Oscillating water column (OWC) systems are among the most credited solutions for an effective conversion of the notable energy potential conveyed by sea waves. Despite a renewed interest, however, ...they are often still at a demonstration phase and additional research is required to reach industrial maturity. Within this framework, this study provides a wave-to-wire model for OWC systems based on an impulse air turbine. The model performs a comprehensive simulation of the system to estimate the attendant electric energy production for a specific sea state, based on analytical models of the primary (fixed chamber) and secondary (air turbine) converters coupled with the tertiary converter (electric generator). A rigid piston model is proposed to solve the hydrodynamics, thermodynamics, and hydrodynamics of the chamber, in a coupled fashion with the impulse turbine aerodynamics. This is solved with a novel method by considering the cascades as sets of blades, each one consisting of a finite number of airfoils stacked in the radial direction. The model was applied for two Mediterranean sites located in Tuscany and Sardinia (Italy), which were selected to define the optimal geometry of the turbine for a specified chamber. For each system, the developed analytical wave-to-wire model was applied to calculate the performance parameters and the annual energy production in environmental conditions typical of the Mediterranean Sea. The selected impulse turbines are able to convert 13.69 and 39.36 MWh/year, with an efficiency of 4.95% and 4.76%, respectively, thus proving the interesting prospects of the technology.
Ocean Thermal Energy Conversion is an important renewable energy technology aimed at harvesting the large energy resources connected to the temperature gradient between shallow and deep ocean waters, ...mainly in the tropical region. After the first small-size demonstrators, the current technology is focused on the use of Organic Rankine Cycles, which are suitable for operating with very low temperatures of the resource. With respect to other applications of binary cycles, a large fraction of the output power is consumed for harvesting the resource – that is, in the case of OTEC, for pumping the cold and hot water resource. An exergy analysis of the process (including thermodynamic model of the power cycle as well as heat transfer and friction modelling of the primary resource circuit) was developed and applied to determine optimal conditions (for output power and for exergy efficiency). A parametric analysis examining the main design constraints (temperature range of the condenser and mass flow ratio of hot and cold resource flows) is performed. The cost of power equipment is evaluated applying equipment cost correlations, and an exergo-economic analysis is performed. The results allow to calculate the production cost of electricity and its progressive build-up across the conversion process. A sensitivity analysis with respect to the main design variables is performed.
Modern textile stenters are designed to reduce the inefficiency of the process and to recover the flow stream, which still contains a relatively high energetic value. In recent years, research has ...focused on the recovery of the energy content of the low-temperature exhaust flow; nonetheless, another important aspect that may increase the efficiency of the process is the reduction of the ambient air suction. In the present research, an innovative way to improve both machine insulation and energy savings, by using preheated air, was numerically evaluated. The proposed solution utilizes an air stream transverse to the fabric (generally called air curtain), either preheated or not, to create soft gates both at the inlet and at the outlet section of the drying machine. Several valuable advantages can be listed when using this solution: reduction of the dispersion of heat and humid polluted air to the work environment, limitation of air ingestion from outside, and effective heat recovery coupled to a uniform temperature profile around the textile fabric. To analyze the insulation capability of the air curtains in terms of mass and energy transfer, a two-dimensional CFD model of the machine was realized. A test matrix including three possible fabric speeds (20, 40 and 60 m/min), three tilt angles (−15°, 0° and 15°), four mass flow rates (0% with no air curtains and 3%, 5% and 7% of the total flow rate through the machine, where the 5% case is equivalent to the flow rate ingested from the ambient) and two temperatures (15 °C and 70 °C) of the plane jets exiting from the air curtains was considered, thus covering a wide range of possible practical applications. The obtained results demonstrate that warm air curtains at both the inlet and outlet are very effective in a fabric speed range up to 40 m/min; at higher fabric speed, entrainment of warm gases from inside the machine at the fabric outlet becomes relevant, and the adoption of a cold air curtain (capable of better insulation) can be recommended in this position.
Oscillating water column (OWC) devices are the technical solution more favourably considered for a significant future exploitation of the energy potential of sea waves. While theoretically quite ...simple, these systems are indeed rather complex in terms of correct tuning between the caisson and turbine. Recent studies showed that only a holistic approach, also including turbine control, is the way of effectively performing their precise design.
