Cryogenic valves play a crucial role in the production and transportation of liquefied natural gas(LNG),and are primarily responsible for efficiently controlling the inflow and outflow of LNG and regulating pressure.H...Cryogenic valves play a crucial role in the production and transportation of liquefied natural gas(LNG),and are primarily responsible for efficiently controlling the inflow and outflow of LNG and regulating pressure.However,due to their operation in low-temperature and high-humidity environments,crucial components such as drip trays are susceptible to frosting,which may lead to LNG leakage,thereby causing severe safety incidents.In this study,the user-defined function(UDF)is employed to redevelop Fluent,which integrates the frost growth model with the Eulerian multiphase flow model,to conduct a quantitative analysis of frosting on drip trays of cryogenic valves.The effects of environmental parameters,such as wind speed,ambient temperature,air humidity,and cold surface temperature on the growth of the frost layer were analyzed.This study reveals a limiting wind speed between 1 m/s and 2 m/s.Upon reaching this limit speed,the growth of the frost layer reaches its maximum,and further increases in the wind speed have no significant effect on the growth of the frost layer.Furthermore,the influence of the change in the flow field on droplet impingement and freezing during the growth of the frost layer is considered through the coupling method of the kinematic characteristics of water droplets and the collection coefficient of water droplets.This study identifies the influence of different parameters on the droplet impact efficiency,leading to the modification of the frost layer on the drip tray.展开更多
Frosting is a common phenomenon of the ASHP under the heating mode in winter,and the outdoor air flow rate flowing through the evaporator of the ASHP was always thought to be a major contributor.In order to validate i...Frosting is a common phenomenon of the ASHP under the heating mode in winter,and the outdoor air flow rate flowing through the evaporator of the ASHP was always thought to be a major contributor.In order to validate its contribution,effects of outdoor fan airflow rate on the performance of air source heat pumps(ASHPs)were investigated under the winter heating condition.The experiment was conducted in a laboratory at the standard 2℃ air dry bulb temperature(DB)/1℃ air wet bulb temperature(WB)frosting condition,which enabled the analysis of the operating performance,frosting performance,and heating performance of the ASHP unit by changing the airflow rate of the outdoor fan.Results showed that as the airflow rate of the outdoor fan reduced from 100%to 36%,the operating performance decline and the elevated frosting-defrosting loss were observed.Meanwhile,both the frosting rate and the operating efficiency during frosting-defrosting cycles showed an increasing trend then followed by decreasing tendency.The maximum frosting rate and operating efficiency were 0.92 g/m^(2).min and 2.92,respectively,which were observed at 74%airflow rate of the outdoor fan of the ASHP unit.The observation implied the existence of the“minimum frosting suppression airflow rate”.At 36%airflow rate of the outdoor fan of the ASHP unit,however,the performance of the ASHP unit was attenuated greatly,with the frosting-defrosting efficiency loss coefficient of 0.47,the heating capacity and COP reduction by 51.5 and 38.8%,respectively.These findings provided significant references to the optimization of ASHPs performance with variable airflow rate of the outdoor fan under frosting conditions.展开更多
In refrigerating industry,frost commonly deposits on the confined cold surfaces of heat exchangers,which affects the heat transfer performance.Along the confined flow path of the heat exchanger,the frosting at downstr...In refrigerating industry,frost commonly deposits on the confined cold surfaces of heat exchangers,which affects the heat transfer performance.Along the confined flow path of the heat exchanger,the frosting at downstream is affected by the parameters from the upstream.In this study,a numerical model considering the confinement effect has been proposed to predict frosting characteristics in plate-fin heat exchanger.Convection-diffusion equations for humid air and empirical correlations for local frost density are employed in the numerical prediction.Frosting behavior and heat transfer in the confined channel are investigated with different humid air parameters and cold surface temperatures.The results indicate that frost thickness in the confined channel is thicker than that in open space under the same inlet parameters.The frost layer is thicker and fluffier along the confined channel.In addition,the air temperature difference between inlet and outlet of the confined channel enlarges with frosting.Under the same average temperature of upper and lower surfaces,the heat and mass transfer of frosting are enhanced with diminishing temperature difference of upper and lower surfaces.In such condition,frosting is mainly influenced by the cold surface with the lower temperature.展开更多
Considering the comprehensive morphology and genesis of Podzols of the Stolowe Mountains,and the still-possible impact of frost actions and other processes related to cold climate on these soils,the main aims of this ...Considering the comprehensive morphology and genesis of Podzols of the Stolowe Mountains,and the still-possible impact of frost actions and other processes related to cold climate on these soils,the main aims of this study were to determine whether(i)the heterogeneous Podzols in the Stolowe Mountains underwent a phase of development in a cold climate,resulting in frost action features visible on the micromorphological level,and whether(ii)contemporary cryopedogenic traces are masked by the translocation of organic matter due to the podzolisation process.Four soil profiles were investigated,revealing distinct layers corresponding to different periods of soil formation.Under field observation,no explicit frost-related characteristics were observed.Nevertheless,micromorphological analysis revealed cappings of fine materials on grains or peds,as well as development of granostriated(or any striated)b-fabric that resulted from the alternating effects of thawing and freezing processes.Moreover,micromorphological analysis revealed the presence of microstructures that could be the result of cryogenic processes,such as platy,angular blocky and lenticular features,as well as plane,vugh and star-shaped void types.The translocation of organic matter during podzolisation modified or concealed the frost-related features that developed during the late Pleistocene and early Holocene.This is evident,for instance,in the accumulation of organic matter on cappings and within soil voids,which further hinders the identification of frost-related characteristics and the interpretation of the soil's evolution.Macromorphological observations enhanced with micromorphological analyses revealed three distinct layers:(i)a young upper layer composed of loose,sandy material;(ii)a deeper layer containing a spodic horizon with frost actions,involving pedofeatures associated with the Pleistocene cold climate and(iii)a deeper subsoil basal layer.The abovementioned microstructures,combined with lithological discontinuity,support the hypothesised polygenetic origin of Podzols in the studied region.展开更多
