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As a distributed energy production technology, micro gas turbines (mGTs) offer a great potential for small-scale combined heat and power (CHP) production, adding flexibility to the electricity system. Nevertheless, due to the evident climate change, a very low greenhouse gas (GHG) emission is a fundamental requirement for our future energy systems. For this purpose, combining an mGT with a carbon capture (CC) plant might offer an effective carbon clean energy production. In the literature, several studies are available, addressing individual aspects of this attractive energy solution; however, an in-depth analysis focusing on the energy integration and strategy optimisation of an mGT working in CHP mode with CC has never been performed. This work is the continuation of the previous thermodynamic analysis in which an mGT and a micro Humid Air Turbine (mHAT) have been directly connected with a CC unit without heat recovery. In the current study, the aim is to find the best plant layout and the best operating strategy based on the electrical, thermal and global cycle performance. Results show that the full CHP operation of the mGT offers the highest global efficiency between all plant layouts. Contrary to what may be expected from previous analyses on cycle humidification, the mHAT does not entail a better performance when the turbine cycle and the CC unit are energetically integrated. Direct heat recovery, which reduces the CC thermal demand, is a preferable measure which involves a lower energy degradation. Sankey and Grassmann diagrams are presented to support the numerical results.

This study addresses turbulence modelling issues related to the simulation of flow over complex terrain using a coupling between NWP (numerical weather prediction) code and a classical CFD (computational fluid dynamics) code. A new planetary boundary layer (PBL) parameterization scheme, which is specifically formulated for coupling purposes, is presented. The capability of the developed closure models to be applied to the whole atmospheric boundary layer, not only to the surface layer is assessed by performing idealized simulations and comparing the results with the Leipzig dataset. CFD simulations sustained with inflow conditions acquired from mesoscale simulations are performed with different turbulence closures for the Askervein Hill case and their performances are evaluated in comparison with wind speed and turbulence kinetic energy measurements. Finally, the proposed turbulence modelling methodology is applied to the Ria de Ferrol Case. The new PBL scheme is implemented and tested with the open source mesoscale code, Weather Research and Forecasting (WRF) model. Microscale simulations and the turbulence model implementation are performed with the open source computational fluid dynamics (CFD) toolbox, OpenFOAM v. 2.3.1.

This study focuses on bridging the gap between the turbulence modelling methodologies of meterological and engineering codes by proposing a novel methodology to define the closure coefficients of Reynolds-Averaged Navier-Stokes turbulence models consistently with the physics of the atmospheric boundary layer. In this framework, different turbulence closures have been developed and tested on different full-scale test cases corresponding to different atmospheric stability conditions by performing microscale simulations with the inflow conditions provided by a numerical weather prediction (NWP) code. Developed turbulence models have been implemented into the open source computational fluid dynamics (CFD) toolbox, OpenFOAM and the inflow conditions have been acquired with another open source code, the Weather Research and Forecasting (WRF) model.

The large employment of renewable energies requires flexible, efficient and low-carbon production from fossil fuels. From all non-renewable power production routes, the electricity produced with micro Gas Turbines (mGTs) running on natural gas has a very high load flexibility and the lowest CO2 emissions. However, if we want to move towards full carbon clean power production, then CO2 in the exhaust must be captured. In this scenario, mGTs coupled with a Carbon Capture (CC) plant could be a suitable option, but only a few numerical and experimental analyses are available which assess their real potential. The low concentration of CO2 in the mGT exhaust gas is disadvantageous from a CC point of view, however the concentration can be increased by performing Exhaust Gas Recirculation (EGR). Furthermore, the efficiency loss introduced by the CC plant can also be reduced by using the concept of micro Humid Air Turbine (mHAT). In this study, both the dry and the wet operations of the Turbec T100 coupled with a chemical-absorption plant are simulated and compared using the software Aspen Plus®. The goal of these simulations was to investigate state-of-the-art measures which could be applied to small-scale generation to assess what the energy impact of a carbon clean production would be. Simulation results show that applying EGR to a mGT or mHAT can reduce the exhaust gas mass flow rate by 50% and it can increase the concentration of CO2 by three times the traditional cycle. The humidification of the mGT can entirely compensate for the efficiency losses of the EGR application. Both cycle performances are strongly affected by the thermal input from the stripping process, decreasing the global electric efficiency by around 7.9 absolute percentage points in the mGT case and by 8.3 absolute percentage points in the mHAT case in full load conditions. The results of this paper can be used as a starting point for new cycle concepts between the mGT and CC plant.

From all fossil fuel power production routes, the electricity produced with Gas Turbines (GTs) running on natural gas has the lowest CO2 emissions. However, if we want to move towards full carbon clean power production, the CO2 in the exhaust must be captured. The energy impact of a Carbon Capture plant (CC) applied to the micro Gas Turbine (mGT) still remains unclear because few quantitative analyses are available. The low concentration of CO2 in the GT exhaust gas is disadvantageous from a CC point of view. Exhaust Gas Recirculation (EGR) is one of the technologies used to increase the CO2 concentration in the GT flue gas. It is potentially an effective method to reduce the high energy-penalty caused by the carbon capture. A typical capture method is an absorber–stripper system where the absorbent is commonly a 30wt% aqueous monoethanolamine (MEA) solution. In this work, a Turbec T100 mGT coupled with a chemical-absorption plant is considered. The entire plant has been simulated using Aspen Plus®. Simulation results show that the specific reboiler duty is rather constant (around 4.3 MJ/kgCO2) when varying the electrical power output of the mGT. The cycle performance is strongly affected by the thermal energy requirement for the stripping process, decreasing the global electric efficiency around 6.2 absolute percentage points. These results could be a starting point for future energy integrations between the mGT and the CC plant.

