Serhan Küçüka

Flow through a rectangular thermosyphon at specified wall temperatures

In this study, closed loop rectangular thermosyphon was studied using experimental and numerical techniques. In the experimental part of this study, a closed loop thermosyphon was built. The heat transfer sections of this thermosyphon were designed as concentric tube heat exchangers. Two-dimensional numerical models were solved using uniform wall temperature boundary condition in the vertical heated and cooled sections of the thermosyphon loop. In two-dimensional model, results for laminar flow case were obtained by solving the momentum and the energy equations through the SIMPLEX Algorithm. It was shown that the two-dimensional model was appropriate for estimating the heat transfer and the flow characteristics of the loop at the uniform wall temperature.

The Formation of Banded Condensate Films in Weak Ammonia–Water Mixtures

This experimental and analytical study focuses on the formation of banded condensate films on a horizontal tube, when the ammonia mass fraction of the vapor is less than 0.0126. The experimental results show that there is a step change in the heat transfer coefficient when a banded film is formed. This change develops when the vapor mass fraction is approximately 0.004 and the heat transfer coefficient at the end of the change is 15% greater than the value expected for steam. The banded films are initiated at the base of the tube; midway between the regions where droplets detach. Photographs taken during the tests show that the development starts with the formation of a single band; when this band is complete, secondary bands are formed on either side and then further bands are added until the complete tube surface is covered with a banded film. The reason for the delay in the formation of the bands is examined using a simple two-dimensional force balance. The success of this examination provides an insight to the mechanisms employed in the formation of banded films.