CN109146208B - Road deicing salt usage amount prediction method - Google Patents
Road deicing salt usage amount prediction method Download PDFInfo
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- 150000003839 salts Chemical class 0.000 title claims abstract description 133
- 238000000034 method Methods 0.000 title claims abstract description 42
- 239000012266 salt solution Substances 0.000 claims abstract description 116
- 238000006243 chemical reaction Methods 0.000 claims abstract description 33
- 238000002844 melting Methods 0.000 claims abstract description 26
- 238000007710 freezing Methods 0.000 claims abstract description 23
- 230000008018 melting Effects 0.000 claims abstract description 23
- 230000008014 freezing Effects 0.000 claims abstract description 21
- 230000008859 change Effects 0.000 claims abstract description 19
- 238000010309 melting process Methods 0.000 claims abstract description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 128
- 230000008569 process Effects 0.000 claims description 22
- 238000012546 transfer Methods 0.000 claims description 22
- 239000007787 solid Chemical class 0.000 claims description 18
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 15
- 230000008020 evaporation Effects 0.000 claims description 14
- 238000001704 evaporation Methods 0.000 claims description 14
- 230000004907 flux Effects 0.000 claims description 9
- 238000001556 precipitation Methods 0.000 claims description 8
- 238000012360 testing method Methods 0.000 claims description 7
- 238000004090 dissolution Methods 0.000 claims description 6
- 239000007788 liquid Substances 0.000 claims description 4
- 238000000859 sublimation Methods 0.000 claims description 4
- 230000008022 sublimation Effects 0.000 claims description 4
- 230000036962 time dependent Effects 0.000 claims description 4
- NAWXUBYGYWOOIX-SFHVURJKSA-N (2s)-2-[[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]amino]-4-methylidenepentanedioic acid Chemical compound C1=CC2=NC(N)=NC(N)=C2C=C1CCC1=CC=C(C(=O)N[C@@H](CC(=C)C(O)=O)C(O)=O)C=C1 NAWXUBYGYWOOIX-SFHVURJKSA-N 0.000 claims description 2
- 229920006395 saturated elastomer Polymers 0.000 claims description 2
- 230000000694 effects Effects 0.000 abstract description 6
- 239000003795 chemical substances by application Substances 0.000 description 3
- 238000012423 maintenance Methods 0.000 description 3
- 238000011160 research Methods 0.000 description 3
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000011384 asphalt concrete Substances 0.000 description 2
- 239000012267 brine Substances 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 2
- 201000004569 Blindness Diseases 0.000 description 1
- 206010039203 Road traffic accident Diseases 0.000 description 1
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 150000001412 amines Chemical class 0.000 description 1
- 239000010426 asphalt Substances 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 239000004202 carbamide Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000011033 desalting Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000004141 dimensional analysis Methods 0.000 description 1
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- 238000009413 insulation Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 229910001629 magnesium chloride Inorganic materials 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 235000015598 salt intake Nutrition 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
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Abstract
The invention provides a method for predicting the use amount of road deicing salt, which comprises the following steps: predicting the temperature change trend of the road salt solution in the ice melting process according to the data of the outside air temperature and the outside wind speed; and B: obtaining the temperature of the salt solution when the deicing reaction of the deicing salt is finished; and C: obtaining the freezing point temperature of the salt solution when the deicing reaction of the deicing salt is finished; step D: obtaining the concentration of the salt solution at the end of the ice melting reaction; step E: and D, calculating the predicted dosage of the deicing salt according to the thickness of the ice layer, the surface area of the ice layer to be melted and the concentration of the salt solution in the step D. Based on the method for predicting the amount of the deicing salt used for the road, the amount of the deicing and snow melting agent to be adopted by the iced road surface under the conditions of different external temperatures, different wind speeds, different ice layer thicknesses and the like can be determined, and the amount of the deicing salt used for the road is reduced as much as possible on the premise of considering the deicing effect.
Description
Technical Field
The invention relates to the field of pavement engineering, in particular to a method for predicting the dosage of deicing salt for a road.