Accurate numerical prediction of frosting patterns is essential for the efficient layout and timing defrosting of heat exchangers under frosting conditions.In this study,a numerical model is developed to predict the s...Accurate numerical prediction of frosting patterns is essential for the efficient layout and timing defrosting of heat exchangers under frosting conditions.In this study,a numerical model is developed to predict the spatio-temporal frosting habits on curved surfaces in combination with the correlations of frost density and thermal conductivity.In the model,frost melting is considered.After verification,the frosting and heat transfer characteristics along the flow path are investigated under various structural and operating conditions.Frost thickness along the path is mainly affected by the cooling surface temperature,while the heat and mass transfer rates are strongly correlated with the humidity ratio.The proportions of latent heat and sensible heat are distributed more unevenly in parallel flow case than in counter flow case.Frost deposition is facilitated by a smaller radius of curvature of the cooling surface.More uniform frosting characteristics along the path and smaller heat transfer obstruction are presented with a smaller length-to-height ratio of the flow path.展开更多
Understanding the phenology and productivity of Populus species is crucial for effective management and conservation strategies amid climate change.We investigated leaf budbreak timing,susceptibility to cold damage,le...Understanding the phenology and productivity of Populus species is crucial for effective management and conservation strategies amid climate change.We investigated leaf budbreak timing,susceptibility to cold damage,leaf dynamics,and biomass production of 168 Populus genotypes with diverse provenances in the southeastern United States.Our study revealed significant variation in budbreak timing across different taxa and years,with genotypes inheriting traits adapted to their parents’local climates.Temperature emerged as a key factor triggering budbreak,while leaf development depended on other environmental cues such as photoperiod.Notably,budbreak occurred approximately 20 days earlier in 2023 compared to 2022 due to higher accumulated degree days(ADDs).Short-rotation-coppice(SRC)management delayed budbreak by five to ten days.Cold damage was significant in 2023,particularly for genotypes from northern provenances and those with P.maximowiczii parentage.Severe damage was also observed in eastern cottonwood(Populus deltoides×Populus deltoides(D×D))genotypes,despite most having southeastern US parentages.Leaf dynamics,including leaf duration and leaf area index(LAI),varied across taxa and sites,with earlier budbreak correlating with extended growing seasons and increased LAI.Biomass production was intricately linked to phenological events,with earlier budbreak leading to increased biomass production and greater susceptibility to cold damage.Our findings highlight the importance of genetics,environment,and coppicing management in understanding and managing Populus phenology and biomass production.These insights provide valuable guidance for developing effective breeding,conservation,and management strategies for Populus species in the context of climate change.展开更多
One reference in the original manuscript contained incorrect bibliographic information and cited a non-existent publication:Traczyk A(1999)Pleistocene debris cover beds and block-debris tongues in the north-western pa...One reference in the original manuscript contained incorrect bibliographic information and cited a non-existent publication:Traczyk A(1999)Pleistocene debris cover beds and block-debris tongues in the north-western part of theŚlęża Massif(Poland)and their formation under permafrost conditions.Geographia Polonica 81(1).This erroneous reference has now been removed from the references list.展开更多
Frost heave in water-bearing rock masses poses significant threats to geotechnical engineering.This paper developed a novel three-dimensional(3D)frost model,based on the combined finite-discrete element method(FDEM),t...Frost heave in water-bearing rock masses poses significant threats to geotechnical engineering.This paper developed a novel three-dimensional(3D)frost model,based on the combined finite-discrete element method(FDEM),to investigate the frost heave process in rock masses where thermal transfer,water migration,water-ice phase transition(ice growth)and ice-rock interaction are explicitly simulated.The proposed model is first validated against existing experimental and analytical solutions,and further applied to investigate path-dependent frost heave behavior under various freezing conditions.Results show that freezing direction plays a vital role in the dynamic ice growth and ice-rock interaction,thus affecting the frost heave behavior.In the top-down freezing regime,ice plugs form first at the crack's top surface,sealing the crack and preventing water migration,which can amplify ice pressure.Parametric studies,including rock Young's modulus,ice-rock friction,and rock hydraulic conductivity,further reveal that the temporal aspects of ice development and rock mechanical response strongly affect ice-rock interaction and hence the frost heave mechanism.Furthermore,some typical phenomena(e.g.water/ice extrusion and frost cracking)can also be well captured in this model.This novel numerical framework sheds new light on frost heave behavior and enriches our understanding of frost heave mechanisms and ice-rock interaction processes within cold environment engineering projects.展开更多
Subgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)inve...Subgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)investigate track-subgrade frost heave and develop a dynamic model of vehicle-track-subgrade frost heave;(2)explore the transfer relation between subgrade frost heave and track structure deformation;(3)examine the characteristics of interlayer debonding;(4)study the influence of subgrade frost heave on the dynamic response of vehicles in high-speed railways in seasonally frozen regions.A Fourier series was used to fit the frost heave waveform and simulate the behavior of subgrade uneven frost heave using data collected on-site.The results show:(i)The position of frost heave significantly affects the transfer of deformation to a slab track.The largest deformation of the track slab,with the amplitude transfer ratio reaching 20%,was recorded when the frost heave occurred near the joint of the base plate.(ii)At the same frost heave amplitude,long-wave frost heave causes smaller deformation and debonding of the track structure than short-wave frost heave.In the wavelength range of 10-30 m,the main frequency of the acceleration spectral density was concentrated between 3.5 and 3.7 Hz,with larger frost heave wavelengths producing smaller superposition on the vertical acceleration of the vehicle.