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Posts tagged ‘thermal’

Top Five Blog Posts in 2017

In case you missed them the first time around, here are the most popular Environmental Biophysics.org blog posts in 2017.

Soil Moisture Sensors: Why TDR vs. Capacitance May Be Missing the Point

Researcher holding a soil sensor in front of a field

Soil moisture sensor

Time Domain Reflectometry (TDR) vs. capacitance is a common question for scientists who want to measure volumetric water content (VWC) of soil, but is it the right question?  Dr. Colin S. Campbell, soil scientist, explains some of the history and technology behind TDR vs. capacitance and the most important questions scientists need to ask before investing in a sensor system. Read more

Get More From your NDVI Sensor

Looking up at tree branches from the ground

Modern technology has made it possible to sample Normalized Difference Vegetation Index (NDVI) across a range of scales both in space and in time, from satellites sampling the entire earth’s surface to handheld small sensors that measure individual plants or even leaves.  Read more

Improved Methods Save Money in Future Borehole Thermal Energy Storage Design

Image of a city with many buildings

Globally, the gap between the energy production and consumption is growing wider. To promote sustainability, University of California San Diego PhD candidate and ASCE GI Sustainability in Geotechnical Engineering committee member, Tugce Baser, Dr. John McCartney, Associate Professor, and their research team, Dr. Ning Lu, Professor at Colorado School of Mines and Dr. Yi Dong, Postdoctoral Researcher at Colorado School of Mines, are working on improving methods for borehole thermal energy storage (BTES), a system which stores solar heat in the soil during the summer months for reuse in homes during the winter. Read more

New Weather Station Technology in Africa

Happy students gathered around an ATMOS 41 weather station

Weather data, used for flight safety, disaster relief, crop and property insurance, and emergency services, contributes over $30 billion in direct value to U.S. consumers annually. Since the 1990’s in Africa, however, there’s been a consistent decline in the availability of weather observations. Read more

Electrical Conductivity of Soil as a Predictor of Plant Response

Corn stalks looking up at the sky from the ground

Plants require nutrients to grow, and if we fail to supply the proper nutrients in the proper concentrations, plant function is affected. Fertilizer in too high concentration can also affect plant function, and sometimes is fatal.  Read more

And our three most popular blogs of all time:

Estimating Relative Humidity in Soil: How to Stop Doing it Wrong

Image of a tree in the desert

Estimating the relative humidity in soil?  Most people do it wrong…every time.  Dr. Gaylon S. Campbell shares a lesson on how to correctly estimate soil relative humidity from his new book, Soil Physics with Python, which he recently co-authored with Dr. Marco Bittelli.  Read more

How to Measure Water Potential

Plants sprouting out of the sand

In the conclusion of our three-part water potential series, we discuss how to measure water potential—different methods, their strengths, and their limitations. Read more

Do the Standards for Field Capacity and Permanent Wilting Point Need to be Reexamined?

Image of rolling fields in front of mountains

We were inspired by this Freakonomics podcast, which highlights the bookThis Idea Must Die: Scientific Problems that are Blocking Progress, to come up with our own answers to the question:  Which scientific ideas are ready for retirement?  We asked scientist, Dr. Gaylon S. Campbell, which scientific idea he thinks impedes progress.  Here’s what he had to say about the standards for field capacity and permanent wilting point. Read more

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See weather sensor performance data for the ATMOS 41 weather station.

Explore which weather station is right for you.

Download the “Researcher’s complete guide to soil moisture”—>

Scientists Measure Thermal Properties in Famous Japanese Tomb

Named for the tall pine tree that sits at the top of the tumulus earth mound, Takamatsuzuka Tomb is located in the Asuka village, just south of Nara, Japan. Located within the tomb are some of the most beautiful and famous Japanese wall paintings. Discovered in 1972, the paintings are believed to have been made at the end of the seventh and beginning of the eighth centuries.

Mural painted in the inner tomb

Mural in the inner tomb.

Though it is unknown who is actually buried in the tomb, the murals are worthy of a nobleman. They depict a small-scale universe, including star constellations, the sun, the moon, and guardian gods, for the deceased.

In 2001 this national treasure became threatened by mold growing on the interior lime plaster walls. High humidity and high water content of the lime plaster walls are believed to be the main contributor to mold growth. As a short-term solution, a cooling system was put in the structure to prevent further growth. To optimize efficiency, scientists used the transient line heat source method to determine the thermal properties of the tomb and surrounding soil.

