LATEST ARTICLES
Details of the latest articles published in the Journal. Includes the most recent InPress papers (uncorrected proofs of accepted papers awaiting publication in a Journal issue).
Date: Thu, 08 Jul 2010 14:51:56 GMT
In an effort to answer the current needs for more performing and energy efficient gas turbine engines, unsteady pressure gain devices are currently under great focus. This article describes the performance analysis of a novel turbine engine utilizing an internal combustion wave rotor. The performance of this engine is compared to that of a conventional engine, first using its original bypass ratio–fan pressure ratio configuration, and then an optimized configuration. The novel cycle engine is found to be more efficient, reducing specific fuel consumption by approximately 37 per cent for the non-optimized condition, whereas the optimized engine has a potential for reducing by about 40 per cent the fuel needed for a typical long-range aircraft mission. This high potential reduction in fuel consumption encourages more detailed studies based on more sophisticated models, taking into account cycle losses, emissions, and transient behaviours.
- Content Type Journal Article
- DOI 10.1243/09576509JPE984
- Authors
Date: Thu, 08 Jul 2010 14:51:56 GMT
In this article, the authors performed the thermodynamic optimization of organic Rankine cycles (ORCs) using several working fluids and considered the effect of three heat rejection media in the condenser: cooling water, ambient air, and hot water at high temperature for co- or trigeneration applications. The ORC system was modelled and optimized using the Aspen Hysys process simulator. The objective function is the maximization of turbine power output. Most natural gas compression stations use no heat recovery system. In this study, they applied the optimization procedure to the recovery of waste heat from gas turbines used to drive natural gas compressors in natural gas pumping stations. They used operational data from an existing pumping station to illustrate the potential benefits of ORC systems for this application, taking into account also non-thermodynamic aspects such as toxicity, flammability, and investment cost return. The highest ORC turbine output powers were obtained with aromatic hydrocarbons, then with aromatic fluorocarbons, n-hydrocarbons, and siloxanes (in that order). For the case studied here – a gas turbine of 2.6 MW of mechanical power– the proposed ORC can produce around 1 MWe, with a thermal efficiency of up to 24 per cent depending on the working fluid and condensing temperature.
- Content Type Journal Article
- DOI 10.1243/09576509JPE998
- Authors
- I Saavedra
- J C Bruno
- A Coronas
Date: Thu, 08 Jul 2010 14:51:56 GMT
Tidal stream systems make use of the kinetic energy of tidal movement to power turbines, in a similar manner to the way in which windmills extract energy from the wind. This method of renewable energy generation is gaining in popularity because of the high predictability of tides, the lower investment needed for tidal turbines, and the lower ecological impact, as compared with other schemes involving barrages or lagoons. It is generally considered that a mean spring tide peak current of at least 2 m/s is required for tidal stream power to be worth exploiting. In the Severn Estuary, the peak tidal current exceeds 2 m/s, with a corresponding minimum depth of greater than 20 m, and it is thereby a potential location for tidal stream power. Previous studies cannot provide the detailed and precise distribution of tidal stream power in this estuary, and it has therefore been deemed appropriate to undertake a numerical model assessment of tidal stream energy resources in the Severn Estuary. In the present study, an existing finite volume numerical model has been refined, with the inclusion of an algorithm for computing the power density and its mean value across the estuary. The refined model has also been validated against (a) measured tidal currents at four sites, using the method of harmonic analysis; (b) measured tide level hydrographs at five tide gauging stations, taken over a 15-day period and covering the full spring–neap cycle; and (c) in situ velocity measurements at two sites. Finally, the validated model has been used to assess the potential tidal stream energy resources without and with the Severn Barrage, including the distributions of the mean power density over a spring–neap cycle in the Severn Estuary and a detailed assessment of the tidal stream energy resources at two sites near the coast of South Wales. The model predictions indicate that at two sites, the annual power output with the presence of barrage could be reduced by 70–80 per cent, as compared with the value without any structure.