(ii)The maximum wheel-rail force occurs when the front bogie passes the frost heave peak,with greater frost heave amplitudes producing greater wheel-rail force.From these results,we conclude there is a clear need to control the frost heave deformation of the track to reduce the dynamic response of the vehicle and in turn improve train operatSubgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)investigate track`-subgrade frost heave and develop a dynamic model of vehicle`-track`-subgrade frost heave;(2)explore the transfer relation between subgrade frost heave and track structure deformation;(3)examine the characteristics of interlayer debonding;(4)study the influence of subgrade frost heave on the dynamic response of vehicles in high-speed railways in seasonally frozen regions.A Fourier series was used to fit the frost heave waveform and simulate the behavior of subgrade uneven frost heave using data collected on-site.The results show:(i)The position of frost heave significantly affects the transfer of deformation to a slab track.The largest deformation of the track slab,with the amplitude transfer ratio reaching 20%,was recorded when the frost heave occurred near the joint of the base plate.(ii)At the same frost heave amplitude,long-wave frost heave causes smaller deformation and debonding of the track structure than short-wave frost heave.In the wavelength range of 10-30 m,the main frequency of the acceleration spectral density was concentrated between 3.5 and 3.7 Hz,with larger frost heave wavelengths producing smaller superposition on the vertical acceleration of the vehicle.(iii)The maximum wheel`-rail force occurs when the front bogie passes the frost heave peak,with greater frost heave amplitudes producing greater wheel`-rail force.From these results,we conclude there is a clear need to control the frost heave deformation of the track to reduce the dynamic response of the vehicle and in turn improve train operations.ions.展开更多
The frost deterioration and deformation of porous rock are commonly investigated under uniform freeze-thaw(FT)conditions.However,the unidirectional FT condition,which is also prevalent in engineering practice,has rece...The frost deterioration and deformation of porous rock are commonly investigated under uniform freeze-thaw(FT)conditions.However,the unidirectional FT condition,which is also prevalent in engineering practice,has received limited attention.Therefore,a comparative study on frost deformation and microstructure evolution of porous rock under both uniform and unidirectional FT conditions was performed.Firstly,frost deformation experiments of rock were conducted under cyclic uniform and unidirectional FT action,respectively.Results illustrate that frost deformation of saturated rock exhibits isotropic characteristics under uniform FT cycles,while it shows anisotropic characteristics under unidirectional FT condition with both the frost heaving strain and residual strain along FT direction much higher than those perpendicular to FT direction.Moreover,the peak value and residual value of cumulative frost strain vary as logarithmic functions with cycle number under both uniform and unidirectional FT conditions.Subsequently,the microstructure evolution of rock suffered cyclic uniform and unidirectional FT action were measured.Under uniform FT cycles,newly generated pores uniformly distribute in rock and pore structure of rock remains isotropic in micro scale,and thus the frost deformation shows isotropic characteristics in macro scale.Under unidirectional FT cycles,micro-cracks or pore belts generate with their orientation nearly perpendicular to the FT direction,and rock structure gradually becomes anisotropic in micro scale,resulting in the anisotropic characteristics of frost deformation in macro scale.展开更多
This paper presents the development of a coupled modeling approach to simulate cryogenic thermo-hydro-mechanical(THM)processes associated with a freezing medium,which is then implemented in the combined finite-discret...This paper presents the development of a coupled modeling approach to simulate cryogenic thermo-hydro-mechanical(THM)processes associated with a freezing medium,which is then implemented in the combined finite-discrete element method code(FDEM)for multi-physics simulation.The governing equations are deduced based on energy and mass conservation,and static equilibrium equations,considering water/ice phase change,where the strong couplings between multi-fields are supplemented by critical coupling parameters(e.g.unfrozen water content,permeability,and thermal conductivity).The proposed model is validated against laboratory and field experiments.Results show that the cryogenic THM model can well predict the evolution of strongly coupled processes observed in frozen media(e.g.heat transfer,water migration,and frost heave deformation),while also capturing,as emergent properties of the model,important phenomena(e.g.latent heat,cryogenic suction,ice expansion and distinct three-zone distribution)caused by water/ice phase change at laboratory and field scales,which are difficult to be all revealed by existing THM models.The novel modeling framework presents a gateway to further understanding and predicting the multi-physical coupling behavior of frozen media in cold regions.展开更多
Permafrost in Northeast China is undergoing extensive and rapid degradation,and it is of great importance to understand the dynamics of vegetation response to permafrost degradation during different periods in this re...Permafrost in Northeast China is undergoing extensive and rapid degradation,and it is of great importance to understand the dynamics of vegetation response to permafrost degradation during different periods in this region.Based on the meteorological station data and MODIS land surface temperature data,we mapped the distribution of permafrost using the surface frost number(SFN)model to analyze the permafrost degradation processes in Northeast China from 1981 to 2020.We investigated the spatiotemporal variation characteristics of vegetation and its response to permafrost degradation during different periods from 1982 to 2020 using the normalized difference vegetation index(NDVI).We further discussed the dominant factors influencing the vegetation dynamics in the permafrost degradation processes.Results indicated that the permafrost area in Northeast China decreased significantly by 1.01×10^(5) km^(2) in the past 40 a.The permafrost stability continued to weaken,with large areas of stable permafrost(SP)converted to semi-stable permafrost(SSP)and unstable permafrost(UP)after 2000.From 1982 to 2020,NDVI exhibited a significant decreasing trend in the seasonal frost(SF)region,while it exhibited an increasing trend in the permafrost region.NDVI in the UP and SSP regions changed from a significant increasing trend before 2000 to a nonsignificant decreasing trend after 2000.In 78.63%of the permafrost region,there was a negative correlation between the SFN and NDVI from 1982 to 2020.In the SP and SSP regions,the correlation between the SFN and NDVI was predominantly negative,while in the UP region,it was predominantly positive.Temperature was the dominant factor influencing the NDVI variations in the permafrost region from 1982 to 2020,and the impact of precipitation on NDVI variations increased after 2000.The findings elucidate the complex dynamics of vegetation in the permafrost region of Northeast China and provide deeper insights into the response mechanisms of vegetation in cold regions to permafrost degradation induced by climate change.展开更多
