This thesis describes a 6 year long study to improve the performance of an ammonia air cooler which is an important device in the search for low carbon cooling. The aim was to develop understanding of the internal flow regime, pressure drop and heat transfer as seen in ammonia air coolers. This included the effects of straight horizontal tubes, the effect of horizontal and vertical 1800 return bends and the liquid interface with the tube wall. A test rig was designed by the author and built to investigate the internal ammonia flow regime, pressure drop and heat transfer. With an increased understanding of these areas, it was identified that the use of stainless steel as a tube material in LPR ammonia air cooler coils resulted in poor heat transfer. Flow visualisation identified that stratified flow mostly occurs in LPR ammonia air coolers. Due to stainless steel’s poor conductivity, little cooling effect occurred at the top of the tube. To maintain the same heat transfer from the aluminium fins, a large temperature difference is required across a stainless tube which results in poor heat transfer performance. It was identified that a different tube material was required to conduct the cooling effect around the tube and reduce the temperature difference between the ammonia and the air. Aluminium was chosen to replace the poor conductivity stainless steel tube. Aluminium was found to highly conductivity and the material is compatible for use in ammonia refrigeration systems. A new LPR ammonia air cooler with an aluminium tube was designed, manufactured and installed on a site to replace an existing stainless steel tube LPR ammonia air cooler. The heat transfer co-efficient was over 100% greater for aluminium tube when the same cooler fin surface area was compared.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:570872 |
| Date | January 2009 |
| Creators | Cotter, Dermot |
| Publisher | London South Bank University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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