Background
Under the condition of low-temperature rain and snow weather in winter, the road surface is very easy to freeze and accumulate snow, which can cause the reduction of the friction coefficient of the road surface, the difficulty of vehicle running and the increase of the braking distance, thereby causing the great increase of the traffic accident rate. In order to effectively solve the difficult problems of road icing and snow accumulation in cold seasons, the deicing salt is widely applied to the prevention and control of road icing disasters in winter in the world, has the advantages of high efficiency, convenience, low cost, wide application range and the like, and can quickly achieve the aim of road deicing, thereby ensuring the traffic safety of roads.
However, many researches in recent years find that most salt snow-melting agent products have great side effects, deicing salt is easy to corrode and damage road structures and motor vehicles, and can pollute soil, water, atmosphere and the like and damage ecological environment. Road deicing salt is not scattered much and scattered in a mixed manner, which is a common knowledge of road maintenance departments, however, the use of deicing salt by the current road maintenance departments has certain blindness, and most of the deicing salt is scattered by maintenance personnel according to the usual experience. Sometimes, this practice wastes resources and also brings more environmental risks in order to enhance the deicing effect and even increase the dosage blindly.
Excessive use of deicing salts can cause significant economic losses, but if too little is dispensed, it can lead to difficulties in thoroughly removing road ice. Therefore, under the current deicing technical conditions, the artificial randomness of the using amount of the deicing salt is changed, the using amount of the deicing agent and the reasonable configuration of the deicing measures are optimized as much as possible, and the method has great practical significance.
In fact, the thickness of the ice layer under different conditions and the amount of deicing salt required by different icy roads are different, and the related theory and experimental analysis are needed according to the amount of deicing salt. According to different external conditions, such as air temperature, wind speed, snow fall amount, road surface temperature, snow (ice) layer thickness and the like, the quality of the deicing salt used in unit area is properly adjusted, so that the expected deicing effect can be achieved, and the using amount of the deicing salt for roads can be reduced.
Disclosure of Invention
Accordingly, the present invention provides a method for predicting the amount of deicing salts used for roads, the method comprising the steps of,
step A: predicting the temperature change trend of the road salt solution in the ice melting process according to the data of the outside air temperature and the outside wind speed;
and B: obtaining the temperature of the salt solution at the end of the deicing salt deicing reaction from the variation trend in the step A;
and C: obtaining the freezing point temperature of the salt solution at the end of the deicing salt deicing reaction from the temperature of the salt solution in the step B;
step D: obtaining the concentration of the salt solution at the end of the ice melting reaction from the freezing point temperature in the step C;
step E: and D, calculating the predicted dosage of the deicing salt according to the thickness of the ice layer, the surface area of the ice layer to be melted and the concentration of the salt solution in the step D.
In a specific embodiment, the temperature of the salt solution at the end of the deicing salt deicing reaction is assumed to be equal to the freezing point temperature of the salt solution at the end of the deicing salt deicing reaction in the prediction method.
In a specific embodiment, a heat transfer model of the road deicing salt deicing process is constructed in the prediction method through finite element software COMSOL.
Starting from the phase change principle and the heat and mass transfer reaction in deicing, the invention establishes a road deicing salt deicing temperature prediction model by researching the temperature change rule of a deicing salt solution and the ice point change rule of the deicing salt solution, explains the interaction mechanism between different substances of road surface ice-water-deicing salt under the condition of deicing, and has the following advantages compared with other methods: (1) the method has the advantages that the thickness of the road surface ice-setting, the ice-setting temperature and the influence of the atmospheric environment are considered, the optimal configuration and the ice-removing effect evaluation are carried out on the using amount of the deicing salt, and the operation in practical application is facilitated; (2) the deicing mechanism of the road deicing salt is disclosed in principle, a theoretical basis is provided for the optimized use of the deicing salt, and the purpose of optimized quantitative analysis of the deicing salt is achieved.