The contents of waste glass powder(WGP)(0%,10%,15%,20%,25%)and water-binder ratio(W/C)(0.24,0.26,0.28)were used as influencing factors,and the quality loss rate(Δm)and compressive strength loss rate(Δfc)were used as...The contents of waste glass powder(WGP)(0%,10%,15%,20%,25%)and water-binder ratio(W/C)(0.24,0.26,0.28)were used as influencing factors,and the quality loss rate(Δm)and compressive strength loss rate(Δfc)were used as characterization parameters.The Ca/Si ratio and main element contents of C-S-H gels with different WGP content were investigated by energy dispersive spectrometry(EDS).The pore structure evolution characteristics of WGP composite cementing materials were investigated by low field nuclear magnetic resonance(NMR).UsingΔfc as the index of frost resistance degradation and Weibull function,the frost resistance degradation of glass doped pervious concrete(WGP-PC)was modeled.The results show that,with WGP,for the same number of cycles,Δm andΔfc decrease and increase with the increase of WGP.Under the same WGP content,Δm andΔfc decrease first and then increase with the increase of W/C.After 100 freeze-thaw cycles,the samples with WGP content of 20%and W/C of 0.26 have the best freeze-resistance.Microscopic tests show that with the increase of WGP content,the Ca/Si ratio of C-S-H gel decreases at first and then increases with the increase of WGP content.The extreme value of Ca/Si is 2.36 when WGP is added by 20%.The pore volume of hardened paste with 20%WGP content decreased by 18.6%compared with that of cement system without WGP.The overall compactness of the specimen was improved.On the basis of the test data,a life prediction model was established according to Weibull function.The experiment showed thatΔfc could be used as a durability degradation index,and the slope of the reliability curve became gentle after WGP was added,which reduced the damage degradation rate of PC.W/C was 0.26.It's about 5000 hours.展开更多
This study introduces a novel artificial heating technique aimed at addressing frost heave issues in embankments on frozen ground,offering a sustainable solution.Initial evaluations assessed various heating systems,in...This study introduces a novel artificial heating technique aimed at addressing frost heave issues in embankments on frozen ground,offering a sustainable solution.Initial evaluations assessed various heating systems,including boilers,heat pumps,solar heaters,and electric heaters,focusing on their thermal performance and applicability.The study subsequently designed and implemented a direct-expansion ground source heat pump(DX-GSHP)system as the primary heat source for embankment warming.Rigorous testing confirmed the DX-GSHP system's ability to maintain a heat-supply temperature above 40℃ and a heat-absorption temperature below -3.5℃,effectively extracting geothermal energy for transfer to the topsoil layers.With a demonstrated coefficient of performance(COP)of 3.49,the DX-GSHP system not only proves its energy efficiency but also suggests a potential role in reducing the strain on electricity supply systems.Installation of DX-GSHPs,with heating capacities ranging from 1.0 to 2.0 kW and spaced at intervals of 2.0-4.0 m,provides a rapid thermal response to frost heave in singletrack railway embankments,thereby potentially mitigating frost-induced damage in cold climate regions.展开更多
Based on the conventional observation data and NCEP/NCAR reanalysis data,the circulation situation,influencing systems and causes of the heavy rain during September 20-21,2010 in Ulanqab City were analyzed from the ev...Based on the conventional observation data and NCEP/NCAR reanalysis data,the circulation situation,influencing systems and causes of the heavy rain during September 20-21,2010 in Ulanqab City were analyzed from the evolution process of weather circulation situation and the changes of various physical quantity fields.The results show that there was an obvious frontal zone between 45-52°N,which brought strong cold air.The transport of warm and humid air outside the subtropical high and typhoon was the main water vapor source of the strong precipitation,and the southwest jet at 700 hPa transported abundant water vapor.There was a broad inverted trough to the south of 45°N,with a central value of 1000.0 hPa.Ulanqab City was on the top of the inverted trough,stable and less moved,which was conducive to the occurrence of systematic heavy precipitation.The rainstorm was a strong precipitation process caused by the intersection of cold air brought by the southward movement of the upper frontal zone and warm and humid air outside the subtropical high.After the precipitation,the invasion of strong cold air brought frost and cold wave weather to Ulanqab City.展开更多
基金officially supported by the National Natural Science Foundation of China(Grant Nos.42276225,51879125)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.SJCX23_2208)。
文摘Cryogenic valves play a crucial role in the production and transportation of liquefied natural gas(LNG),and are primarily responsible for efficiently controlling the inflow and outflow of LNG and regulating pressure.However,due to their operation in low-temperature and high-humidity environments,crucial components such as drip trays are susceptible to frosting,which may lead to LNG leakage,thereby causing severe safety incidents.In this study,the user-defined function(UDF)is employed to redevelop Fluent,which integrates the frost growth model with the Eulerian multiphase flow model,to conduct a quantitative analysis of frosting on drip trays of cryogenic valves.The effects of environmental parameters,such as wind speed,ambient temperature,air humidity,and cold surface temperature on the growth of the frost layer were analyzed.This study reveals a limiting wind speed between 1 m/s and 2 m/s.Upon reaching this limit speed,the growth of the frost layer reaches its maximum,and further increases in the wind speed have no significant effect on the growth of the frost layer.Furthermore,the influence of the change in the flow field on droplet impingement and freezing during the growth of the frost layer is considered through the coupling method of the kinematic characteristics of water droplets and the collection coefficient of water droplets.This study identifies the influence of different parameters on the droplet impact efficiency,leading to the modification of the frost layer on the drip tray.
