• Energy Research

Pumps as turbines (PaTs) are becoming more and more attractive in Small Hydropower. PaTs are considered a cost-effective alternative to conventional turbines as long as their turbine characteristic curves can be predicted. Indeed, manufacturers need of a tool that could support them to predict the turbine mode performance from the knowledge of pump characteristics, in order to be competitive on the market. In this framework, a new 1-D prediction model is proposed for manufacturers in order to predict the entire characteristic of a PaT, by taking into account detailed geometrical information of the machine, hydraulic losses and the influence of the flow deflection with respect to the outlet blade angle of the runner during turbine operation.

<div class="section abstract"><div class="htmlview paragraph">The upcoming regulations to achieve zero-emission passenger transport present challenges for designing new ferry powertrains. The proposed work investigates the feasibility of using a Proton Exchange Membrane Fuel Cell (PEMFC) power system to power a long-haul ferry. The paper describes the zero-order cell model as well as the method for estimating cell degradation. The stack modeling, heat balance equations, and auxiliary modeling are also presented. The proposed model enables the simulation of the fuel cell under different operating conditions and includes the use of air or oxygen as an oxidizer. A thermal management strategy for the overall PEMFC system is also proposed. The model was calibrated on the characteristic curves of the PEMFC Ballard FCvelocity™ HD6 (150 kW) and validated by reproducing experimental results. Then, a real load profile of a ferry, as well as the proposed powertrain is considered as case study. The presented results are related to a single daily mission and its deterioration throughout the set mission cycle is finally presented.</div></div>

Nowadays, mobility represents a key sector to achieve the goal of carbon neutrality. Indeed, the development of hybrid powertrains is contributing to a reduction in the environmental impact of vehicles. One of the most promising energy-saving solutions is regenerative braking, which enables deceleration while recovering energy, otherwise wasted. Even though much scientific community effort has been addressed to the optimization of this technology in the automotive field, the increase of energy storage systems efficiencies enables the overcoming of the constraints related to the reuse of electric energy in railway vehicles. This solution could be extremely useful for those railway vehicles which operate on non-electrified lines, where traction is usually provided by diesel engines. For this reason, the present work focuses on how regenerative braking technology could be exploited in diesel-powered rail applications. In further detail, a diagnostic train working on real railway lines has been considered as a case study. Given the real duty-cycle of the vehicle, a simulation model has been developed with the aim of evaluating the amount of energy recovered during braking phases and, consequently, the fuel saving and the avoided CO2 emissions. As a result, the analysis shows an improved energy efficiency of propulsion system. Compared with a pure diesel operation, it leads to fuel savings of 20%, a reduction of CO2 emissions of 22.3 kg with 23.25 kWh stored in the battery at the end of the route.

Even if researchers are working on the exploitation of marine energy for more than thirty years, blue energy is not yet a consolidated reality and still contributes marginally to the world energy mix. For this reason, in the last years, the effort of the scientific community has been significantly intensified to further improve the know-how on marine energy harvesting. The goal is to allow ocean energy to effectively contribute to a more sustainable energy production in the next future. In the wide range of technologies for wave energy harvesting, Oscillating Water Column (OWC) devices are counted among of the most mature ones. Due to the oscillating nature of the generated air flow, which continuously inverts its direction, OWC devices need to be coupled with self-rectifying turbines, such as Wells, impulse, or biradial turbines. Wells turbines can reach high efficiencies, but their performance can show a hysteretic behaviour due to dynamic stall phenomena, especially in presence of high amplitude flow rate oscillations. Moreover, under dynamic stall conditions, during the flow deceleration, the shaft torque evidence the presence of gradually damped fluctuations, which delay the flow reattachment, superposed to the hysteresys loop. In order to better characterize this phenomenon, a new experimental campaign was performed in the open wind tunnel of the Polytechnic University of Bari on a 3D-printed Wells turbine model. The interest is mainly focused on the dependency of these torque fluctuations on the amplitude and frequency of the oscillating flow.

Abstract In small hydropower systems, Pumps as Turbines (PaTs) represent a cost-effective alternative to conventional turbines as long as the turbine mode performance can be predicted before their installation. A closed-loop test rig for experimental studies on hydraulic pumps and turbines has been built at the Department of Mechanics, Mathematics and Management of the Polytechnic University of Bari, in order to experimentally support the theoretical studies on PaTs. A single stage centrifugal pump has been tested in both direct and reverse mode. Furthermore, a literature survey of PaT models has been conducted and a new model, with a more general applicability, has been proposed.

Abstract Hydrogen is gaining momentum in the current global energy transition framework. In fact a great and widespread enthusiasm is growing up towards it, as indicated by the current worldwide economic and political strategies, which endorse the carbon neutrality by 2030 and a fast transition to clean energy. Green hydrogen has the potential to create a virtuous cycle for the future renewables-based electricity grids, as it can provide the much-needed flexibility to power systems, acting as a buffer to non-dispatchable renewable generation. Indeed, the excess energy, provided by conventional and renewable power plants, can be stored as hydrogen and then employed to produce electricity (fuel cells or power systems), heat (combustion) or both (co-generation), abating drastically the greenhouse gas production. In this scenario, it is important to understand what benefits could derive from the use of hydrogen. For this reason, the present work not only aims at reviewing the recent updates on hydrogen economy (in terms of the main advantages and drawbacks) but also focuses on determining the impact that this hydrogen may have in various sectors (transport, industry and power generation). Different assessments have been carried out showing how hydrogen can effectively contribute to the carbon neutrality goal. This work points out that hydrogen can be really sustainable if produced via electrolysis powered by renewable energies. Furthermore, for the mobility, the use of fuel cells currently turns out to be less efficient than the adoption of Li-ion batteries, but at the same time far less polluting ( CO 2 , eq ) and labor intensive. Finally, a near-term solution to contrast the power generation carbon footprint, namely the blending of fossil fuels with hydrogen, has been investigated. Thus, a real Combined Cycle Gas Turbine power plant has been selected as a case study, in order to assess the impact of the hydrogen employment in terms of power output and emissions with respect to the current status of the plant fueled with 100% natural gas. As a result, using a mixture with 70% CH 4 and 30% H 2 a remarkable reduction of CO 2 can be achieved (0.28 Mt CO 2 / year ).

In the open wind tunnel of the Polytechnic University of Bari a new 3D-printed prototype of a Wells turbine is investigated under steady-state and pulsating flow conditions. The flow rate is modified by changing sinusoidally the frequency of the control drive, hence the rotational speed of the suction fan. The Wells turbine is a scaled prototype designed to operate in a 1:10 scaled model of a REWEC3 breakwater for ocean application. The Wells turbine characteristics are evaluated in terms of torque coefficient and pressure drop coefficient vs. flow coefficient. A delayed onset of stall can be observed, with a clockwise hysteretic loop, when the turbine experiences large sinusoidal variation of the flow coefficient at high mass flow rates. The variation of the turbine performance under dynamic flow conditions is crucial for a correct design of the Wells turbine.