Proceedings of the Institution of Mechanical Engineers,Part A: Journal of Power and Energy

This article presents an optimization study of a semiclosed combined cycle for CO₂ capture, based on the combined cycle (CC) gas turbine side, and where the produced water is extracted by condensation; its results are compared with those from the classic open CC. In this study, besides the overall pressure ratio (OPR) influence on the global efficiency, the influence of gas composition is also presented showing that it can change significantly the optimum OPR. Additionally, the sensitivity of the global efficiency to the maximum gas turbine temperature T _4t , gas turbine components efficiency, and cooling bleeds, the representative parameters of components technology level, is included. The optimum OPR shows that this type of cycles is not out of the current technology. Influence of gas composition on components performance maps is not considered, only some considerations on maps scaling. Also, starting from a baseline concept, some alternatives have been studied looking for a global efficiency improvement; the cooling down of the gas turbine entry conditions and the use of N₂ from the air separation unit as high-pressure turbine cooling, by means of the efficiency sensitivity to the blade cooling, are considered. Finally, it also provides efficiency close to the classic open CC and inside the efficiency of related cycles.

In this article, an attempt is made to utilize the exhaust gases of a small gas turbine to augment power output through the employment of a thermoacoustic system. A simple gas turbine cycle is selected as the base cycle and it is assumed that the thermoacoustic system is powered only by the waste heat of the base gas turbine. A comprehensive cycle analysis of the integrated gas turbine thermoacoustic engine (IGTTE) is carried out from an energy and exergy point of view. Exergy efficiency and internal exergy efficiency are calculated for the different components of the base gas turbine engine as well as the IGTTE. Value and exergy flow diagrams are used to investigate the possible improvements. Furthermore, a sensitivity analysis is performed by considering different conditions for the thermoacoustic system. The results clearly indicate some improvements with respect to exergetic efficiency from a simple thermodynamic point of view.

Existing attempts to optimize the operation of combined heat and power (CHP) systems for building applications have two major limitations: the electrical and thermal loads are obtained from historical weather profiles; and the CHP system models ignore transient responses by using constant equipment efficiencies. This article considers the transient response of a building combined with a hierarchical CHP optimal control algorithm to obtain a real-time integrated system that uses the most recent weather and electric load information. This is accomplished by running concurrent simulations of two transient building models. The first transient building model uses current as well as forecast input information to obtain short-term predictions of the thermal and electric building loads. The predictions are then used by an optimization algorithm (i.e. a hierarchical controller that decides the amount of fuel and of electrical energy to be allocated at the current time step). In a simulation, the actual physical building is not available and, hence, to simulate a real-time environment, a second, building model with similar but not identical input loads are used to represent the actual building. A state-variable feedback loop is completed at the beginning of each time step by copying (i.e. measuring, the state variable from the actual building and restarting the predictive model using these ‘measured’ values as initial conditions). The simulation environment presented in this article features non-linear effects such as the dependence of the heat exchanger effectiveness on their operating conditions. The results indicate that the CHP engine operation dictated by the proposed hierarchical controller with uncertain weather conditions has the potential to yield significant savings when compared with conventional systems using current values of electricity and fuel prices.

In this article, a supercritical CO₂-based solar Rankine cycle system (SRCS) with a novel-concept thermally driven pump is studied. The thermally driven pump is a refrigerant-circulating pump composed of two expansion tanks and having merits of low power consumption and high reliability in comparison with conventional mechanical pump. The application of the present thermally driven pump in the supercritical CO₂-based SRCS shows that an oscillatory flow is realized in the system and the system thermal efficiency is enhanced compared to the SRCS using the mechanical feed pump.

The physical design space of a wind-battery system enables a system designer to understand the trade-offs between different system design variables, the physical limits of the major decision variables, and arrive at an optimum solution subject to an appropriate design objective. An improved methodology for design of isolated wind-battery systems by accounting for the uncertainty associated with wind speed is proposed in this article. Chance-constraint programming technique is used to incorporate resource uncertainty in system sizing; thereby, facilitating system design corresponding to a specified reliability requirement. It is found that the cut-in speed of the wind turbine plays a critical role in delivering desired power supply reliability. A feasible design solution is obtained only when the probabilities associated with the cut-in and the cut-off wind speeds are accounted for along with the specified system reliability requirement. All feasible combination of system variables generated through a time-series simulation are represented on a rotor diameter versus generator rating diagram with minimum battery bank size as parameter. Solutions obtained by the proposed method are validated by sequential Monte Carlo simulations. Optimum system configuration for a given reliability requirement is determined based on minimum cost of energy (US$/kWh). It is shown that wind-battery systems cannot be designed to provide power supply reliability beyond a maximum value.

