Welcome to the GeoStudio 2012 video series.
This tutorial video will discuss how to use the internal estimation algorithms for defining thermal material properties in TEMP/W version 8.
This tutorial demonstrates the procedure for estimating the thermal property functions in each of the material models available in TEMP/W.
These material models include the simplified thermal model,
full thermal model, and coupled convective thermal model.
Each of the thermal properties and functions associated with each will be described,
including the frozen and unfrozen thermal conductivities and volumetric specific heat capacities.
First, we will start on a new page with a steady state TEMP/W analysis already open.
We will start by going to KeyIn
Materials
and choosing the simplified thermal model.
This material model can be used for phase change scenarios where the volumetric water content does
not change during the simulation and the freezing function is very steep.
In this model type, the phase change is expected to occur only at the phase change temperature
instead of over a range of temperatures.
In the simplified thermal model, the unfrozen and frozen thermal conductivities and volumetric
specific heat capacities are assumed to be constant with change in temperature.
The water content of the domain is assumed to remain constant for the duration of the analysis.
The frozen and unfrozen thermal conductivities define the soils ability to transmit heat by conduction
or the quantity of heat that will flow through a unit area soil
of unit thickness in unit time under a unit temperature gradient.
The units are in joules per second per meter per degree Celsius
or BTU per hour per foot per degree Fahrenheit.
Generally the thermal conductivity of an unfrozen soil will increase with increasing water content.
The thermal conductivity of a frozen soil is also generally higher than that of an unfrozen soil as a
result of the higher thermal conductivity of ice when compared to unfrozen water.
To estimate the thermal conductivity of a dry natural soil, the dry density of the soil can be used.
Here, the dry density of the soil
is assumed to be in kilograms per cubic meter.
You can also estimate the saturated unfrozen bulk thermal conductivity by using the porosity and thermal conductivity of the soil minerals and water.
The saturated frozen bulk thermal conductivity can also be estimated using the porosity,
unfrozen water content and the thermal conductivity of the soil minerals, water, and ice.
These calculations are based on the literature
by Johansson 1975.
The volumetric specific heat capacity
is defined as the quantity of heat required to raise the temperature of the volume of soil by a unit degree.
Its units are in joules per cubic meter per degree Celsius
or BTU per cubic foot for degree Fahrenheit.
The bulk volumetric specific heat capacity can be estimated by using the soils dry density,
specific heat capacity of the soil, water, and ice, and the unfrozen and frozen water contents
as based on the equations by Johnston et al. 1981.
Next, let's take a look at the full thermal model.
Here, the thermal conductivity and unfrozen water content functions become dependent on temperature
and are no longer held constant during the simulation.
The assumptions of a constant unfrozen and frozen volumetric specific heat capacity and water content still remain in this model type.
The unfrozen water content function is defined as the percentage of soil water volume
that remains unfrozen at a specified temperature.
The function becomes steeper for coarser soils, indicating that soils of high gravel content will freeze the pore water at a much smaller temperature range
than a soil with mostly clay particles.
Note, the unfrozen water content is normalized water content here
and must be defined from 0 to 100%.
Now, when we return to our KeyIn Materials window,
we can see that may require the inputs of thermal conductivity and unfrozen water content functions.
Let's first look at the thermal conductivity vs. temperature function by clicking on the "..." button.
In the popup window, our function uses the spline datapoint function option from the drop down menu,
so we will click on estimate.
Here, we can choose the soil sample type from the drop down menu
and enter the frozen and unfrozen thermal conductivities.
These values would be similar to the constant values used in the simplified thermal model.
Once entered, the estimation algorithm will generate a curve using the unfrozen and frozen thermal conductivities as the extreme values
with the function slope based on the material type.
Next we will move on to the unfrozen water content function
by clicking on the "…" button.
In this popup window, we will add a new function
and choose a spline datapoint function again.
We will choose to estimate the function and simply choose the soil material type from the drop down menu.
This will automatically generate the unfrozen water content function
based simply on the soil type.
This has completed the full thermal model requirements
as the constant volumetric specific heat capacities
and water content have been carried over from the simplified thermal model.
The last thermal model that we will review in this tutorial is the coupled convective model.
As you can see here, all constant values disappear from the thermal properties available and only three functions are available.
The unfrozen water content function will still remain as one of the required functions, while the other two functions must yet be defined.
The coupled convective thermal model requires that the thermal conductivity
and volumetric specific heat capacity functions are dependent on volumetric water content and the
unfrozen water content remains dependent on temperature.
This thermal model must be coupled with SEEP/W to define the volumetric water content function,
as the soil water content is allowed to change during the simulation.
This model is also required if the heat transfer process is required in the AIR/W analysis.
We will go back into the KeyIn Materials window and click on the "…" button beside the thermal conductivity function.
Here, we added in our new function and chose the spline datapoint function option from the drop down menu.
This time, when we hit the estimate button, the required inputs for the estimation algorithm are simply the material mineral thermal conductivity,
which we will assume is 1.2 joules per second per meter per degree Celsius,
and our volumetric water content function that has already been defined.
If the volumetric water content function has not been created,
or needs to be visualized, the "…" button can be used to see the function.
We can see our current saturated water content is set to 0.5.
Now the thermal connectivity function for water content ranging from 0 to 1 will be created,
but only the data on the function from 0 to 0.5
will be used based on the volumetric water content function.
Next we will choose the "…" button for a volumetric specific heat capacity function and choose the
function that was created previously and click on the estimate button.
Here we can see that we require a mass specific heat which is the specific heat capacity of the mineral soil,
which we will assume is 0.71 joules per gram per degree Celsius.
We will then choose our volumetric water content function from the drop down menu and click OK.
This will cause the estimation algorithm to create a function that defines the volumetric specific heat capacity
for water contents from 0 to 1.
Again, only water contents from 0 to 0.5 will be used in this analysis
based on the saturated water content of the volumetric water content function.
The unfrozen water content function will remain the same as defined in the full thermal model.
To summarize this tutorial, the three main thermal model types in TEMP/W have been described.
The first type was a simplified thermal model, which assumes that phase change occurs at a specific temperature,
the phase change temperature, instead of a range of temperatures.
Latent energy storage changes are calculated assuming that all water in the pore space freezes or thaws when the phase change temperature is
crossed. The thermal conductivity and volumetric specific heat capacity are uniquely defined for the frozen and
unfrozen states and the volumetric water content is assumed constant.
In contrast, the full thermal model acknowledges that phase change occurs over a range of temperatures.
Consequently,
the model requires a definition of the normalized unfrozen volumetric water content function.
This function is used to calculate latent energy storage changes based on the change in unfrozen water content
that occurs over a range of phase change temperatures.
The thermal conductivity is allowed to vary continuously with temperature
and a definition of the unfrozen and frozen volumetric heat capacity is required.
As with a simplified thermal model, the volumetric water content is assumed constant during the simulation.
The coupled convective thermal model must be used when thermal properties are expected to change with changing volumetric water content.
In this third model type, the coupling to SEEP/W is required for the definition of the volumetric water content function.
The unfrozen water content function is still used in this third model type
and is dependent on temperature.
We have now reached the end of this tutorial.
Note that not all of the powerful features of version 8 of TEMP/W have been used or discussed here.
Further information on each command can be found in the online help, supporting documentation, as well as in other tutorial videos.
Thank you for watching.