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International Heat Transfer Conference 16

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

RISING FILM EVAPORATION: FLUID DYNAMICS AND HEAT TRANSFER PERFORMANCE OF A PILOT PLANTS

Stefan Jahnke
Technische Universität Braunschweig, Institute for Thermal and Chemical Process Engineering Langer Kamp 7, 38106 Braunschweig

T. Rittmeier
Technische Universität Braunschweig, Institute for Thermal and Chemical Process Engineering Langer Kamp 7, 38106 Braunschweig

Stephan Scholl
Technische Universität Braunschweig, Institute for Thermal and Chemical Process Engineering Langer Kamp 7, 38106 Braunschweig

DOI: 10.1615/IHTC16.bae.020902
pages 623-630


KEY WORDS: Two-phase/Multiphase flow, Heat transfer enhancement, Droplet Entrainment

Abstract

At a pilot scale rising film evaporator (RFE) experiments with water have been conducted investigating fluid dynamics and integral heat transfer performances at different operating conditions. Variations of feed rate, driving temperature difference and process pressure examine the influence of the relative liquid height, specific gas load, wetting density and area-averaged overall heat transfer coefficient (OHTC). Mean logarithmic temperature differences between service and product side vary from 40 K to 63 K and specific feed rates are between 50 kg/(m²h) and 170 kg/(m²h). Highest OHTC between 670 W/(m²K) and 990 W/(m²K) can be derived from the experiments for relative liquid heights between 25 % and 30 %. A comparison at different split ratios reveals the most relevant performance parameters. The specific wetting density at the tube outlet and the relative liquid height in the tube estimate boundaries for appropriate operating conditions. Further, the beginning of an increasing specific wetting density at the evaporation tube outlet indicates the total evaporation capacity of the RFE for given operating conditions. Any further increase of the specific feed rate results in an increasing concentrate rate while the distillate rate remains constant.

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