Physikalisch-Technische Bundesanstalt

When determining thermal transport properties, natural convection can easily provoke considerable measurement errors in liquids and gases. An arrangement, for which a patent has been applied for, is designed to prevent exactly this. So far, during a run, it has been possible to prevent or reduce convection of the sample fluid only by microgravity (e. g., in a drop tower) with measurements being performed at low temperature differences, at small layer thicknesses or by a fast transient technique. These precautions, however, lead to correspondingly high signal-to-noise ratios – which, in turn, has a negative impact on the measurement uncertainty. The new sensor concept allows thermal conductivity to be determ ined practically without the influence of convection. The sample fluid is fed into a suitable porous material until saturation is reached. Then, solely the thermal conductivity of the gas- or liquid-filled porous material is determined by a transient or steady-state method. With the aid of a calibration curve, the thermal conductivity of the sample fluid is evaluated.