn soil.(2)The operating characteristics of the gravity heat pipe were analyzed through field tests.The maximum heat pipe axial temperature difference during normal operation was 3.7℃,the total heat pipe thermal resistance order of magnitude was 10-2k·w-1,and the maximum heat transfer power of single heat pipe was 202W;the lawn soil temperature in the heat pipe area was raised about 6～7℃on average compared with the control group,and the maximum could be raised 9-10℃,and no freezing of lawn soil occurred in the heat pipe area during the observation period.The average temperature difference of the system in the continuous operation mode of gravity heat pipe was 2.1℃,and the average starting temperature difference of heat pipe in the intermittent operation mode was 5.4℃.The mean temperature had a highly significant effect(P≤0.05)on soil temperature in the test and control groups and was positively correlated;the mean temperature of the condensation section of the heat pipe correlated well with soil temperature in the test group and was positively correlated,with a regression equation of y=0.978x-0.11,R2=0.852.The test group turned green 25 days earlier than the control group,and the lawn withering was delayed by 45 days throughout the observation period The greening period of the lawn of the test group was extended by 70 days compared with the control group,and the lawn had good greening effect.(3)The change of soil temperature field of lawn under the heating condition of gravity heat pipe was analyzed by numerical simulation.When the tube diameter was 5 cm,the heat transfer range of gravity heat pipe unit in soil was 30.8 cm in horizontal direction and 32.8 cm in vertical direction,and the surface soil temperature field was uniform when the spacing of gravity heat pipe unit was 15 cm,but the uniformity of temperature field decreased when the spacing was increased to 20 cm.The soil temperature field uniformity in the grass root area was good when the gravity heat pipe burial depth was 10cm,and the soil temperature in the grass root area was lower when the burial depth was increased to 15 cm.The fitted relationship between the influence range of heat pipe(Y)and the diameter of heat pipe(X)was established,Y=0.409X+9.59(R2=0.976),and the diameter of gravity heat pipe unit and influence range were linearly related,and the influence of heat pipe diameter on the influence range of temperature field was extremely significant(P<0.01).The numerical simulation results were validated,and the validation results showed that the temperature field simulation results can reflect the lawn soil nighttime temperature field change pattern more realistically.(4)The water requirements for winter lawn green retention conditions were analyzed.The amount of irrigation water for the lawn was determined by means of literature study,using 85%of the field holding capacity(FC)as the upper limit of irrigation and 40%of the field holding capacity(FC)as the lower limit of irrigation.ETO was calculated for the reference crop evapotranspiration during the observation period,and the total reference crop evapotranspiration during the observation period was 246.5 mm.the evapotranspiration evaporation during the early observation period was 54.7 mm,which accounted for 22.19%of the total reference crop evapotranspiration evaporation.In the later period,the evapotranspiration evaporation was 191.8 mm,accounting for 77.81%of the total reference crop evapotranspiration evaporation.The research provides theoretical basis and technical support for increasing the temperature of lawns,extending the green period and exploring new ways of geothermal energy utilization. |