This article explores the possibility of coupling a tidal current energy converter (TCEC) with an energy storage system. The purpose of this study is two-fold: first, to show that storage can decrease the loss of output from a TCEC, when there are transmission constraints present. Second, to specify the properties of the storage system (efficiency, capacity, input/output power limit, and self-discharge rate) required in order to produce either demand-matching or base-load output from a TCEC. Models of such systems are constructed. These are run over several spring/neap cycles, to determine the time dependence of the whole system. It is shown that a 1.2 MW tidal current energy converter associated with a 1-MWh storage system of modest efficiency can offer significant advantages over the generator working alone.

During normal operation, compressor is mainly affected by fouling due to air pollution, which causes its performance to degrade over time. The main solutions to reduce compressor fouling are off-line compressor washing, on-line compressor washing, and advanced air filtration systems. Overall, the choice of the best recovery system for each gas turbine in the specific power plant is not trivial. The aim of this study is to provide a guide to identify the best washing or filter devices for a gas turbine (GT) in a specific power plant site, using literature information and GT users data.

Two procedures were conceived in order to have an user-friendly tool. ‘Best cleaning device’ was developed to help a GT user in the choice of the best devices for recovering compressor performance. Gathering information about GT performance and environmental conditions from real applicatios and literatures, a value of recommendation for each technology is provided.

‘Best cleaning time’ is based on the thermoeconomics theory of ‘best maintenance time’ and it provides the user an estimation about the best time to perform a compressor off-line or on-line washing.

Both procedures have been proved on a few real cases, showing good results and indications to more in-depth development.

A row of airfoil-shaped support struts has been proposed to be installed on both sides of the rotor, so as to remedy the configuration asymmetry of a conventional fully reversible fan in its forward and reverse flow modes. In the forward mode, the upstream support struts act as inlet guide vanes (GVs), and the downstream ones as outlet GVs; whereas in the reverse mode, the roles played by the two support-strut rows switch over. Among the five representative airfoils, symmetric airfoil NACA0012-64 is found to be the most suitable airfoil used as the section of the two rows of the airfoil-shaped support struts. Detailed numerical investigations on four such new fans, whose design points cover a wide range, reveal that the installation of the two rows of blades improves the performance of the new type fan, when compared with the one-rotor fully reversible axial-flow fan without such support-struts. The upstream blade row has little influence on the direction of incoming flow and causes little aerodynamic losses. By contrast, the downstream blade row plays an important role in efficiency improvements: (1) the downstream blade row, which acts as outlet GVs, significantly reduces the rotor-exit tangential velocity and recovers part of the swirl energy in the flow downstream of the rotor, although sometimes the aerodynamic losses caused by such support-strut-like outlet GVs may be high at a large incidence; (2) due to the obviously reduced tangential components of the flow velocities downstream of the outlet GV, the air travels a much shorter distance toward the exit of the annular diffuser, compared with that in the fan without outlet GVs. This leads to a markedly reduced friction loss. In addition, the larger the equivalent divergence angle of the annular diffuser is, the more effectively does the installation of the two rows of the support-strut-like blade improve the performance of the new type fans.

This article studies the effect of changing the flow path length on development of total pressure loss in diffuser flows. The studies incorporate quasi-one-dimensional (conical diffuser), two-dimensional (linear blade cascade), and three-dimensional (annular blade cascade) flows. This article concludes that the consequence of decreasing the flow path length is to decrease total pressure loss, provided that the adverse streamwise pressure gradient remains subcritical. The loss calculation technique and measurement data published by Lieblein were post-processed in this article. On this basis, this article elaborates a method for estimating the total pressure loss as well as its modification due to change of flow path length in blade cascade flows. This method can contribute to preliminary axial flow rotor blade design. It was pointed out that, in comparison to free vortex design, controlled vortex design that is applied to straight axial flow rotor blades tends to represent an additional source of total pressure loss farther from the endwalls. This is due to elongation of the length of flow paths on the blade suction side, due to intensified radial outward flow. This adverse effect can be counterbalanced by incorporation of forward sweep in controlled vortex design, via shortening the flow paths on the suction side, without the beneficial features of the controlled vortex design being lost. This article presents a literature-based comparative case study to illustrate such loss-reducing effect of incorporating forward sweep in controlled vortex design, away from the endwalls.

