I’m Gaylon Campbell, a senior research scientist here at METER Group. In this lesson, we’ll be talking about how to measure and understand thermal properties of materials. All of these measurements and modeling capabilities that we’ve just discussed—and more—are built into METER’s TEMPOS thermal properties analyzer, which connects to four separate probes. We’ve already talked about the 100 millimeter long by 2.4 millimeter diameter soil probe.
A shorter, more robust, 60 millimeter long by 3.9 millimeter diameter rock probe is available. You can use a 60 millimeter long by 1.3 millimeter diameter general purpose probe to measure thermal conductivity of viscous liquids, solids, or almost anything else.
The dual probe that we have also just discussed is also shown. The TEMPOS runs on batteries, so it can be used in the field or in the laboratory, and it provides accurate measurements of thermal properties within minutes. The TEMPOS collects the data, does the analysis, and reports the thermal properties for whatever probe you have connected. The menus take you through the measurement process.
The meter monitors conditions during the measurement to make sure that the measurement requirements are met. Now, as we previously mentioned, the thermal properties of soil or other porous materials depend on water content. The TEMPOS could be used with a bunch of different samples at different water contents to obtain a thermal dryout curve, which is the relationship between thermal conductivity and water content that I showed you earlier.
An easier way to obtain a thermal dryout curve is with our VARIOS, which consists of a balance for measuring the water loss from a sample, a needle that goes through the sample and cylinder for the soil sample, and a logger to measure and record the data and do the measurements and calculations.
To begin using the VARIOS, a sample of wet soil is loaded in the stainless steel cylinder. As water evaporates from the sample, the balance measures the water loss, and the sample’s water content is continuously computed from those measurements. The needle sensor measures the thermal conductivity. After the sample is dried, you have a complete and detailed thermal dryout curve for the sample.
Now, an important part of thermal properties measurements are the standards that provide guidance for the way the measurements are to be completed and reported. One of three standards is commonly followed for thermal properties measurements: the ASTM D 5334. This stadnard was recently revised, and it provides excellent guidance and information for the measurement and analysis methods.
The IEEE 442 standard was reissued in 2017 but not brought up to date at that time. It represents 60 year old technology and is therefore—in my opinion, at least&mdah;not very useful.
The third standard, from the Soil Science Society of America or SSSA, is also good but not as widely used as the others.
This table gives some comparisons to the specifications of the three standards, and S means not specified. Differences have to do with the time required for testing, the way the data are recorded, and the way they’re analyzed.
The ASTM and Soil Science Society of America methods will give results in a minute. The IEEE method requires 10 minutes. The ASTM and SSSA method specify electronic recording of the data. The IEEE says to record it by hand.
The ASTM and SSSA recommend regression analysis. The IEEE says to fit a line through two points. The ASTM also recognizes the need for a time offset, and it shows how to make use of that or how to do the calculation with that.
I hope this has been a useful overview of thermal properties measurements, that it’s given you an idea of what they are, how they’re used, what kinds of problems can be tackled with them, and how to make the measurements. There are a lot of additional resources on the METER website, the location shown here, or you can get in touch with us at metergroup.com. We’re experts on thermal properties, we can provide the help you need. Thank you much for being with us today.