基金supported by the Shandong Provincial Natural Science Foundation with the granted number ZR2022ME148.
文摘Frosting is a common phenomenon of the ASHP under the heating mode in winter,and the outdoor air flow rate flowing through the evaporator of the ASHP was always thought to be a major contributor.In order to validate its contribution,effects of outdoor fan airflow rate on the performance of air source heat pumps(ASHPs)were investigated under the winter heating condition.The experiment was conducted in a laboratory at the standard 2℃ air dry bulb temperature(DB)/1℃ air wet bulb temperature(WB)frosting condition,which enabled the analysis of the operating performance,frosting performance,and heating performance of the ASHP unit by changing the airflow rate of the outdoor fan.Results showed that as the airflow rate of the outdoor fan reduced from 100%to 36%,the operating performance decline and the elevated frosting-defrosting loss were observed.Meanwhile,both the frosting rate and the operating efficiency during frosting-defrosting cycles showed an increasing trend then followed by decreasing tendency.The maximum frosting rate and operating efficiency were 0.92 g/m^(2).min and 2.92,respectively,which were observed at 74%airflow rate of the outdoor fan of the ASHP unit.The observation implied the existence of the“minimum frosting suppression airflow rate”.At 36%airflow rate of the outdoor fan of the ASHP unit,however,the performance of the ASHP unit was attenuated greatly,with the frosting-defrosting efficiency loss coefficient of 0.47,the heating capacity and COP reduction by 51.5 and 38.8%,respectively.These findings provided significant references to the optimization of ASHPs performance with variable airflow rate of the outdoor fan under frosting conditions.
基金supported by the National Natural Science Founda-tion of China(Grant No.:U21B2084)the Youth Innovation Team of Shaanxi Universities.
文摘In refrigerating industry,frost commonly deposits on the confined cold surfaces of heat exchangers,which affects the heat transfer performance.Along the confined flow path of the heat exchanger,the frosting at downstream is affected by the parameters from the upstream.In this study,a numerical model considering the confinement effect has been proposed to predict frosting characteristics in plate-fin heat exchanger.Convection-diffusion equations for humid air and empirical correlations for local frost density are employed in the numerical prediction.Frosting behavior and heat transfer in the confined channel are investigated with different humid air parameters and cold surface temperatures.The results indicate that frost thickness in the confined channel is thicker than that in open space under the same inlet parameters.The frost layer is thicker and fluffier along the confined channel.In addition,the air temperature difference between inlet and outlet of the confined channel enlarges with frosting.Under the same average temperature of upper and lower surfaces,the heat and mass transfer of frosting are enhanced with diminishing temperature difference of upper and lower surfaces.In such condition,frosting is mainly influenced by the cold surface with the lower temperature.
基金financed by the Wroclaw University of Environmental and Life Sciences(Poland)。
文摘Considering the comprehensive morphology and genesis of Podzols of the Stolowe Mountains,and the still-possible impact of frost actions and other processes related to cold climate on these soils,the main aims of this study were to determine whether(i)the heterogeneous Podzols in the Stolowe Mountains underwent a phase of development in a cold climate,resulting in frost action features visible on the micromorphological level,and whether(ii)contemporary cryopedogenic traces are masked by the translocation of organic matter due to the podzolisation process.Four soil profiles were investigated,revealing distinct layers corresponding to different periods of soil formation.Under field observation,no explicit frost-related characteristics were observed.Nevertheless,micromorphological analysis revealed cappings of fine materials on grains or peds,as well as development of granostriated(or any striated)b-fabric that resulted from the alternating effects of thawing and freezing processes.Moreover,micromorphological analysis revealed the presence of microstructures that could be the result of cryogenic processes,such as platy,angular blocky and lenticular features,as well as plane,vugh and star-shaped void types.The translocation of organic matter during podzolisation modified or concealed the frost-related features that developed during the late Pleistocene and early Holocene.This is evident,for instance,in the accumulation of organic matter on cappings and within soil voids,which further hinders the identification of frost-related characteristics and the interpretation of the soil's evolution.Macromorphological observations enhanced with micromorphological analyses revealed three distinct layers:(i)a young upper layer composed of loose,sandy material;(ii)a deeper layer containing a spodic horizon with frost actions,involving pedofeatures associated with the Pleistocene cold climate and(iii)a deeper subsoil basal layer.The abovementioned microstructures,combined with lithological discontinuity,support the hypothesised polygenetic origin of Podzols in the studied region.
基金the National Natural Science Founda-tion of China(Grant No.:51976150)the Fundamental Research Funds for the Central Universities,and the Youth Innovation Team of Shaanxi Universities.