To this end, the research presents the application of an analytical wave-to-wire model of an OWC device for the preliminary optimisation of these systems for a small installation in a moderate wave climate in the Mediterranean Sea. More specifically, scatter matrices were determined for imposing the wave states of a selected location positioned in Tuscany (Italy). Regarding previous similar studies, a novel joint optimisation of the caisson and controlled turbine is proposed for the specific site. Either monoplane isolated Wells turbines and axial impulse turbines were analysed. The operating curves, performance parameters, and attended annual energy harvesting were calculated, providing an interesting overview of the functioning of the system. The optimised devices with the Wells and impulse turbomachines convert 36.71 and 42.17 MWh/year operating with a global efficiency of 6.82% and 7.84%, respectively.
•Comprehensive wave-to-wire model of oscillating water column systems.•Analysis of the processes of energy conversion from sea wave to the electric wire.•Original modelling of monoplane isolated Wells and axial impulse turbines.•Application to a real site considering annual and seasonal wave conditions.•Integrated optimisation of the oscillating water column chamber and air turbines.
This paper investigates waste heat (WH) valorisation on maritime vessels from a systemic perspective. It aims to demonstrate how a set of innovative waste heat recovery (WHR) technologies can ...synergistically work together to valorise waste heat in multiple ways. It proposes and develops a dedicated techno-economic analysis framework and model, surpassing previous literature that focused on individual technologies or specific combinations. Employing a Mixed Integer Linear Programming (MILP) approach, this study evaluates the dynamic and flexible operation of the WHR system throughout the round-trip journey of a vessel. Identifying the most profitable WHR system layout, determining the capacity of technologies, optimising the interconnections between technologies, and establishing strategic WH dispatching are all among the key objectives of the study.
An average-scale vessel with a 36 MW diesel engine, is selected for this study which involves a 17-day journey with multiple stops in Northern Europe. The vessel adequately represents the complexity of onboard energy systems in terms of types and variability of demands, as well as WH availability. The proposed WHR system, which is tailored for the selected vessel, integrates three active technologies: an isobaric expansion engine (IEE) to contribute to mechanical power demand, a sorption system for providing cooling, and an advanced Organic Rankine Cycle (ORC) for trigeneration of power, heating, and cooling. All technologies are supported by the passive WHR technology of Thermal Energy Storage (TES). The results show that deployment of the optimised WHR system onboard the selected vessel enhances energy efficiency by 5 to 7.5 percentage points and reduces fuel consumption by 13%. The study also explores economic key performance indicators (KPIs), such as the Internal Rate of Return (IRR) which is found at about 15%, clearly evidencing a compelling solution to ship owners. Additionally, the discussion includes a detailed analysis of the contribution of individual technologies in covering onboard demands, as well as their synergistic interactions.
This work clarifies the role, value, and benefit of WHR technologies onboard, advancing the understanding from individual WH recovery interventions to a system-level approach. This is especially valuable in practice, considering its adaptability across various vessel types within the global fleet.
•Comprehensive techno-economic analysis of waste heat recovery on maritime vessels•Unified techno-economic framework for integrated optimization of multiple technologies•Emerging technologies considered such as ORC, thermal energy storage, Sorption•Promising technical and economic potential, up to 14% energy savings•Identified technology and system-level advancements needed to increase competitiveness
Despite the huge potential, energy harnessing from sea waves is often still at a demonstrative stage. Oscillating water column (OWC) wave energy converters have proven to be one of the few suitable ...solutions to this end. A wave-to-wire analytical code modelling an entire wave energy converter based on the OWC technology, operating with either a Wells or an impulse turbine, was developed. The hydrodynamics, thermodynamics, and aerodynamics of the caisson were determined with a rigid piston approach. Two original low-order aerodynamic models were created for the two turbines, providing an interesting compromise between accuracy and computational cost. Finally, a control strategy was applied to monitor the instant rotor angular velocity and torque in both design and off-design conditions. The simulation tool was applied to screen the geometry of two typologies of air turbines for a specific chamber under the wave conditions of a selected Mediterranean site located in Sardinia (Italy). In particular, annual and seasonal scatter matrices were utilised to define the wave conditions of the site, providing an overview of the seasonal performance variation. The designed Wells and impulse turbines are capable of converting 47.67 and 41.14 MWh/year and operate with an overall efficiency of 5.77% and 4.98%, respectively.
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•Complete wave-to-wire model of an OWC wave energy converter.•Novel engineering simulation models for Wells and impulse turbines.•Joint solution of the interactions among chamber, turbine, and generator.•Tested on a real site with seasonal scatter matrices of wave conditions.•Critical analysis of conversion efficiency variation during the year and the seasons.
•Quantitative literature review on novel waste heat recovery technologies.•More than 200 references are assessed through a unifying approach.•13 classes of waste heat recovery technology described ...and characterized.•Challenges and opportunities for waste heat recovery in ships.•Advanced ship modelling is needed to understand waste heat recovery benefits.
