Thermal Conductivity, Thermal Resistivity, Thermal Diffusivity, Soil Moisture, and Electrical Conductivity
1. Thermal Conductivity (k)
- Definition: A measure of how efficiently heat passes through soil (Units: W/m·K).
- Significance: Important for evaluating heat transfer in geotechnical projects, underground pipelines, and energy systems.
- Measurement: Performed using the transient hot-wire method – a heated needle is inserted into the soil, and the thermal response is measured.
2. Thermal Resistivity (ρ = 1/k)
- Definition: A measure of the soil's resistance to heat transfer (Units: °C·cm/W).
- Use: Critical in the design of underground systems – high resistivity means poorer heat dissipation.
3. Thermal Diffusivity (α)
- Definition: The rate at which heat spreads through the soil (Units: m²/s), calculated by:
α = k / (Volumetric Heat Capacity) - Use: For analyzing the soil's transient thermal response, such as daily temperature fluctuations.
Soil Moisture and Electrical Conductivity
4. Volumetric Water Content (VWC)
- Definition: The ratio of water volume to total soil volume.
- Instruments: TEROS sensors by METER use capacitive technology to measure with ±3% accuracy.
5. Electrical Conductivity (EC)
- Definition: A measure of ion concentration in soil – indicates salinity and fertilizer levels.
- Instruments: The TEROS 12 sensor measures both moisture and EC directly in the field.
METER Group Instruments
TEMPOS – Thermal Properties Analyzer
- A portable needle probe device for measuring thermal conductivity, resistivity, and diffusivity (including specific heat).
- Accurate and fast (approx. 1 minute), suitable for both field and lab use, complies with ASTM D5334 and IEEE 442 standards.
- Operates in tough conditions: wet, frozen, or liquid soils.
VARIOS – Thermal Drying System
- An advanced laboratory instrument for measuring changes in thermal conductivity during soil drying.
- Produces accurate thermal curves relative to soil water content.
- Fully automated, ideal for advanced lab analysis.
TEROS Sensor Series (Field Use)
- Rugged sensors for continuous field monitoring.
- TEROS 10/11 – Measure moisture and temperature.
- TEROS 12 – Measures moisture, temperature, and electrical conductivity.