文摘Accurate numerical prediction of frosting patterns is essential for the efficient layout and timing defrosting of heat exchangers under frosting conditions.In this study,a numerical model is developed to predict the spatio-temporal frosting habits on curved surfaces in combination with the correlations of frost density and thermal conductivity.In the model,frost melting is considered.After verification,the frosting and heat transfer characteristics along the flow path are investigated under various structural and operating conditions.Frost thickness along the path is mainly affected by the cooling surface temperature,while the heat and mass transfer rates are strongly correlated with the humidity ratio.The proportions of latent heat and sensible heat are distributed more unevenly in parallel flow case than in counter flow case.Frost deposition is facilitated by a smaller radius of curvature of the cooling surface.More uniform frosting characteristics along the path and smaller heat transfer obstruction are presented with a smaller length-to-height ratio of the flow path.
基金funded by the USDA National Institute of Food and Agriculture(USDA-NIFA)through the APPS grant(Advancing Populus Pathways in the Southeast,2018-68005-27636)United States Department of Energy(DOE)through the PoSIES(Populus in the Southeast for Integrated Ecosystem Services,DE-EE0009280)USDA-NIFA McIntire Stennis grant(MISZ-067050).
文摘Understanding the phenology and productivity of Populus species is crucial for effective management and conservation strategies amid climate change.We investigated leaf budbreak timing,susceptibility to cold damage,leaf dynamics,and biomass production of 168 Populus genotypes with diverse provenances in the southeastern United States.Our study revealed significant variation in budbreak timing across different taxa and years,with genotypes inheriting traits adapted to their parents’local climates.Temperature emerged as a key factor triggering budbreak,while leaf development depended on other environmental cues such as photoperiod.Notably,budbreak occurred approximately 20 days earlier in 2023 compared to 2022 due to higher accumulated degree days(ADDs).Short-rotation-coppice(SRC)management delayed budbreak by five to ten days.Cold damage was significant in 2023,particularly for genotypes from northern provenances and those with P.maximowiczii parentage.Severe damage was also observed in eastern cottonwood(Populus deltoides×Populus deltoides(D×D))genotypes,despite most having southeastern US parentages.Leaf dynamics,including leaf duration and leaf area index(LAI),varied across taxa and sites,with earlier budbreak correlating with extended growing seasons and increased LAI.Biomass production was intricately linked to phenological events,with earlier budbreak leading to increased biomass production and greater susceptibility to cold damage.Our findings highlight the importance of genetics,environment,and coppicing management in understanding and managing Populus phenology and biomass production.These insights provide valuable guidance for developing effective breeding,conservation,and management strategies for Populus species in the context of climate change.
文摘One reference in the original manuscript contained incorrect bibliographic information and cited a non-existent publication:Traczyk A(1999)Pleistocene debris cover beds and block-debris tongues in the north-western part of theŚlęża Massif(Poland)and their formation under permafrost conditions.Geographia Polonica 81(1).This erroneous reference has now been removed from the references list.
基金supported by the Natural Sciences and Engineering Research Council of Canada(Grant Nos.Discovery 341275,and CRDPJ 543894-19)NSERC/Energi Simulation Industrial Research Chair programState Key Laboratory of Geohazard Prevention and Geoenvironment Protection Open Fund(Grant No.SKLGP2024K001).
文摘Frost heave in water-bearing rock masses poses significant threats to geotechnical engineering.This paper developed a novel three-dimensional(3D)frost model,based on the combined finite-discrete element method(FDEM),to investigate the frost heave process in rock masses where thermal transfer,water migration,water-ice phase transition(ice growth)and ice-rock interaction are explicitly simulated.The proposed model is first validated against existing experimental and analytical solutions,and further applied to investigate path-dependent frost heave behavior under various freezing conditions.Results show that freezing direction plays a vital role in the dynamic ice growth and ice-rock interaction,thus affecting the frost heave behavior.In the top-down freezing regime,ice plugs form first at the crack's top surface,sealing the crack and preventing water migration,which can amplify ice pressure.Parametric studies,including rock Young's modulus,ice-rock friction,and rock hydraulic conductivity,further reveal that the temporal aspects of ice development and rock mechanical response strongly affect ice-rock interaction and hence the frost heave mechanism.Furthermore,some typical phenomena(e.g.water/ice extrusion and frost cracking)can also be well captured in this model.This novel numerical framework sheds new light on frost heave behavior and enriches our understanding of frost heave mechanisms and ice-rock interaction processes within cold environment engineering projects.
基金This work is supported by the National Key R&D Program of China(No.2021YFF0502100)the National Natural Science Foundation of China(Nos.52022085 and 52278461)+1 种基金the Sichuan Provincial Youth Science and Technology Innovation Team(No.2022JDTD0015)the Research and Development Program of China State Railway Group Co.,Ltd.(No.N2022G033),China.
