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Comparisons of dropwise condensation heat transfer using various types of surfaces on a horizontal tube.

Number: pap. n. 93

Author(s) : LEE S., CHENG K., KIM K.

Summary

Condenser is an important component of absorption chillers. In this work, heat transfers by dropwise condensation (DWC) were measured using various surfaces on copper condenser tubes including; plain, polished, hydrophobic, and hydrophilic surfaces on plain and fin-patterned tubes. All condenser surfaces were polished using sand papers and steel wools and cleaned for further surface preparations and condensation tests. Hydrophobic and hydrophilic condenser surfaces were prepared by chemical treatments on the polished and fin-patterned surfaces. To characterize the surfaces properties, the liquid contact angles on the surfaces were measured and the morphologies of condenser surfaces were investigated using a Scanning Electron Microscope (SEM). Condensation heat transfer tests were conducted with the test setup consisting of a test section, a cooling loop, and a boiler and the test section was composed of a condensing chamber, view ports, and measuring instrument. Water was used for working fluid with a saturation pressure range of 97.8 - 67.5 kPa and the water coolant inlet temperature range of 50°C - 90°C with a typical flow rate of 1.51x10-4 m3/s. The subcool temperature obtained during the tests is in the range of 1 - 20°C. Steam condensation tests with visual observations were also conducted to evaluate heat transfer performance using the surfaces. The sizes of droplets at the top of tubes, at the middle of tubes, and at the bottom of tubes were estimated with the ranges of 4.6 – 8.7 mm, 1.8 - 3.3 mm, and 2.7 – 10.2 mm, respectively. The sizes of condensates on the polished surface were smaller than those on other surfaces, while the sizes of condensates on the hydrophobic surface were the largest. Based on the visual observations for the surfaces on the plain tubes, the fin-patterned tubes were mechanically manufactured trying to limit the condensate sizes on condenser surfaces. The fin-patterned tubes had a thickness of 0.35 mm, a width of 1.5 mm and a spacing of 1 mm, respectively. Although all tested surfaces showed higher heat fluxes and higher heat transfer coefficients than those obtained from the filmwise correlation, the heat transfer results became similar to that of filmwise condensation when subcool became higher than 15°C. The polished surface showed the higher heat transfer results than other surface with the maximum condensation heat flux and heat transfer coefficient of 192 kW/m2 and 149 kW/m2-K, respectively.

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Pages: 14 p.

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Details

  • Original title: Comparisons of dropwise condensation heat transfer using various types of surfaces on a horizontal tube.
  • Record ID : 30013905
  • Languages: English
  • Source: International sorption heat pump conference (ISHPC2014), College Park, United States, March 31-April 2, 2014.
  • Publication date: 2014/03/02

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