Cooling system installed at Takamatsuzuka Tomb to prevent fungal growth

Cooling system installed at Takamatsuzuka Tomb
to prevent fungal growth.

As a long-term solution, the Agency of Cultural Affairs has decided to move the stone interior of the tomb to another location where the environment can be more easily controlled.

What Are Thermal Properties?

Thermal properties tell scientists important things about soil or other porous materials.  Thermal conductivity is the ability of a material to transfer heat. Thermal resistivity, the inverse of conductivity, illustrates how a well a material will resist the transfer of heat. Volumetric heat capacity is the heat required to raise the temperature of unit volume by 1℃, and thermal diffusivity is a measure of how quickly heat will move through a substance.

Laser focused on the human eye

Thermal property measurements help scientists understand the effects of lasers, cauterization, or radiation on surrounding tissue.

Who Should Measure Thermal Properties, and Why?

Thermal property measurements are needed in varying industries and research fields. One example is underground power cable design. Electricity flowing in a conductor generates heat. Any resistance to heat flow between the cable and the ambient environment causes the cable temperature to rise. This can harm the cable and may even cause power outages in large sections of major cities. When cables are buried, soil forms part of the thermal resistance, and thus soil thermal properties become an important part of cable design.

Other popular applications for thermal property measurements include thermal conductivity of concrete, thermal conductivity of nanofluids, thermal resistivity of insulating material, and thermal properties of food. Unique applications range from measuring human tissue to adobe houses. 

The Transient Method is the Only Way to Measure Moist, Porous Materials

The standard technique for measuring thermal properties is called the steady-state technique (guarded hot plate method). The steady state technique requires a needle to be heated until it comes to a steady state, at which time it measures the temperature gradient and determines the thermal properties of the measured material.

The transient line heat source method differs in that heat is only applied to the needle for a short amount of time, and temperature is measured as the material heats and cools.  The steady state technique is a good fundamental method because it uses the simplest equation.  However, it takes a full day to make a measurement because of the wait for steady state.  In addition, when measuring a porous material that contains moisture, heat flow will make moisture move away from the heated area and condense on the cold area.  Thus, the thermal properties of the material will change.  

This means there’s no way to measure the properties of moist, porous materials with the steady state method. The transient line heat source method, however, is able to measure the thermal properties of moist, porous materials, and it can even measure thermal conductivity and thermal resistivity in fluids.

Learn more about measuring the thermal properties of soils or other materials.

Download the “Researcher’s complete guide to soil moisture”—>

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Improved Methods Save Money in Future Borehole Thermal Energy Storage Design

Globally, the gap between the energy production and consumption is growing wider. To promote sustainability, University of California San Diego PhD candidate and ASCE GI Sustainability in Geotechnical Engineering committee member, Tugce Baser, Dr. John McCartney, Associate Professor, and their research team, Dr. Ning Lu, Professor at Colorado School of Mines and Dr. Yi Dong, Postdoctoral Researcher at Colorado School of Mines, are working on improving methods for borehole thermal energy storage (BTES), a system which stores solar heat in the soil during the summer months for reuse in homes during the winter. Baser says, “We are running out of finite energy resources. We need to come up with new strategies to use free and renewable energy resources such as solar energy for a sustainable future.”

Borehole thermal energy storage

Baser’s BTES design.

How it works

BTES systems are an approach to provide efficient renewable resource-based thermal energy to heat buildings. They are configured to store thermal energy collected from solar thermal panels during the summer and discharge the heat to buildings during the winter. They function by circulating a fluid within a closed-loop pipe network installed in vertical boreholes to inject heat collected from solar thermal panels. During winter, cold fluid is circulated through the heat exchangers to recover the heat from the subsurface and distribute it to the buildings. Baser explains, “The subsurface provides an excellent medium to store this heat due to the relatively lower thermal conductivity and lower specific heat capacity especially when the soil layer is in the vadose zone. Lower thermal properties allow us to concentrate the heat in a specific array and the heat losses to the environment are potentially low. These systems typically include an insulation layer and a hydraulic barrier near the ground surface to reduce heat and vapor losses to the atmosphere.”

Image depicts BTES construction

BTES construction.

Why do we need improved methods?

