Evaluation of Ejector Performance for an Organic Rankine Cycle 1 Combined Power and Cooling System 2 3 Kun Zhang 1,2 , Xue Chen 3 , Christos N. Markides 2 , Yong Yang 3 , Shengqiang Shen 3 4 5 1 School of Ocean and Civil Engineering, Dalian Ocean University, Dalian, China, 116023 6 2 Clean Energy Processes (CEP) Laboratory, Department of Chemical Engineering, Imperial College London, 7 London SW7 2AZ, United Kingdom 8 3 School of Energy and Power Engineering, Dalian University of Technology, Dalian, China, 116024 9 10 Abstract: Power-generation systems based on organic Rankine cycles (ORCs) are well suited and 11 increasingly employed in the conversion of thermal energy from low temperature heat sources to 12 power. These systems can be driven by waste heat, for example from various industrial processes, 13 as well as solar or geothermal energy. A useful extension of such systems involves a combined 14 ORC and ejector-refrigeration cycle (EORC) that is capable, at low cost and complexity, of 15 producing useful power while having a simultaneous capacity for cooling that is highly desirable 16 in many applications. A significant thermodynamic loss in such a combined energy system takes 17 place in the ejector due to unavoidable losses caused by irreversible mixing in this component. 18 This paper focuses on the flow and transport processes in an ejector, in order to understand and 19 quantify the underlying reasons for these losses, as well as their sensitivity to important design 20 parameters and operational variables. Specifically, the study considers, beyond variations to the 21 geometric design of the ejector, also the role of changing the external conditions across this 22 component and how these affect its performance; this is not only important in helping develop 23 ejector designs in the first instance, but also in evaluating how the performance may shift (in fact, 24 deteriorate) quantitatively when the device (and wider energy system within which it functions) 25 are operated at part load, away from their design/operating points. An appreciation of the loss 26 mechanisms and how these vary can be harnessed to propose new and improved designs leading 27 to more efficient EROC systems, which would greatly enhance this technology’s economic and 28 environmental potential. It is found that some operating conditions, such as a high pressure of 29 the secondary and discharge fluid, lead to higher energy losses inside the ejector and limit the 30 performance of the entire system. Based on the ejector model, an optimal design featuring a 31 smoothed nozzle edge and an improved nozzle position is found to achieve an improved 32 entrainment ratio, significantly better performance and reduced energy losses in the ejector. 33 34 Keywords: Ejector; Refrigeration; Combined Cooling, Heating and Power 35 36 37 Nomenclature 38 39 Abbreviations 40 COP Coefficient of performance 41 EORC Organic Rankine cycle plus ejector 42 ER Entrainment ratio 43 1 Corresponding author: Kun Zhang. Tel: +86 15542663303. Email: cruiseer@hotmail.com