文摘Subgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)investigate track-subgrade frost heave and develop a dynamic model of vehicle-track-subgrade frost heave;(2)explore the transfer relation between subgrade frost heave and track structure deformation;(3)examine the characteristics of interlayer debonding;(4)study the influence of subgrade frost heave on the dynamic response of vehicles in high-speed railways in seasonally frozen regions.A Fourier series was used to fit the frost heave waveform and simulate the behavior of subgrade uneven frost heave using data collected on-site.The results show:(i)The position of frost heave significantly affects the transfer of deformation to a slab track.The largest deformation of the track slab,with the amplitude transfer ratio reaching 20%,was recorded when the frost heave occurred near the joint of the base plate.(ii)At the same frost heave amplitude,long-wave frost heave causes smaller deformation and debonding of the track structure than short-wave frost heave.In the wavelength range of 10-30 m,the main frequency of the acceleration spectral density was concentrated between 3.5 and 3.7 Hz,with larger frost heave wavelengths producing smaller superposition on the vertical acceleration of the vehicle.(ii)The maximum wheel-rail force occurs when the front bogie passes the frost heave peak,with greater frost heave amplitudes producing greater wheel-rail force.From these results,we conclude there is a clear need to control the frost heave deformation of the track to reduce the dynamic response of the vehicle and in turn improve train operatSubgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)investigate track`-subgrade frost heave and develop a dynamic model of vehicle`-track`-subgrade frost heave;(2)explore the transfer relation between subgrade frost heave and track structure deformation;(3)examine the characteristics of interlayer debonding;(4)study the influence of subgrade frost heave on the dynamic response of vehicles in high-speed railways in seasonally frozen regions.A Fourier series was used to fit the frost heave waveform and simulate the behavior of subgrade uneven frost heave using data collected on-site.The results show:(i)The position of frost heave significantly affects the transfer of deformation to a slab track.The largest deformation of the track slab,with the amplitude transfer ratio reaching 20%,was recorded when the frost heave occurred near the joint of the base plate.(ii)At the same frost heave amplitude,long-wave frost heave causes smaller deformation and debonding of the track structure than short-wave frost heave.In the wavelength range of 10-30 m,the main frequency of the acceleration spectral density was concentrated between 3.5 and 3.7 Hz,with larger frost heave wavelengths producing smaller superposition on the vertical acceleration of the vehicle.(iii)The maximum wheel`-rail force occurs when the front bogie passes the frost heave peak,with greater frost heave amplitudes producing greater wheel`-rail force.From these results,we conclude there is a clear need to control the frost heave deformation of the track to reduce the dynamic response of the vehicle and in turn improve train operations.ions.
基金This research was supported by the National Natural Science Foundation of China(52108370)Jiangxi Provincial Natural Science Foundation(No.20212BAB214062,20224BAB204061).
文摘The frost deterioration and deformation of porous rock are commonly investigated under uniform freeze-thaw(FT)conditions.However,the unidirectional FT condition,which is also prevalent in engineering practice,has received limited attention.Therefore,a comparative study on frost deformation and microstructure evolution of porous rock under both uniform and unidirectional FT conditions was performed.Firstly,frost deformation experiments of rock were conducted under cyclic uniform and unidirectional FT action,respectively.Results illustrate that frost deformation of saturated rock exhibits isotropic characteristics under uniform FT cycles,while it shows anisotropic characteristics under unidirectional FT condition with both the frost heaving strain and residual strain along FT direction much higher than those perpendicular to FT direction.Moreover,the peak value and residual value of cumulative frost strain vary as logarithmic functions with cycle number under both uniform and unidirectional FT conditions.Subsequently,the microstructure evolution of rock suffered cyclic uniform and unidirectional FT action were measured.Under uniform FT cycles,newly generated pores uniformly distribute in rock and pore structure of rock remains isotropic in micro scale,and thus the frost deformation shows isotropic characteristics in macro scale.Under unidirectional FT cycles,micro-cracks or pore belts generate with their orientation nearly perpendicular to the FT direction,and rock structure gradually becomes anisotropic in micro scale,resulting in the anisotropic characteristics of frost deformation in macro scale.
基金supported by the Natural Sciences and Engineering Research Council of Canada (NSERC)Discovery Grants 341275,NSERC CRDPJ 543894-19,and NSERC/Energi Simulation Industrial Research Chair programfunding he received from Lassonde International Graduate Scholarship in Mining at the University of Toronto+1 种基金supported by the FCE Start-up Fund for New Recruits at the Hong Kong Polytechnic University (P0034042)the Early Career Scheme and the General Research Fund Scheme of the Research Grants Council of the Hong Kong SAR,China (Project Nos.PolyU 25220021 and PolyU 15227222).
文摘This paper presents the development of a coupled modeling approach to simulate cryogenic thermo-hydro-mechanical(THM)processes associated with a freezing medium,which is then implemented in the combined finite-discrete element method code(FDEM)for multi-physics simulation.The governing equations are deduced based on energy and mass conservation,and static equilibrium equations,considering water/ice phase change,where the strong couplings between multi-fields are supplemented by critical coupling parameters(e.g.unfrozen water content,permeability,and thermal conductivity).The proposed model is validated against laboratory and field experiments.Results show that the cryogenic THM model can well predict the evolution of strongly coupled processes observed in frozen media(e.g.heat transfer,water migration,and frost heave deformation),while also capturing,as emergent properties of the model,important phenomena(e.g.latent heat,cryogenic suction,ice expansion and distinct three-zone distribution)caused by water/ice phase change at laboratory and field scales,which are difficult to be all revealed by existing THM models.The novel modeling framework presents a gateway to further understanding and predicting the multi-physical coupling behavior of frozen media in cold regions.
基金funded by the National Natural Science Foundation of China(41641024)the Science and the Technology Project of Heilongjiang Communications Investment Group(JT-100000-ZC-FW-2021-0182)the Field Scientific Observation and Research Station of the Ministry of Education-Geological Environment System of the Permafrost Area in Northeast China(MEORS-PGSNEC).