- Content Type Journal Article
- DOI 10.1243/09576509JPE938
- Authors
- J Xia, Hydro-environmental Research Centre, School of Engineering, Cardiff University, Cardiff, UK
- R A Falconer, Hydro-environmental Research Centre, School of Engineering, Cardiff University, Cardiff, UK
- B Lin, Hydro-environmental Research Centre, School of Engineering, Cardiff University, Cardiff, UK
Date: Thu, 08 Jul 2010 14:51:56 GMT
A simulation study of several schematic models of both water- and air-cooled single-effect LiBr–H2O absorption chillers energized by a high-potential, low-temperature (73 °C) geothermal source has been carried out using IPSEpro refrigeration software package. All the simulated models were validated against a lithium bromide–water pressure–temperature DÜhring chart. The results obtained show that when the coefficient of performance, heat input into the generator, and cooling mass flowrates are fixed, the cycle parameters are highly affected by variation of the coolant temperature. This information will be useful to designers of absorption refrigeration systems.
- Content Type Journal Article
- DOI 10.1243/09576509JPE916
- Authors
- S A Masheiti, School of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne, UK
- B Agnew, School of the Built Environment, Northumbria University, Newcastle upon Tyne, UK
Date: Wed, 23 Jun 2010 13:44:04 GMT
Various micro-radial compressor configurations were investigated using one-dimensional meanline and computational fluid dynamics (CFD) techniques for use in a micro gas turbine (MGT) domestic combined heat and power (DCHP) application. Blade backsweep, shaft speed, and blade height were varied at a constant pressure ratio. Shaft speeds were limited to 220 000 r/min, to enable the use of a turbocharger bearing platform. Off-design compressor performance was established and used to determine the MGT performance envelope; this in turn was used to assess potential cost and environmental savings in a heat-led DCHP operating scenario within the target market of a detached family home. A low target-stage pressure ratio provided an opportunity to reduce diffusion within the impeller. Critically for DCHP, this produced very regular flow, which improved impeller performance for a wider operating envelope. The best performing impeller was a low-speed, 170 000 r/min, low-backsweep, 15° configuration producing 71.76 per cent stage efficiency at a pressure ratio of 2.20. This produced an MGT design point system efficiency of 14.85 per cent at 993 W, matching prime movers in the latest commercial DCHP units.
Cost and CO2 savings were 10.7 per cent and 6.3 per cent, respectively, for annual power demands of 17.4 MWht and 6.1 MWhe compared to a standard condensing boiler (with grid) installation. The maximum cost saving (on design point) was 14.2 per cent for annual power demands of 22.62 MWht and 6.1 MWhe corresponding to an 8.1 per cent CO2 saving. When sizing, maximum savings were found with larger heat demands. When sized, maximum savings could be made by encouraging more electricity export either by reducing household electricity consumption or by increasing machine efficiency.
- Content Type Journal Article
- DOI 10.1243/09576509JPE996
- Authors
Date: Wed, 23 Jun 2010 13:44:04 GMT
This article describes the development of a new through flow method for the analysis of axial multi-stage compressors. The method is based on a stream function approach and a finite-element solution procedure. It includes a high-fidelity loss and deviation model with improved correlations and end-wall boundary layer calculation. A radial distribution model of losses and a new spanwise mixing model are applied to simulate three-dimensional flow effects. The calibration of the models is made by calculating a number of test cases with different configurations with the aim of achieving high accuracy and optimum robustness for each of the test cases considered.
The code was applied to flow analysis and performance prediction of a newly developed gas turbine compressor. Comparison of the predicted results and measured test data for the overall compressor performance and a number of parameters under different operating conditions showed good agreement. The results of the validation confirm that this method based on cali-brated correlations can be applied as a reliable tool for flow analysis and parameter variation during the design phase for a wide range of compressor configurations.