Based on the method for predicting the amount of the deicing salt used for the road, provided by the invention, the amount of the deicing and snow melting agent to be adopted by the iced road surface under the conditions of different external temperatures, different wind speeds, different ice layer thicknesses and the like can be determined, and the amount of the deicing salt used for the road is reduced as much as possible on the premise of taking ice melting effect into consideration.
Drawings
FIG. 1 shows the time-varying law of the temperature of the salt solution and the freezing point of the salt solution in the process of actually measuring the deicing, the salt and the ice-melting of the road.
FIG. 2 is a heat transfer model of road deicing salt deicing stage I.
FIG. 3 is a heat transfer model of road deicing salt ice melting stage II.
FIG. 4 is a finite element geometric model of deicing of road surface with deicing salt.
FIG. 5 shows the predicted variation of the temperature of the salt solution during the melting process.
Detailed Description
The present invention is further illustrated by the accompanying drawings and specific examples, but the scope of the invention is not limited thereto, and the claims are to be read.
As will be appreciated by those skilled in the art, after the industrial salt is spread on the ice layer, the solid industrial salt will also dissolve as the ice melts, forming a salt solution. Examples of the industrial salt include sodium chloride, magnesium chloride, urea, and amines.
(1) The relation between the temperature of the deicing salt solution and the freezing point thereof is obtained by a test method
In order to obtain parameters representing the deicing process of deicing salt, a design experiment verifies the relation between the temperature of the salt solution and the temperature of the salt solution in the deicing process of deicing salt of the road. Freezing point (freezing point) refers to the temperature at which the salt solution changes from a liquid state (water) to a solid state (ice). The deicing salt ice-melting test result is shown in fig. 1, and the result shows that the temperature of the salt solution of the road is close to the freezing point of the road in the deicing salt ice-melting process. And when the temperature of the salt solution is close to the freezing point of the salt solution, finishing the reaction of forming the salt solution in the road deicing, salt melting and ice melting process. The freezing point of the salt solution is related to the concentration of the salt solution, so that the temperature change of the salt solution can be used for predicting the required quality of the salt solution.
(2) Construction of mass balance equation and heat transfer balance equation in deicing process of deicing salt based on phase change principle and heat transfer mass transfer equation
In the process of deicing, salt and ice on roads, the ice layer is continuously melted, and the mass M of ice in the systemiThe change law of the mass can be represented by the following formulas (1) to (4) along with the change of the time:
mif＝vifρice (2)
mil＝αil(ρva-ρvs)θi (3)
wherein:
mifkg · m is the increase in the mass of ice and snow caused by snowing per unit time-2·s-1；
milIs the loss of ice mass in kg m due to sublimation in unit time-2·s-1；
miwThe loss of ice mass in kg · m, due to melting in a unit time-2·s-1；
t is time, unit s; alpha is alphailIs the sublimation coefficient;
(f) (t) is a function of the amount of snowfall, and f (t) is 1 when there is snowfall and f (t) is 0 when there is no snowfall;
viffor the snowing speed, m.s-1；ρiceThe density of ice and snow on the road surface is kg.m-3；
ρvaIs the density of water vapor in the air, kg.m-3；
ρvsIs the density of water vapor on the road surface, kg.m-3；
θiRepresents the mass percentage of ice in the whole system comprising ice, salt solution and solid salt;
vwsis the wind speed, taken as a constant, m.s-1；
Quality of water (M) in the system during the process of deicing, desalting and melting ice on roadsw) The time-dependent change law is shown as formula (5):
mwf＝vfwρw (6)
mwl＝αwl{ρva-ρvs(1-φ)}(1-θi) (7)
wherein:
mwf(kg·m-2·s-1) Is the amount of rainfall in a unit time,
mwl(kg·m-2·s-1) Is the evaporation capacity of water in unit time;
(t) as a function of precipitation, when there is precipitation f (t) 1, and when there is no precipitation f (t) 0;
vifas the rate of precipitation, m.s-1；ρw998 kg.m, which is the density of water-3；
αwlVolume factor for water evaporation;
vwsthe wind speed of the saline solution surface, i.e. the wind speed of the road surface, m.s-1；
Phi is the ratio of the current air humidity to the saturated air humidity;
mass M of solid salt in the system as a function of timessAnd mass M of liquid saltslThe time-dependent law is shown in formula (9) and formula (10), wherein msl(kg·m-2·s-1) Mass of dissolved solid salt per unit time;
considering that whether the deicing salt is dissolved or not has great influence on the heat transfer process, the whole heat transfer process can be divided into two stages, namely a stage I and a stage II according to whether the deicing salt is dissolved or not; in the stage I, from the beginning of putting in the deicing salt to the end of completely dissolving the deicing salt, the heat exchange process is shown in FIG. 2, and according to the assumption, the deicing salt layer isolates the brine layer from the air, so that the heat exchange between the brine layer and the air and the evaporation of water are not considered in the stage I;
the heat balance equation of the salt solution layer in the stage I is established as follows:
in the formula: rhoswIs the density of the salt solution, kg/m3
CswThe specific heat capacity of the salt solution, considered constant, J/(kg. degree. C.)
