ASTM D2717 Standard Test Method for Thermal Conductivity of Liquids
6. Apparatus
6.1 Thermal Conductivity Cell, consists essentially of a thin, straight platinum filament sealed axially in a borosilicate glass tube. The filament is held taut by a platinum spring. Two heavy gage platinum studs support the filament at either end and permit the filament itself to serve as the element and a four-lead platinum resistance thermometer. Details and cell construction are shown in Fig. 1.
6.1.1 A tube of 5.00 +/- 0.01 mm inside diameter shall be used for liquids of low viscosity as these may create thermal convection problems in the 10.47-mm tube.
6.2 Temperature Conditioning Bath, capable of maintaining temperature in the vicinity of the thermal conductivity cell constant and uniform to within +/- 0.001°C at the test temperature.
6.3 Resistance Measuring Device, capable of measuring up to 50 Ω with a sensitivity of at least 10(-4) Ω. A Mueller bridge assembly with commutator for 4-lead resistance thermometer service or digital multimeter with equivalent sensitivity and a minimum of six digit resistance resolution with 4-lead measurement capability are acceptable.
6.4 Potential Measuring Device, capable of measuring up to 1 V with a precision of 10(-6) V or a potentiometer assembly with sensitivity of at least 1 µV or a digital multimeter with equivalent sensitivity, range, and a minimum of six digit resolution is acceptable.
6.5 Resistor, 1-Ω, precision type, with accuracy of +/- 0.0005 % and stability of +/- 0.001 % per year.
6.6 Platinum Resistance Thermometer 4-lead long stem with quartz sheath.
6.7 Power Supply, 24-V dc.
NOTE 1 - Two 12-V automobile batteries in series have proved satisfactory as a power supply. They should be relatively new and fully charged.
6.8 Power Supply, constant-voltage, for potentiometer.
6.9 Standard Cell, unsaturated cadmium type, for potentiometer.
6.10 Switches, low thermal emf, knife or rotary.
6.11 Silicone Oil, dimethyl, viscosity at 25°C of 350 to 500 mm2/s (500 cSt).
