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International Heat Transfer Conference 16

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

CONVECTIVE DROPWISE CONDENSATION FROM HUMID AIR

Ferdinand Eimann
Institute of Thermal Engineering, TU Bergakademie Freiberg, Gustav-Zeuner-Str. 7, 09599 Freiberg, Germany

Shaofei Zheng
Institute of Thermal Engineering, TU Bergakademie Freiberg, Gustav-Zeuner-Str. 7, 09599 Freiberg,Germany

Christian Philipp
Institute of Thermal Engineering, TU Bergakademie Freiberg, Gustav-Zeuner-Str. 7, 09599 Freiberg, Germany

Ulrich Gross
Institute of Thermal Engineering, TU Bergakademie Freiberg, Gustav-Zeuner-Str. 7, 09599 Freiberg, Germany

DOI: 10.1615/IHTC16.cod.021456
pages 2315-2322


MOTS CLÉS: Condensation, Measurement and instrumentation, Heat Transfer Enhancement

Résumé

A new facility feasible for the experimental determination of dropwise condensation heat transfer coefficients at a vertical polymer surface (9×6 mm, L×H) will be described in detail. The droplets condensate out of humid air, which flows through a rectangular channel (12×32 mm, B×H) and passes the sub-cooled sensor surface. The sensor is flush mounted into the vertical channel wall beyond a hydrodynamic entry length of 550 mm. Variable experimental parameters are: temperature, water content and flow speed of the humid air, as well as the cooling temperature of the sensor. The procedure is based on the synchronous evaluation of temperatures, determined by means of thermocouples and infra red thermography. A parameter variation has been carried out, covering Reynolds numbers between 6850 and 22 130, relative humidities between 44 and 93% and air temperatures between 30 and 46 °C for a broad range of cooling temperatures. Since the latter influences the temperatures of the droplet surfaces, it determines, together with the water content of the bulk, the driving force for mass transfer. The droplet heat transfer coefficient, hd, considers both, heat conduction through the droplets and the augmentation of heat transfer due to inner convection. hd was found to be influenced by the Reynolds number of the bulk flow and the driving force for mass transfer. The experimental data has been used to create a correlation. This is crucial for the experimental determination of dropwise condensation total heat transfer, which will be done in future.

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