VswVolume of saline solution, m3·m-2
TswIs the average temperature of the salt solution layer, deg.C
qswIs the heat exchange between the salt solution layer and the salt layer in unit time, W.m-2；
qiwIs a salt solution layer and an ice layer in unit timeHeat exchange of (2), W.m-2；
qslThe heat absorbed by the salt dissolved in water per unit time, W.m-2；
qilW.m is the amount of heat absorbed by the ice melting in a unit time-2；
Wherein:
in the above formula: lambda [ alpha ]swIs the thermal conductivity of the salt solution, W.m-1·K-1；
λsIs the thermal conductivity of the salt layer, W.m-1·K-1；
λiIs the thermal conductivity of the ice layer, W.m-1·K-1；
hswIs the thickness of the salt solution layer, cm; h issw＝0.425exp(-726/t)；
hsIs the thickness of salt layer, cm, hs＝0.5-0.5t/1230；
hiIs the thickness of the ice layer, cm;
Tstaking the average temperature of the salt layer as the external environment temperature at DEG C;
Tithe average temperature of the ice layer, DEG C;
rcfor the heat flux resistance, take rc＝0.6×10-3m2KW-1；
The heat flux of the deicing salt solution in the system can be represented by the following formula:
qsl＝msl·Lsl (14)
in the above formula: m isslThe dissolving amount of solid salt in unit area in unit time is related to the system temperature and the concentration of salt solution, and deicing is carried out according to the test result of road deicing, salt deicing and ice meltingThe salt dissolution rate can be represented by formula (15):
msl＝7.174×10-4kg·m-2·s-1 (15)
Lslthe latent heat absorbed for a unit mass of dissolved solid salt is:
Lsl＝-3.88/(58.44×10-3)kJ·kg-1
the heat flux for melting the ice layer in the system can be represented by the following formula:
qil＝mil·Lil (16)
in the above formula: m isilThe mass of the melted ice in unit area in unit time is related to the system temperature and the salt solution concentration, and is taken as
mil＝3400·exp(-726/t)/t2(kg·m-2·s-1) (17)
Wherein L isilThe latent heat absorbed per unit mass of ice melted,
Lil＝-335kJ·kg-1
the stage II is a stage from complete dissolution of the deicing salt to the end of the melting reaction, and the heat exchange process is shown in FIG. 3:
different from the stage I, in the stage II, because the solid deicing salt is completely dissolved and the salt layer disappears, the heat exchange caused by the convection heat exchange between the salt solution layer and the air and the water evaporation needs to be considered; the phase II heat balance equation is established as follows:
in the formula: rhoswIs the density of the salt solution, kg/m3
CswThe specific heat capacity of the salt solution is considered to be constant J/(kg. DEG C.)
