[home] [Personal Program] [Help]

---

Session: Volumetric expanders I
Session starts: Tuesday 08 October, 09:00
Presentation starts: 09:00
Room: Van Beuningen Zaal

---

Guo-Dong Xia ()
Ye-Qiang Zhang ()
Yu-Ting Wu ()
Chong-Fang Ma ()
Yan-Hai Peng ()
Wei-Ning Ji ()

Abstract:
INTRODUCTION An Organic Rankine Cycle (ORC) is a promising process for conversion of low and medium temperature heat to electricity. The ORC process works like a Rankine steam power plant but uses an organic matter as working fluid instead of water. Today, Organic Rankine Cycles are commercially available in the MW power range, but very fewsolutions are actually suitable for the 1kW~100s kW. However, a lot of small and middle scale ORC technology applications exist such as biomass combined heat and power, solar power plant, geothermal energy, waste heat recoveryand so on [1,2]. Performance of the ORC system strongly correlates with those of the expander.Turbines are mainly designed for larger-scale applications andshow a higher degree of technical maturity. While, displacement expanders are more appropriate to the small-scale ORC system,because they are characterized by lower flow rates and higher expansion ratios than turbines. Single-screw expander is a new type of displacement expander with one rotor and two gaterotors. In an action cycle, three working processes,which are gas admission, gas expansion, and gas discharge, are shown by Figure 1. Figure 1.Working principle graph of single-screw expander Single-screw expander can be used as prime mover in small-sized ORC system. It has many advantages, such as long working life, balanced loading of the main screw, high volumetric efficiency, low noise, low leakage, low vibration and simple configuration, etc. Single screw expander can realize 1-200 kW range of power output, and it is suitable for saturatedsteam,superheated steam, gas-liquid two phases or heat liquid[3]. A single screw expander prototype with 195 mm diameter screw is developed by us. The main task of this paper is to carry out the performance test for the single-screw expander, and obtain the influence law of rotational speed and inlet pressure of working fluid on the prototype performance. EXPERIMENTAL SYSTEM The experiment used compressed air as working fluid. Air compressor provided high pressure air to gas tank, whichwas the stable gas source for the test. Compressed airwith different pressure from gas tank entered into expander by adjusting the inlet valve. Exhaust gasled to outdoors. Through aneddy current dynamometerfor the load, theshaft power of expander was changed to heat carried away by cooling water. The parameters of volume flow, inlet and outlet pressure,inlet and outlet temperature, rotational speed and torque, thepower and temperature drop performance of the prototypewere obtained. Experimental platform is shown in Figure 2. Figure 2. Experimental platform EXPERIMENTAL PERFORMANCES ANALYSIS Performance tests are carried out by varying the inlet pressure (pin) from ranged 7bar to 15bar and by varying the speed of 1200rpm to 3200rpm. Power output The power output ( ) is an important parameter for evaluating the performance of the single-screw expander. The effects of inlet pressure and rotational speed to power output are shown in Figure 3. (a) (b) Figure 3:Power output versus inlet pressure and rotating speed Adiabatic efficiency Adiabatic efficiency is an important parameter for evaluating the effect of internal irreversibilities during adiabatic processes, which is defined as (1) Where is the actual enthalpy drop of work fluid between inlet and outlet of expander, is the ideal enthalpy drop of work fluid during adiabatic processes. The variation of adiabatic efficiency with inlet pressure and rotational speed are shown in Figure 4. (a) (b) Figure 4: Adiabatic efficiency versus inlet pressure and rotating speed Total efficiency The total efficiency is the most important parameter for evaluating the performance of the single-screw expander, which is defined by (2) Where is the ideal power output during adiabatic processes. The variation of total efficiency versus inlet pressure and rotational speed are shown in Figure 5. (a) (b) Figure 5:Total efficiency versus inlet pressure and rotating speed CONCLUSIONS Through the experiment for the prototype of single-screw expander, following conclusions can be given: (1) The power output increases with the increase of intake pressure and rotational speed. The total efficiency and air-consumption ratio are not regular, but can obtain best values at 2800rpm. (2) Higher power output and higher total efficiency are along with higher intake pressure. (3) For the self-developed single-screw expander, the highest adiabatic efficiency is 66.43% and total efficiency are 66.43% and 62.23%, respectively. The biggest power output is 51.08kW. ACKNOWLEDGEMENTS The authors are also grateful to the financial support by the National Basic Research Program (also called 973 Program) of China under grant number 2011CB710704 and 2011CB707202. Reference [1] Canada, S., G. Cohen, R. Cable, D. Brosseau, H. Price. Parabolic trough organic rankine cyclesolar power plant, NREL/CP-550-37077.In: The 2004 DOE Solar Energy Technologies, Denver, USA. [2] Drescher, U., D. Bruggemann. Fluid selection for the Organic Rankine Cycle (ORC) in biomasspower and heat plants. Applied Thermal Engineering, 2007(27): 223-228. [3] Wei Wang, Yu-ting Wu, Chong-fang Ma, et al.Preliminary experimental study of single screw expander prototype. Applied Thermal Engineering, 2011(31):3684-3688.