Ejector Solar Cooling

In recent times, there has been a rise in popularity of comfort cooling systems, mainly based on electrically driven heat pumps. The accompanying peak loading on electricity grids is proving to be particularly problematic and expensive for electricity utilities, notwithstanding the greenhouse gas emissions associated with the electricity consumption of these het pumps. An alternative is to generate cooling effect using waste heat or solar heat. The means to achieve this now coincides with the imperative to do so. Heat driven cooling technologies have existed for some time but only recently has research effort been applied to comfort cooling. One such technology is the ejector heat pump. An ejector is a thermally driven compressor that can substitute for an electrically driven compressor in a heat pump cooling system, thereby alleviating peak electricity consumption and associated emissions. Although ejectors have been used as steam driven vacuum pumps for almost a century, they are usually designed empirically and there is little understanding of the flow mechanisms within an ejector. Ejector heat pumps offer further advantages of exceptional reliability, potential for low cost and ease of control. Since their use in the early 1900s, researchers have grappled with analytical analyses of ejectors with limited success, hampered somewhat by the complexity of the flow mechanisms within the ejector. Ejector flows are characterised by supersonic jets, turbulent shear mixing and metastable thermodynamic states. Over the last ten years, a number of researchers have endeavoured to use Computational Fluid Dynamics (CFD) to elucidate these mechanisms and thereby improve ejector design. The volume of scientific literature in ejector CFD has been steadily increasing, indicating a growing interest and confidence in the application of CFD to ejectors. As yet, there are only a limited number of experimental datasets for CFD model validation, but early studies report good agreement at ejector design conditions albeit with a Chapter ** In: CFD Modeling in Development of Renewable Energy Applications. pp.***-*** ISBN xxxxxxxxxxxxx © 2011 International Energy and Environment Foundation. All rights reserved. 2 range of possible flow structures. However, off-design modelling is generally poor. There is a need for improved turbulence modelling of jet and shear mixing layer and a need for improved real gas modelling. Furthermore, there is currently insufficient knowledge in this application of CFD although progress is accelerating. A critical point in the application of CFD in ejector design comes when researchers have sufficient confidence in the CFD models to rely primarily on CFD to design better ejectors, thereby enabling a new range of environmentally friendly heat pumps to be marketed. Copyright © 2011 International Energy and Environment Foundation All rights reserved.