VswVolume of saline solution, m3·m-2
qswIs the heat exchange between the salt solution layer and the salt layer in unit time, W.m-2；
qiwIs the heat exchange between the salt solution layer and the ice layer in unit time, W.m-2；
qilW.m is the amount of heat absorbed by the ice melting in a unit time-2；
qaIs the heat exchange between the ice salt system and the outside air in unit time, W.m-2；
qwaW.m is the amount of heat absorbed by water evaporation per unit time-2；
qa＝αa(Twis-Ta) (19)
In the above formula: alpha is alphaaIs the heat exchange coefficient of the salt solution and the air and the wind speed vaIn connection with, alphaa＝10.4va 0.7+2.2，TwisTemperature of the salt solution, deg.C; t isaAmbient temperature, deg.C;
qwa＝mwa·Lwa (20)
mwathe evaporation rate of water in the salt solution per unit time was taken to be 1.11X 10-5kg·s-1·m-2(ii) a Latent heat of water evaporation LwaThe value was-2260 KJ/Kg.
(3) The purpose of predicting the deicing process of deicing salt is achieved through temperature model prediction
Based on the theory that the freezing point of the salt solution is close to the temperature of the salt solution in the deicing process, and the mass balance equation and the heat transfer balance equation in the deicing process. A heat transfer model of the road deicing salt ice melting process is constructed through finite element software COMSOL, so that the aim of predicting the use amount of road deicing salt in winter is fulfilled through the temperature prediction of the deicing salt solution.
The COMSOL finite element model establishment process is as follows:
when the geometric model is established, in order to enable the established model to be consistent with the field test condition, three-dimensional analysis is adopted, and a certain section of the road structure in the deicing process of deicing salt is taken as a deicing model for research. The ice melting model is divided into an ice removing salt layer, a salt solution layer, an ice layer and an asphalt pavement layer from top to bottom as shown in figure 4.
The finite element geometric model has 21 boundaries, the material layer is respectively endowed with solid salt parameters, salt solution parameters, ice parameters and asphalt concrete parameters from top to bottom, and specific numerical values are shown in table 1.
TABLE 1 finite element model Material parameters
After the model definition is completed, heat transfer analysis needs to be carried out on each area, the internal heat transfer mode of the asphalt concrete layer is solid heat transfer, the internal heat transfer mode of the ice layer and the internal heat transfer mode of the solid salt layer are defined as phase change heat transfer, the boundary condition of the salt solution layer and the ice layer is a second type, the thermal contactil(ii) a The second type of boundary condition between the salt layer and the salt solution layer and assuming complete thermal contact, there is a heat flux qsl(ii) a The upper boundary of the saline solution layer is set as the second type of boundary condition, and heat flux q existswaAnd q isa. Because the geometric model is taken as a certain section of the road structure, the boundaries of the left side and the right side of the geometric model are arranged to be thermally insulated.
In model solid heat transfer, there is the governing equation:
thermal insulation is arranged on the left side and the right side of the geometric model, and the control equation is as follows:
for full thermal contact heat transfer, there are:
for the phase change heat transfer inside the ice layer, there is a control equation:
equations (21) to (24) are internal calculation equations of the finite element geometric model, and the contents of these equations are known to those skilled in the art.
The latent heat of phase change from phase 1 (ice) to phase 2 (water) was 335[ kJ/kg ].
During simulation, other external environment parameters are shown in the table 2;
TABLE 2 Heat flux variables
Before the last step of the invention:
the freezing point of the salt solution is related to the temperature and concentration of the saline solution, and under the condition of standard air pressure, the relationship between the freezing point of the salt solution and the concentration of the saline solution and the temperature of the saline solution can be expressed as follows:
Tb＝-0.02c2-0.39c-0.36 (25)
wherein, TbFreezing temperature of salt solution, DEG C; c is the concentration of the salt solution;
Msis the mass of salt in the salt solution; miThe mass of water in the salt solution in the reaction process, namely the mass of ice melted in the whole reaction process;
according to the deicing salt and deicing test result, the temperature T of the salt solution at the end of the deicing reactionsw' approximately equal to the freezing point T of the salt solution at this timeb', there are:
Tsw′＝Tb′ (27)
let c' be the concentration of the salt solution at the end of the deicing salt-deicing reaction, Ms' is the mass of salt in the salt solution at the end of the reaction; mi' is a reactionThe mass of water in the salt solution during the process; in combination with formula 25, there are:
Ms' equal in value to the mass of deicing salt charged at the start of the reaction, Mi' is equal in value to the mass of ice layer melted during the reaction.
