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This paper provides simple analytical correlations for selected thermodynamic and fluid transport properties for the mixture dry air and water vapor. These correlations are derived from theory as well as from numerical fitting procedures and give expressions for density , viscosity , thermal conductivity k, specific heat c p , and Prandtl number Pr at a working pressure of pϭ1 bar and for a temperature range from 100°C to 200°C. The main purpose is to present a comparatively simple set of equations, as the correlations do not reflect in every case the underlying physical background. Since experimental data are scarce for the properties under investigation, it was in some cases necessary to extrapolate the available correlations to temperatures or water vapor contents where no experimental data could be found. The derived equations are compared with the pure component values for dry air and water vapor and, as far as possible, also for air-water vapor mixtures.

When applying hot-wire anemometry to velocity measurements in air, it is standard practice to neglect the effect of humidity. In this paper the influence of the thermodynamic and transport properties of humid air on hot-wire measurements is examined on the basis of the correlations for Nusselt number proposed previously by other researchers. Experimental results at controlled levels of relative humidity between 30% and 90% at 30 • C, 50 • C and 70 • C are reproduced satisfactorily by the theoretical approaches of two of these equations. A corrective term is defined to expand formulae designed for dry air to work in a humid environment. The error in velocity by omitting the influence of humidity is estimated in terms of temperature and relative humidity.

The development of a laser diode absorption spectrometer that uses a strong water vapor absorption at 1393 nm is reported. Three spectroscopic techniques were compared in approximately 0.4 m of laboratory air, namely, frequency modulation, wavelength modulation, and two-tone frequency modulation spectroscopy. The first two techniques use a single-frequency modulation at 9.2 GHz and 1 kHz, respectively, generated either by a phase modulator operating at 9.2 GHz or injection current modulation at 1 kHz. The two-tone method requires modulation at two frequencies, in this case 9.19 and 9.21 GHz. It is shown that the two-tone method should provide the highest sensitivity for a trace moisture detection system.

Laser absorption spectroscopy offers the potential for fast and precise trace moisture detection in gases at atmospheric pressure with a small cross sensitivity towards other molecules. We report on the development and calibration of a fibre-coupled tunable diode laser absorption spectrometer operating in the 1 - 100 ppm humidity range. The spectrometer was tested at three European humidity standards laboratories. The performance of the spectrometer was characterized by monitoring constant water vapour concentrations over several hours, yielding a good long-term stability, reproducibility and accuracy. The standard deviations of the measured water vapour concentrations for values above 5 ppm were below ±2%. Comparisons of the instrument with chilled mirror hygrometers demonstrated its fast response time. The dependences of the signal upon the flow rate and temperature are discussed.

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The generation of well defined trace humidity concentrations is of interest for several applications and especially for sensor calibration purposes. While in national standards laboratories accuracy and stability are the most important criteria and slow generation processes are acceptable, faster generators are needed in industry. After reviewing several concepts for trace humidity generation, this paper presents a fast trace humidity generator based upon a two-stage dilution and mixing principle. The developed generator establishes a known concentration of water vapour in air or any other carrier gas at ambient pressures and a constant flow rate in the range of 1 l min-1. The generated humidity volume fractions cover a range from 100 ppb to 1000 ppm, equivalent to a frost point temperature range from about -90 to -20 °C. The layout and construction of the saturator and the drying unit conditioning the two gas streams to be mixed are also described. A detailed analysis of the uncertainty range of the generated humidity concentrations yields optimized operational parameter settings for a minimized uncertainty in the selected humidity concentration. The generator has been characterized by means of a recently developed laser spectrometer for trace humidity detection.

A. Reisener, M. Still und H. VenzkeEs wird cine Schadgashewitterungskammcr vorgestellt, die fur Korrosionsuntersuchungen iln BronLeund Kupferprobcn im Labormalktab am Bayerischcn Landesamt lur Denkmalpflege installiert wurde. In dieser Kammcr wird der EinfluB cines S02/N02 Schadgasgemisches bei Bctauung der Proben untersucht. Dazu wird innerhalb der Karnmcr mit Hilfe eines reproduzierhar einstellbaren Wechselklimas eine kunstlichc Bewillerung des Probenmaterials erzeugt Die Einstellung dcs Schadgasgehaltes sowie der Luftfeuchtigkeil im zugefiihrten Testgas crfolgt iiher eine Gasmischapparatur. Dic pcriodischen Bewitterungsund Trockenzyklen werden uher Ahkuhlung bzw. Auiheizung der Proben gesteuert. In der vorlicgenden Arbeit wird die Konzcption und die Verwirklichung der Anlage beschriehen. Dabei wird auf die Auswahl und Konstruktion der Einzelkornponenten sowie auf die eigentlichc Klimagenerierung eingegangen. Untcrsuchungen zur Homogenitat des Kammerklimas sowie zur Temperaturverteilung uber die einzelnen Proben schliekn die lnbctriebnahme der Bewitterungskammer ab. This paper describes an apparatus for the investigation of corrosion o f coppcr and bronze samples on a laboratory scale at the Bayerisches Landcsanit Tur Denkmalpflege. Munich. The chamber allows the influence of SO2 and NO? contaminated test gas on the samples to be studied in combination with dew formation on the sample surface. By means ok' cooling and heating nf the samples and the use of a gas mixing unit. a defincd amount of dew and contamination can be reproducibly applied to the samples. The design and realization o f the apparatus, including the component selection and details of construction t o satisfy experimental demands, are discussed. Results of commissioning tests arc shown, quantifying the homogenity of the chamber climate and the temperature distribution across the samples.