An experimental and theoretical study on the concept of dropwise condensation

Dropwise condensation heat transfer on ion implanted aluminum surfaces

Experimental observations of dropwise condensation of water vapor on a chemically textured surface of glass and its detailed computer simulation are presented. Experiments are focused on the pendant mode of dropwise condensation on the underside of horizontal and inclined glass substrates. Chemical texturing of glass is achieved by silanation using octyl-decyl-tri-chloro-silane (C 18 H 37 C 13 Si) in a chemical vapor deposition process. The mathematical model is built in such a way that it captures all the major physical processes taking place during condensation. These include growth due to direct condensation, droplet coalescence, sliding, fall-off, and renucleation of droplets. The effects arising from lyophobicity, namely the contact angle variation and its hysteresis, inclination of the substrate, and saturation temperature at which the condensation is carried out, have been incorporated. The importance of higher order effects neglected in the simulation is discussed. The results of model simulation are compared with the experimental data. After validation, a parametric study is carried out for cases not covered by the experimental regime, i.e., various fluids, substrate inclination angle, saturation temperature, and contact angle hysteresis. Major conclusions arrived at in the study are the following: The area of droplet coverage decreases with an increase in both static contact angle of the droplet and substrate inclination. As the substrate inclination increases, the time instant of commencement of sliding of the droplet is advanced. The critical angle of inclination required for the inception of droplet sliding varies inversely with the droplet volume. For a given static contact angle, the fall-off time of the droplet from the substrate is a linear function of the saturation temperature. For a given fluid, the drop size distribution is well represented by a power law. Average heat transfer coefficient is satisfactorily predicted by the developed model.

/pdf/dropwise-condensation-underneath-chemically-textured-1er397rah5.pdf

Dropwise Condensation Underneath Chemically Textured Surfaces: Simulation and Experiments

A review of dropwise condensation: Theory, modeling, experiments, and applications

Dropwise Condensation Underneath Chemically Textured Surfaces: Simulation and

Parameter study on the performance of dropwise condensation

By the use of photon correlation spectroscopy in a heterodyne technique, the ultrasonic velocity of transparent fluids can be determined. The quantity measured is the intensity correlation function that forms a damped oscillation. The oscillation frequency value can be found easily by the application of a numerical Fourier transformation. However, a dependence on the sample time of the applied correlator and the oscillation decay time must be taken into account. An estimation for the accuracy of the deduced frequency is given on the basis of a Fourier transformation of noisy synthetic data. For example, we find that a sampling interval of 100 ns, the sound frequency from scattering 514.5-nm light at an angle of 3° would be determined to ±0.3% for a typical near-critical fluid with a sound velocity of 100 m/s. For larger sound velocities, and for fluids far from the critical point, the uncertainty would decrease rapidly.

Kjeld Kraft

Papers

Parameter study on the performance of dropwise condensation

Sound velocity measurements by the use of dynamic light scattering: data reduction by the application of a Fourier transformation.

Thermal diffusivity and sound velocity of Round-Robin R134a

Determination of the sound velocity of transparent fluids near the critical point using photon correlation spectroscopy

Spectroscopic determination of selected thermophysical properties of transparent fluids