Meanwhile, according to the assumption of a temperature model, the bottom areas of the ice layer and the salt solution layer are always kept consistent in the ice melting process; thus, equation (28) can be further simplified as:
wherein h issIs the thickness of the deicing salt layer put in at the initial moment, cm; h isiThe thickness of the melted ice layer in the whole ice melting process is cm;
according to the formula (29), in the practical application of the deicing salt, the thickness of the deicing salt needed to be used can be determined according to the thickness of the ice layer of the unit area road.
According to the research, the finite element model established in the method can accurately predict the temperature of the deicing salt solution under different external conditions. Therefore, based on the formula (29), the road deicing salt dosage prediction under different conditions can be realized by combining the deicing salt solution temperature prediction model.
The road deicing salt dosage prediction idea is as follows:
the thickness of the ice layer to be melted → the temperature change trend of the road salt solution is predicted according to different conditions (outside air temperature and wind speed) → the temperature at the end of the deicing salt and deicing reaction is obtained → the ice point at the end of the deicing salt and deicing reaction is obtained → the concentration of the salt solution at the end of the deicing reaction is obtained → the dosage of deicing salt can be converted according to the concentration of the salt solution which is the dosage of deicing salt/the volume of the ice melting layer.
And predicting the deicing salt consumption of the road ice layer under the specific external condition according to the thought, and comparing and verifying the prediction result through an indoor deicing salt experiment. The external environmental parameters are as in table 3.
TABLE 3 test Condition parameters
According to the road deicing salt solution temperature prediction model established by the invention, the temperature change rule of the deicing process under the conditions of the table 3 is shown in fig. 5.
As can be seen from fig. 5, at the end of the ice melting reaction, the temperature of the salt solution finally stabilized at-8.7 ℃, namely: t issw＝-8.7℃。
Converted from the formula (29) in hiIn the case of 1cm, the thickness of the deicing salt layer required to melt the ice layer is about 0.12 cm.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions and substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
Claims (3)
1. A method for predicting the dosage of deicing salt for roads comprises the following steps,
step A: predicting the temperature change trend of the road salt solution in the ice melting process according to the data of the outside air temperature and the outside wind speed;
and B: obtaining the temperature of the salt solution at the end of the deicing salt deicing reaction from the variation trend in the step A;
and C: obtaining the freezing point temperature of the salt solution at the end of the deicing salt deicing reaction from the temperature of the salt solution in the step B;
step D: obtaining the concentration of the salt solution at the end of the ice melting reaction from the freezing point temperature in the step C;
step E: d, calculating the predicted dosage of deicing salt according to the thickness of the ice layer, the surface area of the ice layer to be melted and the concentration of the salt solution in the step D;
in the prediction method, the temperature of the salt solution at the end of the deicing salt and the freezing point temperature of the salt solution at the end of the deicing salt and deicing reaction are assumed to be equal;
constructing a heat transfer model of the road deicing salt ice melting process through finite element software COMSOL in the prediction method;
in the step A, the step B is carried out,
in the process of deicing, salt removing and ice melting of roads, the ice layer is continuously melted, and the mass M of ice in the ice salt systemiThe change law of the mass can be represented by the following formulas (1) to (4) along with the change of the time:
mif＝vifρice (2)
mil＝αil(ρva-ρvs)θi (3)
wherein:
mifkg · m is the increase in the mass of ice and snow caused by snowing per unit time-2·s-1；
milIs the loss of ice mass in kg m due to sublimation in unit time-2·s-1；
miwThe loss of ice mass in kg · m, due to melting in a unit time-2·s-1；
t is time, unit s; alpha is alphailIs the sublimation coefficient;
(f) (t) is a function of the amount of snowfall, and f (t) is 1 when there is snowfall and f (t) is 0 when there is no snowfall;
viffor the snowing speed, m.s-1；ρiceThe density of ice and snow on the road surface is kg.m-3；
ρvaIs the density of water vapor in the air, kg.m-3；
ρvsIs the density of water vapor on the road surface, kg.m-3；
θiRepresents the mass percentage of ice in the whole ice salt system comprising ice, salt solution and solid salt;
vwsis the wind speed, taken as a constant, m.s-1；
In the step A, the step B is carried out,
quality M of water in ice salt system in road deicing processwThe time-dependent change law is shown as formula (5):
mwf＝vfwρw (6)
mwl＝αwl{ρva-ρvs(1-φ)}(1-θi) (7)
wherein:
mwfis the amount of rainfall in unit time, kg.m-2·s-1，
mwlIs the evaporation capacity of water in unit time, kg.m-2·s-1；
(t) as a function of precipitation, when there is precipitation f (t) 1, and when there is no precipitation f (t) 0;
vfwas the rate of precipitation, m.s-1；ρw998 kg.m, which is the density of water-3；
αwlVolume factor for water evaporation;
vwsthe wind speed of the saline solution surface, i.e. the wind speed of the road surface, m.s-1；
Phi is the ratio of the current air humidity to the saturated air humidity;
mass M of solid salt in ice salt system as a function of timessAnd mass M of liquid saltslThe time-dependent law is shown in formula (9) and formula (10), wherein mslMass of dissolved solid salt per unit time, kg m-2·s-1；
Considering that whether the deicing salt is dissolved or not has great influence on the heat transfer process, the whole heat transfer process can be divided into two stages, namely a stage I and a stage II according to whether the deicing salt is dissolved or not; in the stage I, from the beginning of putting in the deicing salt to the end of completely dissolving the deicing salt, the salt water layer is isolated from the air by the deicing salt layer according to the assumption, so that the heat exchange between the salt solution layer and the air and the evaporation of water are not considered in the stage I;
the heat balance equation of the salt solution layer in the stage I is established as follows:
in the formula: rhoswIs the density of the salt solution, kg/m3
CswThe specific heat capacity of the salt solution, considered constant, J/(kg. degree. C.)
VswVolume of saline solution, m3·m-2
TswIs the average temperature of the salt solution layer, deg.C
qswIs the heat exchange between the salt solution layer and the salt layer in unit time, W.m-2；
qiwIs salt dissolution in unit timeHeat exchange between liquid layer and ice layer, W.m-2；
qslThe heat absorbed by the salt dissolved in water per unit time, W.m-2；
qilW.m is the amount of heat absorbed by the ice melting in a unit time-2；
Wherein:
in the above formula: lambda [ alpha ]swIs the thermal conductivity of the salt solution, W.m-1·K-1；
λsIs the thermal conductivity of the salt layer, W.m-1·K-1；
λiIs the thermal conductivity of the ice layer, W.m-1·K-1；
hswIs the thickness of the salt solution layer, cm; h issw＝0.425exp(-726/t)；
hsIs the thickness of salt layer, cm, hs＝0.5-0.5t/1230；
hiIs the thickness of the ice layer, cm;
Tstaking the average temperature of the salt layer as the external environment temperature at DEG C;
Tithe average temperature of the ice layer, DEG C;
rcfor the heat flux resistance, take rc＝0.6×10-3m2KW-1；
The heat flux for de-icing salt dissolution in an ice salt system can be represented by the following formula:
qsl＝msl·Lsl (14)
in the above formula: m isslThe dissolving amount of solid salt per unit area in unit time is related to the temperature of the ice salt system and the concentration of the salt solution according to the standardThe de-icing salt de-icing test results show that the de-icing salt dissolution rate can be represented by formula (15):