文摘Permafrost in Northeast China is undergoing extensive and rapid degradation,and it is of great importance to understand the dynamics of vegetation response to permafrost degradation during different periods in this region.Based on the meteorological station data and MODIS land surface temperature data,we mapped the distribution of permafrost using the surface frost number(SFN)model to analyze the permafrost degradation processes in Northeast China from 1981 to 2020.We investigated the spatiotemporal variation characteristics of vegetation and its response to permafrost degradation during different periods from 1982 to 2020 using the normalized difference vegetation index(NDVI).We further discussed the dominant factors influencing the vegetation dynamics in the permafrost degradation processes.Results indicated that the permafrost area in Northeast China decreased significantly by 1.01×10^(5) km^(2) in the past 40 a.The permafrost stability continued to weaken,with large areas of stable permafrost(SP)converted to semi-stable permafrost(SSP)and unstable permafrost(UP)after 2000.From 1982 to 2020,NDVI exhibited a significant decreasing trend in the seasonal frost(SF)region,while it exhibited an increasing trend in the permafrost region.NDVI in the UP and SSP regions changed from a significant increasing trend before 2000 to a nonsignificant decreasing trend after 2000.In 78.63%of the permafrost region,there was a negative correlation between the SFN and NDVI from 1982 to 2020.In the SP and SSP regions,the correlation between the SFN and NDVI was predominantly negative,while in the UP region,it was predominantly positive.Temperature was the dominant factor influencing the NDVI variations in the permafrost region from 1982 to 2020,and the impact of precipitation on NDVI variations increased after 2000.The findings elucidate the complex dynamics of vegetation in the permafrost region of Northeast China and provide deeper insights into the response mechanisms of vegetation in cold regions to permafrost degradation induced by climate change.
基金Funded by the National Natural Science Foundation of China(No.52468037)the Foster Foundation of ISMI,Gansu Province(No.GII2022-P03)the Gansu Provincial Department of Education(No.2024QB-028)。
文摘The contents of waste glass powder(WGP)(0%,10%,15%,20%,25%)and water-binder ratio(W/C)(0.24,0.26,0.28)were used as influencing factors,and the quality loss rate(Δm)and compressive strength loss rate(Δfc)were used as characterization parameters.The Ca/Si ratio and main element contents of C-S-H gels with different WGP content were investigated by energy dispersive spectrometry(EDS).The pore structure evolution characteristics of WGP composite cementing materials were investigated by low field nuclear magnetic resonance(NMR).UsingΔfc as the index of frost resistance degradation and Weibull function,the frost resistance degradation of glass doped pervious concrete(WGP-PC)was modeled.The results show that,with WGP,for the same number of cycles,Δm andΔfc decrease and increase with the increase of WGP.Under the same WGP content,Δm andΔfc decrease first and then increase with the increase of W/C.After 100 freeze-thaw cycles,the samples with WGP content of 20%and W/C of 0.26 have the best freeze-resistance.Microscopic tests show that with the increase of WGP content,the Ca/Si ratio of C-S-H gel decreases at first and then increases with the increase of WGP content.The extreme value of Ca/Si is 2.36 when WGP is added by 20%.The pore volume of hardened paste with 20%WGP content decreased by 18.6%compared with that of cement system without WGP.The overall compactness of the specimen was improved.On the basis of the test data,a life prediction model was established according to Weibull function.The experiment showed thatΔfc could be used as a durability degradation index,and the slope of the reliability curve became gentle after WGP was added,which reduced the damage degradation rate of PC.W/C was 0.26.It's about 5000 hours.
基金supported by the National Natural Science Foundation of China(Grant Nos.42001059,52178340)the Natural Science Foundation of Hebei Province,China(Grant No.E2020210044)+1 种基金the Key Laboratory of Mechanical Behavior Evolution and Control of Traffic Engineering Structures in Hebei(Grant No.SZ 2022-03)the Overseas Expertise Introduction Project for Discipline Innovation("111 Project",Grant No.B21011).
文摘This study introduces a novel artificial heating technique aimed at addressing frost heave issues in embankments on frozen ground,offering a sustainable solution.Initial evaluations assessed various heating systems,including boilers,heat pumps,solar heaters,and electric heaters,focusing on their thermal performance and applicability.The study subsequently designed and implemented a direct-expansion ground source heat pump(DX-GSHP)system as the primary heat source for embankment warming.Rigorous testing confirmed the DX-GSHP system's ability to maintain a heat-supply temperature above 40℃ and a heat-absorption temperature below -3.5℃,effectively extracting geothermal energy for transfer to the topsoil layers.With a demonstrated coefficient of performance(COP)of 3.49,the DX-GSHP system not only proves its energy efficiency but also suggests a potential role in reducing the strain on electricity supply systems.Installation of DX-GSHPs,with heating capacities ranging from 1.0 to 2.0 kW and spaced at intervals of 2.0-4.0 m,provides a rapid thermal response to frost heave in singletrack railway embankments,thereby potentially mitigating frost-induced damage in cold climate regions.
文摘Based on the conventional observation data and NCEP/NCAR reanalysis data,the circulation situation,influencing systems and causes of the heavy rain during September 20-21,2010 in Ulanqab City were analyzed from the evolution process of weather circulation situation and the changes of various physical quantity fields.The results show that there was an obvious frontal zone between 45-52°N,which brought strong cold air.The transport of warm and humid air outside the subtropical high and typhoon was the main water vapor source of the strong precipitation,and the southwest jet at 700 hPa transported abundant water vapor.There was a broad inverted trough to the south of 45°N,with a central value of 1000.0 hPa.Ulanqab City was on the top of the inverted trough,stable and less moved,which was conducive to the occurrence of systematic heavy precipitation.The rainstorm was a strong precipitation process caused by the intersection of cold air brought by the southward movement of the upper frontal zone and warm and humid air outside the subtropical high.After the precipitation,the invasion of strong cold air brought frost and cold wave weather to Ulanqab City.