- Content Type Journal Article
- DOI 10.1243/09576509JPE991
- Authors
- M V Petrovic, Faculty of Mechanical Engineering, University of Belgrade, Belgrade, Serbia
- A Wiedermann, MAN Turbo AG, Oberhausen, Germany
- M B Banjac, Faculty of Mechanical Engineering, University of Belgrade, Belgrade, Serbia
Date: Wed, 23 Jun 2010 13:44:04 GMT
The theoretical analyses and optimization studies of two novel multi-evaporator transcritical CO2 refrigeration systems using constant pressure mixing ejector are presented in this article. Comparisons of novel hybrid compression–ejection CO2 cycles, based on coefficient of performance (COP) improvement over conventional cycle and other optimum parameters, are also done for various operating conditions. Study shows that the cycle performance is dependent on allocation of evaporator cooling capacities for both cycles. The optimum discharge pressure for both cycle layouts compared to corresponding basic cycle reduces by the use of ejection–compression. For both cycle layouts, the effect of gas cooler exit temperature on COP improvement is negligible, whereas the COP improvement at optimum condition increases with the increase in temperature difference between evaporators. Results reveal that the CYC1 is superior due to lower discharge pressure and significantly higher COP improvement (maximum of 38.1 per cent for CYC1 whereas 21.4 per cent for CYC2 at optimum condition for the studied ranges).
- Content Type Journal Article
- DOI 10.1243/09576509JPE957
- Authors
Date: Wed, 23 Jun 2010 13:44:04 GMT
In the present article, thermodynamic and thermoeconomic analysis are applied to find the optimum values of design parameters for water-tube heat recovery steam generators (HRSGs) in combined cycle power plants. Design variables optimized in this article are pinch point and gas-side velocity. Optimization is carried out based on two different objective functions. The first one is thermodynamic, which is the summation of exergy loss due to an outflow of hot gas escaping from the HRSG through stack, and exergy destruction due to internal irreversibility inside the HRSG. The second one is a thermoeconomic objective function, which is the summation of exergy loss and destruction in terms of expenses including the cost of fuel and electricity, and the capital cost of HRSG in terms of the future value of money according to the interest rate. The capital cost of HRSG includes procurement and erection of piping and insulation, electrical panels and wiring, control and instrumentation equipment, insurance, tax, engineering, and supervision. The effects of pinch point and gas-side velocity on the components of objective functions are investigated in details. The pinch point and gas-side velocity that make these objective functions minimum are called optimum values.
- Content Type Journal Article
- DOI 10.1243/09576509JPE953
- Authors
- A Behbahani-nia, Department of Mechanical Engineering, K N Toosi University of Technology, Tehran, Iran
- S Sayadi, Department of Mechanical Engineering, K N Toosi University of Technology, Tehran, Iran
- M Soleymani, Fann Azmayan Pooyandeh (FAP) Company, Tehran, Iran
Date: Wed, 23 Jun 2010 13:44:03 GMT
Centrifugal compressors have reached advanced stages of their development, and it is only through a detailed understanding of their complex airflows that improvements in the overall performance will be achieved. This article presents a numerical investigation of unsteady flows through the different components of a radial compressor, emphasizing on the impeller–vaneless-diffuser–scroll interactions. A transient rotor–stator simulation model was used for the calculations carried out by means of the code CFX-TASCflow, at design point and near stall and choke operating conditions. Spectral analyses of the pressure fluctuation-related different component interactions have resulted in the amplitudes and speeds of rotation of the main energetic modes and have revealed that the flow presents a space–time periodic behaviour that may be described by the double Fourier decomposition. The spatial mode analysis was therefore introduced to describe the interaction mechanisms, whereas the time mode analysis during the working time of the machine has permitted to determine different frequencies, and hence the most prevailing modes and their originating sources. These spectral analyses have permitted a good understanding of the flow interaction mechanisms and revealed the computations limits, depending on whether one-passage or a full-rotor simulation is considered. Principally, these limitations are related to an underestimation of pressure fluctuation amplitudes and a failure in detecting all harmonics lower than the number of passages per component. Finally, this study may help in envisaging the local treatments to reduce noise levels and increase the compressor stability.