The effects of changing the stator–rotor axial gap on the performance and flow field of a low-reaction supersonic axial turbine are studied at design and off-design conditions. The objectives are gaining a better understanding of the effects and giving information and recommendations that a designer can use in his work. Three different axial gaps are modelled numerically with computational fluid dynamics at design and low off-design conditions. The geometry with the smallest axial gap is also measured at intermediate off-design conditions. The efficiency of the turbine decreases when the axial gap increases. The efficiency decrement is steeper at the off-design than the design conditions. It is concluded that the efficiency drop is mainly caused by the increased total pressure losses at the axial gap. It is recommended that the axial gap should be as small as possible. The smaller axial gap makes the rotor inlet flow angle distribution less curved, which is recommended to be taken in account when designing the turbine rotor for the studied turbine type. At the rotor outlet, the changing axial gap changes the absolute flow angle.

Film cooling effectiveness has been studied by using a computational approach based on solving the Reynolds-averaged Navier–Stokes equations. A wind tunnel test configuration is considered with a total of four cooling hole geometries as a cylindrical hole, a cylindrical hole with an upstream wedge (called ‘ramp’ thereafter), a shaped diffuser, and a double console slot. In all cases, the hole centreline has an inclination angle of 35° against the mainstream airflow and the blowing ratio is unity. Choosing the cylindrical model as a baseline, simulations have been carried out for grid convergence and turbulence model influence studies. Results are compared with available experimental data and other numerical predictions and good agreement has been achieved. Further computations continue with three remaining geometries, using the baseline flow conditions and configuration. Comparing to the results from the baseline model, it was found that the centreline adiabatic cooling effectiveness has shown incremental increases for the ‘ramp’ model, while results from the console slot model and the shape diffuser model have exhibited significant improvements by a factor of 1.5 and 2, respectively. The reason for such a step change in cooling effectiveness is mainly due to the weakening of the vortex structures in the vicinity of the hole exit, thus significantly reducing the entrainment of surrounding ‘hot’ fluids.

The effect of sealing clearance and step geometries on the discharge and heat transfer characteristics of the stepped labyrinth seals with honeycomb and smooth lands was investigated. The Reynolds-averaged Navier–Stokes equations coupled with standard k − ω turbulent model were adopted and numerically solved. The heat transfer coefficient as well as the discharge coefficients and meridian flow fields were calculated at two kinds of sealing clearance of stepped labyrinth seals and compared to the experimental data. The obtained results show that the present three-dimensional periodic model and numerical approach can give a good prediction of the discharge behaviour and heat transfer coefficients for both smooth labyrinth seal and honeycomb seal. Moreover, a range of H/C_r (step height to clearance) and t_s /t (step axial position to pitch) were conducted to investigate the sealing clearance and step geometries on the discharge and heat transfer characteristics of the stepped labyrinth seal with smooth and honeycomb lands. The detailed leakage flow and heat transfer coefficients distributions and corresponding influence mechanisms in stepped labyrinth seals were also illustrated and discussed.

Wind energy is developing very rapidly and over 30 GW of capacity was installed worldwide in 2009. It is also continuing to mature, with rotor diameters and ratings steadily increasing. Now there are several commercial designs available with rotor diameters exceeding 100 m and ratings exceeding 5 MW. Although the majority of developments are installed onshore, offshore wind is slowly taking off and there are plans for around 40 GW in Great Britain alone. The rapid growth has been accompanied by better understanding of the design issues, so that blades, towers, and other components are now lighter than they were 30 years ago and can be produced more efficiently. The most significant trend in recent years has been the move towards direct-drive generators, eliminating gearboxes that have, at times, been troublesome. Permanent magnet generators are delivering further weight savings, and research that is funded both by governments and manufacturers promises to deliver further improvements in cost effectiveness.