Evaluation of three measurement techniques for water-vapor mass transfer in case of droplet condensation

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Abstract

Mass transfer in moist air flows with droplet condensation is governed by the mutual interaction of convective and latent heat transfer. To characterize the physical mechanisms of such flows, it is necessary to measure the condensation rate precisely. For this purpose, we applied three sophisticated measurement techniques to determine the mass transfer for droplet condensation on a cooled surface. The experimental set-up consists of a rectangular box with a mixed convective airflow. Droplet condensation occurs on a subcooled panel, which has a polymer surface with a droplet contact-angle of 80.07(28) degrees. Time series of the total water mass on the cooled surface, the mass transfer-rate, and total heat transfer are measured in a Reynolds number range from 300 to 900 and relative humidities between 29% and 83% (at 25°C air temperature). The considered measurement methods are: strain gauges for total water mass, self-calibrated capacitive humidity probes for mass difference between the inlet and outlet of the sample, and microscopy for the surface droplet-distribution. By means of these measurement techniques a total mass-transfer uncertainty lower than 0.01% of the maximum value is obtained with an uncertainty of the mass-transfer rate below 0.01 mg/s (1% of maximum value). At the conference we would like to present the evaluation and comparison of these measurement techniques, lead a discussion on their respective advantages and disadvantages and present results to verify the scaling of latent and convective heat transfer in mixed convective air flows with droplet condensation.

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• Evaluation of three measurement techniques for water-vapor mass transfer in case of droplet condensation. (deposited UNSPECIFIED)
  • Evaluation of three measurement techniques for water-vapor mass transfer in case of droplet condensation. (deposited 30 Mar 2023 13:38) [Currently Displayed]