To fully embrace its opportunities in future decentralized power production, the current mGT has to become more flexible in terms of operation, i.e. decoupling heat and power production. Cycle humidification during periods with low heat demand is a possible route to handle this issue. Indeed, cycle humidification has already been proven to increase the mGT electrical efficiency. Nevertheless, even when applying the most advanced humidified cycle concept, i.e. the REgenerative EVAPoration cycle, the electrical performance increase remains rather limited. In this perspective, the more recent Maisotsenko (or M-power) cycle concept offers a larger potential for humidification, even though its potential was only proven on large-scale gas turbine cycles and never applied to the smaller mGT scale. In this paper, the concept of this M-power cycle is applied to a 100 kWe mGT (Turbec T100) to assess its performance, using Aspen Plus® simulations. Moreover, the impact of various inputs, component performance and control parameters is studied using a sensitivity analysis. The numerical results highlight that the M-power cycle has the highest waste heat recovery and thus the highest electric efficiency (up to 147 kWe electric power output with an electric efficiency of 42.1% at constant rotational speed and 41.1%, corresponding to an 8.3%point absolute increase, at constant power output). Moreover, this cycle concept allows to approach the thermodynamic limit for cycle humidification. Indeed, a large exergy destruction is avoided by not going for direct water injection, but rather using a gradual injection and evaporation. Additionally, from a technological point of view, the M-power cycle is also preferable for the small-scale mGT. Indeed, in the M-power cycle, saturation tower, aftercooler, recuperator and economizer are combined in one single component, significantly reducing the complexity of the cycle. The main limitation is the saturator, that requires a wet bulb effectiveness of up to 98% to achieve the simulated performance, which can be technological very challenging.

Most promising Generation IV nuclear reactor concepts are based on a liquid metal coolant. However, at low Prandtl (Pr ) numbers such as those of liquid metal, classical approaches derived for unity, or close to unity, Pr fail to accurately predict the heat transfer. This paper assesses the RANS modeling of forced turbulent convection at low Pr and in channel flow. Reference results at high Reynolds (Re ) number are required to ensure that the Peclet number is sufficiently high. Therefore, new reference results were obtained by performing a wall-resolved Large-Eddy Simulation of turbulent channel flows at a friction Reynolds number Reτ=2000Reτ=2000 and at Pr=0.01Pr=0.01 and 0.0250.025 (this also corresponds to the highest Re Direct Numerical Simulation (DNS) available in the literature for the flow, but without heat transfer). The LES velocity statistics are in very good agreement with those of the DNS and, as validated by the authors in previous publications, the LES approach used here accurately predicts the temperature statistics at low Pr . The LES results are used to assess RANS heat transfer modeling based on the effective turbulent Prandtl number (PrtPrt) concept. Among existing PrtPrt correlations, the correlation by Kays (1994) [10] is shown to yield the best results. Since it is also shown that the near-wall temperature profile does not follow a log-law, a new “law of the wall for temperature” is here proposed, which does not use any blending function. Its use as a wall-function is also validated in actual RANS simulations.

This paper deals with the issue of modeling convective turbulent heat transfer of a liquid metal with a Prandtl number down to 0.01, which is the order of magnitude of lead–bismuth eutectic in a liquid metal reactor. This work presents a DNS (direct numerical simulation) and a LES (large eddy simulation) of a channel flow at two different Reynolds numbers, and the results are analyzed in the frame of best practice guidelines for RANS (Reynolds averaged Navier–Stokes) computations used in industrial applications. They primarily show that the turbulent Prandtl number concept should be used with care and that even recent proposed correlations may not be sufficient.

In the development of accelerator driven systems, ADS, free surface lead–bismuth spallation targets are considered as promising solutions due to their possibility for compactness, their lifetime, and their ability to transport the heat deposited by the proton beam away from the spallation zone. Experiments to characterise the hydraulics of the targets are needed to allow the validation of numerical models and to improve the design. Such experiments have been performed in water on a new concept labelled “detached flow” geometry. This name was chosen because the liquid undergoes a free fall between the nozzle exit where the main free surface (that separating the void of the beam line from the liquid) is created and a second free surface downstream. The void surrounding the liquid jet plays the role of a buffer. The experiments show that a very stable main free surface with a small recirculation is obtained using this geometry thanks to the presence of the second free surface and the nozzle geometry. The experiments confirm that the level of the second free surface has no influence on the characteristics of the main free surface, improving the main free surface control. The influences of the mass flow rate and of the inlet velocity are evaluated. The free surface level rises linearly with an increase in mass flow rate. The recirculation zone is also stronger in this case. The opposite is found when the mass flow rate is decreased. For all mass flow rates studied, a stable free surface is obtained. Moreover, the outer shape of the liquid jet is similar at all mass flow rates. It is only dictated by the nozzle exit angle. Increasing slightly the inlet velocity for a given mass flow rate has a positive effect on the recirculation stability. The “detached flow” target is a promising design for ADS.