msl＝7.174×10-4kg·m-2·s-1 (15)
Lslthe latent heat absorbed for a unit mass of dissolved solid salt is:
Lsl＝-3.88/(58.44×10-3)kJ·kg-1
the heat flux for melting the ice layer in an ice salt system can be represented by the following formula:
qil＝mil·Lil (16)
in the above formula: m isilThe mass of the melted ice in unit area in unit time is related to the temperature of the ice-salt system and the concentration of the salt solution, and is taken as
mil＝3400·exp(-726/t)/t2，kg·m-2·s-1 (17)
Wherein L isilThe latent heat absorbed per unit mass of ice melted,
Lil＝-335kJ·kg-1
stage II is a stage from complete dissolution of deicing salt to the end of melting reaction,
different from the stage I, in the stage II, because the solid deicing salt is completely dissolved and the salt layer disappears, the heat exchange caused by the convection heat exchange between the salt solution layer and the air and the water evaporation needs to be considered; the phase II heat balance equation is established as follows:
in the formula: rhoswIs the density of the salt solution, kg/m3
CswThe specific heat capacity of the salt solution, considered constant, J/(kg. degree. C.)
VswVolume of saline solution, m3·m-2
qswIs the heat exchange between the salt solution layer and the salt layer in unit time,W·m-2；
qiwis the heat exchange between the salt solution layer and the ice layer in unit time, W.m-2；
qilW.m is the amount of heat absorbed by the ice melting in a unit time-2；
qaIs the heat exchange between the ice salt system and the outside air in unit time, W.m-2；
qwaW.m is the amount of heat absorbed by water evaporation per unit time-2；
qa＝αa(Twis-Ta) (19)
In the above formula: alpha is alphaaIs the heat exchange coefficient of the salt solution and the air and the wind speed vaIn connection with, alphaa＝10.4va 0.7+2.2，TwisTemperature of the salt solution, deg.C; t isaAmbient temperature, deg.C;
qwa＝mwa·Lwa (20)
mwathe evaporation rate of water in the salt solution per unit time was taken to be 1.11X 10-5kg·s-1·m-2(ii) a Latent heat of water evaporation LwaThe value was-2260 KJ/Kg.
2. The method according to claim 1, wherein in steps B to E,
the freezing point of the salt solution is related to the temperature and concentration of the saline solution, and under the condition of standard air pressure, the relationship between the freezing point of the salt solution and the concentration of the saline solution and the temperature of the saline solution can be expressed as follows:
Tb＝-0.02c2-0.39c-0.36 (25)
wherein, TbFreezing temperature of salt solution, DEG C; c is the concentration of the salt solution;
Msis the mass of salt in the salt solution; miTo reactThe mass of water in the salt solution in the process, i.e. the mass of ice melted in the whole reaction process;
according to the deicing salt and deicing test result, the temperature T of the salt solution at the end of the deicing reactionsw' approximately equal to the freezing point T of the salt solution at this timeb', there are:
Tsw′＝Tb′ (27)
let c' be the concentration of the salt solution at the end of the deicing salt-deicing reaction, Ms' is the mass of salt in the salt solution at the end of the reaction; mi' is the mass of water in the salt solution during the reaction; in combination of formulae (25) and (26), there are:
Ms' equal in value to the mass of deicing salt charged at the start of the reaction, Mi' is equal in value to the mass of ice layer melted during the reaction.
3. The method according to claim 2, wherein in steps B to E,
according to the assumption of a temperature model, the bottom areas of the ice layer and the salt solution layer are always kept consistent in the ice melting process; thus, equation (28) can be further simplified as:
wherein h issIs the thickness of the deicing salt layer put in at the initial moment, cm; h isiThe thickness of the melted ice layer in the whole ice melting process is cm;
according to the formula (29), in the practical application of the deicing salt, the thickness of the deicing salt needed to be used can be determined according to the thickness of the ice layer of the unit area road.
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