Intercomparison of Measurements of the Thermophysical Properties of Polymethyl Methacrylate

Abstract

Results of an intercomparison of measurements of thermal conductivity, thermal diffusivity, specific heat capacity, and density of polymethyl methacrylate (PMMA) in the temperature range between −70 • C and +80 • C are presented. The purpose of this comparison is to investigate the variability of the results among guarded hot-plate (GHP) and guarded heat-flow meter (GHF) techniques on the one hand and among GHP/GHF and other measuring instruments on the other. The primary objectives are to characterize the material properties mentioned and to quantify the effects of thermal contact resistances and temperature measurements. With regard to future use of PMMA as a reference material, reference data for the thermal conductivity are derived.

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

“…♦, Hulstrom et al [17]; , Powell et al [18]; , Milano et al [19]; , Matsumoto and Ono [20]; , Pillai and George [21]; , Log and Metallinov [22] It was argued that the most probable reason for this discrepancy was the improperly treated effect of contact resistance. In order to prove independently that the thermal contact resistance was adequately taken into account, in the same article, values obtained at PTB by two different methods (guarded hot plate, transient hot strip) were also reported [8]. The deviations of these values, shown in Fig.…”

“…Their density was found by weighing them and determining their volume, equal to 1,200 kg · m −3 at 293.15 K. Further properties of this specific material can be found in the literature [8]. The two samples of BK7 employed in this article were manufactured and supplied by Schott AG, and were also made available to our laboratory by PTB.…”

“…In 2004, Rudtsch and Hammerschmidt [8], also aiming to propose a thermal conductivity reference material candidate, coordinated in PTB an intercomparison project for PMMA involving 17 European laboratories. Unfortunately the thermal conductivity values produced even at 30 • C ranged from 0.16 W · m −1 · K −1 to 0.21 W · m −1 · K −1 .…”

“…PMMA was proposed by NPL as a possible candidate for a thermal-conductivity reference standard in 2003 [7]. However, a more recent intercomparison among 17 laboratories organized by Physikalisch-Technishe Bundesanstalt (PTB) [8], showed uncertainties of 8 % to 13 % in the thermal conductivity values, which far exceeded the laboratories' quoted uncertainties. Hence, the employment of PMMA as an acceptable thermalconductivity standard is still under consideration.…”

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

“…However, a more recent intercomparison between 17 laboratories, organized by Physikalisch-Technische Bundesanstalt (PTB) [7], showed uncertainties in the thermal conductivity values between 8 and 13%, which far exceeded the laboratories' quoted uncertainties. Hence, the employment of PMMA as an acceptable thermal conductivity standard is still under consideration.…”