Method and apparatus for measuring thermal conductivity of small, highly insulating specimens

A thermal conductivity measurement process, utilizing:

• a heated disc and a cooled disc;
• an insulating ring;
• said ring includes an inner diameter and an outer diameter;
• said ring resides between and engages said heated disc and said cooled disc;
• a heat source;
• a fluid source;
• said heated disc includes an aperture therein in communication with said heat source said cooled disc includes a passageway therethrough in communication with said fluid source;
• a first insulating disc and a second insulating disc;
• said first insulating disc includes a first inner surface and a second outer surface;
• said second insulating disc includes a first inner surface and a second outer surface;
• said first inner surface of said first insulating disc affixed to said heated disc and said first inner surface of said second insulating disc affixed to said cooled disc;
• said heated disc, said cooled disc and said inner diameter of said ring forming a specimen test volume;
• a specimen of unknown thermal conductivity residing in said specimen test volume;
• a clamp;
• and, said clamp operating between said second outer surface of said first insulating disc and said second outer surface of said second insulating disc securing said heated disc, said cooled disc and said insulating ring together;
• an aluminum housing cylinder;
• first and second support rods;
• said first and second support rods interengage said first and second insulating discs;
• said aluminum housing cylinder includes first and second end portions;
• said first and second support rods interengage said first and second end portions of said aluminum housing cylinder suspending said first and second insulating discs, said heated disc, said cooled disc, and said insulating ring within said aluminum housing cylinder;
• a cooling coil wrapped around said aluminum housing cylinder;
• a cooled plate and an insulating box;
• said aluminum housing cylinder with cooling coils wrapped therearound engaging said cooled plate;
• said insulating box surrounding said aluminum housing cylinder;
• comprising, the steps of:
• utilizing a specimen in the sample volume of unknown thermal conductivity but in the range of 0.5 to 1.5 times that of air;
• supplying heat, Qtotal, to said heated disc, measuring the temperature of said heated disc, and adjusting said supply of heat to attain a desired heated disc temperature;
• supplying fluid to said cooled disc, measuring the temperature of said cooled disc, and adjusting said supply of fluid to attain a desired cooled disc temperature;
• supplying fluid to said cooling coil wrapped around said aluminum housing cylinder, measuring the temperature of said aluminum housing cylinder, and adjusting said supply of fluid to attain a desired aluminum housing cylinder temperature;
• observing said temperatures of said heated disc, said cooled disc and said aluminum cylinder for a period of time to achieve steady-state;
• repeating said steps of supplying heat to said heated disc, measuring the temperature of said heated disc, and adjusting said supply of heat to attain a desired heated disc temperature;
• supplying fluid to said cooled disc, measuring the temperature of said cooled disc, and adjusting said supply of fluid to attain a desired cooled disc temperature;
• and, supplying fluid to said cooling coil wrapped around said aluminum housing cylinder, measuring the temperature of said aluminum housing cylinder, and adjusting said supply of fluid to attain a desired aluminum housing cylinder temperature;
• observing said temperatures of said heated disc, said cooled disc and said aluminum cylinder for a period of time to achieve steady-state, as necessary to achieve the desired temperatures at steady state;
• measuring said heat supplied, Qtotal (W), to said heated disc at steady state when said temperatures of said heated disc, said cooled disc and said wall temperatures have been attained;
• determining Qlost (W);
• subtracting Qlost (W) from Qtotal (W) to determine Q1D, one dimensional heat transfer (W);
• and,
• determining thermal conductivity, ksample, from the equation
• Q
• 1
• ⁢
• D
• =
• (
• k
• sample
• l
• )
• ⁢
• A
• ⁢
• ⁢
• Δ
• ⁢
• ⁢
• T
• ,
• where A is the area of the sample volume and ΔT=Th−Tc.

A thermal conductivity measurement process for determining heat lost for a subsequent calibration, utilizing:

• a heated disc and a cooled disc;
• an insulating ring;
• said ring includes an inner diameter and an outer diameter;
• said ring resides between and engages said heated disc and said cooled disc;
• a heat source;
• a fluid source;
• said heated disc includes an aperture therein in communication with said heat source said cooled disc includes a passageway therethrough in communication with said fluid source;
• a first insulating disc and a second insulating disc;
• said first insulating disc includes a first inner surface and a second outer surface;
• said second insulating disc includes a first inner surface and a second outer surface;
• said first inner surface of said first insulating disc affixed to said heated disc and said first inner surface of said second insulating disc affixed to said cooled disc;
• said heated disc, said cooled disc and said inner diameter of said ring forming a specimen test volume;
• an air specimen residing in said specimen test volume, said first insulating disc and said second insulating disc securing said heated disc, said cooled disc and said insulating ring together;
• an aluminum housing cylinder;
• said first and second insulating discs, said heated disc, said cooled disc, and said insulating ring suspended within said aluminum housing cylinder;
• a cooling coil wrapped around said aluminum housing cylinder;
• a cooled plate and an insulating box;
• said aluminum housing cylinder with cooling coils wrapped therearound engaging said cooled plate;
• said insulating box surrounding said aluminum housing cylinder;
• comprising the steps of:
• utilizing an air specimen in the sample volume;
• supplying heat, Qtotal, to said heated disc, measuring the temperature Th of said heated disc, and adjusting said supply of heat to attain a desired heated disc temperature within a range of acceptable values of Th;
• supplying fluid to said cooled disc, measuring the temperature Tc of said cooled disc, and adjusting said supply of fluid to attain a desired cooled disc temperature within a range of acceptable values of Tc;
• supplying fluid to said cooling coil wrapped around said aluminum housing cylinder, measuring the temperature Tw of said aluminum housing cylinder, and adjusting said supply of fluid to attain a desired aluminum housing cylinder temperature within a range of acceptable values of Tw;
• observing said temperatures of said heated disc, said cooled disc and said aluminum cylinder for a period of time to achieve steady-state;
• repeating said steps of supplying heat to said heated disc, measuring the temperature of said heated disc, and adjusting said supply of heat to attain a desired heated disc temperature within a range of acceptable values;
• supplying fluid to said cooled disc, measuring the temperature of said cooled disc, and adjusting said supply of fluid to attain a desired cooled disc temperature with a range of acceptable values;
• and, supplying fluid to said cooling coil wrapped around said aluminum housing cylinder, measuring the temperature of said aluminum housing cylinder and adjusting said supply of fluid to attain a desired aluminum housing cylinder temperature within a range of acceptable values;
• observing said temperatures of said heated disc, said cooled disc and said aluminum cylinder for a period of time to achieve steady-state, as necessary to achieve the desired temperatures at steady state;
• measuring and recording said heat supplied, Qtotal (W), to said heated disc at steady state when said temperatures of said heated disc, said cooled disc and said wall temperatures have been attained;
• measuring and recording said temperatures of said heated disc Th, said cooled disc Tc and said wall Tw within said range of acceptable values;
• repeating the steps above for different values of Th, Tc and Tw within said respective ranges of acceptable values;
• and,
• determining Qlost (W) as an equation based on regression analysis of test data for values of Th, heated disc temperature (° C.), Tc, cooled disc temperature (° C.), Tw, wall temperature of aluminum housing (° C.) and Qtotal for use in a subsequent calibration.