- Content Type Journal Article
- DOI 10.1243/09576509JPE948
- Authors
Date: Wed, 23 Jun 2010 13:44:03 GMT
This article presents the energy analysis of a coupled power–refrigeration cycle which eliminates the requirement of electrical power for driving the compressor of the vapour compression refrigeration cycle. The coupled cycle which uses pentafluropropane R-245ca as the working fluid in top power loop and bottom refrigeration loop have been assessed with different combinations such as cycle with recuperator, reheater, and economizer with a view to augment its performance. In the condenser temperature range of 30–42 °C and recuperator effectiveness range of 0.7–0.9, the overall coefficient of performance (COP) of the coupled cycle with the introduction of the recuperator, increased by 19.5–50.7 per cent and in the cycle with recuperator, reheater and economizer, it increased by 41.6–59.3 per cent. Overall COP at a constant turbine inlet temperature remains almost invariant with boiler pressure in the condenser temperature range of 30–42 °C for a coupled power–refrigeration base cycle and cycle with recuperator, reheater, and economizer. Significant decrease in overall COP is observed for boiler pressure greater than 5 MPa at constant turbine inlet temperature and recuperator effectiveness for the coupled cycle with recuperator.
- Content Type Journal Article
- DOI 10.1243/09576509JPE894
- Authors
- M Dubey, Department of Mechanical Engineering, MANIT, Madhya Pradesh, India
- S P S Rajput, Department of Mechanical Engineering, MANIT, Madhya Pradesh, India
- P K Nag, Department of Mechanical Engineering, IIT Kharagpur, West Bengal, India
- R D Misra, Department of Mechanical Engineering, NIT Silchar, Assam, India
Date: Wed, 23 Jun 2010 13:44:03 GMT
An improved aerodynamic optimization technique for two-dimensional wind turbine airfoils is presented in this article. On the basis of the combination of response surface method and uniform experimental design, a space filling design of experiment, this technique optimizes the lift-to-drag ratio of an airfoil at the design angle of attack. In order to reduce the number of design variables, the upper and lower surfaces of a reference airfoil are, respectively, fitted by using two B-spline curves with only four control points each. By using the ordinates of the eight control points as design variables, the ranges of the design variables are set and the airfoil is parameterized. Then, according to the uniform design tables, the values of each design variable at different levels are determined and various airfoil shapes are generated by using the specified combinations of the design variables. Finally, the optimal ordinates of the eight control points are obtained using a quadratic polynomial expression that is the regression of the computational results of flows around the airfoils. The computational results of flows around the optimized shapes of four airfoils reveal that the proposed technique, compared with some other optimization methods in the literature, is a time-saving and effective method to seek better aerodynamic performance for wind turbine airfoils.
- Content Type Journal Article
- DOI 10.1243/09576509JPE888
- Authors
Date: Wed, 23 Jun 2010 13:44:03 GMT
This article describes the construction and preliminary testing of a pre-prototype thermoacoustic electricity generator to test the concept of a low-cost device for application in remote or rural areas of developing countries. A travelling-wave thermoacoustic engine with a configuration of a looped-tube resonator is designed and constructed to convert heat to acoustic power. Air at atmospheric pressure is used as the working gas, PVC tubing is utilized for the feedback pipe, whereas an inexpensive commercially available loudspeaker is adopted to convert the acoustic power, produced by the engine, to electricity. Preliminary experimental results are presented and discussed in detail. The results show that the approach is feasible in principle and it is possible to produce the electrical power levels in the order of 4–5 W with overall heat-to-electric efficiencies in the order of 1 per cent. Further work towards optimizing the device from the performance, manufacturing, and cost points of view is outlined.
- Content Type Journal Article
- DOI 10.1243/09576509JPE864
- Authors
- Z Yu, School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester, UK
- A J Jaworski, School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester, UK
- S Backhaus, Condensed Matter and Thermal Physics Group, Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Date: Wed, 23 Jun 2010 13:44:03 GMT
This article presents the virtual prototype of the tracking system used for improving the energetic efficiency of a photovoltaic panel. From the point of view of the efficiency and safety, a polar dual-axis system has been designed. Both motions (daily and seasonal) are driven by rotary actuators, which are coupled with worm gears for blocking the system in the stationary positions. The tracking system is approached in mechatronic concept, by integrating the mechanical structure of the solar tracker and the electronic control system at the virtual prototype level. The tracking strategy aims at reducing the angular field of the daily motion and the number of actuating operations, without significantly affecting the incoming solar energy. At the same time, an algorithm for determining the optimal actuating time for the step-by-step tracking is developed. For performing the energy balance, the incident solar radiation is obtained using a method based on the direct radiation and the angle of incidence, while the energy consumption for accomplishing the tracking is determined by simulating the dynamic behaviour of the solar tracker. Finally, the validation of the simulation results is performed by comparing the virtual prototype analysis with the data achieved by experimental measurements.
