The seasonally-operating cooling devices (SHOW) intended for freezing and cooling plastichnomorzlyh thawed soil at the base of a ventilated constructions underground and without, around transmission line supports and piping, along the embankments of railways and highways to increase their carrying capacity and to prevent buckling of piles in areas where permafrost. More information about the technology of thermal stabilization of soils can be on this page website.
The task of modeling the thermal effect on the seasonally active cooling devices today soils can be effectively addressed in the software package Frost 3D Universal. To do this, you need the following data:
1.Meteorological data (Table. 1): air temperature, wind speed, and the thickness of the snow cover;
2.Engineering and geological structure of the soil(Table. 2) and initial temperature at the start date of calculation (Table. 3);
3.Thermophysical properties of geological strata (Table. 4): thermal conductivity and heat capacity in the thawed state and morzlom, curve unfrozen water, phase transition temperature, soil density;
4.Technical characteristics of a thermal stabilizer (Table. 5).
Table. 1 - Climatic data
|Air temperature, aboutFROM||-27,3||-24,3||-16||-5,3||4,8||13,2||16,4||12,5||4,1||-5||-19,5||-26,8|
|Wind speed, m / s||2,3||2,1||2,1||2,4||2,4||2,1||1,8||1,8||1,9||2,3||2,3||2,4|
|Snow depth, m||0,28||0,31||0,32||0,27||0||0||0||0||0||0,14||0,19||0,25|
|snow density, kg / m3||275||300||320||330||0||0||0||0||0||180||220||240|
Table. 2 - Capacity of soils for each well
|Power geological layer, m|
|Name of geo-cal layer||wells. 1||wells. 2||wells. 3||wells. 4|
Table. 3 - The temperature distribution on the soil depth 01.10.2016
|Depth, m||Temperature, aboutFROM|
rice. 1 - Location of geologic wells in 2D Editor software package
Table. 4 - Thermal properties of soils
|Parameter Identification of the substance||Identification of the substance|
|Temperature, aboutFROM||The temperature distribution on the ground at a depth of 01.10.2016|
|Volumetric heat capacity of the unfrozen soil, MJ /(m3•aboutFROM)||2,78||3,17||3,17||2,78||2,31||2,39||2,31|
|Volumetric heat capacity of the frozen ground, MJ /(m3•aboutFROM)||2,06||2,41||2,41||2,26||2,14||2,08||2,14|
|The thermal conductivity of unfrozen soil, W /(м•aboutFROM)||1,91||1,57||1,57||2,26||1,62||2||1,62|
|The thermal conductivity of frozen soil, W /(м•aboutFROM)||2,14||1,8||1,8||2,62||1,74||2,2||1,74|
|The total weight of soil moisture, d.e.||0,14||0,29||0,57||0,23||0,27||0,21||0,18|
|The density of dry soil, kg / m3||1550||1450||1030||1590||1470||1630||1710|
|the phase transition temperature, aboutFROM||-0,1||-0,21||-0,26||-0,24||-0,31||-0,27||-0,32|
Table. 5 - Technical characteristics and thermal stabilizer circuit
1 - part of the capacitor;
2 - the transport of the;
3 - evaporation of the
|The length of the aerial part, m||1,5|
|type ribs||cross, round|
|The diameter of the ribs, mm||70|
|step ribs, mm||2,5|
|The number of edges, PC,||300|
|The thickness of the ribs, mm||1|
|Material ribs; thermal conductivity, W /(m∙aboutFROM)||Aluminum; 203,5|
|Evaporator (without inserts)|
|The length of the underground part, m||13|
|The length of the insulated portion, m||2|
It is necessary to calculate the thermal state of the soil under impact seasonally active cooling device for 5 years of use with 01.10.2018 by 01.05.2024.
Three-dimensional Computational Domain
Geological lithology soil, consisting of various elements geotechnical (IGE), recovering on the basis of several geotechnical wells using методов трёхмерной интерполяции.
The dimensions of the modeled area must be taken in such a way, to the annual variation of temperature does not affect the thermal condition of the soil deeper than zero temperatures of heat exchange. It is also necessary to take into account the impact of heat stabilizer and postpone the side and lower bounds on the computational domain as, so at this distance was not its effect on soil thermal distribution. On the basis of these considerations, it was decided to take the calculated area size 25h25h30 meters (rice. 2). tk. known geological structure of the ground only to 14 meters from the ground surface, it was decided to increase the capacity of the last layer of soil (IGE-7) More on 16 m.
rice. 2 - A three-dimensional computational domain
Thermal properties of soils (Table. 4) you need to create the database software package data (rice. 3), then assign them for each of the layers of soil, and set the initial temperature for the entire depth of the computational domain (rice. 4). Curve unfrozen water, you can set a table or dependence in accordance with SNIP 2.02.04 depending on the number of soil plasticity.