The growing intensity of international commerce and the high share of total global greenhouse gas emissions by the maritime sector have motivated the implementation of regulations by the International Maritime Organisation to curtail vessel emissions. In this context, waste heat recovery (WHR) is an effective way to improve ship energy efficiency, lower amounts of wasted energy rejection to the environment, and therefore ultimately curb green-house gas emissions. Presently, there exists a heterogeneity within the body of literature concerning WHR technologies for on-board applications, study scope and results, complicating the interpretation and cross comparison of the outcomes. Sporadic attempts have been made to review and systematise this landscape, leaving some key areas uncovered. Therefore, the present article aims at filling these gaps by providing and holistic review of WHR technologies development and on-board applications. Further, the energy systems and available waste heat characteristics in large vessel types are overviewed, before both existing and developmental on-board waste heat recovery technologies for maritime applications are reviewed. Emphasis is placed on the performance of these technologies within the broader on-board energy system. Common key performance indicators are drawn from existing systems, experimental prototypes, and simulations, to quantitatively compare the different technologies. This review indicates that a wide range of technological options for embedding waste heat recovery in on-board energy systems are emerging. In particular, traditional turbocompounding is already fully implemented within the marine waste heat recovery (WHR) context. Conversely, ORC systems and absorption refrigeration systems have not yet been suitably adapted for marine applications due to a lack of research and prototypes, despite their deployment in conventional WHR contexts. Other technologies, such as thermal energy storage devices, hybrid refrigeration systems, isobaric expansion engines, Kalina Cycles, and adsorption desalination and cooling systems, are still at the research and development stage, while thermo-electric generation systems continue to incur high deployment costs. The development of research on these innovative technologies, the reduction of their cost and their synergistic integration could lead to significant improvements inengine fuel efficiency and emissions reduction, especially when coupled with existing waste heat recovery measures.
Over recent years, the Tesla turbine gained a renewed interest from the scientific community, as its simple structure guarantees low cost and reliability. These are key aspects of the success of an ...expander suitable for small-distributed energy systems.
The reference case for the computational analysis was selected from the available data of an experimental campaign conducted with R1233zd(E) as the working fluid. The analysed turbine has an efficiency of 29% and a power output of 0.57 kW. The fluid dynamics inside the stator, the stator-rotor gap and the rotor was assessed by means of a 3-D computational model. The comprehensive evaluation of the three regions is of paramount importance to determine the machine flow field and the related performance, as they are significantly affected by the interactions amongst the internal components. The effects of the discrete admission to the rotor are relevant in terms of flow field distortion, while the effects on the performance parameters (power and efficiency) are of minor importance. The performance results of the 3-D computational fluid dynamics are in line with those of the analytical 2-D code, which assumes the uniform admission to the rotor. Finally, after that the detailed analysis of the selected test case was conducted, several simulations with different thermodynamic conditions were carried out and compared to the results of the 2-D analytical code and the experiments.
•Tesla turbine performance analysis in two-phase condition via CFD and analytical model.•The phase change model is adapted to R404a based on saturation temperature.•1D-homogeneous analytical model ...estimation is comparable with 3D nonhomogeneous model.•The surface roughness effect is more pronounced at lower gaps between the disks.•The two-phase tesla turbine produced ~ 0.8 W and torque of 3.6 mN-m at 2000 RPM.
The scenarios on the future energy systems invariably point to heat pumps as an emerging technology to reach efficiency goals alongside energy and CO2 reduction targets. Moreover, they may progressively foster the use of chillers and refrigeration units. In this study, a technology that could enhance the efficiency of systems based on inverse cycles is analysed. Particularly, the two-phase flow behaviour of a Tesla turbine is numerically investigated. The main objectives are to clarify the role of the second phase, the actual operating range, and examine the flow mixing. Two computational approaches are developed, relying on a customised home-built mathematical model and CFD analyses carried out with a commercial software. The calculations are performed for two-phase R404a fluid over significant ranges of rotational speed, plate gap size, and plate roughness. All the critical liquid–vapour interactions are determined and discussed utilising the CFD solution of the Eulerian-Eulerian approach with a frame motion technique. The other model is a homogeneous finite-difference solution, and the mass transfer is directly determined based on the phase diagram of the fluid neglecting other phase-interaction parameters. The two approaches are compared to some available experimental results from the literature, revealing an excellent agreement. The results show the average power output of 0.8 W with a delivered torque of 3.6 mN-m at a rotational speed of about 2000 RPM. The numerical analysis explains the different effects of the two-phase conditions on the turbine efficiency, paving the way to an accurate design of boundary layer turboexpanders operating under these conditions.
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