Numerical simulation of novel axial impeller patterns to compress water vapor as refrigerant Qubo Li a, * , Janusz Piechna b , Norbert Müller a a Michigan State University, East Lansing, MI 48824, USA b Warsaw University of Technology, Warsaw, Poland article info Article history: Received 1 August 2010 Received in revised form 13 February 2011 Accepted 15 February 2011 Available online 31 March 2011 Keywords: Axial compressor Flow control Operating range Water vapor refrigerant abstract Through means of 3-D CFD (Computational Fluid Dynamics) method, a novel axial compressor with different impeller shapes compressing water vapor as refrigerant was investigated. The numerical simulation focuses on the fluid flow from compressor impeller inlet to outlet. The overall performance level and range are predicted. Different blade patterns with different hub sizes were compared regarding the aerodynamic performance. Independent of the blade pattern, in this numerical investigation the largest hub diameter shows the highest pressure ratio and efficiency at narrowest operating range. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction An application of the investigated preliminary compressor design is in mechanical compression refrigeration units that utilize water (R718) as refrigerant. The use of water as refrigerant in vapor compression system offers several potentially significant advan- tages and fulfills most of the fundamental requirements of a refrigerant [1]. The first main advantage of using water as refrigerant is because it is a green refrigerant; it is environment friendly, non-toxic and non-flammable. Besides these, as a green refrigerant it has zero ODP (ozone depletion potential) and zero global warming potential, which means there are no risks using water as refrigerant in the future. The second main advantage of using water as refrigerant is because it’s be a green energy: it can be obtained for free and readily available; it also has no disposal problem; most importantly, it has a potential to save energy about 20e30% than conventional refrigerants [2]. However, compressing water vapor as refrigerant imposes specific challenges for the compressor designer. Fig. 1 compares the traditional refrigerant R134a to R718 and shows that this compressor needs to compress under vacuum environment varying between 900 Pa and 1800 Pa; Such a low pressure thus lower down density and produce a huge volume flow rate for compressors to handle [3]. In addition, the pressure ratio for water vapor as refrigerant has to reach about five which is roughly two or three times higher than conventional refrigeration cycles [2]. To achieve such as high performance, especially a high compression pressure ratio, it would be a big challenge for volume displacement compressors such as scroll compressors and turbo compressors are good candidates for the task. Wight et al. [4] carried out a detailed scoping analysis of turbo- compressor technology applied to steam compression in a water- based refrigeration cycle. Because of low efficiency (less than 75% for the radial bladed unit considered), huge impellers (ca. 6.0 m in diameter) and very high tip speed (ca. 671 m/s) were employed. It was concluded that a single stage compressor was not feasible for compressing water vapor as refrigerant and that these factors combined yield extremely high capital cost and technically chal- lenging compressor design and development. In order to achieve such a high performance, a two stage centrifugal compressor was evaluated and showed more favorable results. The investigation showed that a lower tip speed of around 490 m/s and efficiencies of 80% with large impeller diameters are technically possible for this task. However, in terms of total size and performance, it is identi- fied that the most promising compressor technology is multi-stage axial compressor configuration consisting of between six and seven stages. When compared with centrifugal compressors, it is * Corresponding author. Department of Mechanical Engineering, Michigan State University, 2500 Turbomachinery Lab, East Lansing, MI 48824, USA. Tel./fax: þ1 517 899 0759. E-mail address: liqubo@egr.msu.edu (Q. Li). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2011.02.017 Energy 36 (2011) 2773e2781