3D Carbon-fiber reinforced carbon composites (3D C f /C) are widely used as thermostructural protections in various applications. Among them, thermal protection systems for atmospheric re-entry encounter one of the most aggressive environments, where 3D C f /C are exposed to strong ablation. Because flight tests are
A novel approach to analyze null-point calorimeter data in high enthalpy and high pressure plasma flows is described. Although null-point calorimetry is a well-known measurement technique, the measurements of recent campaigns showed unphysical effects. Usually, radial heat flux profiles, i.e., heat flux profiles perpendicular to the flow axis, are recorded. These profiles show asymmetries, although the generator's setup is symmetric. Within this paper, the reasons for this asymmetry are shown by a theoretical approach using finite element modeling. One major concern is that because of the short measurement times, the thermocouple inertia becomes crucial. In the present case, surface heat flux is therefore determined by solving the inverse heat conduction problem using a noninteger identified model as a direct model for the estimation process. The sensor calibration is performed using high-power laser radiation. With the new calibration data, the asymmetries vanish and it is discussed that the measured heat flux profiles can be reasonably interpreted with the present methodology according to turbulent freejet theory. Nomenclature c p = specific heat, J=kg K D = differentiation operator, m E = energy, J f = function T = temperature, K t = time, s V T = thermocouple signal, V x = distance, m , = model parameters, V = emissivity = thermal conductivity, W=m K = density, kg=m 3 = heat flux, W=m 2
3D carbon-fibre reinforced carbon composites (3D C f /C) are used as thermal protection systems for atmospheric re-entry, where they are exposed to strong ablation. Particularly, sublimation of the carbonaceous material plays an important role during the re entry. To study this, an arc image furnace under controlled Argon flow is used, with heat fluxes of 8 MW m −2 to 10 MW m −2 . The furnace and the sample thermal response have been numerically simulated prior to the experiments and match in-situ temperature measurements. Scanning electron microscopy and 3D profilometry with digital optical microscopy were used in order to characterise the epi-macro-structural and the epi-micro-structural roughness of the composite surface, evidencing a faster recession of the fibres as compared to the matrix. Carbon nanotextures have been assessed by using High-Resolution Transmission Electron Microscopy and Polarised Light Optical Microscopy, showing that the matrix is more organised than the fibre.
International audienceAn improved miniaturized heat flux sensor is presented aiming at measuring extreme heat fluxes of plasma wind tunnel flows. The sensor concept is based on an in-depth thermocouple measurement with a miniaturized design and an advanced calibration approach. Moreover, a better spatial estimation of the heat flux profile along the flow cross section is realized with this improved small sensor design. Based on the linearity assumption, the heat flux is determined using the impulse response of the sensor relating the heat flux to the temperature of the embedded thermocouple. The non-integer system identification (NISI) procedure is applied that allows a calculation of the impulse response from transient calibration measurements with a known heat flux of a laser source. The results show that the new sensor leads to radially highly resolved heat flux measurement for a flow with only a few centimetres in diameter, the so far not understood non-symmetric heat flux profiles do not occur with the new sensor design. It is shown that this former effect is not a physical effect of the flow, but a drawback of the classical sensor design
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.