Baser and her team are trying to improve the understanding of heat storage mechanisms and evaluate changes in the rate of heat transfer and heat storage in the vadose zone where the soil is unsaturated. The goal of the project is improve conventional methods by generating models to fit different soil types and situations.  She says, “The European community introduced us to the borehole thermal energy storage systems to provide heat specifically for domestic use, but there is still a chance for us to design them more efficiently by having a full understanding of the thermal response of these systems that is specific to the ground material and subsurface conditions. The primary objective of this research is to understand the mechanisms of coupled heat transfer and water flow in unsaturated soil profiles during the heat injection and subsequent heat extraction into these different arrays and different dimensions of borehole heat exchangers.”

Solar panels propped up outside of a ware house

Solar panels.

Baser and her team working on designing numerical models based on finite element method which improve some of the numerical models in the literature used to characterize the thermal response of the systems. The new models add new considerations, such as the heat pipe effect in different soil types. Baser explains, “Because thermal and hydraulic properties of soils are highly coupled and are specific to soils, the thermal response of a BTES system will be different when it is installed in different types of soils. For example, you see the heat pipe effect where there is evaporation and subsequent condensation in fine grained soils rather than coarse soils because in coarse grain soils the pore characteristics are different. The duration of the heat pipe effect (or convective cycle) is longer in fine grain soils. We conclude that considering coupled heat transfer and water flow in the thermal response of Borehole Thermal Energy Storage system is important.”

Image of a hole which is being used for an in-group heat exchanger

In-ground heat exchanger

Experiments in the field and in the lab help verify the new models

To fully understand heat transfer mechanisms and water flow in unsaturated soils, the research team installed two different SBTS systems at different scales, one in Golden, Colorado School of Mines campus, and the other at the UC San Diego research campus.  Baser says, “The subsurface characteristics of both sites are different, and this gives us the opportunity to investigate the impact of the different soil layers on the thermal response experimentally in a full scale. In addition, the scales of each Borehole Thermal Energy Storage system are different, and we also apply different heat injection rates. We have used these data to further validate our coupled heat transfer and water flow model so that we can use it for design purposes.”

Diagram of soil moisture sensor locations

Soil moisture sensor locations.

Baser started with laboratory heating experiments, in which soil in a large tank is heated by heat exchangers. She installed soil moisture sensors to measure volumetric water content and the temperature and then used the KD2 pro thermal property analyzer (recently updated to TEMPOS) to monitor thermal properties during heating experiments to characterize the coupled thermo-hydraulic relationships. For the field experiments the team uses soil moisture sensors equipped with temperature sensors and the KD2 pro to monitor subsurface temperature fluctuation because during the summertime the air temperature is higher, thus ambient air temperature fluctuation and penetration may become significant.

Baser also uses thermistor strings that include six thermistors at different depths and thermistor pipe plugs, voltage input modules, and flow meters.  She says, “Thermistor pipe plugs and flow meters are used in the manifold to monitor the inlet and outlet fluid temperatures and flow rates in each loop to calculate heat transfer rate into the ground. Flow meters were installed to control flow in each loop because you don’t want to over or underload the borehole loops. The amount of energy that you collect from the solar loop and the amount of energy that you inject into the ground can be used to define the efficiency of the system.” Baser says thermistor strings help monitor the ground temperature during the summer heat loading at different depths. They’re also used to monitor borehole wall temperature over time. The team installed one thermistor string 9 meters away from the heat storage array to see if far field is affected by the heat transfer within the array.

Image of a borehole with insulation to prevent heat loss to the environment

Insulation prevents heat loss to the environment.

The new models will save money in future Borehole Thermal Energy Storage design

Baser says building numerical models and solving them was very complicated and time consuming, but they’ve had good results. She explains, “We’ve recently proved, both experimentally and numerically, that considering coupled thermal and hydraulic relationships are very important for thermal response analysis. Thus, our recommendation is that it’s fine to use the analytical models and user-friendly numerical models that consider constant thermal properties in the design analyses for saturated soils. However, in unsaturated soils, there is a very high possibility that the contribution of heat transfer evaporation and condensation would be missing and the Borehole Thermal Energy Storage system would be oversized, costing a significant amount of money. When dealing with soils in the vadose zone, coupled thermo-hydraulic constitutive relationships in the modeling efforts need to be considered.”

You can learn more about Tugce Baser’s research here.

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our