6 Analysis of an axial flow expander Text

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Politecnico di Milano MSc. Energy Engineering – Power Production Energy Conversion A Prof. Gianluca Valenti PROJECT 6 ANALYSIS OF AN AXIAL- FLOW EXPANDER a.y. 2015/16 Giulia Boschi Omar Brembilla Alessandro Mosca 2 I) COMPARISON BETWEEN THE THREE CONFIGURATIONS Our purpose consists in comparing the different conditions in which an uncooled expander operates changing the number of stages of the machine. The following data are known: - Fluid Characteristics: • 𝑀𝑀 = 30 𝑘𝑔 𝑘𝑚𝑜𝑙 • 𝛾 = 1.33 - Maximum peripheral velocity: 𝑢𝑚𝑎𝑥 = 350 𝑚 𝑠 - Rotational speed: 𝑁 = 10 000 𝑟𝑝𝑚 - Inlet total pressure: 𝑝 = 5 𝑏𝑎𝑟 - Inlet total temperature: 𝑇 = 850°𝐶 - Fluid flow rate: 𝑚̇ = 10 𝑘𝑔 𝑠 In particular, we will analyse the following configurations. - Configuration A: 3 stages - Configuration B: 2 stages - Configuration C: 1 stage The results obtained adopting Axtur are given in the following table. 3 stages 2 stages 1 stage A1 A2 A3 B1 B2 C 𝜼𝒈𝒍𝒐𝒃𝒂𝒍[%] 92.14 92.14 92.14 90.53 90.53 84.45 𝑲𝒊𝒔 3.1 2.8 2.3 5.0 3.0 6.8 𝒓 ∗ 0.43 0.47 0.46 0.44 0.41 0 𝜟𝒉𝒊𝒔 [ 𝑱 𝒌𝒈] 159 013 147 851 123 990 274 537 168 633 414 790 𝑻𝟎𝒊𝒏 [𝑲] 1 123.15 1 001.61 888.02 1 123.15 928.55 1 123.15 𝑻𝟎𝒐𝒖𝒕[𝑲] 997.13 882.63 787.52 907.07 793.39 808.74 3 Configuration A – 3 stages The three-stage turbine works at the highest efficiency, that reaches the value of 92% in each stage. Moreover, here we have the lowest outlet total temperature: it means that also the kinetic energy at the discharge will be lower. The stage reaction coefficient results close to 0.5 for each stage, which is the optimum value for a reaction stage, hence we expect a low value of the load coefficient (𝐾𝑖𝑠). Furthermore, keeping the peripheral velocity below a certain value , and fixed the enthalpy jum p on the stage, it’s consistent that the load coefficient…