- Content Type Journal Article
- DOI 10.1243/09576509JPE871
- Authors
Date: Thu, 27 May 2010 14:29:55 GMT
The effect of positive- and negative-curved blade stackings on the cavitation performance of a mixed-flow pump impeller has been investigated in the present study. To this end, two types of pump impellers with different blade stackings with no significant difference in the non-cavitating hydrodynamics were compared. A numerical simulation based on the validated computational fluid dynamics code has been carried out to analyse the detailed flow dynamic phenomena in the mixed-flow pump impeller. From the predicted characteristic curves pertaining to both the stacking conditions, superior suction performance of the mixed-flow pump impeller with the negative-curved blading has been demonstrated over the normal operating flow range. The computational analysis method and a design parameter presented herein can be effectively applied to the hydraulic design optimization process of general-purpose centrifugal and mixed-flow pump impellers.
- Content Type Journal Article
- DOI 10.1243/09576509JPE986
- Authors
Date: Thu, 27 May 2010 14:29:55 GMT
Performance and economic analyses of a hybrid thermoelectric (TE) solar water heater have been studied. The hybrid TE solar water heater was composed of transparent glass, air gap, an absorber plate, TE modules, water-cooled heat sinks, and storage water tank. The incident solar radiation heats up the absorber plate creating a temperature difference between the TE modules that generate a direct current. Only a small part of the absorbed solar radiation is converted to electricity, while the rest increases the temperature of the absorber plate. The water flows through each heat sink located under the TE modules to gain heat. The heated water then flows to the upper section of the absorber plate where it receives additional heating from the absorber plate. Improvements to the thermal and overall efficiency of the system can be achieved by the use of the double-pass collector system and TE technology. The experiment shows that the thermal and overall efficiencies increase as the water flowrate increases. The maximum and overall efficiencies were 74.9 per cent and 77.3 per cent, respectively, at the water flowrate of 0.33 kg/s. Meanwhile, the electrical-power output and the electrical-power generation efficiency depended on the temperature difference between the hot and cold sides of the TE modules. At a temperature difference of 27.1 °C, the unit achieved a power output of 3.6 W and the electrical-power generation efficiency of 0.87 per cent. Moreover, economic analysis indicates that the payback period of the hybrid TE solar water heater operating at the water flowrate of 0.33 kg/s is shorter and yields a higher internal rate of return.
- Content Type Journal Article
- DOI 10.1243/09576509JPE944
- Authors
- C Lertsatitthanakorn, Faculty of Engineering, Mahasarakham University, Khantarawichai, Thailand
- A Therdyothin, School of Energy, Environment and Materials, King Mongkut's University of Technology Thonburi, Bangkok, Thailand
- S Soponronnarit, School of Energy, Environment and Materials, King Mongkut's University of Technology Thonburi, Bangkok, Thailand
Date: Thu, 27 May 2010 14:29:54 GMT
This article evaluates the compressor performance using five eco-friendly refrigerants in comparison to R12. Experimental apparatus of a complete refrigeration system with reciprocating compressor was developed and the performance of the system with selected refrigerants was evaluated. The results obtained showed that only R134a and R152a have their coefficients of performances close to that of R12 with 6.6 per cent and 3.1 per cent reductions, respectively. Comparison between refrigeration capacities showed the superiority of R152a with 4.9 per cent higher than that of R12. The volumetric efficiencies obtained were 75.8 per cent, 74.4 per cent, and 77.9 per cent for R12, R134a, and R152a, respectively, whereas those of R23, R32, and R143a were 56.8 per cent, 60.6 per cent, and 69.7 per cent respectively. Therefore, R134a and R152a will perform well as substitutes for R12 in vapour compression refrigeration system.
