Development of the Trilateral Flash Cycle System: Part 3: The Design of High-Efficiency Two-Phase Screw Expanders

Abstract

has led to an improved level of understanding of how Lysholm twin screw machines may be used to recover power from two-phase flash expansion processes. The mode of operation of such machines is described together with the various types of rotor shapes used. Details are given of a computer simulation of the expansion process which was used to analyse 636 test results. These were obtained from earlier investigations as well as those of the authors and include three diyerent working fluids, varying rotor profiles and sizes and power outputs of 5350 kW. Good agreement was obtained between predicted and measured pegormance parameters and statistical analyses of the results indicate that this is unlikely to be improved without the development of more refined methods of two-phase flow analysis than are currently in use. Included in the tests are a set of measurements of pressure-volume changes within the expander carried out by the authors which confirmed a hitherto unappreciated feature of the expansion process. This is the relatively large pressure drop associated with the initial filling of the volume trapped between the rotors and the casing. The analytical technique thus developed was used both to explain the poor results of earlier studies with water expanders and to estimate optimum design performance. It is shown that, when expanding wet organic fluids, adiabatic eficiencies of over 70 per cent may be obtained at outputs of only 25 kW while multi-megawatt outputs are possible from machines no bigger than large compressors with efficiencies of more than 80 per cent. Two-phase screw expanders may be used not only for large-scale power generation in trilateral flash cycle (TFC) systems, but also in place of throttle valves in vapour compression systems to drive screw compressors in sealed 'expressor' units. The coeficient of performance of large refrigeration, air conditioning and heat pump systems may thereby be raised by up to approximately 8 per cent. A Adis.rnax A S U C Asuc.max C d e E G h H m M P Q Re

3D CFD analysis of a twin screw expander

“…Their expansion efficiency depends on several factors that include the leakage flows, the size and shape of the high pressure port and the volume ratio of the machine, as reported by Smith et al (1). The analysis of such machines has been reported in several papers by Stosic, Smith and Kovacevic (2), (3) using a quasi 1D thermodynamic model.…”

Comparison of Organic Rankine Cycle Systems under Varying Conditions Using Turbine and Twin-Screw Expanders

“…This is based on the quasi one dimensional analysis of twin-screw machines as described by Stosic and Hanjalic [9], which has been validated for a range of working fluids and operating conditions [10,11]. The calculation procedure requires the rotor geometries to be specified in order to calculate machine performance.…”

Thermodynamic simulations of rankine, trilateral and supercritical cycles for hot water and exhaust gas heat recovery

“…For the trilateral cycle, Smith et al (1993Smith et al ( , 1994Smith et al ( , and 1996 reported that expansion efficiency is about 70 % when using Lysholm twin screw expander. Ohman et al (2013) reported the adiabatic efficiency change against vapor quality at the inlet of Lysholm screw expander.…”

“…Smith et al (1993Smith et al ( , 1994Smith et al ( and 1996 evaluated the performance and cost of trilateral flash cycle with Lysholm twin screw turbine. They reported that the adiabatic efficiency of the expander can reach 70 %, and that the trilateral flash cycle can produce 1.8 times larger output power than simple Rankine cycle for hot steam of 100-200 ℃.…”