Snow-melting Performances Of The Road Unit Driven By A Hydronic System In The Severely Cold Region

Snow on roads can block traffic,waste fuels,cause accidents,and even endanger lives.Efficient snow removal technologies have been proposed to remove snow immediately and ensure road safety.Among these snow removal technologies,the hydronic snow-melting system can actively remove snow,strongly control operation,efficiently utilize energy,widely selected heat source,easily install components,and has huge development potential and broad application prospects.However,the system still has problems such as unreasonable energy consumption and incomplete system evaluation.Therefore,this study combined experiments and numerical simulations to deeply study the snow-melting performances based on hydronic snow-melting systems in severely cold regions.An experimental hydronic snow-melting system in the severe cold region was established,and the effects of embedded pipe depth(60～100 mm),ambient temperature(-14.25～-5.70 ~oC),snow-layer density(50～150 kg/m~3),and snow-layer thickness(14～90 mm)on the average road-surface temperature,road snow-free ratio,stage duration,and average system energy consumption were compared and analyzed.The results indicated that the embedded pipe depth of 80mm has better snow-melting performances,and it is suitable for reducing road cracking and protecting pipelines.The snow-melting performances were similar when the ambient temperature differences were less than 1.5 ~oC or the snow-layer densities were in the range of 100～150 kg/m~3,and they were effective when the snow-layer thickness was 43 mm.The heterogeneous porous concrete structure was randomly generated via the Monte Carlo method,the road heat-transfer model was constructed,and the concrete heat transfer performances as affected by aggregates and air voids were analyzed.The Response Surface Method was applied to analyze the influence of the concrete component factors.The results showed that the air void ratio had a significant effect on the road temperature,the aggregate areal ratio can be appropriately increased and the air void ratio can be decreased to improve the heating rate.The new prediction equations of concrete thermal properties were proposed,and the greatest influence concrete components for the thermal conductivity,specific heat capacity,and thermal diffusivity were sand/cement ratio,water/cement ratio,and sand/cement ratio,respectively.Snow properties combined the energy and the mass conservation equations based on the road heat-transfer model to establish the static snow-melting model.The effects of the snow-layer thickness(10～90 mm),wind velocity(1～5 m/s),ambient temperature(-25～-5 ~oC),embedded pipe depth(60～100 mm),embedded pipe spacing(100～180 mm),and supplied-fluid temperature(25～45 ~oC)on the average road-surface temperature and snow-melting rate were compared and analyzed.The results showed that when the targets were the maximum snow-melting rate and the final road-surface temperature,the most influential factors were the embedded pipe depth and supplied-fluid temperature,respectively.The embedded pipe depth and spacing were recommended to be set as 80 and 140 mm,respectively.The energy-saving control strategy is that the supplied-fluid temperature should be25 ~oC within the heating time of 0～1 h,then gradually increase to 35 ~oC within 1～4 h,and finally drop to 25 ~oC within 4～6 h.A new moisture-heat transfer coupled model was established based on the heat-transfer model to analyze the energy consumption(E_a)and utilization efficiency(η)as affected by the supply-fluid temperature(30～50 ~oC),ambient temperature(-25～-5 ~oC),snowfall rate(0.1～1.0 mm/h),and wind speed(2～4m/s).The results showed that when the supply-fluid temperature increased from 30~oC to 50 ~oC,E_a increased by 599 W/m~2(57%),indicating that supply-fluid temperature had the greatest impact on E_a.When the snowfall rate increased from0.1 mm/h to 1.0 mm/h,E_a increased by 50 W/m~2(4%)with minimal impact on E_a.ηdecreases gradually during the snow-melting process,and the averageηwas between 50%and 58%.The road-heating,snow-melting,and system performances of the ground source heat pump(GSHP)snow-melting test bench were explored,and the heating load,power consumption,and COP were obtained.The results revealed that when the set supply-fluid temperature increased from 25 ~oC to 35 ~oC,the average system COP decreased from 3.01 to 1.92,and the average heat pump and system COP for the whole static snow-melting process were 2.49 and 2.04,respectively.The prediction equations between the average road-surface temperature and time,system COP,and heating load were proposed,and the average system COP of variable frequency control increased by 19.8%.