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D2717-95 – Standard Test Method Technical Guide
📐 Scope and Apparatus Specifications
ASTM D2717 −95 (Reapproved 2009), under the jurisdiction of Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants, provides a standardized test method for determining the thermal conductivity of nonmetallic liquids. The method is specifically designed for liquids that: (1) are chemically compatible with borosilicate glass and platinum; (2) are moderately transparent or absorbent to infrared radiation; and (3) have a vapor pressure less than 200 torr at the test temperature.
⚠️ High Pressure Safety Precautions: For materials with vapor pressures exceeding 200 torr, the standard permits testing up to 345 kPa (50 psia) absolute if the thermal conductivity cell is adequately pressurized to repress volatilization. The usual safety precautions for pressure vessels must be strictly followed under these circumstances.
⚙️ Test Procedure and Measurement Principles
The core apparatus consists of a straight, four-lead, platinum resistance thermometer element located concentrically in a long, small-diameter, precision-bore borosilicate glass tube. Thermal conductivity (KL) is determined by measuring the temperature gradient (ΔT = Tf − Tb) produced across the liquid sample by a known amount of energy introduced via electrical heating (I²R) of the platinum element. The energy units are precisely defined: 1 Cal (International Table calorie) = 4.1868 absolute J, and 1 Btu = 1055.07 absolute J. A rounded value of 4.19 J/cal is used for working purposes.
| 🟦 Symbol | 📏 Definition | 📐 Unit |
|---|---|---|
| Tf | Filament temperature | °C |
| Tb | Bath thermostat temperature | °C |
| ΔT | Tf − Tb (Temperature Gradient) | °C |
| rf | Filament radius | cm |
| ri | Internal radius of the glass tube | cm |
| ro | External radius of the glass tube | cm |
| L | Effective length of the tube | cm |
| R | Resistance of the filament | Ω |
| I | Electric current through the filament | A |
| KL | Thermal conductivity of the liquid | cal/s·cm·°C |
| KG | Thermal conductivity of the glass tube | cal/s·cm·°C |
💡 Calculation Constants: The derived formula for KL uses the geometric constants A = [ln(ri/rf)]/2π L (cm⁻¹) for the liquid layer and B = [ln(ro/ri)]/2π L KG (s·°C/cal) for the borosilicate glass tube resistance, allowing for precise isolation of the liquid’s thermal conductivity.
📊 Key Measured Properties and Data Interpretation
The primary property measured is the thermal conductivity (