- Content Type Journal Article
- DOI 10.1243/09576509JPE936
- Authors
Date: Thu, 27 May 2010 14:29:54 GMT
In this article, an attempt has been made to investigate the exergetic performance of a solar photovoltaic (PV) array. A detailed energy and exergy analysis has been carried out to calculate the operating and electrical parameters, exergy destruction components, and exergy efficiency of a typical PV array. The operating and electrical parameters of a PV array include PV array temperature, overall heat loss coefficient, open-circuit voltage, short-circuit current, maximum power point voltage, maximum power point current, etc. Some corrections have been done on the overall heat loss coefficient. Further, a new equation for the exergy efficiency of a PV array has been derived in terms of exergy destruction components. A computer simulation program has also been developed in order to calculate the operating and electrical parameters of a PV array. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Furthermore, the new exergy efficiency obtained in this article is in fair agreement with the one given by the previous literature. Finally, parametric studies have been carried out. It is observed that PV array temperature has a great effect on the exergy efficiency, and the exergy efficiency can be improved if the heat can be removed from the PV array surface. On the other hand, design parameters such as PV array area have a little effect on the exergy efficiency.
- Content Type Journal Article
- DOI 10.1243/09576509JPE890
- Authors
- F Sarhaddi
- S Farahat
- H Ajam
- A Behzadmehr
Date: Thu, 27 May 2010 14:29:54 GMT
An experimental study is described to investigate the influence of diffuser vane leading edge on the noise behaviour of a centrifugal fan. The geometric shapes of the diffuser vane leading edge refer to the diffuser inlet radius, and the broken and inclined leading edges. The sound pressure level and pressure rise of the centrifugal fan were measured in a semianechoic chamber. The rotational speed of the test fan varied from 20 000 to 35 000 r/min; the flow coefficient was in the range of 0.02–0.14. The results show that: (a) by using the inclined leading edge vaned diffuser (ILEVD) with proper inclined angle, the overall fan noise is reduced by 3.6 dB(A), and the fan performance is improved; (b) when the diffuser leading edge radius R3/R2 increases from 1.03 to 1.07, the tones are reduced whereas the broadband noise is almost unchanged; and (c) the influence of the broken leading edge diffuser on the overall fan noise and performance is negligible, although the tonal noise is reduced by 4 dB(A). In order to better understand the behaviour of the ILEVDs, a numerical simulation has been carried out on steady three-dimensional flows. The results indicate that the flow condition improves by the application of the ILEVD.
- Content Type Journal Article
- DOI 10.1243/09576509JPE869
- Authors
Date: Wed, 19 May 2010 20:29:50 GMT
Simulation of centrifugal compressors performance is widely performed by one-dimensional analysis because of relatively reliable results by this method, considering some major modifications in gas properties and analysing compression stages. The compressed medium is mixture of various gasses with different thermodynamic properties and molecular weights, which lead to considerable changes owing to different process and site conditions in many oil and gas applications. The mentioned characteristic changes are not considered in traditional performance prediction methods and result in large errors during estimation. In this paper, modified two-zone and one-dimensional models are presented, in which major variations are considered and numerical solutions are employed to successfully achieve satisfactory performance estimation. Results are verified with experimental data for stage pressure ratios and rotor efficiencies. These comparisons show that the proposed one-dimensional and two-zone models are revised in comparison to conventional techniques and effectively simulate compressors performance.
- Content Type Journal Article
- DOI 10.1243/09576509JPE914
- Authors
- M Karimi, Namvaran Consulting Engineers Managers, Iran
- E Hashemi, Department of Mechanical Engineering, Qazvin Islamic Azad University, Baragin, Iran
Date: Wed, 19 May 2010 20:29:50 GMT
This paper presents a post-processing analysis that combines several statistical tools to validate experimental results in a particle image velocimetry analysis on unsteady flows in the turbomachinery field. The method was developed in three steps: verification of the number of acquired images, verification of the meaningfulness of the velocity averages, and identification of the zones characterized by the greatest error on the average estimation. The statistical approach allows one to identify the possible error sources, discriminating between experimental problems due to the test rig, the turbulent nature of the flow, and structures unidentifiable by a single frequency.
- Content Type Journal Article
- DOI 10.1243/09576509JPE889
- Authors
- G Cavazzini
- G Pavesi
- G Ardizzon