Deans, JoeMcFeaters, JohnMorrison, James2020-07-082020-07-081996https://hdl.handle.net/2292/52063Full text is available to authenticated members of The University of Auckland only.This thesis describes an experimental investigation of the condensation of down-flowing ammonia-water vapour mixtures on a horizontal tube. The aim of the research was to gain insights in to the mechanisms governing the process, and to provide information on the rates of condensation. The equipment built for the investigation used an 18 kW in-tube vaporiser to generate controlled, low velocity vapour flows with compositions from O to 30%ammonia concentration by mass (0-30wt%). The test section involved a 25mm diameter, 145mm long horizontal tube with a spiral insert governing the internal cooling water flow. The tube was instrumented with a surface thermocouple and could be rotated through 360°. The overall heat transfer was measured by a cooling water heat balance across the tube and by measuring the mass flow of condensate. The equipment was commissioned during a series of steam condensation tests. The ammonia-water mixture tests showed that the condensation heat transfer rates for ammonia-water mixtures were generally less than for steam. The condensation heat transfer rate for a vapour composition of 27wt% ammonia was 12% of that for steam condensation at a similar condition. This decrease in heat transfer was due to an increased vapour film resistance, but could be improved by increasing the vapour velocity and temperature driving force. These findings were consistent with the work of previous researchers. Also, during the ammonia-water tests, the condensate film exhibited non-smooth behaviour. Five types of condensate film behaviour were identified: smooth, banded, rippled, alternate film and dry bands, and pseudo droplet condensation. This behaviour was caused by the Marangoni effect. The non-smooth behaviour in the ammonia-water tests reduced the condensate film heat transfer resistance. At very low concentrations (0.23-0.88wt%ammonia) this resulted in an overall increase in the heat transfer rate compared to steam condensation. At a concentration of 0.71wt% ammonia, the condensate film heat transfer was enhanced by 32%, resulting in an overall enhancement of 13%. This is the first reported instance where the binary condensation heat transfer rate exceeds that of a pure component. This overall enhancement of heat transfer is expected to have applications in industry, particularly for condensers used in power generation.Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.Restricted Item. Full text is available to authenticated members of The University of Auckland only.https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htmThesisCopyright: The authorQ112853210