Use Of New Generation Instruments In Measurement Of New Steam Expander
For the past twenty years the Centre for Positive Displacement Compressor Technology, at City University, has employed experimental techniques for the measurement of screw compressors’ performance where both experimental data and predicted mathematical models are found to be in agreement with each other. Some of the experimental measuring techniques involve the use of pressure and temperature transducers installed in the housing to determine the vital thermodynamic process characteristics and functioning performance of compressors. Moreover, as advanced technologies were available, measurements were performed in an optical compressor with a transparent window near the discharge port to allow the application of a laser technique, Laser Doppler Velocimetry (LDV), to investigate the axial mean flow and turbulence characteristics inside the working chamber of the male rotor. Recently a prototype two-phase screw steam expander has been designed and developed as a means of power recovery from liquid geothermal brine. An experimental setup has been designed by using a set of new generation instruments to complement the unit’s numerical modeling, from which predictions of an adiabatic efficiency in the order of 70%, were obtained. The testing includes measurements of instantaneous pressure and temperature in the suction and discharge port, instantaneous torque, speed and flow rate as well as monitoring the temperature and pressure of its lubrication system. Furthermore, four miniature high resolution pressure transducers were installed in the expander unit to measure the main rotor inter lobe temporal pressures with respect to crank angle of the main rotor. The high dynamic characteristics and response of the instrument are captured by a real time processor, National Instrument Compact-RIO, data logger and the programming is done using LabVIEW. The paper presents the measuring method, preparation of the instruments, acquisition and processing of the results obtained during experimental investigation of the two-phase screw expander.
Development of the Trilateral Flash Cycle System: Part 3: The Design of High-Efficiency Two-Phase Screw Expanders
An extensive research and development programme carried out at City University, London, 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 different working fluids, varying rotor profiles and sizes and power outputs of 5–850 kW. Good agreement was obtained between predicted and measured performance 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 efficiencies 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 coefficient of performance of large refrigeration, air conditioning and heat pump systems may thereby be raised by up to approximately 8 per cent.
Mechanics of deformable directed surfaces
Abstract The paper develops a simple, yet complete and consistent non-linear dynamic thermo-elastic shell theory based on the concepts of a two-dimensional directed continuum. The constitutive equations are postulated in a general form. Stress-strain relations are derived using the equation of energy balance and the two entropy production inequalities, which are rewritten in a special form. The linear theory is discussed in detail. The structure of the stress-strain relations is presented in the most general form and then specialized to concrete examples, in particular, to the classical shell theory, using their invariance properties with respective to certain symmetry groups. The elastic moduli are determined by demanding the coincidence of the frequency dispersion surfaces obtained using the two-dimensional theory with the lowest foils of the corresponding surfaces resulting from the three-dimensional theory of elasticity.