For subsequent modeling of the effects on the SDA primers, on the three-dimensional scene created by a part of its evaporative (rice. 5). The transport part is not modeled, tk. it has no effect on the thermal state of the soil and is seasonally active layer, capacitor part is also explicitly modeled, and a record of all the design parameters of the MCS is described in a special boundary condition in the database Frost 3D Universal.
FEATURES Simulation of heat stabilizers
As previously mentioned, only simulated evaporation of the SDA, to which is given the appropriate boundary conditions at SOU GU, created in the database (rice. 6). The State on SDA must set the following values:
- The annual course of air temperature in the given area.
- heat transfer coefficient, which determines the intensity of the convective heat transfer of the condenser to the atmosphere. This ratio can be calculated in the calculator heat transfer conditions Frost 3D Universal depending on the speed and design features of the capacitor (rice. 7, 8).
- temperature difference - temperature loss between the ground and a capacitor, value consisting of superheat of the refrigerant to start its nucleate boiling, refrigerant temperature glide, hydrostatic depression and loss due to the absorbed visible condenser and heat radiation. Temperature glide - temperature loss during the transition from liquid to vapor. Temperature depression - loss of temperature to overcome the hydrostatic pressure of vapor bubbles. If the evaporator gently sloping, or if the supply of the liquid refrigerant is small, the temperature depression is close to zero.
- The thermal resistance of a heat stabilizer - here: The useful part of the temperature difference between the ground and a capacitor, referred to the heat flux from the condenser to the atmosphere, К⁄(Вт⁄м2). This value can be calculated, multiplying thermal resistance (К⁄Вт) between the ground and the condenser at high temperature differences (allowing negligible thermal losses) condenser area.
- The design parameters of the MCS:
- evaporative pipe radius portion;
- area of the evaporator, the contacted ground;
- area of the condenser fins, contactee with the environment.
The "Automatic shutdown SDA» SDA provides a work stoppage, provided, if the surface temperature of the fin condenser part higher than the average ground temperature, the contacted part with evaporative heat stabilizer, taking into account the temperature difference.
rice. 6 - Setting the parameters of a new boundary condition for the seasonally-acting cooling device
The boundary conditions ON THE VERGE computational domain
After creating the three-dimensional model of the computational domain, it is necessary to set the following facets of the boundary conditions, which also first need to create a database:
- The top of the computational domain is necessary to set the boundary condition 3 kind (rice. 9), where it is necessary to introduce air temperature varies periodically with respect to time (rice. 10) and heat exchange coefficient (rice. 11). Soil heat transfer coefficient of air is calculated from the wind speed. In the cold season on the heat transfer coefficient is also affected by snow depth (rice. 12) and its density (rice. 13), the values of which can be set in the corresponding parameters of the boundary condition.
- On the side surface is set equal to zero heat flux, tk. the side faces are at a distance sufficiently distant from the MCS and supposed, that the soil temperature of the lateral boundary of the computational domain will match the estimated temperature inside the border region in its.
- permafrost constant temperature is set at the lower face of the computational domain is equal to -0,34 OC, tk. the lower boundary lies at a sufficient distance from heat sources and it will not affect the work of the JMA.
rice. 9 - Setting the boundary conditions on the ground surface
Thermal design a computer model was made on 5 years, beginning with 1 October 2018 and ending the year 1 May 2024 of the year. Effect seasonally active cooling device is provided below the ground in the form of color temperature distribution and the proportion of unfrozen water in the simulated domain on 15 of each month (rice. 14, 15).
rice. 14 - Temperature regime Soil cross-sectional area in place of the simulated location JMA
rice. 15 - Ratio of unfrozen water in the ground cross-section area in place of the simulated location JMA
On the basis of the calculation results, automatically creates a graph of cooling capacity of the entire surface of the evaporator of the SDA (rice. 16). This graph can be used to assess thermal stabilizer effectiveness in these climates.
rice. 16 - Automatically create a graph the cooling capacity of the JMA for all time simulation