Thermal Conductivity of Polymethyl Methacrylate (PMMA) and Borosilicate Crown Glass BK7

Abstract

The thermal conductivity of polymethyl methacrylate (PMMA) and borosilicate crown glass BK7 has been studied. The transient hot-wire technique has been employed, and measurements cover a temperature range from room temperature up to 350 K for PMMA and up to 500 K for BK7. The technique is applied here in a novel way that minimizes all remaining thermalcontact resistances. This allows the apparatus to operate in an absolute way and with very low uncertainty. The method makes use of a soft silicone paste material between the hot wires and the solid under test. Measurements of the transient temperature rise of the wires in response to an electrical heating step over a period of 20 µs up to 5 s allow an absolute determination of the thermal conductivity of the solid, as well as of the silicone paste. The method is based on a full theoretical model with equations solved by a two-dimensional finite-element method applied to the exact geometry. At the 95% confidence level, the standard deviations of the thermal conductivity measurements are 0.09% for PMMA and 0.16% for BK7, whereas the standard uncertainty of the technique is less than 1.5%.

New Measurements of the Thermal Conductivity of PMMA, BK7, and Pyrex 7740 up to 450K

“…Also, measurements presented only in graphical form have not been included. In all three cases, our previous measurements [4,5] performed with an uncertainty of 1.5 % agree very well with the present measurements performed with [12] the lower uncertainty of 1 %. Only at one temperature in BK7, the measurements are just over the mutual uncertainties of the two instruments.…”

“…where the coefficients a i and the values of λ (298.15 K) are shown in [5], and Pyrex 774 [4], as well as measurements of other investigators, are also shown. We have chosen not to present here the values of investigators who report only one measurement and that at "room temperature" quoting no exact reference temperature, and no uncertainty in their measurements.…”

“…3Thermal-conductivity measurements of PMMA as a function of temperature, and their percentage deviations from the values calculated by Eq. 1: •, present work; , Assael et al[5]; _ , Tye and Salmon[7];…”

“…1: •, present work; Assael et al[5]; , Kubicar et al[15];, double-plate data; , laser-flash data; Ebert[16] …”

Conductive cooling in white organic light emitting diode for enhanced efficiency and life time

“…This value has ranged from 0.02 to 0.1 mm 2 /s as obtained from different methods for other organic materials. [21][22][23] In these reports, it has been observed by Lim et al, 21 Assael et al, 22 and Cahill 23 that the variation observed in these measurements are the limitation of measurement techniques. Therefore, the variation in diffusivity value obtained in all four devices, in our case, may be due to the limitation of the measurement technique.…”